In my previous post, having quartered the wheels I tested the chassis with the coupling rods just slipped over the pins. The next step was to add the retaining nuts that will keep the rods from falling off to then cut the pins to length.
Before fixing the rods in place I double checked both rods, removing some slight burrs from the washers that keep them from rubbing the face of the wheels, and opened out the holes in the rods slightly. With the nuts just resting in place this seemed to work nicely so I took the plunge and carefully applied some Loctite 243 to fix the nuts in place. The excess crank pin was then carefully cut away with a jewellers saw.
After a little panic where it wouldn't move at all (one of the wires had come loose from the motor; they aren't soldered on yet) I was more than relieved to see it still working nicely. You may notice it moves smoother left to right than it does right to left. After watching it closely this seems to be becuase the gearbox can rock slightly on the axle when moving right to left as the retaining bracket I fitted doesn't hold it as tight as the chassis does when going the other way. I think that should be easy enough to tweak though.
So next steps are to fix the gearbox retaining bracket, clean up and paint the coupling rod retaining nuts, and then tidy up the wiring. After all that the chassis will be finished!
I find all chassis I build seem to work better in one direction, I put it down to whether the worm is pulling or pushing the worm wheel, it definitely changes how the motor behaves especially without a flywheel.
ReplyDeleteI'm usually happy if the chassis I build move at all! Fortunately in this case it's better going forward than backwards so even if I can't improve the running I'll still be happy.
DeleteI was always told this is to do with backlash in the motor. Shim the worm so it doesn't move back and forth and the problem will go away. Can't remember the last time I did this though.
ReplyDeleteI've seen backlash a lot on other motors (usually the tiny coreless ones I used in things like the OO9 24hp Hundson-Hunslet kit) but there doesn't seem to be much with this Mashima motor. The gearbox does rock a lot more than I'd like though when going to the left so hopefully if I can sort this things will run a bit smoother. Unfortunately not much I can do to shim the worm now as that's fixed in place..... although I suppose a U shaped piece might be an option.... hmmm
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