We are in need of intelligent hints/ideas to allow us to continue development of our Junior Robocup custom robot. System specifications - 3x 4cm omni directional wheels, direct coupling to COPAL 16mm gearhead 12v motors (63mm total length). We have looked inside the COPAL gearheads and found the planetary system to be plastic based gears.Robot base diameter is 22cm, wheels mounted 120 degrees apart. Control is via PWM motor controllers, servo to PWM convertors and MIT Handyboard.Total system weight is 5lbs, height is 20cm. Problem: far too much force on the geartrain/shaft is giving us a very short gearhead motor lifetime, the planetary gears are stripping teeth and supports being broken in the gear train.
Attempted solution: we made an aluminium bracket with two mounting holes for the gearhead motor system. This provides much more support for the gearhead but only extends the overall lifetime by a small amount.
We are still at high school, not studying mechanics and we are involved in subjects that are way beyond our teachers knowledge skills. We need hints or to be pointed in the right direction to find out about these things:
a) How can we calculate the radial and axial forces involved when this robot is in motion? Would it require special test instruments?
If we had this information, we could match it to the gearhead motor specifications which we feel are currently being well exceeded.
b) When working, the movement of the robot 3 axis system is beautiful, however as the motor is constantly being changed in speed of rotation and direction (often in a fraction of a second) - is this a special situation we need to take into account when choosing a motor? The motor can be rotating at 5000rpm and then almost instantly be reversing - this must be creating a great deal of stress on the geartrain? Can we reduce this strain? Would making the geartrain stop before reversing help much? and wouldnt this make for a rather 'jerky'movement?
c) If we redesigned the drive system to an axle type - make the gearhead shaft longer and supported by another bracket and mount the wheel in the centre of this drive shaft. Would this not greatly reduce the radial and axial forces the gearhead is subjected to?
d) How do we work out the change of forces from a 'standard' motor system (2 wheels) which are driven 'straight ahead' and just turn by having more or less power applied to one wheel? The omni system has each wheel set at 120 degrees in a circle format and when moving straight forward, the wheels are actually moving at an angle but forward.This must be substantially increasing the radial force being applied to the drive shaft?
e) If we use something like the Faulhaber gearhead motor system
I hope this posting has enough information for ideas and looking forward to your input. (We just finished competing in Padua Italy and got to the quarter finals fine but then the motors (all of them!) geartrain failed and the replacements just didnt do the job well enough.)
TWAIN Sydney Australia Jeffery Sinclair