(ET) Speed control repaired

["Christopher Zach" <czach computer org>]

This afternoon I repaired the sticking speed control on the E20. Took a 
bit,
but here's how I got it working smoothly...

The foot pedal switch assembly is a box with two covers, secured by four
screws. If you back the screws out, you can slide off the outside cover,
which gives access to the outside end of the slide. Now if you take the
screws out all the way, you can remove the inside cover and see the 
switches
and activator.

The activator is basically an angle shaped piece of metal with a dowel in
it. Looks like a guilotine, and works pretty much the same way: As the
activator comes down, it presses more and more microswitches. These
microswitches then trigger relays which control the speed.

A note about the microswitches: They look pretty small, and could probably
get gummed up if someone sprayed WD40 or something like that in there. A
stuck microswitch will basically kill the tractor; as the interlocks 
prevent
initial motion if any of the switches are down.

So I started by cleaning off all the oil, grease and gunk that was on the
activator and the casing. For this I used good ole brake cleaner on a paper
towel. Brake cleaner (not to be confused with brake fluid) cleans grime
extremely well yet doesn't total the paint. The switches looked clean, so I
left them alone. If they had been dirty, I would have used electrical
cleaner on them (not brake cleaner; electronics parts cleaner cleans then
evaporates so it doesn't leave any residue) In fact tuner cleaner might 
work
to clean and lube the switches.

Once done I lubed the washer that slides on the case with a bit of bearing
grease. A thin bit is all that you need, especially when it is on a clean
surface. Too much grease will just lead to build-ups sticking in there and
gumming up the works again. Then the inside cover was replaced.

The outside cover was a different story. On my E20, there was an L shaped
bracket attached to the activator dowel, then a long screw with a bolt on
the top went down through a spring, through a fixed L bracket (attached to
tractor) and then terminated in the pedal. The spring would provide the
tension because it was between the two L shaped brackets. However the top L
seemed to ride at an angle, thus causing it to "dig in" to the case when 
the
throttle pedal was released. Thus it would stick. Someone had tried a lot 
of
lube, which just gummed up.

I cleaned off the outside of the case (and all the parts) with brake
cleaner, then put a washer on the dowel between the L bracket and the case.
The washer now takes the load of the L bracket and transfers it more 
eavenly
to the case. Once again, a bit of bearing grease on the parts and on goes
the top cover. If I had the parts, I would probably also put a nut below 
the
top L part and sandwitch it between two nuts (which would help keep it at a
90 degree angle with respect to the dowel)

The pedal now works *perfectly*. Quite smooth and prompt control when
letting up (no delay before the tractor responds). Much much safer. If it
loads up with crud again, I might try lithium grease or something like 
that,
but it should be fine.

Next stop: Fixing those brakes. I'm also a bit concerned about the front
end: It isn't very heavy up there, and I'm worried that accidentally going
to full power will cause a wheelie, or worse: Having 800 pounds of tractor
flip end over end and smash me like a grape. I wonder if I can build a 
small
time delay circuit that would wait a second or two between speed changes to
allow the tractor to catch up. Waiting an extra 5 seconds to go from flat
zero to full speed isn't a big deal...

Chris


Chris