Halloween Forum banner

1 - 20 of 31 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter #1
Is anyone familiar with how to control a wiper motor with DMX? I have tried to use a Matrix dimmer/switch pack, but the pack continuously outputs a small voltage even when no signal is being sent. I currently run the show on a VSA RAPU and I would like the controller to be compatible with it. Have you guys ever tried this?
Thanks!
 

·
Registered
Joined
·
1,204 Posts
I haven't tried it, but I would be very interested in doing so. I look forward to hearing from anyone with experience in this area. I just switched over to all DMX just last year. I was using regular servo controllers, the SSC-32 from Lynxmotion and though it was economical, the issues with running long distances and the sheer number of wires and connections became daunting. It is much simpler now with DMX.

What I do know about using a wiper motor in that fashion, is that you will need a high powered H-Bridge and a circuit that can interpret the servo signal coming from the controller which is in the DMX line. The real problem is finding an H-Bridge that can handle the current created by a wiper motor under load. It can easily reach 30 or 40 amps if it is under high torque. It requires a power supply that can provide that much current, and an H-Bridge that won't burn up when it starts using it.

I did this with a SSC-32 board several years ago. I can try to find the equipment and tell you where I got the H-Bridge. There are many more options available today if you search around, and I'm sure others on this forum already are using some. Here's a video (poor quality as it is) of how I set it up. It isn't using DMX, but by controlling it like a servo, that doesn't matter. DMX can control a servo just the same way as a serial controller.

https://www.youtube.com/watch?v=AdE37lKmkyE

I hope this helps.

Bob
 

·
Registered
Joined
·
1,204 Posts
Possibly, but there are issues involved. That would allow you to simply change directions from forward to backwards and run it for a per-determined duration, but a board like that could not handle the current required for the torque a wiper motor provides. There would also be no way to adjust the speed at which it moves or precise positioning. Something I didn't mention, but shows up in the video is that I fitted a potentiometer to the top of the wiper motor that turns along with the motor. That, in conjunction with the H-Bridge essentially turns the wiper motor into a giant powerful servo. One that draws an incredible amount of current. There is no servo controller card that would survive that much heat from the current draw on that. The power has to be fed to the H-bridge separately, and the H-Bridge needs to be designed to handle the power. You can see the large heat sinks on the one I was using.
 

·
Registered
Joined
·
3,529 Posts
Wow Bob, not sure what type of wiper motor you're using but 30-40 amps? Really? My props that use wiper motors run on a 5A power supply and that's probably overkill.
 

·
Registered
Joined
·
1,204 Posts
It's not what kind of motor, it's what are you trying to lift or move with it. All wiper motors will have that kind of current draw if stalled. If you are lifting heavy prop arms with it, you will require a lot of current. I can run mine on a 5A power supply as well. It just will severely limit the amount of torque that the wiper motor has. It won't be able to life as much weight. If you are using a 5A power supply, you might as well use a much smaller motor because the lifting power of the wiper is very low at that power rating. You can run it on .5 amps or less if there's no load. I specifically used a wiper motor because of it's ability to provide crazy amounts of torque, but the only way to get that kind of load capacity out of it, is to feed it LOTS OF POWER. I'm talking current here, not so much voltage. You can run it on 5 Volts, but that is less than half of what it was designed for, so it will move more slowly, and will again have less torque. It all depends on the application and what you are trying to move or lift.
 

·
Registered
Joined
·
3,529 Posts
Yep, I know how electric motors function in regards to voltage/amperage/torque. I just meant that for most wiper motor prop applications a 5A power supply usually does the trick. If I need crazy amounts of torque, I go pneumatic, but that's just me. ;)
 

·
Registered
Joined
·
1,204 Posts
Yes, you're right. In most cases, you don't need that much torque. For me, I had one thing that needed that much and the other 45 servos ion the setup were just fine as they were. It didn't make sense for me to add pneumatics for that one feature, and have two systems going on, so I used the wiper motor with all the accessories to enable it to do the heavy lifting.
 

·
Registered
Joined
·
188 Posts
OK, the control/speed issue makes total sense. I was thinking basic off/on.

Bob, not to derail this thread but help me figure out the issue why current draw matters to a control board if you are using a relay?? I plan on hooking up a couple of wiper motors to my Medusa board so before I make a $100 whisp of blue smoke help me understand the logic flaw.

The board just triggers a 12v relay which is hooked up to the voltage for the motor. If you pulling serious draw that may fry your relay but it "shouldn't" backtrack to your control board. At least that's my understanding of one of many reasons why you would use the relay.
 

·
Registered
Joined
·
3,529 Posts
OK, the control/speed issue makes total sense. I was thinking basic off/on.

Bob, not to derail this thread but help me figure out the issue why current draw matters to a control board if you are using a relay?? I plan on hooking up a couple of wiper motors to my Medusa board so before I make a $100 whisp of blue smoke help me understand the logic flaw.

The board just triggers a 12v relay which is hooked up to the voltage for the motor. If you pulling serious draw that may fry your relay but it "shouldn't" backtrack to your control board. At least that's my understanding of one of many reasons why you would use the relay.
This is perfectly fine and exactly what relays are designed for, I use them all the time for loads that the controller can't handle.
 

·
Registered
Joined
·
1,204 Posts
It doesn't matter if you are using relays. It would only make a difference if you wanted to control precise positions and speed by using it as a servo. If you only care about on/off and which direction it is going, just make sure the relay you are using has contacts rated for the current draw you expect to see.
 

·
Registered
Joined
·
1,204 Posts
You are correct about the relays. If you do melt the contacts from excessive current, it will have no effect on the controller board. It's a completely separate pathway.
 

·
Registered
Joined
·
369 Posts
The dimmer pack may have a way to set it as a relay... Check that.
The dimmer sends a small amount of current to keep lamp filament warm so the shock of rapid changes does not reduce the life of a lamp a much...
Trying a true relay is best...
There should be away to wire the relay so the polarity of the voltage is reversed depending on your needs.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #18
Good idea. It is $255. I have used their products in the past and they are top notch. I may go with a simple on/off control. I believe the motor may draw more than 5A.
 

·
Registered
Joined
·
3,529 Posts
A pair of SPDT relays will allow you to control on/off and forward/reverse. Here's a simple diagram of how the relays are wired. When neither relay is active, GND is connected to both sides of the motor. When one of the relays is active it will run the motor in one direction, when the other relay is active it will reverse the direction. If you can energize the relays from your existing controller you are good to go otherwise you may need a DMX relay board.
 

Attachments

·
Registered
Joined
·
21 Posts
Discussion Starter #20
That seems straightforward. I really appreciate your input. My background is in DMX lighting and video, so I'm relatively new to mechanics/automation. Where can I find more info on relay boards? Can the board handle the current?
 
1 - 20 of 31 Posts
Top