Powering more then 2-3 servos on a robot can became a rather large pain in the side. I've never addressed the concern for powering several servos at once before with out either burning out a voltage regulator or just using batteries in the proper range for the servos.
With my new robot David, a small humanoid, about the size of a toddler, I needed to power 6 servos from a 12 source. David's power is going to be a 12volt SLA rechargeable battery, but for now is is powered by a plug in Ac-DC source. Originally I designed a power system with a 12 volt regulator (7812) to provide power to a (7805) 5 volt regulator for logic circuits and a (7806) 6 volt regulator for the servo power. I soon found my design was flawed in several ways as all of my regulators were getting hot and in certain circumstance they would go into thermal shutdown and stop working.
I really wanted to create a power system that was simple, cheap and would provide all of David's power needs from a single power source. His power needs include Basic Stamp IIe, a mini Serial Servo Controller II board, (6) standard servos, a laser tag gun, several sensors for motion and object detection, (2) 12V dc drive motors and PWM control boards for the DC motors. When Davids motors are running, the amperage demands can really add up.
Through discussions on the TRCY.org Yahoo Messageboards, several members contributed ideas to my issues which lead me to discover a few things.
1.) I needed to get rid of the 7812 12volt regulator, as it was rated for 1 amp, it was doing none of the other systems any good.
2.) I was mistakenly powering the mini Serial Servo Controller II board from the 7805 5volt source. The documentation states the logic power needs to be 7-15 volts as the board has it's own regulator.
3.) I had no heatsink or supporting filtering caps on the 7805, I added a heatsink and a 10uf cap on the input side of the 7805 regulator.
4.) The 7806 was doing me no good as the servos did not need that much power. I replaced the 7806 with an interesting setup for dual 7805 regulators wired in parallel, with heatsinks and 2 filtering 220uf caps and a filtering 100nf cap.
5.) The 12volt dc motors and PWM control boards get their power from 12 volt power source, not through a 7812 regulator like I was trying to use.
6.) Large diodes like the 1N4001 can help drop the input voltage down going into 7805 regulators by as much as a volt for each diode used. When you consider ever volt over what the regulator requires is often wasted as heat, diodes can come in very handy.
This method so far is working well for me. I did find it hard to find good reference sources for powering more than 2-3 servos from anything other than directly from a battery source rated for the needs of the servos. So I wanted to share what I learned from my experience.
Heatsinks are a MUST! Caps help a lot! Discussing your designs problems in a group like TRCY is a wonderful resource!
As an added note, a couple of good suggestions that the discussion in the TRCY group offered were to use a premade 1.5 amp regulator board: http://www.wrighthobbies.net/catalog/product_info.php?cPath=28&products_id=146, as suggested by Eddy Wright of http://www.wrighthobbies.net
And another interesting idea I might try in the future is to use an individual 7805 regulator for each servo. This prevents an overdraw of current and will help reduce heat. My dual setup works for, but considering how cheap 7805 regulators can be when purchased in bulk, it's an interesting design idea submitted by "David" AKA robots42
Another product I came across that looks promising is a 10w Adjustable Switching Regulator designed to fit in the space a of 78xx series regulator: http://www.robotshop.com/dimension-engineering-de-swadj-1.html
P.S. I want to thank HVLabs for posting their circuit design online, which is where I got the idea for my modified dual 7805 regulator setup. See the original circuit here: http://www.hvlabs.com/serservo.html
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