gareth Posted June 22, 2012 Share Posted June 22, 2012 I know this has been discussed before - but it was a long time ago, so I thought it was worth re-visiting as a fresh topic. We've got a production coming up in September for whch we need an analogue clock mechanism which can be run in 'real time', but also with the facility to reset it as quickly as possible to another time during scene changes. A DMX-controllable solution of some sort would be something that we'd like to look at - but does such a thing exist as an off-the-shelf product? Perhaps someone has something appropriate kicking around in a storeroom from a past production? Or maybe some wisdom to share regarding the construction of such a beast? (I'm aware of the OptiKinetics projection solution - but that won't work for us, it has to be something capable of driving real physical clock hands - quite large ones, as it goes.) Link to comment Share on other sites More sharing options...
Brian Posted June 22, 2012 Share Posted June 22, 2012 You should find a post of mine somewhere. I still have the unit. Link to comment Share on other sites More sharing options...
themadhippy Posted June 22, 2012 Share Posted June 22, 2012 You should find a post of mine somewhere. I still have the unit. would it be this one? http://www.blue-room.org.uk/index.php?showtopic=22102 Link to comment Share on other sites More sharing options...
gareth Posted June 22, 2012 Author Share Posted June 22, 2012 You should find a post of mine somewhere. I still have the unit. What DMX to stepper motor interface did you use, Brian? Link to comment Share on other sites More sharing options...
Brian Posted June 22, 2012 Share Posted June 22, 2012 You should find a post of mine somewhere. I still have the unit. What DMX to stepper motor interface did you use, Brian?Milford Instruments. Link to comment Share on other sites More sharing options...
gareth Posted June 23, 2012 Author Share Posted June 23, 2012 What DMX to stepper motor interface did you use, Brian?Milford Instruments. Thanking! Link to comment Share on other sites More sharing options...
Dave Kay Posted October 17, 2012 Share Posted October 17, 2012 Hey guys, time to revive an old thread! I am in the process of constructing a DMX controllable clock for our upcoming show of Little Shop. I have extensively used the ideas in these threads - meccano etc! Thanks for the details! The issue I am having is getting the stepper motor to work correctly with the Milford Dual Stepper DMX Interface board. As far as I can see, everything is wired correctly and the DMX input is definately working, but the motor isteslf is just jittering rather than stepping. The motor is from Rapid here. I'm not too hot on stepper motors other than replacing them with the use of a service manual. Does anyone have any thoughts on why my motor isn't behaving?! Any advice appreciated! Dave Link to comment Share on other sites More sharing options...
Modge Posted October 17, 2012 Share Posted October 17, 2012 The issue I am having is getting the stepper motor to work correctly with the Milford Dual Stepper DMX Interface board. As far as I can see, everything is wired correctly and the DMX input is definately working, but the motor isteslf is just jittering rather than stepping. Does anyone have any thoughts on why my motor isn't behaving?! Definitely got the phases on the stepper motor in the right order? A gibbering stepper motor in something home built suggests to me phases on the motor not in the same order as the board expects. Link to comment Share on other sites More sharing options...
Dave Kay Posted October 17, 2012 Share Posted October 17, 2012 Definitely got the phases on the stepper motor in the right order? A gibbering stepper motor in something home built suggests to me phases on the motor not in the same order as the board expects. Yeah, It does sound like phases are out - but as far as I can see, everything is hooked up as required. I think I'll try swapping some wires around when I get to the workshop tomorrow! EDIT: Typo Link to comment Share on other sites More sharing options...
dbuckley Posted October 17, 2012 Share Posted October 17, 2012 Other possibilities include trying to run the motor too fast (or too fast without acceleration), motor / controller voltage mismatch or wrong ballast resister(*), or mechanical overload, though wiring error is the most likely culprit. You are quite lucky that the spec sheet gives the colour code, so its easy to start with which two leads are commons on the six wire motor, rather than having to start with the meter :) I'm not actually a fan of driving steppers via DMX as there is very limited control possible, and you cant make use of the huge advantage stepper motors have over pretty much every other type of motor, namely open loop control with exact positioning to a point. However, if all you need to do is make a clock spin, then precise control may well be overkill. If the clock needs to end up at a specific time, then accurate control makes that much easier. Thus I use a more capable controller (The Eggert SSC1U being one) which lets me drive the motor an exact number of steps. The drawback is it isn't DMX controlled, its RS232. Electrically, thats easy (D connectors to XLRs and a long mic cable) but you need something to issue RS232 next to the lighting desk. * - Walked into Global PC, and asked where they kept the 10W resistors. "What size?" the chap asked. About two inches, I replied... Link to comment Share on other sites More sharing options...
Dave Kay Posted October 20, 2012 Share Posted October 20, 2012 So, I've purchased the stepper motor that was recommended by the Milford Tech support guy, and I'm still having exactly the same issues. A size 17 12v Astrosyn. The motor is just shuddering! I've tried a different DMX source, a Jester, with no fix. Tried a different power source. Still the same! The board has a ninth ouput channel that outputs a switched 12v supply. Having metered this output, it's also jumping all over the place from a few volts upto 12.5v. Pulling my hair out here! Does it sound like a potential issue with the Milford board? EDIT: Clarity - it's early after a late gig! Link to comment Share on other sites More sharing options...
DrV Posted October 20, 2012 Share Posted October 20, 2012 This is a bit basic but it sounds awfully like the PSU is sagging under load. Can you check the supply where it goes into the board? E2A when you say you've tried a different power source, are you sure the PSUs are up to the job? Dave Link to comment Share on other sites More sharing options...
Dave Kay Posted October 20, 2012 Share Posted October 20, 2012 This is a bit basic but it sounds awfully like the PSU is sagging under load. Can you check the supply where it goes into the board? E2A when you say you've tried a different power source, are you sure the PSUs are up to the job? Dave The power supplies are desktop AutoTrip science lab type supplies. Pinched from the physics dept. Max output is 5A DC. It's always handy being based in a school! The supply should be more than enough for the spec of the board / motor. I put a meter over the inputs when running the motor and it's providing a stable 12.4v Thanks anyways! Really can't understand why it's not playing ball Edit: Just to clarify, the outputs are reacting to the DMX input. The switched output isn't live until DMX Chn 5 is at about 80%. Dave Link to comment Share on other sites More sharing options...
DrV Posted October 20, 2012 Share Posted October 20, 2012 The clue may be in that ninth output (which presumably should not be changing at all) - perhaps the back emf from switching the stepper coils is getting back into the board and upsetting the microprocessor. Try replacing the motor coils with dummy loads (say 100ohm resistors to start with). Then you can monitor what happens on the other output. If you've got access to a scope then put that on the outputs - it will give you more idea of what is actually happening. If it is indeed back-emf then catching diodes should cure it. Dave Link to comment Share on other sites More sharing options...
Dave Kay Posted October 20, 2012 Share Posted October 20, 2012 The clue may be in that ninth output (which presumably should not be changing at all) - perhaps the back emf from switching the stepper coils is getting back into the board and upsetting the microprocessor. Try replacing the motor coils with dummy loads (say 100ohm resistors to start with). Then you can monitor what happens on the other output. If you've got access to a scope then put that on the outputs - it will give you more idea of what is actually happening. If it is indeed back-emf then catching diodes should cure it. Dave Great, will try first thing on Monday and let you know! Thanks for the advice! D Link to comment Share on other sites More sharing options...
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