Why am I frying more servos than Gordon?

Hi everyone, I'm getting kinda mad now so please help me before I do something stupid :slight_smile:

So basically I just finished assembling my new robot arm recent ordered from eBay, and with everything mounted it's a bit heavy, anyway it's powered by 6 mg996r. I began by testing one of the servos via a 6v battery pack (4 AA), worked but waay to weak, luckily I had a battery pack used for my old rc car. It was rated 7.2V and 2500mah. The voltage matched exactly the maximum voltage input I the servo, so I simply connected everything and tested it out. Suddenly after a few seconds my room looked like a Jamaican apartment with smoke everywhere.

And yes this was with only 1 servo! Everything was connected properly with jumper wires, common gnd etc so why did I fry the servo? Did it eat more amps than it could handle? And the more important question, how do I fix this problem?

Thanks a bunch in advance.

The voltage matched exactly the maximum voltage input I the servo,

Bad idea, as you have discovered. Battery voltages are given as "nominal" values, not maximum.

Those are beefy servos, with a stall current of 2.5 amperes. To run 6 of them, you will need a 5-6V power supply capable of 10-15 amperes.

I've fried servos with a 2S LiPo.

Unless the servos say they're safe to use with higher voltages, don't go above 6V.

As jremington mentioned, those servos will take a lot of current. There are a bunch of threads discussing ways to power servos.

Here are a few links to these threads.

http://forum.arduino.cc/index.php?topic=366517.0

http://forum.arduino.cc/index.php?topic=370762.0

https://forum.arduino.cc/index.php?topic=368417.0

Where did you purchase your MG996R servos? I purchased four MG996R servos off ebay and they were junk. They had plastic bushings instead of ball bearings and the servos quickly became hot with mild use. Hopefully the ones you purchased are better than the ones I purchased.

I buy lots of stuff off ebay but I no longer purchase servos from ebay sellers. I purchase most of my servos from HobbyKing.

The servo motors will take some abuse , the electronics may not .
If you power them over voltage you may fry the electronics.

DuaneDegn:
Here are a few links to these threads.

Robotic arm help - Project Guidance - Arduino Forum

Servo just stutters - Motors, Mechanics, Power and CNC - Arduino Forum

Servo Array + BT PS3 Controller Feasability - Project Guidance - Arduino Forum

Thank you for the links, so now I'm standing here with my light wallet wondering what to buy, i can either use a LM2596 per servo, or the step-down module you used for your hexapod, or a UBEC that seemed kinda nice. However, jremington said:

jremington:
To run 6 of them, you will need a 5-6V power supply capable of 10-15 amperes.

It got me thinking why not just buy a ac to dc power supply that offers 5V 20A? Founded this on eBay Click me. Will it work? Just hook up to my wall with 230v? Is there any downsides?

And yes i bought my servos on eBay and i honestly have no idea about their build quality. Haven't had the time to open them up yet.

If the eBay power supply works according to specs, it should be fine.

jremington:
If the eBay power supply works according to specs, it should be fine.

Agreed.

I have had trouble powering motors from AC to DC power supplies. I think there's something about the inductive nature of the load which cause trouble for some power supplies. Hopefully this won't be an issue for you.

Its the heavy current draw from a supply with an over-current cutout circuit that's the issue.

For a motor you either have to provide all the stall current, or droop the voltage on overload.
Having an active cut-out circuit is only approriate if the supply can provide all the stall current
without overloading. A simple current-limited supply (like a bench power supply) is a good
approach. Computer supplies are not designed for motors. Sometimes a hefty capacitor bank
can rescue the situation, but that can also interact with the over-current cutout!