4 Mar 12 2:14
I recently built a circuit that interfaces with a MEMS accelerometer to perform a single plane balance. This was done on an electric motor and fan combination (5" diamater). The circuit interfaces with a CRO and generates a sine wave and also filters any unwanted noise coming from the motor.
I had originally placed the fan/motor configuration on a square aluminium beam supported by a fulcrum rod sitting on top of two rare earth magnets. A Velcro strap wrapped around the motor/fan to hold it to the beam. The beam ends have two pieces of silicon tubing that act as a spring/dampener to a ground plane. When the motor spins the whole unit oscillates about the fulcrum. The accelerometer is mounted on top of the fan shroud at a point furthest from the fulcrum point. This is a make shift set-up, crude but worked OK.
When I run this set-up I can perform a good single plane balance. I use a trial weight and measure phase shifts between weight and no-weight runs. All is good.
I decided to construct a proper beam mount with a refined fulcrum. This setup allows the fan/motor to rock about the fulcrum with little oscillation normal to the fulcrum axis. However as nice as the beam mount is, it doesn't work very well. When I place the trial weight and then remove it between runs, I don not get a phase shift as I would with the crude setup. In other words the beam mount seems to be insensitive to changes in unbalance.
I'm not sure what is going on here? How can I build a mount that gives me consistent phase shifting?