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I have assembled my robot and now am trying to figure out why performance is poor. My setup consists of the
TE-091-225 Sabertooth Dual 25A Motor Driver
TE-900-004 Programmable xBee Control Interface Package
TE-090-ADJ Adjustable Switching Regulator Board KitI control the robot using the Arduino/XBee remote. I am experiencing at times good control, no control, motors moving at 1/10 the speed they should, error light on the Sabertooth board lighting up, that same error LED staying lit and buzzing for a few seconds after I make a move, and so on.
My first thought is that I have the grounding or noise suppression screwed up. I have carried the ground from the batteries to the controller first, then to the regulator and then to the Arduino. Should I instead create a ground lug on the chassis and run the grounds in a star configuration, tying them all to the ground lug? My Sabertooth controller is bolted directly to the chassis. My four motors each have the three ferrites and three capacitors.
The switches on the Sabertooth are in the positions they came to me as (1-2 OFF, 3-6 ON). Sometimes I can make the robot move forward and backward, but not turn. In any event, I think the hardware is good and I need to chase down noise demons. Any advise is appreciated.
I added a photo of my setup. In the photo, I had added a ground wire from Arduino to the Sabertooth, but I removed it to avoid having a ground loop.
The file size of your picture is too large to post. If you send your picture to sdr at sdrobots.robotdns.net with your order number, I’d be happy to address your problem here on the forum.
My recommendation is the following:
– Any ground wire currently connected to your Sabertooth ground needs to be disconnected. This is unnecessary since they already share the battery ground.
– Disconnect your Sabertooth from the motors and make sure there is -24V and 24V at max forward and reverse.
– Use shielded wires instead of speaker wires when connecting the Sabertooth to your motors.
– Remove the motor capacitors.Let me know if there is still an issue.
I spent the evening working on the robot. Here is what I did. I attached a couple of pictures.
– I removed all 12 capacitors from the 4 motors
– I cleaned up the wiring to each motor so that it is shielded up to the connections
– I removed the ground line from 0V on the 4 pin header, leaving only the line from Digital 3 to S1 (0V is internally connected to B-)
– 24V comes from the batteries to Sabertooth and then to the regulatorInput to the regulator is 24V, output is trimmed to 9V, which is fine for the Arduino UNO. I disconnected the 4 motors from the Sabertooth board and tried to measure changes to the open outputs, but readings were very unreliable. I imagine leaving them with no load was the problem. I reconnected the motors and measured the voltages across each motor pair as I moved the joystick to full forward and reverse positions. What I found is that the voltage swings were not symmetrical at all. They went from approximately +65V to -8V, a far cry from +/-24V.
The good news is that the noise problem seems to be gone now. After several minutes of testing, the robot only had a couple of instances where moving the joystick did nothing. Overall, it worked very well. I didn’t notice the error light coming on at all.
I also plan to alter the joystick functions. The default performance is froward/reverse in one axis and right/left in the other. Pressing the joystick button gives left/right in one axis, nothing in the other axis and twist gives forward/reverse. What would work better is to have forward/reverse in one axis and twist to do left/right. That way, I can move the robot in a straight line easily and apply a gentle twist to nudge it left or right. This seems to be a more natural way to operate.
Glad to hear the noise issue is resolved. Although, the output of the Sabertooth shouldn’t spike to 65V since it can’t amplify the battery voltage. I would make sure this isn’t the case since you ordered 24V motors. If everything is running properly and your motors haven’t burn up by now, I’d imagine you’re in the clear.
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