tipper


Posted on Feb 6, 2014

I decided to make one for $45 in parts. Judging from the components I ended up using, one can tell. The motors and tires were salvaged from a broken electric wheelchair, the metal was scrap, the battery surplus from a garage sale, all the circuits custom-made. The system has three primary components: a controller circuit


tipper
Click here to download the full size of the above Circuit.

and its sensors (gyroscope and accelerometers), a dual H-bridge motor controller, and the mechanical assembly including the drive motors. The Tipper is controlled by a microcontroller that runs through a loop several hundred times per second reading in sensor data and then commanding two H-Bridge motor controllers. The objective is to always keep the handlebars close to upright. When this invariant is held true, if one leans forward the Tipper will accelerate forward to compensate and keep the handlebars upright. If one leans backward, the Tipper will turn the motors on in reverse to compensate in the opposite direction. This is precisely the desired operation, and it is how the Tipper is controlled. If the rider wants to go forward, just lean forward. In order to do this, the controller needs to know the current tilt of the device. It uses accelerometer and gyroscope data to estimate the physical state of the system. Unfortunately, there is not a reliable tilt sensor that is resistant to offset from acceleration of the entire device, so the controller needs to estimate the tilt with the two sensors it has. The (simplified) intuition behind how this works is that the accelerometer gives a very good long-term estimate on tilt, but is rather poor for any single measurement, whereas the gyroscope is very effective for short-term measurements, but is inaccurate for the long-term. The algorithm it uses to estimate tilt is...




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