Help with 6 servos on BOE (power supply?)

Kudonym

Hello

I'm having a problem getting six standard servos to function properly on a BOE.

I thought of using an external power source for the servos, which worked with 3 servos and two 9V batteries. But when I rig up six servos with 4 batteries, one or two servos turn too much and aren't in the right positions.

Someone told me I may be using too many batteries. Drawing power straight from the board gets very little response from all servos.

What I'm asking is how you would want to power and wire 6 servos on a BOE? Apologies if my problem wasn't explained clearly. All input is appreciated!

Mike Green

Each servo can draw up to 1A when it's just starting to move. The total amount of current needed depends on when and how the servos move. Obviously, if you try to move all of them at the same time from a stopped position, that's 6A needed for a short time. If you're running the servos off the regulated 5V supply (Vdd), the regulator can supply maybe 1A, sometimes a bit more. The amount it can supply also depends on how hot it is, particularly because it doesn't have much of a heatsink. Servos are designed for voltages from about 4.5V to maybe 7.2V. If you run them off voltages at the high end of that range, the lifetime of the little brushes inside the motors is reduced from arcing. If you run them off higher voltages, their lifetime is reduced greatly. The BOE is designed to run off voltages from about 6V to about 9V although it can run off higher voltages if the current drawn is reduced ... any voltage above 5V is turned into heat and the amount of heat depends on the voltage (above 5V) times the current drawn.

The best way to run a BOE with a lot of servos is to use a 6V supply for Vin and run the servos off Vin (via the jumpers near the servo connectors). You could use 5 x AA NiMH cells in series or larger (C or D cells) depending on how long you want things to run before recharging. If you want non-rechargable cells, use 4 cells, AA or larger. Remember that many C or D rechargable cells are really made from AA cells in an empty C or D sized shell ... check the current capacity (mAh). Good quality AA cells are over 2000mAh. D cells are 8000 to 10000mAh.

9V batteries have very low capacity. They're simply not made for this sort of use (motors).

Kudonym

I think I understand.

So all I need to do is hook one 6v power source to Vin and have each servo powered from the other Vin?

Mike Green

Yes

1) You need to connect a 6V power supply to Vin that is capable of supplying at least 1A average current with peak currents of several Amps (depending on how many servos start moving at a time). Vin is the power jack on the BOE.

2) There are jumpers next to the servo connectors on the BOE with two positions (3 pins). One is labelled Vin and the other Vdd. The center pin has to be connected to the Vin pin using the supplied shorting block (the jumper).

erco

Why stop at 6 servos? I used one 6V gel cell to power all 16 servos, visible at 0:18 seconds. The HW board has its own 9V battery.

Kudonym

Thanks for all your help, got it working so far.