Battery for 18 MG996R Servo Motors

I’ve been having difficulty finding batteries with sufficient current to power 18 servos for a robot I’m making.

I’m using an arduino mega and 2 PCA9685 16 channel servo drivers. I’m planning on using one set of batteries to power the mega, and one to power the servos. I’d like to avoid LiPo batteries, and NiMH batteries all seem to not have enough current. How can I find a battery solution with the right amperage?

Introduction to servo motors.

So what servo motors do you have keeping in mind:
"A standard servo will have a stall current around one amp, a micro servo will need a few hundred milliamps, and a giant servo can draw ten amps or more. Since servos run at basically the same voltages, the only ways servos can offer more torque is to have higher gear ratios or to use more current. If two servos have similar speeds at the same voltage but one has five times the stall torque, it will likely draw five times the stall current".

There are plenty of high current (Amp Hour) batteries out there.

Re: PCA9685 - max current draw
Its absolute maximum current is 400mA, or about 25mA per output channel.

So what do your servos draw?

Ron

The MG996R has a 2.5Amp stall current at 6volt.
No LiPo could mean four NiMH per servo :slight_smile:
Leo..

The stall current for the MG996R is 2.5 Amperes, so to avoid a twitching mass of hardware, plan on a power supply capable of 18 times that, or about 45 Amperes minimum.

RC batteries intended for high discharge rates have a "C" rating: if the battery capacity C is 3 Ah, a 10C battery can discharge at 10x3 = 30 A maximum

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So would I be able to plug a battery like this (50C) directly into the driver?

Would I be able to use one for each driver for longer battery life?

Check the manufacturer's voltage rating for the MG996R.

When fully charged, the voltage of the NiMH battery you linked may exceed 8.4V.

Blockquote

Why is it not 7.2V? I thought it was 1.2V per each NiMH cell. Wouldn’t 8.4 require 7 cells not 6? I’m sorry for not understanding I’m new to this. Thank you for all your help!

The typical cell voltage of a NIMH battery is about 1.2 volts per cell so a 7.2 volt NIMH battery is six cells in series.

"The industry standard for the rated voltage of a NiMH cell is 1.2 volts. This value is the nominal voltage of a cell that is discharged at a rate of C/10 at a temperature of 25°C (77°F) to an end voltage of 1.0 volt. This industry standard is used primarily to call out the rated voltage of battery packs. For example, a battery pack made of three cells in series would be rated as a 3.6-volt battery pack. Figure 3.7.2, C/10 Discharge Profile @ 25°C, shows that the nominal voltage of a NiMH cell is just above 1.2 volts".

Just about everything can be found here. :slight_smile:

The link includes discharge rates and discharge curves. Hopefully that helps.

Ron

Why is it not 7.2V?

When you study the link in the previous post, you will notice that when fully charged, NiMH battery voltage is as high as 1.45V.

The voltage drops very shortly after the start of discharge to about 1.2V, but by that time the servo electronics may have been fried.

Battery voltages are nominal. For servos, either a "4.8V" or "6V" NiMH battery is fine.

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