Our drive is a 6 wheel tank drive running off 4 cim motors in a gearbox. Four of the 6 wheels are large 10 inch wheels while the other 2 are 6inch wheels. We have been running into huge issues with our drive when we try to turn and go up ramps. The voltage of our battery drops really low and it causes brownouts. This makes it impossible to drive. Does anyone know how to stop the drive from dropping the voltage of the battery?
This could be caused by several things. How long is your robot? If you have fairly grippy wheels, there may be too much force on the wheels to turn easily. However, going up the ramp shouldn’t be too bad. a couple of things come to mind:
you have inefficiencies in the drivetrain (gearboxes aren’t put together properly, lack of lube, chain/belt over tensioning, you get the idea)
Your gear ratio may be too large for the 10" wheels you are using. (please post again with this info)
Electrical resistance in you system. If you have a bad connection or wire and draw more current when going up the ramp or turning, the higher resistance will cause a significant voltage drop.
I think it’s time to do some serious trouble shooting. let me know what you find out!
If you post some pictures of your robot, we might be able to see why it’s doing that. Without knowing where which wheels are, etc, it’s hard to say. My guess is that the wheels that get good traction are too far apart lengthwise, and too close together widthwise, making it hard to turn.
There are some good CD papers on the topics:
- Skid Steer Turning Analysis: http://www.chiefdelphi.com/media/papers/3022
- Drive Train Basics: http://www.chiefdelphi.com/media/papers/1443
Some common solutions include:
decrease your wheelbase length to width ratio (in other words when the wheel contact points on the floor form a square skid steer will turn better than when the the robot is long and narrow.
Make one set of wheels (front or back) slippery so they slide sideways more easily. What kind of tires/tread?
Change up your gear ratio to get more torque.
4 CIM per side of the drivetrain for a total of 8?
4 CIM with 2 on each side of the drivetrain?
The problem is that you are stalling the motors, and they are drawing huge amounts of current to try and move. That is why the voltage is dropping.