To start, I purchased the Simple-H 20A, 5V to 28V DC Motor Driver (Product Code : RB-Rop-05)
My goal was to control a wiper motor like a servo. I needed a lot of torque, but needed the position control I get with a servo.
Here’s the background. I saw a video online of someone doing EXACTLY what I wanted to do. You can find it here: https://www.youtube.com/watch?v=youtube.com/watch?v=2Ny33eoy3q0 (Skip to 1:30 in for the relevant part)
I took apart an HS-805 large scale servo from HiTec. Removed the board, disconnected the motor and POT. I attached a 5K POT to the wiper Motor shaft in similar manner to what was shown in the video.
I bought the simple H Bridge here and connected it up as shown in this picture: (Once you click on the picture, you’ll have to use your BACK button to return to the post.)
halloweenskulls.com/Issue01.jpg
On CN1, I connected the two motor outputs from the servo controller card to PA and PB. I connected a 5VDC line to EA and a GND connection to the " - " connection. That GND is also connected to my 12VDC power supply which is correcty connected to B+ and B- as shown here:
halloweenskulls.com/Issue02.jpg
The Wiper Motor is connected to M1 and M2. The potentiometers feedback goes directly to the board I pulled from the servo where it used to go.
I ran a routine which told the motor to go in one direction, then hold, then go back, and it seemed to work just fine. Nice and smooth and plenty of torque.
When I added the linkage and gave it something to lift, a strange thing happened. It lifted the load absolutely perfectly. very smooth at any speed, and plenty of torque.
On the way down, it did not go back smoothly at all. I was returning it to it’s starting position, but it was very jerky while gravity was working with it. I noticed that on the way up the green LED on the board came on constantly until it reached the top and stayed on while holding its position, until it started to go back down. At that point, I fully expected it to switch polarity, and for the red LED to come on and stay on until it got back to its starting position, but that didn’t happen.
Instead, it continually switched back and forth between red and green jerking the motor each time it did until it returned to the starting position. It did get back to its starting position and works correctly as far as going where I tell it to at the speed I tell it to, but I can’t figure out this bizarre behavior of switching back and forth.
I have made a brief video showing the issue, so you can see the board responding when the servo board was told to go one direction, then back to the other. That video is here:
youtube.com/watch?v=q6ZvuVMsE-U
In case it makes any difference, I was using VSA software from Brookshire software to control the servo through a DMX servo controller.
I hope I can solve this problem. There’s only one thing I can think of that might be causing this issue, but I haven’t been able to test my theory out. Since this didn’t happen without a load on the motor, I thought that it might be possible that when it starts to go down, there might be a slight bounce when the arm starts down due to the eight and gravity. that bounce could cause the H Bridge to compensate by switching direction to slow it down, which in turn creates another bounce, and a never ending cycle all the way down. I’m sure the commands I send it are not at fault. I simply tell the servo to go from one value, to a higher value, hold there, then back again. It doesn’t get any simpler than that.
If I am right, and there’s no other reason for that, what can I do to correct for this issue? I might be able to put a spring in to create pull in the opposite direction, but that would lighten the load on the way up and may cause the same problem going the other way.
I am hoping that there is something I have overlooked or some way to correct this electronically or by programming it differently. My thoughts on what may be causing this are only a guess at best, so I have no reason to believe that’s what is actually happening. Maybe the H Bridge could use some sort of filter across the terminals or some kind of voltage clamp or something.
I hope someone can help me with this.
Hi HalloweenBob,
First, our suggestion to control a DC motor like a servo would be the Jrk module which is actually made for that purpose.
There are many different versions available depending on your motor specs. HERE
It’s setup with an application through USB so it’s easy to work with.
Your setup is hard to troubleshoot as it is not intended to be used that way.
It could be over-voltage (induce by the motor itself) or over-current.
Is there a way to hook up a voltage clamp that might quiet it down? How would I connect it? I have the resistors left over from a failed attempt to make this work using a Sabertooth 2X32 board hooked up to a Kangaroo X2 board from Dimension Engineering. Couldn’t get it to work consistently, and it kept losing it’s position bit by bit until it was so far off that it wouldn’t function. I then tried a Actobotics Dual Motor Controller which worked fine until I connected the weight the motor was lifting, and suddenly it didn’t have enough torque to lift it all the way. Only went half as high. It would go the rest of the way if I gave it an assist with my hand, so that was useless. This was my third choice for getting the job done, and except for the odd switching behavior on the way back down it works better than every other option at a fraction of the cost. I would like to try the voltage clamp since I am using a power supply and not a battery, so that could be a problem. I just wonder why it’s only happening on the way down, and not when more power is required on the way up? So is there a way to test that? How would it be connected?
Again, hard to troubleshoot.
However the motor on it’s way down might produce voltage as well and could put the controller in error.
To simplify my two voltage system (6VDC for controller cards and hobby servos, and 12VDC for the wiper motor) I decided to just get a powerful 6VDC power supply and use a voltage booster to supply the 12 Volts to the Simple H. For whatever unknown reason, this solved the problem. I was hoping to just simplify my system with fewer wires running and fewer pieces of equipment, but perhaps the voltage regulator (amazon.com/gp/product/B017S … UTF8&psc=1) conditions the power in some way that the simple H likes better, or something. I don’t know what the reason is,but it now works completely as expected, nice and smooth in either direction just as it did without the weight attached to the motor. Since that seemed to have solved the issue, there was no need to try tension springs or anything else. I don’t know if we consider this ‘solved’ exactly, but with the addition of that step up booster, it is now running smoothly.
