Severe Issues with Andymark Swerve and Steer Module

[Tristan Lall]

Originally Posted by Elfonzo

I find it necessary to alert all teams who have already purchased the Andymark Swerve and Steer Module of issues in its performance. Andymark is offering a better, "absolute zero," (as we like to call them,) sensor. This "better" sensor always has a point it can refer to as zero, eliminating the need for pre match centering/zeroing. However, because the gear that the sensor is attached to and reading from is 12 tooth, and the gear used for turning the assembly is 40 tooth, the sensor has effectively 3&1/3 "zero's" This causes HUGE problems when trying to read the position. If you have not completed your electronics board and given the programmer(s) a chance to test it, be prepared to come up with major issues.

Either I'm misunderstanding you, you're misunderstanding gears, or there's something unusual about the configuration of that device.

Considering continuous rotation in one direction, and simplifying the possible permutations of gearing for the moment, the gears will always be in mesh and rotating together at the same pitch circle speed (with angular speeds varying according to the ratio of pitch circle diameters). In other words, the zero point is not about the alignment of any particular tooth with any of 3¹/₃ teeth. Instead, it will lie at a discrete point and will be repeatable, because the rotation of the gears is proportional.

Now in actual fact, there's a bit of backlash in the geartrain (i.e. a small angle through which the gears rotate without engaging, until the opposite sides of the teeth make contact). This becomes evident when you change direction. Maybe that's what you're seeing? It might also have something to do with overshooting and overcorrecting in your centring algorithm.

Also be aware that those sensors treat zero as a discrete digital value based on the encoder's resolution, and you can read back any deviation at a much finer level than the number of teeth you have. (Many of the common absolute encoders are 10-bit, which means 1 024 counts per revolution.)