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I have built a robot from a wheelchair that has worked very well thus far. It is now time for me to take the next step. I need to implement a permanent power circuit with proper protection.

The lowest level of protection I can think of is a fuse, but I would like to take a step further (current/voltage/direction/switches/High/Low voltages). If some one could give some insight on this project of mine any info will be greatly appreciated.

Moderator comment: Please see How do we address questions about related subject areas? before answering. This question is close to the boundary, but is on-topic here.

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  • $\begingroup$ You might be better off asking this on the electrical engineering SO site. $\endgroup$
    – Mark W
    Commented Dec 6, 2012 at 11:02
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    $\begingroup$ The answer will depend on what constitutes "high" voltage and/or current. Can you provide some more information and specs? $\endgroup$
    – Ian
    Commented Dec 6, 2012 at 14:44
  • $\begingroup$ I agree with @MarkW, while your question is perfectly on topic here, migrating the question to electronics.SE will probably give you better answers. If you do want to get it migrated, just flag the question for moderator attention and state in the text box that you'd like it moved there. $\endgroup$
    – ThomasH
    Commented Dec 6, 2012 at 15:00
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    $\begingroup$ While this question may get a more electrically complete answer on Electrical Engineering I suspect that answer here may be more directly relevant to the questioner as they will take into account aspects that electrical engineers without robotics experience might not take into account. $\endgroup$
    – Mark Booth
    Commented Dec 7, 2012 at 15:43

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I think this is a very relevant question for robotics, as you can spent a lot of time fixing your system if something went wrong in this area. Here are a few things to look out for:

  • Insulation: Ideally you don't want any high voltages to reach your equipment in the first place. So one of the most important rules we apply to our electronics is insulate. Try to have as little conductive surfaces flying around as possible. Especially when you system is moving, having something flying around that is conductive can screw you in the literal sense. insulation tape, tubing whatever are the weapons of choice here.

  • Connectors: Try never to use connectors that could be plugged the wrong way, or use the same connectors for different ports. Always check your connector thrice on the running system with a voltmeter before connecting it.

  • Diodes can be useful to prevent overvoltage or reverse polarity, they are however useless if your power source is very powerfull, burns your diode, and gets through anyway. That is what a crowbar circuit will prevent. Its a combination of a fuse and a diode and will fix both overvoltage/overcurrent and reverse current. There are integrated parts available, and I've also successfully used polyfuses for small equipment.

  • Resistors in series for data lines are also quite useful as they limit the current flowing through. Something between 50-100 Ohm should usually do the job.

  • Fuses are generally a good idea, especially when you use power sources with very high current capabilities (e.g. LiPo).

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    $\begingroup$ +1 for resistors in the data lines. Can you add any insight into how to choose values for these? $\endgroup$
    – Ian
    Commented Dec 7, 2012 at 12:50
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    $\begingroup$ This is relevant only because robots use electricity. Would we answer a question about installing RAM in a computer, because robots use computers? Or about inflating tires because robots might use tires? $\endgroup$
    – Josh Vander Hook
    Commented Dec 7, 2012 at 16:12
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    $\begingroup$ Very informative Jakob! +1 $\endgroup$
    – user697
    Commented Jan 3, 2013 at 9:32
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Keeping with the idea of robotics-relevant answers, another thing to take into consideration for mobile/wheeled robotics (albeit not so much with a wheelchair unless you plan to take it off-roading) is vibration and shock. In reviewing your design, ask yourself: is there anything that's going to come loose? Think connectors that aren't a very snug fit or jumper wires connected to a header pin.

There's been some questions with great answers on Electronics.SE that cover this area at the PCB level:

SMD vs. Through-hole components in high vibration environments

Board Design for High Impact Environments

While this is a pushing outside the scope of the question, be sure to account for disconnect/power loss conditions in software when possible as well. There's not a whole lot you can do on the power side if it's a single-supply system, but if you have multiple subsystems powered off of different supplies, you can monitor supply voltages so that one component can be aware of a failure elsewhere and act appropriately.

If your robot is controlled over a serial interface and the onboard controller can't get some kind of "heartbeat" signal from the host system, it needs to fail gracefully and not go careening down a hallway uncontrolled because the last command it received was "go forward".

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