Thanks everyone for your help, The old battery was not puffy when I removed it from the EZ_B. It's almost the same battery that I use for my drone so I'm familiar with charging LIPO batteries and their danger signs.

6 of 8 servos are under load The "shoulder" servos are attached 20 CM long arm sections that weight about 1 KG so I'm near the limit of the HDD servos that come with the JD. Is there some kind of protection mechanism that shuts down the servos if are overloaded or overheat? I will try charging the battery again.

Here is the skeleton.

Very cool skeleton!

If the servos read hdd on the label, they have a shutdown feature if overloaded.

the weight that a servo can lift is calculated by not only the weight, but distance from the shaft. There’s information on our how a servo works page.  But it’s like you would have learned in school with lifting weight with your arm out. 5 pound weights at the end of your arm is way heavier than when it’s closer to you

You may want to think about ways to relieve some of the work of the servos, like using elastic bands that hold the arms in their "rest" position without any work fro the servos, so they are only working when you are in a different position.

Alan

Hey guys I've done the tests. A 1300mAhr ez-robot battery can go from drained to fully charged in 1.5hrs or less (usually 1hr 20mins). You have to remember that the ez-robot v3 charger charges the battery at 1A/hr.

@bmarkert1985 I would definitely recommend using a high current power supply as other have suggested for your build, you can use 5V (you just have to disable the battery monitor in the connection control settings) and it can even be an old computer ATX power supply if you have one.

Yes. You can lower the voltage feed to the 7.5 volt servos but will that lower the available torque? If so will it be a lot? The Op is probably pushing the HDD servos pretty close to the limit as is. Alan gave an excellent suggestion,  give the servos a helper like a band or a spring.

Have you seen your EZB reboot at all? If you are feeding servos directly from the ezb and your servos pull a lot of current away from the ezb it will reboot. To solve this you feed the servos directly from a property sized power supply and not through the ezb. If you are not having this happen that's a good thing. Just something to keep in mind as you move forward.

@Dave Yes, lowering the voltage does lower the available torque but not by much, a 2.5V difference isn't huge. The important thing is to have a power supply that can deliver the current.

The biggest strain will be on the shoulder servos (in the chest area), I wish I had a good idea to mechanically assist them but sadly I do not.

*Edit: Maybe a 3D printed worm gear design? Like inMoov.

2.5v difference from 7.5v is a 32% difference in energy potential. So it will be quite noticeable, but I’m with Alan and Jeremie on the assisted design as well. The shoulder servos are holding A TON of weight. The fulcrum calculation is gonna be off the charts for the length of the arms that the shoulder is holding.

A worm gear is a real good solution. Does the original poster have access to a 3D printer to make one?

A change in voltage will effect the speed of the servos, which in turn does effect the torque, but without the available current needed the motors aren't going anywhere. I guess my advice really is that a 7.5V high current supply is much harder to find than a 5V one, and it would be better to find a supply with the highest current rating possible rather than focusing on keeping everything at a higher voltage. 5V high current supplies are plentiful (ATX, Meanwell, Xbox 360 brick, etc).