Saturday, September 3, 2011

Track Ball Support - First Prototype

First thing this morning, I ordered my Wofgang Engineering TB-650 package kit to replace the current Dremel 300 in my CNC router.  Richard said he would be out this weekend and get starting building it when he gets back.  He expects to have it completed by the end of next week.  I also paid a fair bit extra for him to also build a variable speed DC power supply / controller for it.  I need this new spindle to get ready to route out my own prototype circuit boards.  It should also be able to handle all that the Dremel was doing with much more accuracy. 

I spent several hours working in Alibre Design to refine the first prototype for a ball support socket.  My trusty Logitech Trackman was kind enough to donate its ball for the purpose since my sample balls have not arrived from McMaster-Carr yet.  Its ball is only 1.34 inches around, so I had to scale the model back a bit from the 1.5" balls that are in the mail.

The support socket features three nubbins that actually interface to the ball and a viewport at the bottom where the laser optical sensor will eventually interface with the ball to track movement. 

After the design was done, it was time for the Zenbot Mini to earn its keep.  I routed the prototype out of a piece of 0.375" polycarbonate using a 0.125" (1/8th inch) round nose end-mill.

Lessons Learned:
The optical laser sensor wants about 0.1" (2.5mm) from the base to the ball to measure acurately.  The way the sensor works is much like a camera with no focus capability.  It has to be exactly the right distance from the ball to take good clear pictures and track the features it can see.  This prototype yielded a distance of only 0.03" (0.73mm).  It is a small adjustment to make that larger that is easily done in Alibre for the prototype next run.

The ball doesn't roll terribly smooth on these three nubbins.  I think I'll incorporate threaded holes as an alternative so I can use machine screws to dial-in the ball-to-sensor distance better.  Using metal screws will probably slip better against the ball surface as well. 

Some pictures:

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