House tabs speed

[richardash1981]

There are many versions of LED DMX dimmers available and I see no real reason they cannot be utilized but off the top of my head I think it may need 2 channels, one for speed and the 2nd for direction.

"Constant Voltage" LED PWM dimmers should be fine for conventional brushgear-type DC permanent magnet motors from the motor's point of view - most electronic model train controllers are PWM based.

The cheap (Amazon Marketplace) one I have traced bits of the schematic from doesn't have any output protection however, so there is a good chance of destroying the output FET with inductive voltage spikes. To avoid this, you just need to add a reverse biased power diode in parallel with the output (one capable of carrying the motor current should be fine, so 1N4001 does for most 12V motors).

 

This only gives you DMX variable speed - no direction. The easy way to get direction is a double-pole double throw relay to swap the motor terminals (after the diode!), with the coil powered from a second channel. This "should" be an on-off relay channel, but you could perfectly well use another PWM from the LED module (don't forget a second protection diode!) provided you only send DMX values 0 and 255 out to switch the relay on and off. If you forget you will get a loud buzz, but unlikely to do any harm in the short term.

Making sure you set the relay (direction) correctly before starting the motor is a control programming exercise!

 

Limit switches are probably nice-to-have rather than essential (depending on how it needs to operate), they are normally-closed switches wired in series with the motor, with a diode (1N4001 again) across them so the motor can start in the other direction once operated (or linked to the reverse relay, so they only break the circuit in one direction).

[sunray]

There are many versions of LED DMX dimmers available and I see no real reason they cannot be utilized but off the top of my head I think it may need 2 channels, one for speed and the 2nd for direction.

"Constant Voltage" LED PWM dimmers should be fine for conventional brushgear-type DC permanent magnet motors from the motor's point of view - most electronic model train controllers are PWM based.

The cheap (Amazon Marketplace) one I have traced bits of the schematic from doesn't have any output protection however, so there is a good chance of destroying the output FET with inductive voltage spikes. To avoid this, you just need to add a reverse biased power diode in parallel with the output (one capable of carrying the motor current should be fine, so 1N4001 does for most 12V motors).

 

This only gives you DMX variable speed - no direction. The easy way to get direction is a double-pole double throw relay to swap the motor terminals (after the diode!), with the coil powered from a second channel. This "should" be an on-off relay channel, but you could perfectly well use another PWM from the LED module (don't forget a second protection diode!) provided you only send DMX values 0 and 255 out to switch the relay on and off. If you forget you will get a loud buzz, but unlikely to do any harm in the short term.

Making sure you set the relay (direction) correctly before starting the motor is a control programming exercise!

 

Limit switches are probably nice-to-have rather than essential (depending on how it needs to operate), they are normally-closed switches wired in series with the motor, with a diode (1N4001 again) across them so the motor can start in the other direction once operated (or linked to the reverse relay, so they only break the circuit in one direction).

This is exactly what I was anticipating.One of the DMX modules I have was purchased as LED or motor and does have the diodes, the other modules I've not thought of checking.

If end switches are not fitted it will need very careful controlling, if the motor is not stopped when when flown in the tab will continue going down until the lines run out and at that point the lines will start winding the other way round the winch bar. At that point the operator may not be aware whats happened and runs the risk of trying to fly in but will fly out instead and if it gets as far as flown completely out runs the next risk of trying to wrap the track and tab round the winch bar if there's nothing in the way.

There's no diode required on the end switches.

 

I'm actually starting to think a winch drum a little over 100mm diameter to do just one turn may be easier to control and with careful design it may be possible to build in acceleration/deceleration.

 

[TomHoward]

If you went the sail winch / servo route I believe I have an old Milford Instruments DMX servo board that would do servo position from DMX value that I’d be happy to donate to your project. You’d have to program your acceleration / deceleration in the lighting software.

 

You could still use a shaft but most winch servos are maybe 4-6 turns so you’d just need a thicker shaft with fewer turns... or divert all the lines sideways to one end and winch them all at the side onto the one drum.

Edited January 4, 2021 by TomHoward

[musht]

There`s more DMX stuff around than there was, ESP32 is programmable in Arduino environment

 

https://learn.sparkfun.com/tutorials/sparkfun-esp32-DMX-to-led-shield/all

 

Can modify a normal servo to continuous rotation, lose position feedback but its an easy way of getting a small reversible geared motor.

 

Other drive possibility be arduino/esp with stepper motor and driver, A4988/TMC2130 etc even use a lead screw and nut rather than line and drum, parts like these are easy to find thanks to 3D printers.

[Damian Jay]

Apologies for the delay in logging back in here. Work kinda got in the way for a while. Thank you everyone for even more input on this.

 

Sunray - 'The fly lines will need to over some guides or pullies to control the position or else the tabs will travel acros the stage as the line winds along the shaft.' Notes made as I had not thought of that. I would have kicked myself over that detail.

 

I was playing about with using micro switches in the guides for the safety curtain which would be activated by the curtain when fully in or out. But that won'r solve the start stop positions of any bars flying scenery in / out.

I was hoping that I could control all of this using DMX as I'm familiar with using that. I could then program everything lighting, flying etc and take my time programming each scene and effect and save the cues for later playback. I would need to learn how to set up a motor for DMX control.

Plus with using RGBW LED strip lighting for most of the onstage lighting ... that's probably going to run to two universes alone. But it's doable.

 

Also I keep looking at Arduino or PI as the control systems. These seem to be able to do everything I need, however I'm not sure if you can use more than one Arduino board in the same project. I'd also have to learn coding too (but hey, that's a useful skill to have anyway)

Can I get the same level of control / playback with Arduino ? I think at present my understanding of Klingon is far superior to my understanding of Arduio and Pi.

 

Tom Howard - Thank you that's very kind of you and I am interested in taking you up on your offer. But I need to wrap my head around which will be the best control system first of all.

 

I think I need to get some serious playtime in with both Arduino AND the DMX stuff that Musht linked to. I best spend some money and get a few bits in to play with :-)

 

Thank you all again for your advice and thoughts :-)

[TomHoward]

I'd look at Arduino and leave Pi alone, the devices are too high level for this.

Motor control from DMX or Arduino/ESP32 (fake cheap Arduino) would be possible, I'd use Servos if you could somehow as they already have the positioning sorted, so you wouldn't have to sense the top/bottom stops. Stepper motors on ESP32 would also work, which move a 'step' at a time rather than continuously, so then you'd have to save the current position in software and move so many steps up or down to move something in or out.

 

Servos could be done direct from DMX also and avoid needing to program anything up