Diego – the humanoid biped

In recent days I have had some issues with  Diego’s power system. Ever since I installed four HS645 high-torque servos, the whole robot started shaking and jittering when I flipped the switch. It was obvious that there are problems with power. I searched online for solutions. I have found some very useful message threads on Lynxmotion’s Forums.

In the initial desing I wanted to control all power using 3.3V and 5V stabilizers, LM7805. The TI microcontroller needed 3.3V while the inverter (7404) worked on 5V. The servos give  higher torque on higher voltage. Their nominal upper limit is 6V. This means that I was losing precious torque running the the servos at 5V. Reading up on other’s experience, I realized that there is no need for stabilizers when powering the motors. They can be directly connected to the batteries, provided that they are of appropriate voltage. I use rechargeable Energizer 1.2V AA NiMH batteries at 2450mAh. When I connect 5 of them in series, they provide a nominal voltage of 6V, but when fully charged, they can go up as high as 7V. I connected this power source directly to the servos, without any stabilizers. It seems that the motors can handle well even 7 volts.  Now Diego stands still without shaking. Also the torque is noticably higher, and finally the robot can stand on one foot.