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Motorizing a crank-powered adjustable-height desk

Posted by Ryan on 16 February 2017

One of our customers motorized his crank-powered adjustable-height desk by using a brushed DC motor to drive a chain that turns the crank. He details the project in this blog post. He described the project as a “learning experience”. He started with a Pololu Simple Motor Controller 18v7, which unfortunately did not survive a stall when driving an 18 V drill motor. Some drivers survive over-current situations better than others, but our general recommendation is to choose a motor driver with a continuous current rating above the stall current of your motor.

Cordless drill motors—which typically don’t come with a datasheet—can easily draw tens of amps when stalled. Note that the “peak” current rating is not usually relevant, since a driver might only be able to withstand that current for a few milliseconds. Also, you need to be especially careful when operating at high voltages: an 18 V battery can easily generate spikes above the 40 V limit of this driver if connections are made or broken while the system is powered.

After some technical support from Brandon, he switched to the beefier Pololu Simple High-Power Motor Controller 24v12 (and a lower-current motor with a datasheet, and a current-limiting power supply) to control the motor connected to his drive mechanism made from Actobotics parts. The Simple Motor Controller’s support for limit switches also came in handy for cutting off the motors when the desk reached the maximum or minimum height. He also added some LEDs for under-desk lighting.

After the electronics and mechanisms were all working, he used the Pololu USB Software Development Kit to create a C# desktop application that controls the Simple Motor Controller over USB.

The build log along with more pictures and videos is in this blog post.

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