Diego – the humanoid biped

After extensive mechanical, electrical and programming work, I finally got Diego to stand on his own feet with motors powered. This was a very proud moment for me.

As mentioned before, the electronics board is attached to Diego’s back. Since the servos themselves contain the driving electronics (whew), the circuit board is fairly simple.

The LM7805s are 5V voltage stabilizers. I needed to install a number of them, because each can handle only 1A of current, while each of the servos can draw a lot of current when in stall. I divided the servos between the available 5 regulators. I need to add heat sinks, because they tend to overheat during operation. The LM1084 is a 3.3V voltage regulator which feeds the microcontroller board. The 74HC04 are simple inverters added to decouple the controller from the servos and drive the controlling signals. Prior to this project, I already had a lot of experience with using Texas Instrument’s eZ430-RF2500 microcontroller boards for various purposes. This is why I decided to use this for controlling the robot.

These small wireless boards are powerful and easy to program. Still, they are limited in the number of accessible ports they have. Also the maximum clock rate could prove to be an issue in the future, if I add more servos (arms, head). The wireless capabilities are awesome. Two of these boards can connect to each other wirelessly and exchange information.  I plan to use this ability to control the robot remotely. The controlling program is fairly simple so far. It generates and sends PWM signals to the motors at appropriate times.

In order to drive the legs autonomously, the controlling electronics and batteries have to be attached to the robot. The torso of the robot can be used to hold these parts. I decided to build the torso out of regular aluminum L profiles, which are available in any home improvement store.

The dimensions of the torso were chosen so that it would have similar ratios as the human body. I wanted to build a robot that would be as much antropomorphic as possible. The front side of the torso holds the batteries. It will also hold additional servos for the arms and head. To power the biped I used 4 AA sized and 2 AAA sized batteries connected in series. Only 4 AAs did not provide enough voltage for the LM7805 stabilizers to work properly, that is why I added 2 AAAs more. The back of the torso holds the electronics board:

This way the electronics is pretty woulnerable. I will have to change the design to protect the servo motor connections (seen at the bottom) and the whole board from possible falls. The following article will discuss the electronics design for Diego.