Wheels

I’ve been busy working on my robot lately, and I thought it’s about time to share my progress. The big news is that my humanoid robot now has wheels! I removed the base plate and mounted the torso to a chassis with two modified servos providing the drive and a castor at the rear. The modified servos had the potentiometer removed and replaced with a 10k trim pot. This allows the centre position to be adjusted so that the servos aren’t turning when the centre position signal is sent to them. I also removed the physical stops so that the output shaft can turn around as much as it likes. I allowed enough room on the new chassis to mount the Arduino and my Raspberry Pi (in a case). As I need a USB hub to connect the Arduino, webcam and wifi adapter to the Pi, this had to be mounted to the robot as well. Check out the picture below to see how things are looking.

Rolling Humanoid

BFR-H1 with wheels

The observant among you will notice the addition of the SRF05 sonar sensors to the chassis and the head. The sensor on the chassis should hopefully stop the robot driving into anything when moving forward. I’m not sure this one sensor will provide enough coverage to stop the robot ever hitting anything but I don’t plan on adding any more until it’s required. I added the sonar sensor to the head in place of the sharp IR sensor as it provides a wider beam and a longer range.

Have a look at the picture below to see the back of the robot with the Arduino and Pi mounted. The wiring is a bit of an issue to the looks of the robot and I may have a stab at tidying it up at some point!

Rear of new chassis

Rear of new chassis

The new chassis works well, although the servos are a touch noisy. They are metal geared digital servos and at higher speeds tend to generate a bit of noise. I can live with this for the moment though. The rear castor is one designed for furniture but works great on a robot, particularly for driving on a carpeted floor. You can also see a 7.2V battery attached to the underside of the robot, along with the 6V battery used for servo power which the photo doesn’t show. This is going to be the supply for the Raspberry Pi.

On the software side of things not much progress has been made. I have added data to the serial packet for the new sonar sensors and altered my python code to display these readings on the screen. I have been playing around with OpenCV on the pi and have been struggling to get a decent frame rate whilst keeping the GUI responsive. The main time consumer seems to be getting the data from the camera to the Pi. Instead of streaming video from the camera  I’ve decided to just capture frames and analyse them when required. This is adequate for development and experimentation, but may cause issues in the future, we will see!

I’ve designed and built a couple of new circuits for my wheeled humanoid robot. A regulator to supply the Pi and USB hub so that the robot can drive around untethered and a switch circuit to switch power on and off to the servos via an Arduino pin. My next post should be very soon and will include more details on these two circuits.

 

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