just to be clear, we are using 4 v4 motors on our drivetrain. So basically, after a few seconds, our left side drivetrain fails, and shortly after so does our right side. We think this is a ptc issue, but we are not sure.
Pictures, code, video of this happening… We need something to work with!
Useful information would be internal and external gear ratios, weight of robot, how long if it spins freely if the motors are removed, and if you ever try to push anything from a dead stop.
the robot is at school right now… but all 4 motors are high speed and there are 2 motors on each of the back wheels on a 1 to 1 external gear ratio which then connects to the front wheel via chain and sprocket. this is also a 1 to 1 ratio.
How heavy is your robot? with 4 HS motors u don’t wanna be more than 20 lbs
Honestly I would recommend getting at least a six motor drive train. Four legacy motors is barely enough to drive a 17 pound robot and it won’t get you anywhere in a pushing match. However if your intent on staying with that, go through each of your wheels and spin them freely. If they spin for around ten seconds your fine, but below 6 is where you’ll start having issues. Also check each of your bearings to make sure they are working correctly, and lubricate every moving object, even chain. I recommend 3 in 1 oil for this application so you don’t get in trouble with the refs.
In my experience, each motor should have its own port on the cortex, dont use y splitters. Theres 2 circuit breakers on the cortex, one for ports 1-5 and one for 6-10. You want your drive to be split among the two, not all running on one. Also you want each side of your drive to have its motors split across both breakers. So if right front motor is on port 2, you want right rear motor to be on one of the 6-10. That way if the 1-5 breaker trips, your whole right side doesnt go down, and youre not dead in the water. If that doesnt make sense, tell me which ports on your cortex go to what, and ill tell you how to hook it up.
our left side drivetrain is plugged into ports 1 and 6. Our right side drivetrain is plugged into ports 5 and 7. But the issue still stands. Thanks for the advice, though. This was done without realizing.
here is a video of our robot, sry about the noise in the background
link text
that’s a lotta’ steel you got there
After watching the video, I recommend the following. As has been noted above, either change to 6 motor drive or change the gearing from high speed to torque if you stay with 4 motor drive. As for your motors on the Cortex, don’t use port 1 or 10. Have one of your right side motors plugged into ports 2-5 and the other into ports 6-9 and one of your left side motors plugged into ports 2-5 and the other into ports 6-9. That way if one of the Cortex PTCs trip, you can still drive. Watching the video, it is hard to tell which PTCs are tripping, however given how heavy the robot appears to be, my bet is on the motor PTCs.
if i have a 6 motor drive, which ports should I put the motors in?
@mkinh I had this problem last year with a 4 motor drive… even with a 16lb robot it was very unreliable and just simply not strong enough. What I would recommend is the following:
- Make your robot as light as possible without compromising structural integrity. Only use aluminum
- Make sure there is as little friction as possible in the drive. With no motor attached to the shaft of the wheel it should be able to freely rotate. I usually like to give it a spin and make sure it could spin freely for at least 10-15 seconds.
- I would also recommend using 6 motors on the drive if you want to keep them high speed.
- Split up the ptc’s on the cortex: I usually like to vary them a lot, the only thing you have to be wary about is if you are using and put something on the power expander because different battery voltages will give some motors a slight bit more or less power. I don’t know you full robot setup so the exact ports I can’t really tell you but I can give you an example of what I did in for Starstruck which worked extremely well:
I like thinking about wiring it like this: First I isolate what area of my robot is drawing the most power. Then I try to figure out a way to lose friction or something so it doesn’t need as much power. Finally, I try to wire it so that the most power hungry mechanism is on a ptc with not so intensive mechanisms. In my starstruck case I had my Y-cables basically alone because the claw motors basically do nothing and I put the lift ones on the power expander.
Cortex:
Port 1: Claw 1
Port 2: Right lift 1
Port 3: Left lift 1
Port 4: Right drive front… on power expander
Port 5: Left drive front… on power expander
Port 6: Right lift 2… on power expander
Port 7: Left lift 2… on power expander
Port 8: Right drive back (Y-cabled/2 motors)
Port 9: Left drive back (Y-cabled/2 motors)
Port 10: Claw 2