19 years ago
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
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
say the series 20/1 with 66:1 gear reduction and the
1727-012C motor, this has metal gears but will we be better off or will it
just delay the teeth stripping a little bit?
I hope this posting has enough information for ideas and looking forward to
(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.)