Hello,
I am hacking together a bot, and I am using 2 continuous rotation servos. I have lipoly 7.4v battery packs. 7.4 volts is too high to power the servos directly according to my research, so I am wondering if I can safely power the two servos with the 5v from arduino's voltage regulator. Does the regulator have enough capacity for the servos?
Thanks
It's a little risky. Some servos might never draw enough current to damage the chip, but two servos under load would probably do damage - but I'm guessing without the motor specs and the load.
Safety first - drive them with transistors or an H-bridge. I hacked a pair of servos, then put L293 boards in them (very little boards). Now they are bidirectional, and I can run both of them off 6V easily. You can find lots of H-bridge circuits on the web, and you can listen in on the "motor party" thread in the Hardware/Development forum to hear more than you want to know about the subject of driving servos with Arduino!
I don't think something like an H bridge is necessary. The arduino pins will be controlling the servo speed with low current pulses, so no problem there. However the total current drain on the 5v regulator could be higher than it can handle but the regulator should shut down without damage if the current is more than it can handle. Try it while checking if the regulator gets too hot to comfortably hold your finger on it. If it does or the servos and/or Arduino are running erratically then you need an external 5v regulator for the servos.
The need for an external regulator really depends on which regulator is fitted to your board and the current drain of the servos.
Thanks for the info.
Mem, do you know where I can find the data sheet for the arduino voltage regulator?
It depends on the board you have. Can you see the part number on the regulator (the largish chip next to the power input socket)?
If its an MC33269D then the datasheet is here:
The chip has the following numbers on it:
269-5G
RX719
I just got back from radio shack. I got parts to make a couple of DC-DC power supplies with 7805 regulators. I won't feel bad if I fry those.
Thanks!
There are a few varieties of Arduino boards and a few suppliers that make them. I don't recognize those numbers so can't comment on the current capacity of your onboard regulator. But if you have an external 7805 that should be fine for powering two typical hobby servos. The 7805 will shut down if it is overdriven so you shouldn't fry it if you wire it up correctly.
What is the make and model of the servos, I may have some data on the current requirements.
the part marked "269-5G" is the On Semiconductor version of the Motorolla part:
On Semi MC33269DT[ch8722]5.0
http://www.onsemi.com/PowerSolutions/product.do?id=MC33269
5V @ 800 ma max output.
D
But it's prpbably not a good idea to draw 800 mA from it without a heatsink on it.
Hey!
Thanks for all the help on this thread, it is first rate. I got my little DC to DC power supply built using a schematic found at:
http://www.tkk.fi/Misc/Electronics/circuits/psu_5v.html
I built up two of them on perfboard, and they are working fine.
Mem, the servos are from parallax (off of a boe bot)