Tag Archives: electronics

Fitting the foot force sensors

I finally got round to installing the force sensing resistors to the underside of the Bioloid’s feet. I am using the FSR 400 Short model, with male end connectors, which are small and flat and didn’t fit in the square female header pins which often come at the end of breadboard wires. I didn’t want to solder directly as I’ve damaged these sensors in the past, so I followed a suggestion on the Adafruit website and ended up using these PCB terminal blocks.

The force sensing element of the FSR fits nicely in the pre-existing cut-out on the underside of the Bioloid foot plate, and the pins are fed through a hole in the plate so they can be connected on the topside. However, in the standard Bioloid humanoid configuration, the foot plates are attached at an offset from the ankle angle brackets, which means there is not enough space between the footplate and the bracket to connect the pins. To fix this, I moved the footplates so that the ankle brackets sit along their centres. There is still some free space between the footplates when the Bioloid sits in its resting position, so hopefully the feet will not collide with each other after this change.

For completeness, I also made changes to the CAD model and also added FSR CAD models to the feet, although that is just a cosmetic addition to the model (on a related side-note, I also found a CAD model of the USB2AX which adds to the realism)! The robot’s URDF files and CAD models have been updated on GitHub.

Here are some pictures of the results:

Wiring up the electronics

It’s been a while since the last update! I have mostly been working on the commununication between ROS and the servos, and now have a working read-write ROS servo interface, but will post about this later.

In the meanwhile, I added a bar display made up of 10 green LEDs for information feedback, as well as 4 blue decorative LEDs. I then moved the breadboarded electronics to a more permanent prototype board. I was initially hoping to make a box-shaped board which could fit nicely inside the Bioloid’s hollow “groin”, and would have the LED bar display in the front. However the USB cable connector protruded too much, so the LED bar will have to sit one side of the board. I also managed to squeeze the IMU on the underside of the board. There is still some room above the board, so I may be able to squeeze even more of the wiring/electronics in there.

Once the board was ready, I temporarily put all the hardware parts in roughly the right locations to gauge how much space will be taken up and how long the wiring should be. I have removed the AX-S1 sensor, as I probably won’t have much use for it. I think the Raspberry will sit much better on top of the torso rather than on the back, where the old CM-5 used to be. It’s very tempting to turn the screen into a VR face! As you can see, it will be a struggle to mount the massive 5500 mAh battery on the back, so I am planning on downsizing.

Here are some work-in-progress pictures plus a video: