Sensors to sense the Robots sensors

[Krumlink]

I have been given the task to design a control module to control my F.I.R.S.T. Robotics team's Robot. I was wondering what Kind of sensors I should incorporate into it? These Sensors are to Sense conditions on the robot itself, not to actually be a sensor for the robot. I have listed a couple below.

H-Bridge Temperature Sensor
Motor RPM
Amp rating
Power ON

I also need a little info on how to configure that sensor. Thanks!

 

[mneary]

All of these can be set within the 0-5V capability of the FIRST Robot Control Module.

Are you running out of inputs on the RCM?

 

[Krumlink]

Yeah, we Were going to use the spare I/O pins on the Microcontroller and send it wirelessly. They were going to tackle the wireless feed while I had to design a control box. I was going to design a couple PCBs and have them be underneath the main box. We will configure the PIC and the Rx and Tx later, but I need some ideas for the sensors. We are still in the design phase for our next robot, but we need a nicer looking control box.

Thanks

NOTE: The amp rating on the robot can reach up to 100amps with a safety throw of 120Amps. For the Power on indicator, how would I do that? MUST HANDLE 120AMPs.

 

[Ambient]

You could use a shunt. Just put it in the current path and sample the voltage across it. I believe I saw one on allelectronics.com for cheap. Or you could use a current sensing coil, but those might be expensive for that current rating. You could also measure the voltage drop on the motor wire itself. Just measure the resistance and do the math in the micro. You can use an op-amp to measure the voltages and to buffer it from the micro.

For motor rpm, there was a thread a few months back discussing a good method using filters, but you could also use a hall switch on the wheel and multiply that freq by the gear ratio.

 

[mneary]

MUST HANDLE 120AMPs.

Do you simply want to know that power is ON or do you need to measure the current? For the former, just a resistor divider from switched +12V to 0V would do the trick. For the latter, I would try a Hall Effect sensor next to the wire. Google hall effect sensor measuring current in wire. **broken link removed** looks useful.

By the way, for your secondary controller, consider using the VEX RCM. It probably has all you need, with familiar connections and a common programming environment.

 

[mneary]

You can also sense the voltage across a known length of the power wiring. iirc, the wire is 6 AWG, which would be 1.3 milliohms per meter. A 10 cm length would develop 13 millivolts with 100A. This can be amplified and presented to an analog input. Use the (-) cable, possibly between the main power block and your gold fuse block.