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Resolved Resolved by Dunning-Kruger!

Direct Power Connection Without Battery


I am working on creating a full scale humanoid robot using the EZ-B V4 controller and the servos from the JD robot. The servos are attached to a 3D printed skeleton. The battery would only last about 1 minute before the "my battery is low" warning came on. I thought I damaged the battery. So I purchased a new battery charged it for 1 1/2 hours, installed it into the controller and the controller did the same thing, the battery lasted about 1 minute.
So now I suspect the load is very high on the servos and drains the battery quickly. It there any way to connect the charger directly to controller without a battery? I see other custom robots on community site and they don't appear to be battery powered but using EZ_B V4 controllers.

Thanks for your help,

Related Hardware EZ-Robot EZ-B v4
#13   — Edited
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.
#14   — Edited
@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).;)
Thanks everyone for your support.

I will add the rubber bands (like tendons) great suggestion. I will also purchase a 5V 20 amp power supply.
I redesigned the shoulders with a the 3D printed "strap" that now takes the load off the servo and transfers to the black exoskelton above still allowing the shoulder to rotate.  I agree that I'm pushing the limit of these HDD servos. The rotational inertia is high but I have built the skeleton to be very light but strong. See the pic. 
User-inserted image
Keep us posted on your progress. This is very interesting.