Control/Dimming - Motorised faders for a scratch build lighting control system

[varnis]

For my school's theatre production, which may be using moving heads and/or scanners. A friend and i are developing a computer control system, which, when finished, will be open source - yay - and hopefully awesome.

One apparently insoluble problem, however, is a method of manual control. We do have an existing lighting board, but it is a) only 24 channels in wide (no-crossfading) mode when we will be needing to control > 50 channels - not too bad since if we have the control system up and running, we can assign groups of channels to it and so forth I guess - and b) is a raw DMX board with plain faders, meaning that if we switch into manual mode at any time the channels won't be at their appropriate current value.

What I am looking for, therefore, is some kind of motorised fader component which can be purchased on our quarter-shoestring budget. :P We have a design for a completely DIY one using a rack and pinion gear (in bright colours, hooray) from Acme Whatever Educational Supplies (Rapid Online I believe it was) which would work out at about £3 - £4 + making-time per fader.

Does anyone have any ideas where I could get premade ones for only slightly more than that (£6/£7 each maybe)? I've seen websites which will, but they are of the order-multiples-of-10,000-from-Thailand variety. Any relevant anecdotes would also be welcome. (In case you haven't guessed from the spellings and currency, I'm in the UK.)

Thanks,
Doug/Jono

[derekleffew]

Not to rain on your parade, but why re-invent the wheel? ChamSys is in your backyard, and has already written the best software for moving light control on a personal computer available.

ChamSys Ltd

[mc2880]

Bheringer makes a midi control board called the BCF2000 it comes with 8 motorized faders. It's dirt cheap and already has an API built. Somewhere like that might be a good place to start. The mackie interface is much better, but also much more expensive.

[TimMiller]

have you tried mouser and digikey for motorized faders? What you may want to look into is getting the entec USB to DMX converter to run ChamSys. The BCF2000 actually has USB control, it works like an external fader wing. I'm sure you can make it work with the ChamSys. So you have a motorized fader wing and DMX output. Now if you would like to go for a more DIY, you have to build your own USB to DMX converter, then you will have to draw out your schematic of how you are going to build your fader wing and control the faders. I hope you are familiar with writing and burning EPROMS (if you do not have one an EPROM burner will run you around 100) and it will not be cheap if you have to get someone to write the code for you (around 700). You will have to do some searching and learn how to program the software so that x resistance is x dmx value. Plus be able to patch to different outputs. The processor would then recall the dmx value and based on the resistance of the fader, will move the fader to the appropriate place, unless you have faders using encoders which are commonly used, and then the console counts to that particular tick mark, so inside of the console, you will have to intigrate stepper motor control. Good luck.

[ojno]

We already have a usbdmx.com : The bus powered usb dmx interface : Home Page DMX interface to use, and we are quite happy with coding and electronics (and have plentiful 'stock' components, including PICs and EPROMS). We've looked at the Behringer, yes, it looks like it would be the obvious option if we had money to throw at it, but unfortunately the department head cringed at the cost of a £100 DMX interface :|

We have three months or so in which to complete the entire system, including the control application and the fader wing, so we're trying to go for the cheapest way possible since it's not that urgent. It's ok if we can't get a fader wing at all I guess, since we can always use the DMX in port on the interface to use our old board, but that would be irritating because it's small and we can't bank-switch since it's not motorised. So...

I've also had a look at MagicQ and it doesn't run acceptably on the pitiful second hand PC we have to run the thing :D - I'm writing the app in C# (Mono) to run on a stripped down Linux, just for interest.

I expect the best option is to try and raise funds for a Behringer, despite the manager's financial objections... sigh.

Thanks for your replies
- ojno

[TimMiller]

you would have to really pull apart your lighting console and reverse engineer it to get it to work as an interface.

[tomed101]

Originally Posted by TimMiller

you would have to really pull apart your lighting console and reverse engineer it to get it to work as an interface.

Not really. He said that his interface had a DMX input on it, so if he programs that if Ch1 on the input reads 25% then he could program that to mean fader1 = 25% (I hope that made sense)

[TimMiller]

I did not see the dmx input part, yes you could program it like that

[ojno]

We may have a solution....

Endless faders, using a rubber belt attached to a quadrature rotary encoder. No need for any mechanisation at all, it will all be relative and the position indicator will be an LED bar graph rather than the slide position.

There are still some issues to be ironed out, such as getting the belt the right length and calibration such that the bar graph moves in sync, but it seems extremely promising. It may seem a bit weird to start with though :P

[icewolf08]

Your rotary encoder idea has been the standard for controlling moving light attributes for a long time. However, why do you need a rubber belt? Just attach a wheel to the encoder (like on most modern consoles) and call it a day. At the same time, why bother with the LED bar graph? You are going to have some kind of channel display with levels on the computer monitor, so is there really a need for the redundancy of information?

It really intrigues me that people have such an affinity for the physical faders and the visual feedback from them (I think the latter is why most like them). I use a couple physical faders for submasters, but never individual channel control. Keyboard input is so much faster; typing "1-25@50" is so much easier than running up 25 faders and finding the level you want them at. So, save the encoders for your ML attributes and use the keypad!

Forgive me, but it just seems like a waste of time to reinvent the wheel. I realize that you don't have any money and you want the challenge of writing your own software, but I would love to know a little more about the board that you have, like what it is. You say that it only has 24 faders in single scene mode, but does it support more channels than that? Does it have a keypad? My other concern is that I would never want to use a totally unproven technology to run any show critical element (like lighting). It is one thing to tinker in your garage, but what happens when the system just up and dies in the middle of a show and there is no support number you can call?

I don't mean to come off as harsh and disheartening, it is just my 2 cents.