Student built robot chassis has something you can learn from

This is a four-wheeled robot chassis built by high school students over the summer. They were participating in workshops put on by xbot robotics in Seattle, Washington. The goal is to get them participating in events like FIRST Robotics and LEGO league, and eventually into science related careers.

At first glance we thought: oh, that’s a nice chassis build… on to the next tip. But then the difference in front and rear wheel types caught our eye. The problem with four-wheeled designs is that you need differential steering to overcome the skidding issue when turning. This usually means two independently powered rear wheels and one unpowered front wheel that can swivel. One way to overcome this is to use three omniwheels, each with their own motor. And more recently we have seen four-wheelers that use mechanum wheels to get around the issue… but that takes four motors.

The design seen above uses just two motors, each with a chain to drive both wheels on one side. The rear wheels have rubber grippers which give them great traction. The front wheels are omni-wheels which allow them to move side to side easily during turns while aiding in forward progress when not turning. This gives the robot enough grip to push object around, like you can see in the video after the break.

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Tricycle robot using omni-wheels

[Markus Gritsch] built this six-wheeled robot using omni-wheels. Two wheels are used on each axis in order to ensure perpendicular rotation is possible no matter where the axis rotation stops. The wheels have also been improved by dipping the elliptical components to give them a rubbery coating.

The robot gets its commands wirelessly from a separate controller unit. That controller, as well as the bot seen above, uses a Teensy microcontroller board. Two analog sticks take input from the operator and transmit commands using an inexpensive RF pair. The wheel movement is facilitated by three servo motors which may seem like an odd choice. But we think that it simplifies the electronic side of the build because you do not need an H-bridge to control a servo motors. It’s a bit loud, as you can hear in the video after the break, but it certainly works quite well.

One of the commenters on the thread above asks why [Markus] didn’t use mechanum wheels. These would have allowed him to use just one wheel on each axis but the omni-wheels were so inexpensive that he went this route instead.

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