For the purpose of one new design, I need to control a brushless DC motor, and to read the speed of that motor (RPM). In order to test out my method for control of the motor and measuring the speed of rotation, I needed to create a test fixture that would allow me to collect data and observe and improve my methods for control and measurement. I designed a basic fixture shown below, taking advantage of the capabilities of my 3D printer to make the fixture accurate and easy to assemble:
Simple Test Fixture for Brushless Motor Control
The reason I wanted to share this fixture design is the odd shape to the left side of the picture with 10 holes in it. In the fixture, I need to accurately print holes that are both 1/4" and 8mm in diameter. Actually, I need to print pieces that have holes the correct size for a press fit of both 1/4" and 8mm steel rod.
Since I am making the parts on a 3D printer, I do not have to take a lot of time trying to get the hole diameters exact--I can just print out a range of hole sizes in a test part and then try out the fit. Once I've done that, it's easy to adjust the holes in the pieces that make up the fixture accordingly, for a perfect fit in the final assembly.
The piece with 10 holes in it contains holes that are larger or smaller by about 0.004", allowing me to zero in on the correct size quickly. After a couple of quick prints and test fits, I can adjust the pieces that make up the test fixture, print, and assemble.
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