I appreciate the links. Since you posted this, I've discovered a lot of
other lists with all sorts of different kinds of EV emphasis, which has
been great. It's hard for me to type much, so I'm going to cut-n-paste a
lot from a message I just sent to another person.
You are correct that I’d love to use an off-the-shelf transmission, but
exactly what I need really doesn't exist. I think I am just going to
have to do what most people do -- just use as much off-the-shelf as
possible, and piece the rest in. Then again, I'm also considering a
full-custom gearbox. Doing custom stuff doesn't seem much different in
cost these days than the cost of wheelchair equipment from wheelchair
dealers anyway, assuming I can do the CAD work myself.
Here's the rest:
I'm still in the mode of discovering what's out there. I got on some
other mailing lists that I found out about. It's all pretty fascinating.
I found out the assisted-power bicycle crowd most often uses the range
of power I'm talking about, though I’d need to gear down a bunch more.
By using multiple speeds, they are getting greatly increased range for a
given battery/motor combination, as well as greatly increased
hill-climbing ability.
I found out about the 4QD site which has a number of handy online
calculators. I found out that if I wanted to climb a 60% slope at one
mph with a chair + me + trailer + load totalling 1,000 pounds, I could
expect to draw 30-35 amps at 48 volts with appropriate gearing, not
counting inefficiencies.
Other times I will not want to haul any extra weight, over mostly level
concrete, and at speeds of 10 mph if I'm lucky, otherwise 5 mph will work.
Sure, a person can do all of that with the same gearing with one huge
motor, but there are big drawbacks. A motor big enough in this situation
will have a no-load current draw that would be the entire full-load
current for normal paved situations. The current used with the big load
up the steep hill will suck all the amp-hours out of the batteries, if
they could even supply it in the first place. That would also require a
needlessly-large controller, which would also waste power at the lower
currents used under normal conditions.
This is sort of like an old-timey tractor -- small power plant, which
the need to be able to get one place to another relatively while under
little load, followed with the ability to controllably handle extreme
loads under difficult conditions at slow speeds.
I've been thinking tentatively about gearing down the output of a
Rohloff hub, primarily because it uses planetary gears, and because
everyone seems to have a high opinion of its durability.
I still like the idea of a motorcycle transmission, but I'm just really
not sure about being to get one small enough (I really have no way to
get to any junk yards or bike shops to look at them, though my community
has both). Also, I'm not sure about being able to get a wide enough
gearing range. I thought about a motocross transmission... maybe that
would work, but I'm not sure of the gear ranges there, either.
A dual-range gearbox from an ATV would maybe be the best, but once
again, I'm not certain what gear ranges are available, and they take a
lot of room.
I really want to make this a 4WD, 4-wheel-steered vehicle. I don't know
if differentials are available front-and-back on ATVs. If I remember
correctly, they are, at least on the big ones -- but I need to keep to
small stuff.
I also have to incorporate a suspension, so things get crowded real
quick. :-)
I feel that if I'm lucky, I'll get to actually start on this project
(buying stuff) 4 years from now. I just don't have the money right now.
Any comments anyone has are welcome...
Jeff
Charley Snyder wrote on 12/12/06 11:48:
Jeff, Here's a link to the HPI 3 speed transmission. I understand
that you would prefer using an off-the-shelf tranny, but I thought
that you might like the "r/c" transmission link. It was just a little
food for thought. :)
http://www.hpiracing.com/coolstuff/product_features/3speed_tranny.htm
http://www.trossenrobotics.com/images/productdownloads/011201_emaxx_tranny_assy.pdf
http://auto.howstuffworks.com/transmission.htm - See the 2-speed
diagram in the middle of the page.
-Charley
