Multiple Output voltages for different parts of a robot ?

Aaqil Khan

Hi everybody,
In designing a robot using different parts like servos, DC motors etc, whats the most efficient way to provide regulated voltages to these devices?
My robot has parts that need the following voltages:

1. DC gearhead motors - 7.2V
2. Servos - 6.0V
3. Basic Stamp 2 - 5.0V
4. Servo Controller - 5.0V
5. DC motor controller - 5.0V
3. RF Transceiver - 3.3V

I figured using LM7805, LM2937-3.3 etc in tandem to get the different voltages from one source will generally not be the most efficient way to go. Moreover, the servos (6 giant servos, and 4 gearhead motors will need a lot of juice.

So whats the most efficient way to go?

Thanks everybody for your suggestions.

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E=mc^2

Mike Green

You don't necessarily need regulated voltage for the DC gearhead motors or the servos. Check your servo documentation, you'll probably find that their voltage range is from about 4.8V to 7.2V. The Stamp and the motor controllers probably don't take much current by themselves and would work fine with an LM7805 regulator. The RF transceiver also probably doesn't take much current and should do fine with the LM2937-3.3 regulator running from the 5V supply (to reduce the voltage drop needed). If you're concerned about the efficiency of the LM7805 and LM2937, there are some nice switching regulators designed as replacements for these linear regulators. TI makes a line of these and there are other manufacturers as well. Check TI's website.

Zoot

If I might chime in here -- I concur with runnning your gearhead motors from unregulated battery power if that's an option. In my own project I did that, but I used a linear 6v regulator with a nice heat sink for the servos. The nice thing there is that even as total battery voltage drops as the battery discharges, the servos run at a constant speed (until there is not enough voltage for the reg.).

Mike Green provided invaluable pointers in wiring multiple regulators and loads to a single power supply in this thread: http://forums.parallax.com/showthread.php?p=610598. Following suggestions there I am running 5 loads from 4 different regulated/unregulated voltages without problems. Unshown in that thread is the feeding of the 9v regulated supply into the 5v regulated supply so as not to over-burden the 5v regulator.

Lastly, the addition a few heavy-duty diodes between the battery and the main logic supplies did two things -- helped drop the unregulated battery voltage a bit further to ease the load on the linear regulators and helped prevent a ground-loop lockup on my motor driver when I hit the motor supply kill switch. With switching regulators the burden on the reg. itself is obviously less of an issue. Had I known about some of the integrated switching supplies when I built the boards, I probably would have used them (but they are big).

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When the going gets weird, the weird turn pro. -- HST