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We built a very robust current monitor for speed controls. The negative current return wire from the SC to the fuse block is used at the current shunt. 10 G wire has a resistance of about 0.005 Ohms per foot. This gives 50 mV signal when 10 A of current is flowing.
We simply connect a 24G wire from the negative power supply terminal on the SC to our PC board where a simple Rail-to-Rail op amp circuit amplifies the voltage by a factor of 50 to 200 such that the output voltage is 1V=10A. A variable gain of 1-200 on the op-amp allows us to use a shunt wire length of about 0.5 ft to 10 ft (really no upper limit).
We also use a 10Hz low-pass filter on the output of the op-amp to smooth the square-wave current signal to a stable DC voltage.
Our PC board also has a microcontroller that measures the currents on four SCs 5 times a second to generate a "fuse trip warning" that is transmitted to the RC. The uC uses a heat model to estimate the temperature of the 30 A fuse and alerts the RC when the fuse is within 1 second of tripping. The code in the RC then watches for the warning signals (digital inputs) and shuts down the the SCs when they are close to tripping the fuses. We also have a warning on the dashboard that shows which SCs are overheating the fuses.
The uC is also used to measure two shaft speeds via the optical sensors. The speeds are compared and if one is faster than the other the analog error signal output from the uC is used by the RC to slow one motor down. This keeps our robot going straight.
But in the end, we don't know how useful these little gadgets will be in competition.
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