I’m using 20 large servos for an animatronic project (FT5335M), they are about 1.5x the size of a standard servo and are operated at 7.4v. Ideally during operating they should use about 1-2 amps max each. Does anyone know a good power supply to handle this? Ideally I want to use a lithium ion battery but I’m still in the testing stage.
Ideally during operating they should use about 1-2 amps
Alas, life in not ideal, and those servos draw far more than that.
The servo power supply should be chosen to support at minimum the stall current (which servos draw every time they start moving), times 20, or about 180 Amperes. At 7.4V, that is around 1300 W.
That would be totally unreasonable for a single power supply, so plan on several banks, with a star ground (look that up). Heavy power wiring is required, and choose a battery with appropriate "C rating" to handle the peak current.
See this note from Pololu's FT5335M product page:
Note: This servo can draw bursts of current in excess of 9 A at 7.4 V, so please make sure you have an appropriate power supply. For comparison, a typical standard-size servo might draw around an amp when straining.
You should definitely consider using less powerful servos.
Thanks so much for the info. At this point it may just be more practical to use a lithium ion battery. I would use less powerful servos but the robot is pretty big 
(5 ft tall)
Would several of these batteries do the job? They're rated at 80c.
I downloaded the data sheet from the FEETECH website.
The stall current is only 2.4A and the operating voltage is 8.4 NOT 7.4
6374060417672697026479381.pdf (86.4 KB)
In theory, 80C batteries can deliver 200A for about 3 minutes.
The total battery capacity required depends on how many minutes you want the robot to run.
In that case if I run the motors at 7.4v I should be able to use a 360 W power supply right?
I would sooner believe the engineers at Pololu, who know better than to deceive their customers.
In any case, the OP will find out soon enough. Good luck with your project!
Most of the motors would be relatively still for most of the time, so it probably wouldn't need 200A constantly. Do servos typically draw the stall current on startup?
All brushed DC motors do so. By definition, if the motor shaft is not rotating, it is stalled.
By far the most common servo problem reported on this forum is due to inadequate servo power supplies.
There are some discrepancies between the FT5335M data sheet from FEETECH and the FT5335M data sheet from pololu and specifications on other websites.
If you are intent on using that servo, I would buy one and make some measurements, otherwise look for a different servo from an RC hobby website.
Thanks,
I'm still a newbie to servos, what kind of tests would you recommend?
Do you have equipment that can measure at least10A-12A
Yes I do have a digital meter
You will need an oscilloscope and a small resistance current shunt.
The spec in question is the stall current. So you want to lock the shaft so that it cannot rotate, then command the servo to one of the extreme positions, 0 or 180 but only for a second or less.
Measure the shunt voltage on the scope.
How much resistance should the shunt have?
Also would it be easier to just use an adjustable power supply that has an amp reading on it?
Ah, no, meters are too slow in responding. We are looking for the maximum peak current draw. Only a 'scope is fast enough to show that.
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