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Electronics => Electronics => Topic started by: izua on July 19, 2008, 04:22:29 AM

Title: Need some pointers: DMX-512, 3kw motor choice
Post by: izua on July 19, 2008, 04:22:29 AM

Hey there.
I'm working on a project where I have to design the electronics section of a stage threadmill. It should be controlled via DMX512, so it can be tweaked along with the other stage & lightning equipment. Requirments are 500kgs, ~10m length. We've been guestimating the motors around 3kw to cope with everything and still have some headroom. The design has 2 motors, one on each end, with interconnecting elements.

1.One of problems is maintaining them both at constant speed. I am thinking of optical encoders to balance it. Any better method of reading speed?

2. I want some advice on how to design the power stage.
If we go on AC motors (which seems the obvious choice), it will be hell, at minimum. 3kW variable frequency sinewave sounds like a lot of heatsinking.
If we choose DC motors, all that power needs to be rectified (or maybe a SMPS comes handy here, do they make them at that power?), and then it's a matter of simply varying pulse widths.
Any other choice of motors? How would the design of its respective power stage would end up? What about ac/dc motors? Any improvments?

3. DMX - tbh, i never worked with it before. Standard doesn't seem to be open, although I found a few documents detailing various aspects. Does anyone know some software which can turn the parallel port or serial port in a DMX controller? Where can I get some standards?

Thanks a lot!

Title: Re: Need some pointers: DMX-512, 3kw motor choice
Post by: Asellith on July 20, 2008, 12:08:41 PM

I can help you out a lot. Did a LOT of research into DMX-512. I'll start digging up info as I right this. DMX-512 is hard to buy equipment for because it is RS-485 however it runs way faster then any computer equipment. If memory serves right it runs at like 250 kbs. The protocol is a unique start sequence with a low for like 40 ms and a high for 40 ms. This is all from memory from like a year and a half ago so some of my numbers may be off. After the startup it sends up to 512 data sets. The lights or equipment are set to a channel and just wait. If it sets for channel 5 it gets the start condition then counts to 5 and keeps the 5th set of data while passing the rest down the chain. There is also some talkback features that are kinda crazy not sure how all that works.

Anyway here is a cheap usb to dmx converter

http://www.enttec.com/index.php?main_menu=Products&prod=70303&show=description&name=opendmxusb

about $60.

Some free software to control it

http://www.shmithz.com/

Ok I got one more site that will help you out. They have a lot of custom DMX solutions. Some can be kinda pricey

http://www.bpesolutions.com/dmxproduct.html

But they have a DC motor driver

http://www.bpesolutions.com/dmxproduct.html#anchor524991

A solid state relay board that can do AC or DC

http://www.bpesolutions.com/dmxproduct.html#anchor789380

and a 2 channel relay board

http://www.bpesolutions.com/dmxproduct.html#anchor1315210

If you have any questions let me know and I can try to help. Like I said for work I have done lots of research and worked with DMX a lot. One of the wonders of working on the technical side of a college is I get my hands in some wierd stuff. Audio Systems, lighting system, video systems, and now an entire radio station.