My only excuse is that I’m a software guy trying to learn about hardware. Apparently I don’t know enough yet. I have an RP5, that was working pretty well, and I was tweaking the software when I started smelling something. As it turned out the battery box in the RP5 was melting and falling apart. It’s the battery holder that comes with it.
I was running the motors and a servo. Can someone point me to a tutorial or something that will tell me how to figure out how much current I’ll need and whether that current will melt my batteries?
It is probably a much less subtle problem than current draw from the motors and servos - most likely you simply shorted out the batteries. Did you have any metal parts near the exposed terminals of the batteries? Is there any visible damage on your controller board? What kind of controller are you using?
The wires on the battery holder were too short to reach the controller when I first got it, so I spliced them onto other wires. I checked the splice though and the insulation is intact, doesn’t appear that there was a short.
I’m using an arduino with an Adafruit MotorShield. The controller wasn’t warm at the time - I checked that while hunting for the source of the smell. I do recall wondering why the servo wasn’t running, but I assumed I had a bug in my code and was looking there. At any rate the Arduino still powers up and the hardware looks ok. I’m hesitant to hook it up to anything until I figure out what I did wrong though. When I did the splice I was following instructions here: mmxpress.com/technical/connections.htm
What I am specifically trying to get at is that various pins on your Arduino might protrude downward into the RP5 chassis and make contact with the springs holding in the batteries, or with the batteries themselves. This can happen if you just throw the controller board on top, without any kind of insulation in between. Is it possible that that happened?
No, the Arduino sits on a wooden platform above where the battery is, so its only contact with it is through the wires.
I have a theory though. I unhooked the batteries from the power input of the motor controller and set it aside for a while, and I suspect that the battery wires came into contact when I put it down. I’m going to start putting a piece of electrical tape over one of the leads when I unhook it.
I’m still curious about how to figure out the current requirements though. I don’t think I’ve seen figures like that for motors. Is it ok to probe the wires with a multimeter to see how much current is being used? Do you know of a tutorial that would help someone like me get a clue?
It sounds like you found the problem. One thing we often do is cut power wires to different lengths so that they cannot possibly cause a short like that.
The RP5’s motors are specified on the product web page as “two brushed DC motors with 210 mA free run and 2.4 A stall current at 7.2 V.” That means they will each use between 210 mA and 2.4 A when running at full power, depending on the load. We have a short discussion about motors in the 3pi User’s Guide that might help you understand this.
