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Topic: BTN7970 Motor Driver (Read 17015 times) previous topic - next topic

drewdavis

I will double check the wiring and run the DRC but I believe it should be ok. Thank you so much for your help with this project… I would have been lost on my own!


MarkT

How much current are you expecting worst case?  The high current traces look far too small.

Also the heat spreading topside copper under the devices should be nice and large to help
dissipate heat.
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drewdavis

#47
Aug 07, 2013, 02:24 am Last Edit: Aug 07, 2013, 02:28 am by Drew Davis Reason: 1
I don't know. The motors have no data sheet. With no load they pull about 2amps @ 12v. They should NEVER stall.

Also, I have updated the board a little bit. I had a few traces going to the wrong place.


EDITD:

I forgot to mention I get lots of errors when I run the DEC. Most have to do with the via's not being the right size, however, I just used the default… I never changed the size. Any ideas?


Thanks!

zoomkat

Quote
Re: BTN7970 Motor Driver Finished!!!


So you have actually built the motor driver and it is working with the motor?
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drewdavis

No sorry. I thought the form was finished as it appeared that the PCB was right. In fact I was about to order it untill MarkT found some more problems with it. I have edited the subject line.

Do you think the PCB looks good. Now I'm afraid to order it.




Mark_Grass

Didn't want to start a new thread and this one seemed to be similar.

I have a board that I designed for the dual BTN7970.   I'm running a right angle worm gear motor with it.  Actually, the motor is being used as a very large servo.   I've mounted the feedback pot on the back of the output shaft.  It works great.   What I ultimately need is a dual servo 328P module that receives it's position information serially via RS485.   My BTN module has 3 opto isolated inputs (enable, IN1, and IN2).   I only drive IN1 with a PWM signal.   IN2 is a digital signal that controls direction.   So for reverse, IN2 is high and invert the PWM signal to IN1.   i.e.  100%DC on IN1 would be off and 0% would be full on.   By doing that I can control both servo motors with pin 9 for one and pin 10 used for the second motor.   All that being said,  I seem to have a noise problem when I'm running both servo motors.   It happens when the motor is switching directions.   While servo one is at it's correct position and stable   I have the second servo cycle about +/- 30 degrees.  When this servo hits the end of the sweep and reverses direction the second servo jumps several degrees.   Sooner or later the, servo one will jump back to the correct position.   It's a random occurrence.  The supply for the motor drive is totally separate from the 328P.     The supply for the 328P is the same as for the 328p that is sending the serial rs485 data.   I'm not sure if it's a problem with the changes in vcc for the two 328 chips or not.   I have validated that the target position data for servo one has not changed.  It's stable at  400 (0 to 1023). What has changed is that the analog reading of the feedback pot changes.   I haven't been able to isolate the glitch.   May be a problem of the VCC as the ref. voltage.  may be switching noise.   I would have thought that having the supplies separate would keep that from happening.   AS for the design of the board......The data sheet suggest having 10k resistors in series with the IN and Enable pins.  As mentioned earlier(DC42 mentioned) I also have a 1k resistor from the input pin to ground.   What I'll try doing is removing the resistors that shunt to ground and also try  playing with the slew rate resistor.   The datasheet doesn't give much info on it, but if I drop the supply voltage from 12 v to about 8v, the glitch goes away. 
Anyone have any ideas?

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