power needed for servo motor

i used 7.2v 2600mah lipo battery to control 8 Mg90s metal servoes of a walking robot.I want to lift my mobile phone using that robot. But the servoes cant lift the whole weight of the robot. My question is, what is the reason for that?should it need much powerful battery than this one? Or is there a wiring method of connecting servoes?

There are no 7.2V lipos. Do you mean a 2S 7.4V lipo? What is the C-rating of the battery? That determines how much current it can provide.

There are several different MG90S servos and some are only rated for 6V so you may already be over-powering them and perhaps damaging them.

How exactly are your servos connected? One problem we see is trying to connect servos via a breadboard. They usually cannot handle the current required.


One possibility is that the battery is not able to provide the current.
But even if it is able, perhaps your physical design requires servos with more torque.

Can you post a picture of your robot? And something to give us scale, maybe just a measure of how tall it is.
How much does your robot weigh?
How much does your phone weigh?

The Mg90s servo has 2.2kg/cm torque. If you hang a 2kg weight 1cm away from the center of rotation, the servo should be able to lift it. Are your legs 1cm long? Then each leg should be able to lift 2kg.
But maybe your robot legs are 10cm long. The weight that the servo can lift at 10cm is .2kg.

I ran into problems with this on my hexapod. If I tried to stand from a 'splayed' stance with the legs all the way out, it could not lift off the ground. But if I bent the legs to put the feet closer to the hip, shortening the overall length of the leg, it could stand up without problem.