Design Render

This is my design for a Turntable Traction Drive. It's meant to turn a large theatrical turntable covered in sets and actors in a safe reliable way. It can be built for less than $3000 USD.

I was inspired to take on this project by Alan Hendrickson's chain-driven design featured in Technical Designs Solutions for Theatre Volume 2 (Sammler/Harvey 2002). His design shows how a chain drive can rotate a turntable. I was interested in designing an easier-to-integrate "bolt-on" solution.

Table of Contents

Turntable Traction Drive Safety and Liability

As it's intended use involves live actors on a rotating stage, the safety of the Turntable Traction Drive must be considered seriously. But before we dig into a risk assesment understand this:

I am not an engineer. I write software for a living and am not formally trained to assess safety risks. As such, any risk assesment made here should not be considered comprehensive.

In undertaking this project, and making it publicly available, it behooves me to draw attention to this fact, as well as to to state clearly that I don't guarantee that this design works as intended, and I am not liable for any harm resulting from your use of this design.

Liability

This design is available for use under the Creative Commons Attribution 4.0 International license. By using this design you agree to the terms of this license.

The license includes the following language, which you should read:

Section 5 -- Disclaimer of Warranties and Limitation of Liability.

  a. UNLESS OTHERWISE SEPARATELY UNDERTAKEN BY THE LICENSOR, TO THE
     EXTENT POSSIBLE, THE LICENSOR OFFERS THE LICENSED MATERIAL AS-IS
     AND AS-AVAILABLE, AND MAKES NO REPRESENTATIONS OR WARRANTIES OF
     ANY KIND CONCERNING THE LICENSED MATERIAL, WHETHER EXPRESS,
     IMPLIED, STATUTORY, OR OTHER. THIS INCLUDES, WITHOUT LIMITATION,
     WARRANTIES OF TITLE, MERCHANTABILITY, FITNESS FOR A PARTICULAR
     PURPOSE, NON-INFRINGEMENT, ABSENCE OF LATENT OR OTHER DEFECTS,
     ACCURACY, OR THE PRESENCE OR ABSENCE OF ERRORS, WHETHER OR NOT
     KNOWN OR DISCOVERABLE. WHERE DISCLAIMERS OF WARRANTIES ARE NOT
     ALLOWED IN FULL OR IN PART, THIS DISCLAIMER MAY NOT APPLY TO YOU.

  b. TO THE EXTENT POSSIBLE, IN NO EVENT WILL THE LICENSOR BE LIABLE
     TO YOU ON ANY LEGAL THEORY (INCLUDING, WITHOUT LIMITATION,
     NEGLIGENCE) OR OTHERWISE FOR ANY DIRECT, SPECIAL, INDIRECT,
     INCIDENTAL, CONSEQUENTIAL, PUNITIVE, EXEMPLARY, OR OTHER LOSSES,
     COSTS, EXPENSES, OR DAMAGES ARISING OUT OF THIS PUBLIC LICENSE OR
     USE OF THE LICENSED MATERIAL, EVEN IF THE LICENSOR HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH LOSSES, COSTS, EXPENSES, OR
     DAMAGES. WHERE A LIMITATION OF LIABILITY IS NOT ALLOWED IN FULL OR
     IN PART, THIS LIMITATION MAY NOT APPLY TO YOU.

In plain language: I don't guarantee that this design works as intended, and I am not liable for any harm resulting from your use of this design.

Limitations

The Turntable Traction Drive has the following known limitations/deficiencies:

Key Safety Principals

:warning: The Turntable Traction Drive is a powerful machine. Using it should not be taken lightly. Caution and care must be taken in every integration to ensure that safe operating parameters are configured.

A turntable may pose a hazard on set even when operated manually by backstage technicians, however, unlike backstage technicians this machine has no brain. It doesn't know to stop because a piece of scenery is late during a scene-shift. It is not context-aware. Also, unlike a backstage technician, under the right circumstances this machine can summon inhuman amounts of torque.

:warning: Due to its power and remoteness this machine is not designed as part of an automation system. Rather, it is intended to be manually operated by a user with a clear view of the turntable.

The Turntable Traction Drive has exposed moving parts and therefore poses some first-hand risk of injury to operators. However, when attached to a turntable new hazards may appear.

:warning: A scenic turntable creates risks of injury independant of the drive mechanism. Take care to evaluate the risks not just from the Turntable Traction Drive, but from the system as a whole.

Risk Management

As some risk is unavoidable, my analysis will focus on mitigation strategies. Any requirement layed out in this section must be specifically required in either the Integration Checklist or Operations Checklist.

Risk Mitigation Strategy
Risk of electrical shock Requirements:
Ground VFD appropriately to input mains.
Ground motor appropriately to VFD.
Ground chassis appropriately to the motor chassis.
Pinching hazards from exposed rotating machine parts. Requirement:
Turntable Traction Drive must be in a fully enclosed secure area during operation.
Pinching/Crushing hazards between traction wheels and turntable edge. Requirement:
Interface between the turntable and the traction drive must be fully enclosed during operation.
Risk of unexpected start Requirement:
Enable Unattended Start Protection in VFD by setting c04 to 13 and short P24 to PIN 4
Disconnect power from the system prior to maintenance.
Risk of fall during normal operation Requirements:
Rehearse with onstage personel in order to find safe speeds and acceleration values. Do not deviate from these values without notice.
Risk of fall due to sudden acceleration Requirement:
Use conservative acceleration/deceleration values when configuring VFD. (For Hitachi L-100 see settings f01, f02, and f03)
Risk of fall due to overspeed Requirement:
Set a conservative hard frequency limit in your VFD configuration. (For Hitachi L-100 see settting a61)
Risk of crushing Requirement
Where possible tune-narrowly the current limiting features of your VFD. (For the Hitachi L-100 this configuration may be limited.)
Risk of crushing because of external scenery-based crush points. Requirements:
Turntables must maintain a raidal safety margin sufficient to prevent a person from being caught between a rotating piece of scenery and any adjacent piece of scenery.
Emergency Stop button must located near the turntable.
Cast and crew must be trained on the location of the Emergency Stop button.
Risk of entanglement Requirements:
Operator must have a clear view of the turntable.
Emergency Stop button must located near the turntable.
Cast and crew must be trained on the location of the Emergency Stop button.
Risk of slipping on a free-rotating turntable Requirement
A parking brake (or other disablement device) must be employed to prevent the turntable from turning when the Turntable Traction Drive is not in use.
All on-stage personel must be instructed on the free-rotating-nature of the turntable.
Risk of operator/integrator ignorance Requirements:
All safety requirements and warnings must be clearly printed on a label applied to the machine.
Documentation must be made available.
Risk of structural collapse on turntable Requirement:
Ensure that all scenery is constructed such that it can absorb tortional load such as might result from a sudden change in rotational speed.

Turntable Traction Drive Design

Staples Players was looking for a way to add some automation and motion to its production of Disney's Descendants The Musical. I was interested in creating a solution which could be applied generically to any of the typical turntable configurations they use.

I decided to make a drive unit to rotate a turntable by applying a traction wheel against the edge of the table. Such a device would be easy to integrate in most sets where the turntable sits on top of the stage floor.

Mechanical Considerations

Using drive wheels to turn a turntable seemed pretty straight forward. I'm pretty sure I've seen carnival rides driven in this manner. As a gut-check I did a bit of marketplace research and found that such devices do exist.

Concept

My first idea was to use a motor with a gear reduction and a triangular chain configuration. The friction wheels would be pneumatic tires. The idea was that an idler would pull the chain away from the contact-point of the turntable and allow for easy tensioning of the chain system. However, preliminary research indicated two things: First, chains don't like to be run horizontally they prefer to run vertically. Second, a triangular configuation would result in an uneven distribution of power between the two drive wheels.

Design Layout

Moving away from the single-chain configuration I moved towards a centrally mounted motor with two chains, one going to each drive shaft. I also ditched the idea of pneumatic wheels and prefering instead an off-the-shelf keyed drive roller from McMaster. This simplified sourcing and answered the question: How do I attach the drive shaft to the wheel.

Design Render

With those two decisions made the next step was to make a design in Fusion 360 and start selecting components. I started with the power source. I was eager to use a motor I had sitting on the shelf: A 3 Phase 2HP GE Motor (NEMA Frame 145TC. GE Model 5KE48WN8167) with a Morse 5:1 right-angle gear reduction (Morse 175Q140LR5.) This is a fairly beefy motor with a significant gear reduction.

Motor Shaft Gear Box Output Output Wheel
Ratio 1:1 (1.0) 5:1 (.20) 11:30 (.36)
RPM @ 60Hz 1725 RPM 345 RPM 124 RPM

In addition to the gear reduction on the front-end of the motor, I wanted to further reduce the gearing for two reasons: First, turntables typically require a large amount of effort to break free when turning. Reduced gearing would permit greater starting torque. Second, the native speed of the motor and gearing is 345 RPM (1725 RPM / 5). We want the traction drive gearing to allow us to use as much of the 0-60Hz range of the motor as possible without spinning a turntable too quickly. Therefore care was taken to use a small drive sprocket (11 teeth), a large axle-sprocket (30 teeth), and a small drive wheel (6" diameter".)

Effective Speed Math
Drive Wheel Circumference (feet) 2π * .25' 1.57' Foot Circumference
Linear Feet Per Minute 124 RPM * 1.57' 194 Feet Per Minute
6' Diameter Turntable Max Speed 194 FPM ÷ 19' 10.2 RPM (Measured: 11.3 RPM)
16' Diameter Turntable Max Speed 194 FPM ÷ 50' 3.8 RPM
23' Diameter Turntable Max Speed 194 FPM ÷ 72' 2.6 RPM (Measured: 2.7 RPM)

Integration Note: If you find that the drive speed is not large enough for your large turntable design, your best bet, depending on your choise of motor and VFD, is to overdrive the motor past 60Hz. (Most VFDs let you run up to 360Hz, but you will want to check your motor and drive documentation first.) Alternatively you could swap out the 6" drive wheels for a larger diameter wheel, but be aware that this will reduce the available startup torque.

Right Bearing Gusset

The Turntable Traction Drive is designed to sit on a flat surface. Because of this I couldn't through-bolt the pillow block bearings. That means that the steel would have to be drilled and tapped. Because the steel is only 1/4" I would need additional thickness on the bottom layer in order to have appropriate thread engagement. To resolve this, I designed three "gusset" parts: Two supporting the lower bearings and one supporting the motor mount. They are meant to be welded down then drilled and tapped, such that the threads are continuous.

Turntable Eccentricity

Turntables aren't perfect circles, and they're not always perfectly centered, so I needed somehow to keep the machine pressed against the side of the turntable even if it's out-of-true. I designed the machine with four 200lb springs which could be set to provide significant preload against the side of the turntable.

Pusher Springs

The springs are held captive by a 5/16" bolt welded to the pusher plate. The springs press against a piece of 1.5" angle iron which is lag-bolted through the two slots to the stage floor. This allows the whole machine to slide back and forth in response to bulges or dips in the circumference of the turntable.

Ratchet Straps

When testing we found that a far simpler solution was to use ratchet straps to draw the machine up against the side of the turntable and hold it there. Ratchet straps have some natural elasticity and therefore provide similar preload to a spring-based solution with substantially easier integration. (We can turn a large turntable witout even bolting the machine to the deck!)

Chain Tension

Chain based system must be kept in tension to keep the chain from slipping off the drive sprocket. In order to apply tension to the system we mounted the drive motor on top of an adjustable sled from McMaster. However, we noticed too late that the sled is meant to adjust the position of a motor mounted perpendicularly to the track of the sled. My design called for the motor to be mounted parallel with the track.

Motor Modifications

In order to mount the motor in this orientation we had to drill two additional holes in the motor's NEMA 146TC mounting plate. Once drilled we could use the drive seld to tension the chain and then crank down the motor bolts to lock it in place.

Material

Because I didn't know how much force would be required to turn a loaded-turntable I wasn't able to do any real load calculations. Without this knowlege it seemed the best bet was to over-build the system. So I designed around plasma-cut 1/4" A36 mild steel.

Steel Order

I made a tab-and-slot design such that when assembled the machine would (hopefully) hold itself square long enough for me to weld it together. I allowed for 1/16th of clearance between my tabs and my slots and verified that the steel shop could hold 1/16 tolerance during plasma cutting. Their advice was that as long as no holes were smaller than 0.25" they should have no problems holding 1/16" tol.

Steel Order

I provided the steel shop with a flat DXF file for each part with INCHES as the unit. They sent me back some fully dimensioned scans for me to verify.

Parts Fitup

Chapin and Bangs in Bridgeport, CT made the steel parts. They were made out of A36 steel, plasma cut, delivered dry. The cost was $810 with delivery.

Initial Welds

The biggest problem with 1/4" steel is that my welder is only barely powerful enough to weld it. I ended up using .030 flux-core wire. Flux-core welds don't look great but they're plenty strong and I was able to get reasonable penetration even with my wimpy 120VAC welder.

Parts Sourcing Guide

Finding reliable sources for parts is a challenging problem. If you pick a vendor like Amazon you may find that your item SKUs are no longer available weeks after you've made a purchase. On the other hand if you source parts exclusively from McMaster-Carr and Grainger you'll be paying top-dollar for that consistency.

In order to make parts-sourcing consistant I've chosen McMaster-Carr for most pieces of hardware. The Motor, Gearbox, VFD and Custom Steel you will need to source independently.

Bill Of Material

This project has a Bill of Material. The BOM is a list of all the parts we used construct this machine. Wherever possible I have added links which (hopefully) will not go stale quickly. In addition I've added price estimates, but you should expect these numbers to change with time.

I reccomend that you source the hard parts first before placing a large order with McMaster-Carr. Make sure you can find all the relevant components at a price-point which meets your budget before you click "Check Out."

Sourcing The Motor

The motor, and gearbox can be the most difficult parts to source. If you try to match precisely what I have used you will end up paying top-dollar. A more economical way to source the powertrain is to go on ebay and look for a used parts. Here are the important parameters:

Feature Value
NEMA Frame 145TC
RPM 1725
Voltage 208-230
Phases 3

The frame designation describes the precise size and layout of the motor bolts and face. Motor RPM is listed because a 1725 (or 1800RPM) motor is better suited for high-torque applications. Voltage isn't really your problem (since the VFD will be creating the motor voltage) all you really want to do is make sure you're selected a 200V class motor. Three phase is specified because this is necesary for the inverter to control the speed of the motor.

If you deviate too much from this prescription you may have to customize the Base Plate and Motor Gusset parts in order to fit your motor. You will also have to make sure your gear-reduction fits correctly.

Sourcing The Gearbox

The gearbox we're using, a Morse 175Q140LR5, has a couple of important features:

Feature Value
Drive Ratio 5:1
Frame 143/145TC
Shaft Output Left + Right
Output Shaft Diameter 7/8"

This may be the hardest part to source cheaply. Ebay may be your best bet. You can be a bit flexible regarding the drive ratio and the output shaft diameter (if you vary the output shaft diameter you will have to choosed different sprockets from the BOM.)

Sourcing The Variable Frequency Drive (VFD)

The Variable Frequency Drive (also commonly called an inverter) is an esential component of this system. It provides speed control and safety features neceesary to safely operate the Turntable Traction Drive.

For our implementation we have selected AutomationDirect's DURApulse GS23-22P0 VFD. We used the following selection criteria:

Feature Value Note Required
Number of Input Phases 3 (or 1) This matches the supply we have access to.
We have easy-access to three-phase power, so this is a good choice for our environment.		 YES
Nominal Input Voltage 230 VAC This matches the supply we have access to.
We have 3-phase 208VAC so this is the correct model.		 YES
Horsepower By Phase 2 (or 1) This matches the motor we have selected.
We have selected a 2HP motor, so we want a VFD rated for 2HP. The parentheses indicates that this VFD can power a 1HP motor when configured for single-phase 200VAC service.		 YES
Safe Torque Off (STO) YES This is safety requirement used by our e-stop system.
Having an STO feature means that our e-stop wiring will protect us even from a malfunction of the VFD itself.		 YES
Current Limit Capability 10%-250% This is a safety requirement.
This feature allows us to tune the max current available to the motor. This can help stall the system if there's an unexpected jam.		 YES
UL/CE Listed YES Someone has looked at this device to make sure it meets minimum requirements for electrical safety. NO
Freely available software. YES Having good software makes integration easier and can improve safety. NO
Software Interface USB For PC-based configuration, USB is slightly easier to interface with than RS485. Even USB-B. NO
Cost $208 That's a great price for the feature-set we're looking for. NO
SEO Excellent Let's be honest, the reason I zeroed in on this VFD is that Automation Direct has good online advertising and search engine optimization. NO

120VAC Power Single Phase

We have successfully powered our traction drive using a single 20A 120VAC mains circuit connected to a Hitachi L-100 VFD. If you only have access to single-phase 120VAC power you should seek a VFD which matches this configuration. Be aware that you will never be able to run a 2HP motor at maximum power using a 1HP VFD. You will likely also want to reduce your duty cycle in this configuration and should expect to produce extra heat. That said, we had no difficulty in rotating our 23' turntable on a single 120VAC 20A circuit.

Also be aware that VFDs under load have a nasty habbit of tripping residential breakers (especially RCD/GFCI circuits.)

Sourcing the Custom Steel Parts

I found that it was a relatively simple matter to provide a local steel shop with the 2D DXFs and the Custom Parts Overview. The PDF makes it easy for a sales guy to quote the job without needing CAD. The PDF also communicates expectations around minimum hole diameter and tolerances.

The design allows for 1/16 of slop between slots and tabs. The steel fabiractor must be able to hold 1/16th tolerance. The steel company which we worked with said that their plasma process could hold 1/16" of tollerance, but they had a specific requirement that no holes be smaller than 1/4" in diameter. This is not a problem for this design as we have so indicated in the Custom Parts Overview.

The total weight of the custom parts is around 112 lbs. Make sure you have a spot where the steel shop can deliver the order easily. In our experience the parts are, individually, easy to move around. When bundled together as a single order the steel is a two-person lift.

Turntable Traction Drive Assembly Guide

I've tried to use off-the-shelf parts as much as possible in order to make this design accessible. The vast majority of the hardware is sourced from McMaster-Carr. This should provide a reliable source for maintenance and customizations. In some cases I've gone to Amazon and Ebay to get parts which are otherwise too expensive.

A Complete Bill Of Materials is available here: Bill Of Materials

Note to Makers

By following these instructions and building this machine you will be creating a powerful piece of machinery which will last a long time. Pause to consider both the longevity of the machine and how that may impact your continuing liability.

:warning: Before Proceeding, make sure you have read and understood the SAFETY section of the documentation.

:warning: Before Proceeding, make sure you have read and understood the Limitations section of the documentation.

Parts Arrival

Custom Parts As Delivered

The overall weight of the custom parts for the chassis is approximately 112lbs. Our source delivered the steel parts all bundled together sitting on top of some blocks of wood. No single part it so heavy that it can't be moved by one person, but the bundle was too heavy and bulky for one person to comfortably lift.

Parts Test Fit

The very first thing we did is test fit the parts together. I was expecting to have to make some adjustments with an angle grinder, but none were needed. The parts fit perfectly. Fitment was tight enough that the machine held its shape without clamps.

Welding

Assembly took two days, with the majority of time being spent drilling and tapping holes. The welding of the chassis was a bit time consuming owing to underpowered welder. We used flux-core .030 wire on our 120VAC Hobart Handler 140.

We first welded the Motor Gusset to the base plate using c-clamps for hold-down. The Motor Gusset has two long weld slots cut into it in front of and behind the motor bolts. These slots allow for a good strong hold to prevent the gusset from separating from the baseplate.

Right Caster Gusset Welded

Next the Caster Gussets were welded into place. We used the tabs on the Pusher Plates to locate the slots before welding. C-clamps were used for hold-down. A generous weld-pocket is provided in the drawing in between the slot for the Pusher Plate and the hole for the axle.

Initial Welds

Next the two Side Panels, the Front Plate, and the Pusher Plates are welded. We set them all in their slots and put the Top Plate on top to lock them in place. 90-degree mag-clamps locked everything in place while we put in tack welds. We then then layed about 3" of bead down on either side of each piece.

In almost all cases we're welding an edge to a non-edge piece of steel. It's important to manage your heat to avoid blasting away the edges of the steel. Even on our low-powered welder we had to take care.

:warning: IMPORTANT! Don't weld the top on until you've tapped the holes!

Hardware

In order to mount hardware you must drill then tap the bolt holes. In this design, all bolt holes are undersized for 3/8-24 with the idea being that plasma-cut holes are not very accurate so it's better to drill them after the fact and then tap the perfectly drilled holes. This worked fairly well but we broke plenty of bits and taps.

Drilling and Tapping

We found that the steel fit together perfectly on the day it arrived, but on the second day the top plate no longer fit perfectly on the welded-up sides. It seems like everything moved a little bit as it cooled down from being welded and this caused us some difficulty in assembly. Next time around we will weld the whole machine in a single session. Or perhaps keep the top tacked after the bottom is assembled.

Right Drive Wheel

The right-angle (Left/Right AKA Top/Bottom) configuration of the gear-reducer allows us to run one sprocket on top and another sprocket on the bottom. This is useful since 7/8" ID sprockets are quite beefy. Too beefy to fit both chains on a single output shaft from the gear-reducer. For the right-hand drive wheel we connected a ANSI #40 chain to an 11 tooth sprocket mounted on the bottom shaft.

Left Drive Wheel

On the left-hand of the machine we ran chain from a sprocket mounted on the top shaft of the gear-reducer. On this machine the chain is a bit too close to the top plate. In our next revision we'll try to lower the motor 1/4" by eliminating the motor gusset.

Painted with handles

During our initial assembly we waited to weld the top until we verified that everything fit correctly. This isn't neccesary since all the hardware can be swapped-out even after the chassis is fully welded. After our test assembly we ran the machine at speed, adjusted it and then removed all the hardware for paint. We painted the chassis using oil-based black satin-finish paint.

Painted with handles

We also welded on some store-bought handles in order to make moving the machine slightly less cumbersome.

Drive Chain

Connecting the input and output sprockets can be a bit tricky for a few reasons:

Move the motor forward and backwards as needed using the motor mount sled. When you find the correct chain length and tension tighten the bolts on the motor flange to lock the motor spacing into the system.

While some chain noise is expected, if your machine is much louder than you expect look for the following defects:

If you're still having chain noise try adding grease.

Motor Wiring

Generally speaking wiring up a 3-phase motor is a matter of consulting the label on the side of the motor and connecting the appropriate wires to the VFD. Typically you will connect 3 hot legs and a ground to the VFD. There is no need for a seperate neutral connection.

Motor Wiring

In our General Electric motor the connections look like this:

VFD Connection Motor Connection
Ground Chassis Ground
Leg 1 Brown and Orange
Leg 2 Blue and Pink
Leg 3 Tan and Red
(No Connection) Yellow, Black, Purple (Connected together for Wye configuration)

Be sure to use an appropriate strain relief or grommet to prevent the knockout of the motor's wiring box from abrading the power cable.

VFD Wiring

For control wiring we have decided used 4-pin XLR. Industrial automation hardware tends to work with 24VDC reference signals which we intend to use in our control pendant. For this reason it's important that our choice of cabling no be prone to confusion. 4-pin XLR is unlikely to be accidentally plugged into a dimmer or a soundboard. There is some risk of confusion around theater headsets and around scrollers and TV cameras, but generally it's a lightly-used form factor.

Follow your VFD's instructions for mains wiring. We are using a DURApulse GS23-22P0 in our 3-phase environment. This is a 3phase VFD with a 2HP rating and a STO feature. For reference, we have tested the Turntable Traction Drive on a Hitachi L100 connected to a single 20A 120VAC circuit. So you can definitely use a smaller VFD where required.

DURApulse GS23 Wiring

To Begin: Configure the DI pins into SOURCE mode my adjusting the toggle switch to PNP.

XLR Pin Number VFD Pin Note
XLR Pin 1 +24 Digital Common
XLR Pin 2 FWD/DI1 Forward RUN 3-Wire Configuration
XLR Pin 3 REV/DI2 Reverse RUN 3-Wire Configuration
XLR Pin 4 STO1 Safe Torque Off 1 Interrupting +24V to STO will send e-stop the device.
Operation Condition
Run Forward Short XLR Pin 1 to XLR Pin 2
Run Reverse Short XLR Pin 1 to XLR Pin 3
Emergency Stop (STO) Interrupt +24v between XLR Pin 1 to XLR Pin 4

Hitachi L100 Wiring

XLR Pin Number VFD Pin Note
XLR Pin 1 P24 24VDC Reference
XLR Pin 2 Terminal 1 Forward RUN Default Configuration
XLR Pin 3 Terminal 2 Reverse RUN Default Configuration
XLR Pin 4 Terminal 3 External TRIP Configure to EXT by setting C_03 to 12

In this configuraion you may peform the following operations:

Operation Condition
Run Forward Short XLR Pin 1 to XLR Pin 2
Run Reverse Short XLR Pin 1 to XLR Pin 3
Emergency Stop Short XLR Pin 1 to XLR Pin 4

Control Pendant Wiring

Rather than designing a bespoke pendant I decided to choose from one of the many "Lift Control" pendants available on Amazon. These pendants all seem to feature a rugged enclosure, an e-stop switch and two momentary push buttons. (One added benefit of some crane controls is that they tend to feature mechanical interlocks to prevent the clockwise button and the counter-clockwise button from being pressed at the same time. This isn't strictly necessary but may prevent operator confusion.)

Left Drive Wheel

For our implementation we have made the top momentary switch the RUN FORWARD button. The bottom momentary switch is the RUN REVERSE button:

Pendant Wiring for DURApulse GS23

Connection Purpose
XLR Pin 1 TO EMERGENCY STOP LEFT SIDE 24VDC for the pendant will travel through the e-stop button. If e-stop is activated power is interrupted.
XLR Pin 1 TO RUN FORWARD LEFT SIDE Send 24VDC to the RUN FORWARD button when e-stop is not engaged.
XLR Pin 1 TO RUN REVERSE LEFT SIDE Send 24VDC to the RUN REVERSE button when e-stop is not engaged.
EMERGENCY STOP RIGHT SIDE TO XLR Pin 4 If e-stop is activated interrupt 24VDC to STO1. STO will engage.
RUN FORWARD RIGHT SIDE TO XLR Pin 2 Send 24VDC to the VFD when RUN FORWARD is pressed.
RUN REVERSE RIGHT SIDE TO XLR Pin 3 Send 24VDC to the VFD when RUN REVERSE is pressed.

Pendant Wiring for Hitachi L100

The Hitachi L100 has no STO device. This configuration does not protect against a malfunctioning VFD.

Connection Purpose
XLR Pin 1 TO EMERGENCY STOP LEFT SIDE 24VDC for the pendant will travel through the e-stop button. If e-stop is activated power is interrupted.
EMERGENCY STOP RIGHT SIDE TO RUN FORWARD LEFT SIDE Send 24VDC to the RUN FORWARD button when e-stop is not engaged.
EMERGENCY STOP RIGHT SIDE TO RUN REVERSE LEFT SIDE Send 24VDC to the RUN REVERSE button when e-stop is not engaged.
RUN FORWARD RIGHT SIDE TO XLR Pin 2 Send 24VDC to the VFD when RUN FORWARD is pressed and the e-stop is not engaged.
RUN REVERSE RIGHT SIDE TO XLR Pin 3 Send 24VDC to the VFD when RUN REVERSE is pressed and the e-stop is not engaged.

Turntable Traction Drive Integration Guide

This guide is designed to help scenic designers and technical directors integrate the Turntable Traction Drive into their sets.

:warning: Before Proceeding, make sure you have read and understood the SAFETY section of the documentation.

:warning: Before Proceeding, make sure you have read and understood the Limitations section of the documentation.

Turntable Integration

The Turntable Traction Drive applies significant forces to the side of the turntable where it makes contact. This requires the following considerations:

Critical Dimensions

The two key factors when determining if this machine will work with your turntable are diameter and mass. At present we don't have sufficient information to give guidance about maximum turntable mass. Except to say that we had no difficulty moving a 23' turntable with a 2-story wood and steel "castle" on it.

Dimension Value
Minimum Turntable Diameter 6'
Maximum Turntable Diameter 23' Demonstrated (Maximum Unknown)

If the diameter of your turntable is too large you may have difficulty running it fast enough with the as-designed gearing. If this is the case you have two options:

Another critical factor is the height of the traction-bearing surface relative the bottom of the turntable traction drive. The vertical position of the drive wheels is adjustable, but is ultimately constrined by the spacing between the drive sprockets. That said drive wheels have about 4" of vertical adjustability.

Dimension Value
Minimum Traction Surface Width 1.5"
Maximum Traction Surface Width 3" (Drive Roller Width)
Lowest Possible Traction Surface 3.25" to 4.75" from the bottom of the machine
Highest Possible Traction Surface 5.75" to 7.25" from the bottom of the machine

If the traction surface of your turntable is too high, it may be neccesary to raise the machine so that it contacts the correct portion of the turntable. Conversely, it may be neccesary to mount your traction drive below the stage if your dive surface is too low.

Traction Pressure

The available tractive force of the Turntable Traction Drive is related to the pressure applied by the rollers against the traction surface. In other words, it's not sufficient to place the Turntable Traction Drive next to a turntable, it must be pressed firmly against the side of it.

This "preload" pressure may be created via two integration schemes:

Ratchet Straps

In testing the Turntable Traction Drive we observed that we could apply ample force between the drive wheels and the turntable simply by connecting ratchet straps between the machine chassis and the carrier wheels of the turntable.

This system has several advantages over the Pusher Spring system:

For these reasons ratchet straps are prefered mecahnism for integration.

To attach the turntable via rachet straps:

Pusher Springs

Pusher Springs

The design calls for the use of four pusher springs which ride on 5/16" guide bolts. These pusher springs push the turntable forward, away from two L-iron brackets anchored firmly to the deck. This mechanism allows for approximately 1.8" of eccentricity in the turntable circumference while applying around 200 lbs of force.

To install the pusher springs follow these instructions:

Note: In the pusher spring rendering there is insufficent clearance between the guide-bolts and the lag-bolts. This has been remedied by raising the holes in the pusher plate.

Integration Checklist

To help ensure safe operation of this Turntable Traction Drive please ensure the following REQUIRED conditions have been met:

Requirement Complete
Technical Director/Integrator must read and understand the safety section of this documentation. :black_square_button:
Turntable Traction Drive chassis grounded to motor frame :black_square_button:
Motor frame grounded to VFD :black_square_button:
Turntable Traction Drive is fully enclosed in a secure area :black_square_button:
Drive-wheel interface points are fully enclosed :black_square_button:
Turntable hard-scenery elements don't create opportunities for shearing or crushing :black_square_button:
Emergency stop button located within 6' of Turntable Traction Drive :black_square_button:
Turntable fitted with an external parking brake (or other disablement device.) :black_square_button:

VFD Configuration

DURApulse GS23-22P0 Configuration

Note: These notes are only really useful for the DURApulse GS23. If you're using another VFD consult your documentation.

When configured correctly we desire the following outcome:

DURApulse GS23 Parameters

Parameter Value Notes
P02.00 2 2-Wire Configuration
P01.10 60 Output Frequency Upper Limit
P01.12 1 Acceleration Time 1
P01.13 1 Deceleration Time 1
P06.12 ?? Current Limit 0-250%

Hitachi L100 Configuration

Note: These notes are only really useful for the Hitachi L-100. If you're using another VFD consult your documentation.

P24 provides a 24V field reference voltage for use when powering the Control Terminals.

When configured correctly we desire the following outcome:

Hitachi L100 Parameters

Parameter Value Notes
a01 00 00=Keypad/Potentiometer, 01=Control Terminals, 02=F01 Settings
a02 02 01=Control Terminals, 02=Keypad Run Key
a02 02 01=Control Terminals, 02=Keypad Run Key
a61 60 Set a hard limit on the output frequency of the VFD to never overdrive the motor.
a04 60 Set the "Base" Frequency. (The frequency at which the VFD emits full voltage)
a05 60 Set the "Max" Frequency (The frequency allowed during manual opeation)
a97 00 Set the Acceleration Curve: 00=Linear, 01=S-Curve
a97 00 Set the Deceleration Curve: 00=Linear, 01=S-Curve
c01 00 Configure Terminal 1: 00=Run Forward
c02 01 Configure Terminal 2: 01=Run Reverse
f01 nn Set the target frequency
f02 nn Set the acceleration time (The number of seconds it should take to get spin-up from 0Hz to f01Hz)
f03 nn Set the deceleration time (The number of seconds it should take to get spin-down from f01Hz to 0Hz)

Turntable Traction Drive Operation Guide

This guide is designed to provide procedures for operating the Turntable Traction Drive.

:warning: Before Proceeding, make sure you have read and understood the SAFETY section of the documentation.

:warning: Before Proceeding, make sure you have read and understood the Limitations section of the documentation.

Determining Safe Working Parameters

Once the Turntable Traction Drive has been integrated into your scenery you need to determine safe working values for the various parameters of your VFD.

In particular:

Operating Frequency

The operating frequency is the speed at which the drive motor runs. If a motor has a 60Hz native frequency then you should consider 60Hz to be 100% speed.

Determining a safe operating speed involves many factors and there may not be simple way to determine what's safe.

Observe the following:

Consider the following:

Acceleration/Deceleration

The Acceleration Time and Deceleration Time control how long it takes the drive to come up to full speed and how long it takes to slow down. Anytime that the motor is changing speed there is additional risk to on-stage personel, particularly when acceleration itself changes.

Observe the following:

Consider the following:

Current Limits

If your VFD permits it, consider setting as low a current limit as possible. This will allow your drive and motor to stall if your turntable meets unexpected resistance.

It may be neccesary to tune this parameter so that your VFD has suffient "starting torque" but will still stall if required.

Operations Checklist

Before each use the Turntable Traction Drive should be inspected to ensure that it is properly installed and safe to use.

Checkpoint Ready
Check machine/turntable pressure on left and right sides. :black_square_button:
Check to make sure drive-wheel is contacting the correct portion of the turntable on left and right sides. :black_square_button:
Check to make output-shaft sprockets have not slipped and are aligned with the power-sprockets. :black_square_button:
Visually inspect turntable circumference and remove any obstructions which may cause jamming. :black_square_button:
Remove parking brake (or disablement device) :black_square_button:
Connect controller to Drive :black_square_button:
Connect drive to power :black_square_button:
Test left and right rotation at performance speed. Listen for any unusual noises coming from the Turntable Traction Drive or the turntable itself. :black_square_button:
Test left and right rotation at performance speed. Watch for any unusual rubbing, slippage or stalling. :black_square_button:
Test local emergency stop button. :black_square_button:

Bill Of Materials

Component Units Quantity Unit Cost Notes
Control
Automation Direct DURApulse GS23-22P0* EA 1 $208 Variable Frequency Drive
Automation Direct GS20A-DR-AB EA 1 $5 VFD 35mm DIN rail adapter.
VFD Power Cable EA 1 #10 3-Wire Appliance Cable
VFD Power Connector EA 1 NEMA 5-15P
Control Pendant EA 1 $36 Compact Crane Control Pendant
Emergency Stop Buttons PACK 1 $14 Mushroom Cap E-Stop Buttons
Chassis
Bottom Plate EA 1 -- Custom 1/4" Steel from BottomPlate-TotalSketch.dxf
Motor Gusset EA 1 -- Custom 1/4" Steel from MotorGusset-TotalSketch.dxf
Right Caster Gusset EA 1 -- Custom 1/4" Steel from RightCasterGusset-TotalSketch.dxf
Right Pusher Plate EA 1 -- Custom 1/4" Steel from RightPusherPlate-TotalSketch.dxf
Right Side Panel EA 1 -- Custom 1/4" Steel from RightSidePanel-TotalSketch.dxf
Left Caster Gusset EA 1 -- Custom 1/4" Steel from LeftCasterGusset-TotalSketch.dxf
Left Pusher Plate EA 1 -- Custom 1/4" Steel from LeftPusherPlate-TotalSketch.dxf
Left Side Panel EA 1 -- Custom 1/4" Steel from LeftSidePanel-TotalSketch.dxf
Front Plate EA 1 -- Custom 1/4" Steel from FrontPlate-TotalSketch.dxf
Top Plate EA 1 -- Custom 1/4" Steel from TopPlate-TotalSketch.dxf
Material, Plasma Cutting, Delivery JOB 1 $811 Custom Steel Cuttting to 1/16 Tolerance
Safety Label JOB 1 -- Custom Printed Vinyl Sticker from TurntableTractionDriveLabel.pdf
Input Side
3 Phase Electric Motor EA 1 $600** General Electric 2HP TEFC 5KE48WN8167
Reduction Worm Gear EA 1 $700*** Morse 175Q140LR5 5:1
Adjustable Motor-Mounting Base EA 1 $40 62035K23 Fits NEMA 145 and NEMA 145T Frames
Roller Chain Sprocket 11 Teeth EA 2 $17 6280K654 ANSI 40 Chain, 11 Teeth, for 7/8" Shaft Diameter
Motor Hold-Down Bolts PACK 1 $7 92865A211 Medium-Strength Grade 5 Bolt, 3/8"-24 Thread, 1/2" Long
Motor Cable EA 1 #10 4-Wire Appliance Cable
Output Side
Pillow Block Bearing PACK 1 $5 PGN - UCF204-12, Pack of 4
Keyed Rotary Shaft EA 2 $21 1497K116 - Fully Keyed, 3/4" Diameter, 9" Long
Keyed Drive Roller EA 2 $118 61065K46 - 6" Roller Diameter, 3" Roller Width, for 3/4" Shaft Diameter
Roller Chain Sprocket 30 Teeth EA 2 $68 6236K331 - ANSI 40 Chain, 30 Teeth, for 3/4" Shaft Diameter
Bearing Hold-Down Bolts PACK 1 $15 92865A214 Medium-Strength Grade 5 Bolt, 3/8"-24 Thread, 7/8" Long
Spring Pusher
3" Pusher Spring PACK 1 $13 9657K438 Compression Spring, 3" Long, 0.75" OD, 0.48" ID, Pack of 6
Partially Threaded Spring Guide Bolts PACK 1 $15 91247A126 Medium-Strength Grade 5 Bolt, 5/16"-24 Thread, 3-1/2" Long
Spring Guide Loading Nuts PACK 1 $8 91247A128 Medium-Strength Grade 5 Nut, 5/16"-24 Thread
Miscelaneous
Short Machine Key Steel PACK 1 $3 98870A140 - 3/16" x 3/16", 1" Long, Undersized, Pack of 10
Long Machine Key Steel PACK 1 $9 98870A192 - 3/16" x 3/16", 3" Long, Undersized, Pack of 10
#40 Roller Chain and Tools PACK 1 $36 13 Pieces Roller Chain Disassembly Kit
3/8-24 Drill and Tap Kit EA 2 $10 Drill America - POU3/8-24 3/8"-24

Total Cost Estimate: $2,980

* Choose a VFD that's compatible with your input power availability and which has a Safe Torque Off (STO) feature.

** Price Estimate. There are lots of different motors you can buy. The most important thing is that the power and form-factor be correct.

*** Price Estimate. There are lots of different gear reductions you can buy. Make sure you pick one that will fit the motor you're using when rotated 90 degrees.

Wiring Guide

For the sake of reusability we have wired our VFD into a semi-permanent control panel using DIN terminal blocks to connect the user wiring. This control panel is designed to be fully enclosed in scenery during use.

Assembled Chassis Before Welding (photo)

Be sure to follow the VFD manufacturer's specifications when selecing wiring materials. You don't want to under-spec the mains or motor wiring.

Wiring Guide (For Durapulse GS20)

Terminal Number End Point Name
Input Side
G VFD Ground Ground
TERMINAL1 L1 Input Power Leg 1
TERMINAL2 L2 Input Power Leg 2
TERMINAL3 L3 Input Power Leg 3
Output Side
G VFD Ground Ground
TERMINAL4 T1 Motor Turns 1
TERMINAL5 T2 Motor Turns 2
TERMINAL6 T3 Motor Turns 3
Safety
TERMINAL7 STO +24V 24V Source For Safety Switches
TERMINAL8 STO +24V 24V Source For Safety Switches
TERMINAL9 STO1 Safety Input 1
TERMINAL10 STO2 Safety Input 2
Control
TERMINAL11 DCM Digital Control Common
TERMINAL12 FWD Forward Contactor
TERMINAL13 REV Reverse Contactor

Control Wiring

Wire Pin Terminal Notes
Emergency Stop Button 1 TERMINAL9 STO disabled when shorted to +24VDC Source
Emergency Stop Button 4 TERMINAL7 STO +24VDC Source
Optional Second Emergency Stop Button 1 TERMINAL10 STO disabled when shorted to +24VDC Source
Optional Second Emergency Stop Button 4 TERMINAL8 STO +24VDC Source
Control Pendant 1 TERMINAL11 Voltage Sink for Digital Control
Control Pendant 2 TERMINAL13 REVERSE when shorted to votlage sink
Control Pendant 3 TERMINAL12 FORWARD when shorted to votlage sink

Note: When not using the optional second emergency stop button you must have a jumper between TERMINAL8 and TERMINAL10.

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