# Multiple servos different voltage

I'm working on a project where I'll have 3 or 4 servos doing different things. When the program is run the first servo will spin like a winch. When this completes the second servo will lower an arm. The third servo will then begin working until the end.

I have a 30v skytop bench power supply I can set to a constant voltage but my servos are all different.
The first one will likely be a 20 kg servo. Then a. Mg996r. Then the last action is with a 60 kg servo with a recommended voltage of 7.4 v

I'm new at this but do I need to set the bench power to a constant 7.4 volts and then use resisters on the other two servos to lower the voltage? Or would you just let the all run with 7.4 volts even though it might be a bit high for the smaller servos?

Here's the specs

MG996r 12kg

• Operating Speed: 0.17sec / 60 degrees (4.8V no load)
• Operating Speed: 0.13sec / 60 degrees (6.0V no load)
• Stall torque:12kg/cm(6V)
• Operation Voltage : 4.8 - 7.2 V
• Temperature Range: 0℃ to 55℃
• Power Supply: Through External Adapter

20 kg muizei servo

Idle current(at stopped):4mA(5V)/5mA(6.8V)
Operating speed (at no load):0.16 sec/60°(5V)/0.14sec/60°(6.8V)
Stall torque (at locked):18 kg-cm(5V)/21.5 kg-cm(6.8V)
Stall current (at locked):1.8A(5V)/2.2A(6.8V)

DSServo 60kg

Note: 1. The best use voltage is 7.4v.
It is recommended to use 2s battery for power supply (6v-8.4v)
Speed: 0.17sec/60 degree at(6v) 0.15sec/60 degree at(7.4v) 0.13sec/60 degree at(8.4v) Torque: 58kg.cm.at(6v) 65kg.cm.at(7.4v) 70kg.cm.at(8.4v) Voltage: 6v-8.4v Dead Zoon setting:3 Microseconds

I would experiment with all of them a the same voltage. Motors are generally tolerant of different voltages. Resistors are a bad choice for changing voltage used to supply power because the voltage across the resistor varies with the current, which is not what you usually want. If you don't know it already learn about Ohms law, it is fundamental to electrical circuits.

Run them all at the same voltage 7.4V. Hobby servo specifications aren't really referring to fixed power supply voltages but are always given in terms of the nominal voltage of the batteries expected to be used with them. So 6.8V, 7.2V and 7.4V all refer to different batteries, but all of them when fully charged will be at least 7.4V. Confusing isn't it?

Steve

Definitely not!

We see this misunderstanding frequently. The voltage a resistor drops is proportional to the current flowing through it (and vice versa). This means that if a servo was not driving a load, it would draw very little current and there would be negligible drop across the resistor, so almost the full voltage would be applied, defeating any purpose of using the resistor to drop the voltage.

On the other hand, as soon as the servo finds a load and draws its full current, the voltage would drop substantially and the servo could not operate properly.

If you need to regulate the voltage, you need a voltage regulator. But your quoted specifications indicate that all three servos are intended to operate from your 2S battery in any case.

Run all at 6.8 volts , the maximum the lowest voltage servo will work at , the other servos ( check spec) are then within their operating range of voltages and will be fine .

Well that's a load off (no pun intended). Nice and simple.

I'm just curious how high the risk is of burning out a motor with too much voltage. If I ran a couple servos with 7.4 volts but one of them has a max 6.8 is that little .6 difference enough that the servo will likely fry or does it usually take more then that?

I've seen reviews for servos on Amazon from disgruntled confused customers who tried to use the motor and it stopped working or their whole Arduino is fried.
I'm not using Arduino power or a breadboard so how much wiggle room is there?

There is only one way to tell….

The manufacturers state the voltage for a reason , it may damage the electronics through heat or voltage stress , almost impossible to tell , definitely not good practice . I know from experience of a 4.8v servo that died on 6v .

You gotta ask yourself , do you feel lucky …

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