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Autonomous Rickshaw Pulling Biped

CAD | 3D Printing | Programming | Teamwork

By Sohaib Nadeem

December 1^st, 2018

My Role

This was a group project for an engineering design course. More information about this, and other projects the group completed can be found here.

I worked on the mechanical components - leading design and build, and working with the team to create a high level presentation.

One of the main objectives of this project was to develop and demonstrate human (or other animal) locomotion. I played around with a lot of different leg designs. This one here was one of the early ones that introduced some suspension, inspired from a MacPherson strut.

With only one joint being controlled, this was quickly deemed not good enough. The locomotion was not stable, nor reliable. I won't bore you with the other designs that did not make it. (you can see them in the presentation)

A Four-bar in a Four-bar

The final mechanism I came up with was a two linked four-bar mechanisms with a shared member. By having two pivot points, and constrained crank-rocker motion, the mechanism performed desirably. Here is a video of it being cranked by hand:

Hardware Choices

The biped had two independently controlled legs powered by their own window motor. The window motor was a lifesaver for our team. We struggled to get enough reduction with the plastic gear-set provided in the kit. A motor that was already reduced to a reasonable speed and that we could get for next to nothing from a junk yard ticked all the boxes, except interface-ability. In the end, I decided the benefits of a reliable power platform far outweighed the negatives of having to custom design and create a way to interface the motor with the shafts we were already using. After several iterations, we came to a two piece 3D printed adapter that matched the crank-gear bolt-pattern to transfer torque through the bolts, well away from the shaft where we were experiencing the shaft slipping in the key-hole. A third wheel was added to support the majority of the weight of the motors, so that the motors were only lifting the weight (and friction) of the legs.

Control and Automation

The biped was controlled by two individual motors, one for each leg. By adjusting the speed, and direction of the legs with respect to each other through an admittedly "janky-but-good-enough" open loop with manual initialization, we were able to get coordinated motion. The controls were all done on an Arduino-Nano communicating over Bluetooth to an Android smartphone over Bluetooth where there was a simple GUI to control the rickshaw. There was an ultra-sonic sensor on the front of the rickshaw, which prevented front-ward collisions from occurring, the rickshaw would stop at a safe distance from any obstacles, regardless of the user input. (you could not make it crash even if you wanted to!) When it all finally worked, it was a moment of excitement for the whole group, we knew we had something special!

Presentation

The presentation was top notch for this project. It was a meaningful Powerpoint that used some of the newest features in the presentation software to enhance understanding, and clarity. It really put the bow on a project that took many hours out of our days every day. Ultimately, closing off the project nicely with a very cohesive presentation was symbolic of the effort the group put throughout the semester in all of our projects. Feel free to pause the video of the presentation below at any point: