Major Motor/Gearbox free play.....
The above photograph shows the result of "free play" caused by the worn mechanical motor/gearbox interface
The jaw coupler(s) between the motor and the gearbox turned out to be the problem....
This is actually a surprisingly poor design for the high torques involved.
Firstly, they use a small diameter and short shaft (8mm or 5/16 or .315" OD).
Secondly, the steel shafts (motor and Gearbox) fit into cheap metal diecast receivers in the jaw coupler.
Thirdly, both motor and gearbox use a simple indexing flat to mate the shaft to the coupler.
(RED arrow indicates the motor shaft)
The corresponding gearbox shaft....
And the jaw coupler components.....
The RED arrow shows the wear area on the coupler(s) flat that has become the issue....
(Note that in my case, one of the couplers showed great wear ....)
This wear is caused by a small amount of free rotation. The continual clockwise and counter clockwise motion of the steel shafts eventually wears the softer diecast material in this manor.
For the SegBot project we would ideally like no free play in the mechanical parts. In the real world there will always be a small amount but in this case it is far to excessive.
The Solution?
I have found these nice nylon "back-lash free" D type shaft couplers produced by a UK after market vendor for this style of motor/gearbox interface.
I have some concerns about using nylon but the main gear in the gearbox is nylon so will give it a try.
For £18.00 inclusive it will be no loss if they fail.....
Here is plan "B" if the above fails:
I will now look at dismantling the gearbox (and possible the motor) to use a small diameter hardened "Roll" pins (like shown below). This involves drilling a small hole of the correct size through the shafts and the jaw couplers. This can be difficult depending on the hardness of the shafts that require drilling. If you are not familiar with using roll pins you may need the help of a suitable machine shop.
Note the four warn rubber cylinders (see the photograph showing the jaw components shown on this page) would also need attention.
