I recently ordered a Wild Thumper 6WD robot chassis to build for a school robotics club project. I've built smaller, simple robots before, but I haven't built one with such high power requirements before.
I bought this from Sparkfun, along with a recommended battery - a 7.4V 2200mAh 35C discharge rate LiPo with a Deans connector for output and a jst connector for recharging. I also got their recommended charger/balancer. I plan to get an identical second battery soon, if this one works out. Additionally, I have a Sparkfun Monster Moto shield that they say handles the Wild Thumper well in their usage. It can handle 14A continuous and 30A max per channel.
Each motor has a 420mA no-load and 6.6A stall current draw. So, that means I'll need both wiring and a motor controller that can withstand up to at least 19.8A per channel
So my questions are about wiring the motors to the motor controller and to the battery. The six motors are wired in two groups of three motors, one group per side, to make driving the robot with a differential drive system using a two-channel motor controller.
Pictures are here: http://campl.us/GVZsJcecyGW
First question: What minimum gauge should I use for connecting the battery and motor controller to the motors? The battery uses 12-gauge wire, but the chassis' own wiring harness for the motors uses 20-gauge. So, is mixing different gauges ok?
I would like to use connectors, like the Deans connectors that came with the batter to facilitate unplugging / changing components, as well as a nice switch. I know the chassis power connectors are difficult to see, but can anyone recommend a good connector to fit those?
Third question: Is the Sparkfun Monster Moto shield adequate for the motor performance ratings? The motor datasheet doesn't say what the typical operating current draw would be, presumably because it varies with speed an other usage factors.
Also, would powering the motors with a reduced voltage, say 5V, reduce current enough to use a less expensive motor controller? I don't need it to go fast; just to carry a lot of sensors. The motors have a 34:1 gear ratio with a stall torque of ~ 5kg/cm and a top speed of 7km/h at 7.4 volts. Besides reducing the speed, what effects would restricting the voltage have? I'm not sure how to figure out the changes in current because I'm not sure what the resistance would be at 7.4V
Thanks in advance!