For reasons too complicated to explain, I am trying to drive a small brushed DC motor from the A channel of a Tic T500 board. I get very erratic output from the MP6500 driver which I’m pretty sure is due to brush noise. I can sort of fix the problem at very low currents by adding an inductive filter to the motor leads, but if I try using standard capacitive filtering (cap across motor leads, caps to motor body), the driver won’t drive at all. I’ve done this in the past with other stepper drivers (ST, Allegro), so I’m assuming the MP6500 is particularly fussy.
Does anyone know if it is possible to drive a DC motor using the DRV8834 or DRV8825 drivers on the Tic T834 and Tic T825 boards?
I have used our carrier board for ON Semiconductor’s AMIS-30543 to do current control in a pair of brushed DC motors (these plastic gearmotors) before. That driver has an SPI interface that allows the current to be changed dynamically. I didn’t do a lot of experiments with alternate configurations, but in general, that seemed to work pretty well for making a sprinting robot with differential drive that accelerated rapidly in a straight line without any feedback. In theory, it should be possible to do the same sort of thing with a any of our Tics, but we haven’t actually tried that here.
The current control algorithms in the various stepper drivers we carry vary quite a bit and low resistance, low inductance coils (and high supply voltages) can cause problems for some drivers. I have a summary here that details some problems commonly encountered with that using the DRV8825. It’s not clear to me whether your issue is a similar current control issue, but if it is, the DRV8825 might not be a good choice for you application.
Thanks, Nathan. I don’t think the problem is low inductance or resistance as the driver behaves OK if you lock the rotor. However, once it starts spinning (with the attendant brush switching noise) the indexer goes bonkers and advances which results in the motor starting in one direction but then reversing direction as the winding current is reversed. Good to know that the AMIS-305043 works with brushed DC motors, though. I’ll have a look at that chip’s specs.
-Jeff
We have recently revised our Tic T500 controllers to work better with low-voltage, low-resistance stepper motors at high supply voltages, which could lead to lost steps with the original version. I still suspect this was the source of the trouble you were having trying to control your brushed DC motor, and I think the revised version would work better in your application. We can arrange for free replacements if you email us with your order information.
Cool! I need another board anyway, so I’ll just get a new one to handle my DC motor. Is there anything special I need to specify to make sure I get the new rev?
Not if you’re getting them directly from us. We have pulled all our stock of the original version and are only shipping the new revision now. (We are still working on getting replacements to our distributors, so at least right now, you might still get the old version if you order through one of them.)
