beginner: external power supply

Hey guys.

Im completely new to electronics, so forgive any ignorance!

Im making a sculpture with 5 robotic arms, each with a pan and a tilt motor. The pan motor is this one - http://servocity.com/html/hs-785hb_3_5_rotations.html and the tilt motor is this one - http://servocity.com/html/hs-5665mh_servo.html

Was thinking the most easy and convenient way to power them would be one power supply for the tilts, and one for the pans. Then plug through a breadboard.

So would i be right to say, for example that i would still need to feed the 5 hs-785hb_3_5's 6v's in total?

But how do I decide how many amps I need? Do i need more info than is provided in the link? It tells you the 'Current Drain at no load operating', but i will be carrying some weight. So how do i decide how many amps to allow for??

thanks Rich

The other servo has some information on lock/stall current - several amps.

Without more detailed information on these devices, the only thing you can do is prepare for the worst-case, which is (total number of servos x stall current). In this case that is quite a lot.

If the weight they need to move is small and the speed is slow, you may get away with a lot less. There's really not enough data.

rich_brighton: Im making a sculpture with 5 robotic arms, each with a pan and a tilt motor. The pan motor is this one - http://servocity.com/html/hs-785hb_3_5_rotations.html

There is little information here for this servo about current ratings, other than:

Current Drain (4.8V): 8mA/idle and 230mA no load operating Current Drain (6.0V): 8.7mA/idle and 285mA no load operating

You could probably figure at least 1 amp under load for this servo, but you might want to purchase one (or all) and test it under load.

rich_brighton: and the tilt motor is this one - http://servocity.com/html/hs-5665mh_servo.html

This servo gives better information:

Current Drain (6.0V): 200mA/idle and 2.0 amps at lock/stall Current Drain (7.4V): 240mA/idle and 3.0 amps at lock/stall

...and from it you can potentially infer that even the prior servo could have such a rating at "stall" (so an estimate of "1 amp" may actually be -low-); rarely will you encounter a servo locked or stalled; servos tend to break gear teeth before they stall (unless they have an unusually strong gear-train; but I must say, as someone who has personally broken an all-metal gear-trained gear-motor due to a stall condition - the possibility of stalling before breakage, if the power supply can give the current, might be remote).

Anyhow - let's say you are running all of the servos at 6 volts (since that is a voltage common to all), and that each needs at maximum 2 amps; with 10 servos, that's going to be a maximum of a 20 amp supply - go for a 25 amp supply to be sure.

rich_brighton: Was thinking the most easy and convenient way to power them would be one power supply for the tilts, and one for the pans.

Your first trouble will be finding a 6 volt supply capable of suppling the current; you might either have to build one, or pay a lot of money for one. You could break the number of supplies up (still finding a couple of 6 volt, 10-12 amp supplies will be difficult). You could also (potentially) drop the voltage to 5 volts (as 5 volt supplies with high-amperage are -much- easier to source); though whether the servo for your tilt action can run on 5 volts would be in question. You could also use multiple adjustable voltage bench supplies (with proper current ratings) to drop the supply voltage down to 6 volts. None of these options, except perhaps the "5 volt option" will be inexpensive...

rich_brighton: Then plug through a breadboard.

Standard (solderless) breadboards are rated for 1 amp only; even a solderable breadboard has a low amperage rating (unless you solder on thicker wires to act as "busses" to carry the extra current).

rich_brighton: So would i be right to say, for example that i would still need to feed the 5 hs-785hb_3_5's 6v's in total?

Yes - see above; but you need to know the current needs, for which you only -truely- know for one of the servos...

rich_brighton: But how do I decide how many amps I need? Do i need more info than is provided in the link? It tells you the 'Current Drain at no load operating', but i will be carrying some weight. So how do i decide how many amps to allow for??

Once again, see above.

You might call or email Servo City's support and ask if they know (or have an idea) what the stall current is for that particular servo.

If that doesn't help, though, you can test the current drain of the other servo (that has no spec for "under load") with a multimeter. You can do this with your expected load, or you can go for a "sacrificial" test where you lock the output shaft so it can't turn, attach a power supply of the proper voltage capable of supply as many amps as needed (say, 5 amps or so), hooking up your multimeter, and turning the works on while you quickly record the reading. If you are lucky, the servo stalls without (much) damage. Or, you end up with a servo that busts a gear, burns out the motor, or burns out the controller PCB (or all three).