Hi, I am using a Dagu Wild Thumper 6WD (34:1 gear ratio) with a Roboclaw 15A dual channel controller. My project also includes 2 servo motors that move a DSLR camera up to 5 lb, a Flysky receiver and a simple FPV camera which draws power from the receiver.
I’ve noticed that my rover often gets stuck over simple obstacles, or even grass or a carpet. If one of the wheels loses contact with the ground (usually a front one), that wheel spins in place but others do not. Turning the rover around is a challenge for the same reason - one wheel on either side spins, but not the rest.
My guess is that this vehicle is underpowered and only some motors draw power under load. On flat, hard surfaces, all motors operate as expected.
Should I be upgrading to a higher spec Roboclaw, or could something else be the problem? If upgrade, should I get a 45A / 30 A controller? With 6 motors that have a 6A stall, it looks like peak power requirement would be 36A?
If your robot is underpowered, then I suspect the batteries are more likely to be the limiting factor instead of the motor controller. What are you using to power your Wild Thumper? It is possible to use the RoboClaw’s USB and serial control interfaces to monitor the how much current is being drawn from the outputs; have you tried looking at that?
You might also confirm that your RoboClaw is not configured to limit the current unnecessarily low; however, keep in mind that increasing the current limit will make it allow the motors to draw more power when they encounter heavy loads or stall, which could lead to rapid thermal damage (potentially on the order of seconds). A general recommendation is to keep the continuous current draw to 25% or less of their stall current.
Thank you for your advice. I am using PowerExtra NiMH batteries that operate at 7.2V with a 30A maximum discharge rate. One battery has a capacity of 3000 mAh and the other is 4500 mAh (only one is used at a time).
To use the USB, I think I will have to keep it connected to my computer. How should I simulate load for this test? The current limit seems to be reasonable (default). At 25% of their stall current, would the total power draw be 9A? (6 x 0.25 x 6A, since there are 6 motors)?
As long as your batteries are charged, that seem like a sufficient source for this, and 9A on each channel should be an okay current limit if your motors are connected in parallel to the RoboClaw outputs.
Unfortunately, I do not have many specific suggestions for how you should simulate a load since I do not know what resources you have available. One option might be to find the longest USB cable possible and connect it to a laptop running the control software that you could use to follow the robot around. Alternatively, maybe you can set up something like one of the obstacles where the chassis gets stuck near a desktop work station.
It would still be good to look at the actual current draw to confirm if you can, but given your supply and current limits, a power issue seems less likely. It is possible you might just be approaching the limits of what your Wild Thumper can handle with the weight of your payload. How much of an improvement do you see if your reduce they payload your chassis is carrying, such as by removing the servos and DSLR camera and any other equipment you do not need to just make the robot drive?
