Omni-Directional Robot Part 2 – Hardware

Prototype Omni-Directional Robot
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Hardware for my prototype Omni-Directional Robot.

In this page I am going to post the details of the hardware design for my prototype omni-directional Beetle-Weight robot. This is not intended to be a competing robot but rather a test of the motors and motor controllers as well as a platform to try different control boards.

Motors and Wheels

The first thing I looked for was the gear motors. I settled on 1000rpm 12V gear motors from BangGood. I have seen them used on other Beetle-Weight robots and they seemed like a good budget choice.

Next I needed some wheels. I was thinking I would need to 3D print these but I found some good ones from an Australian supplier. Rotacaster make omni-directional wheels in several sizes and I chose the 35mm robotics wheels. I did need to 3D print a hub to attach them to my gearboxes but Rotacaster supplied an .STL file for a blank hub that I could easily modify to print a hub for my gearboxes.

Electronic Speed Controllers

Since I am on a budget I needed to find the cheapest motor controllers possible but 12V controllers are not both cheap and suitable. I did find these cheap XYS-BD20A 20A Brushed RC Car controllers on eBay but they are only rated for 8.4V max.

After more searching I found a thread on the UK Fighting Robots forum by Rory Mangle explaining that he had bought some of these controllers and inspected the components and found that they could actually handle up to 15V. So I ordered some thinking if they don’t work I can put them in an Ant-Weight. Once I had them I pulled the heatshrink of and had a look at the components and sure enough there wasn’t anything that couldn’t handle 12V but I would need to be careful not to over heat them as there was not heatsink and the PCB was very light weight.

The controllers did need modifying since they were designed for RC cars and power switches that cut power to they 5V regulator and the brake feature was enabled. The brake causes the motor to stop when the throttle is reversed and to reverse the motor the throttle would have to be re-centered before reversing again which is not good for robot use. After inspecting the PCB I found two pads without a component loaded onto them with an arrow pointing to them on the silkscreen. After bridging these two pads the brake function was disabled and the motor would immediately reverse when the throttle was reversed.

Next I removed the power switch and shorted the pads. With each board supplying 5V I would only need one wire (white one) for two of the boards because I don’t want 3 separate voltage supply for the robot controller and receiver.

After this I cut the battery leads off two boards and daisy-chained the input power wires from one board to the next.

Lastly added heatshrink over the boards and cable-tied them together to make one neat little package.

Battery

The Battery is a Turnigy 1000mAh 3S 20C pack. Probably too large for a Beetle-Weight but gives lots of driving time for testing.

Controller

For controlling the robot I am using a Skyline32 Mini Flight Controller. I chose this because it is running Cleanflight, has a magnetometer and was on sale. More on this on the next page.

For a receiver I am using  a 4ch Frsky V8R4 as it is the only receiver I have that works at the moment. This has caused me several problems but I will explain that on the next page as well.

Finally I 3D printed a chassis to mount everything on. I tried to keep it to similar dimensions that a completed Beetle-Weight will be.

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