Saturday, January 20, 2007

Getting the motor working

I know the motor runs on its own, and I know the gears turn - now I have to get them working together.

Optimistically I start the motor with all 6 axles in place. Not a flicker. Turn the power up a little... still nothing.

I'll have to take this slowly. Removing the wheel axles leaves just the worm and worm wheel in contact. The motor turns hesitantly in one direction then stops, still nothing in the other direction. With the power on low, I help the motor through the sticky patches by pulling one side of the worm down with pressure from a pair of tweezers. Soon it's turning under its own power. Still not smooth, but a start.

But the other direction is trickier. With the power off I try to turn the worm. It's very stiff in places but I manage to get it round. After about an hour, it's running both ways on its own. I'm hopeful that some "running in" will resolve the stickiness without me having to check the components.

At least when I add the 3 wheel muffs (still on makeshift axles) it all runs reasonably well, but still not smoothly.

Eventually decide to check the worm wheel axle. On close inspection there is some friction between the muff and axle bearing. I take it out, file the end of the muff and
glass-fibre brush the axle bearings. Do this a few times, with improvement each time. Perhaps that was the problem all along.

Some lubricating oil on the worm wheel also helped. As did unscrewing the motor a quarter-turn from its bearing, but now the motor had to be aligned accurately. I would need to take care when securing the motor to the frame spacer underneath.

Using strips of card and paper, I find that the worm wheel turns fastest with 0.4mm support. Stick this onto the spacers with double-sided tape as a temporary measure.

I don't want to add the wheels and coupling rods until I've got the gears moving as well as possible, so meanwhile I'm going to start on the underframe.

1 comment:

Nigel said...

Set your motor and gears up using an analogue ammeter.

The ammeter sits in series with the motor leads. You are aiming to get the lowest possible current at a given speed, and no flickering of the needle back and forth.

If you get flicks on the needle, it usually means a gear is sticking (burr or dirt on a tooth). By watching the frequency of the needle flicks, and relating those to the rotation of the wormwheel, you can work out which wheel is sticking.

Same trick to reduce friction in quartering.

Analogue meters are better than digital for this, as most cheaper digital meters have considerable lag between measured current and displayed value.