Diego – the humanoid biped

The new servos allowed a fully assembled Diego to make its next half-step:

It can be seen that even though the robot can perform a half-step it could need some more torque. It still seems to be a bit too heavy for the servos to support. Diego has a very high center of mass which makes it hard to balance on one foot. To improve dynamics I decided to reduce its weight by taking out the batteries from the torso and temporarily connecting them with wires to the robot. The videos featuring the reduced mass robot will be shown in the following post.

After adding Diego’s arms and head the robot became too heavy for the servos to support it. I had four HS645 and six HS475 analog servos in the legs. I decided to upgrade to digital ones, because of their higher holding torque. Since, I’m still on a budget I browsed around for cheaper solutions. Finally I decided to give some Chinese servos a try that have received some acceptable comments: the Towardpro MG996R. They can be found on Ebay for under 15$ a piece which is an unbeatable price for digital servos with metal gears and around 10 kg.cm torque.  I gradually replaced all ten leg actuators with these. The horns that ship with the MG996 are not compatible with the Lynxmotion brackets. Therefore I had to use Hitec horns. Here a small problem arose, since the MG’s are marginally compatible with HS horns, so I had to heat up the horns to fit them on the MG996R’s. After installing the motors, they proved to be very responsive and fairly precise with acceptable backlash. On the other hand they are not protected from overheating which allowed me to burn one of them down while it was trying to work against a mechanical barrier. All in all, I would recommend these servos to people on a budget who do not want to spend 50-100$ on higher quality actuators.