Hi all.
I have a (not so) small project that needs between 12 and 16 HS-805BB Mega Servos (still in the design phase. Images at robotsofjoy dot com)
I’m going to (hopefully!) run them off of a SSC-32 Servo Controller and I understand how external power works for the board (got one running on my desk using a DC wall cube) my question is this:
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What would you suggest for powering this thing that can pull out 10-14+ amps?*
This project is by far the biggest servo-based thing I’ve tried and I’ve never run something that a couple wall warts couldn’t take care of…
I’d just rather figure out how I’m going to power them before I drop $450 on the servos
The SSC-32 can handle 15 amps per side, so you should have no trouble if you put 9 servos on each side and run the power right through the board. Yes HS-805 servos can draw a lot of current, but it’s not likely they will all draw the max at the same time. You can even run a separate battery to each side of the SSC-32. I believe NiMH batteries are the most economical battery technology right now. LiPo is also a good but more expensive solution. There is a trade off between run time and weight. The longer you want the robot to be able to run, the heavier battery you will need, which causes the current requirement to go up even more. You need to define how long you want to robot to be able to run, then you can select the proper capacity of the battery.
Another thought. I made a round hexapod using HS-755’s pretty similar to the size and demands as you are trying. I powered the whole thing from a single 7.2vdc 2800mAh NiMH pack. The run time was ballpark 10-15 minutes.
I’ve looked into batteries for her, but here’s what I came to: The insides of the bot are, in fact, a high-powered desktop PC which I’ve decided will have to be tethered to the wall (or have a less-than-useful 5 minutes of run time) and as such I might as well just go with an AC-DC converter off the main line. Any idea where I could pick one of those up for cheap? (It’s a charity project so the more money I save on the build, the more I get to pass on.)
I was thinking of taking the 5V off of an old PC power supply but if there’s something better that I’m missing I’d love to know
The power (torque) available from the servo is significantly reduced at 5vdc compared to 6vdc or 7vdc. I don’t usually recommend powering servos over 6vdc but these large servos don’t have the trouble dissipating heat like the standard size servos do.
Hmm, I’m not sure this suggestion qualifies in the saving money dept. but assuming you are using a 300W or so PC power supply then you could possibly get away with a pair of 10A BECs (battery eliminator circuits, ued in big r/c planes) feeding the VS1 and VS2 inputs of the SSC-32 and powered by the 12V output from the power supply. If you went with the Castle Creations 10A BEC which is programmable I would suggest bumping them up to 7V or so which will help them (the BEC) with power dissipation and you with more headroom for voltage loss due to wiring resistance. I am also thinking the 805s have been tested to something like 8V w/o smoking them so if I am wrong hopefully someone will catch it and post.
If weight isn’t a big issue, and you are supplying 120vac to the bot, then you might try uing a 6v lead acid battery and a battery charger like below to supply the heavy current needs of the servos. The charger could float on the battery keeping it charged.
