time to stop bothering jim with emails and bother the whole forum instead!
i have built two arms using the servo erector set and have 10 hitec 645MG servos altogether. i started off using an OOPicR but dropped it when jim told me they half the available power to the servos. so i dug out my old SSC-12 v1 and got hold of a 7.5V 4A power supply. the little power jumper board i hacked together didn’t work so i thought ‘what the hell’ and plugged the supply straight into the V in on the SSC. my arms worked beautifully - all 10 servos running smoothly at the same time… until i left one arm at full horizontal extension for about 5 minutes, i.e maximum load on the twinned lift servos at the base. the magic smoke got out of one of the servos and the rest felt pretty hot.
so is this the fault of plugging the 4A straight into the miniSSC? or is it because the servo itself was at too much strain for too long? am i giving too much current to my servos anyway? would getting the SSC-32 and plugging the big supply into the seperate servo power connectors solve my problems?
I don’t believe that you have an SSC problem.
From the sound of it, you have a power to weight issue.
If you’re connecting all ten servos together on one arm, I can see why you’d have such problems.
You might think that more servos equals more power, but that’s not the case, unless you’re using two on the same axis.
If you simply have one long arm of (10) 645’s, the problem areas will be the servo connected to the base, and any other servo that is bent more drastically than the others.
Btw, overvolting servos is possible, but not exactly recommended.
Any flaws in your design will be multiplied when you demand more from the servos.
If you’ve got the money to burn, go ahead and overvolt them, but be sure not to leave them in one position for more than a minute or so.
If you’re wondering why leaving them in one position causes so much stress, you can perform this experiment:
Place a textbook in your hand.
Extend your hand out as far as you can and hold it there.
See how long that you can do that.
i guessed as much. the arms are built pretty much like those shown in the examples for the servo erector set arm - with the 2 servos at the base. so with my limited gift for electronics i’m guessing that if the servo is under maximum load it is sucking more voltage from the supply, and the higher the voltage the hotter its going to get?
generally speaking though a 7.5V supply isn’t exactly overcooking it… is it?
Generally speaking, 7.5 volts isn’t overdoing it.
It is very near the servos’ limitations, however.
You’re both wrong and right about the heat.
The higher the voltage, the hotter it will get, but it’s not sucking any more voltage from the supply when under strain.
Think of electricity as a river.
Voltage (volts) is the incline that the river is flowing down.
Current (amperes) is the amount of water flowing past a given point.
When the servos are under strain, they draw more current.
So, you might ask why it is a problem to overvolt them…
It’s a problem because too much voltage will fry your electronics, and too much amperage (due to strain) will overheat the servos and melt their innards.
The problem that you’re having isn’t really part of overvolting them (that’s a separate problem).
I run my servos at 6V, and I’ve had the same problem when I made my Biped Scout stand on one leg for too long.
