Speed reducer / transmission for vehicle motor

I am working on a project that will use electric motors for vehicle propulsion and energy regeneration. I had hoped to use a direct drive
motor, but it would need to be quite large to provide adequate starting and low speed torque. It looks like a two speed transmission with ratios of 4:1 and 1:1 would be a good solution.
I will probably be using a roller chain and sprocket set so I can mount the motor(s) on the frame. One possibility would be two sets of sprockets and two chains, with some way to couple only one at a time to the drive wheel. I'm thinking about magnetic clutches or a mechanically positioned sliding disk on a splined axle with pins to engage holes in either sprocket.
Another idea would be a planetary gear system that would have a 4:1 ratio from the outer ring gear to the sun gear, with the planetary gears held stationary, and then free the planetary gears but lock up the entire assembly together to get a 1:1 ratio.
I would be grateful for any insight any of you may have for a good way to accomplish this. I am an electronics engineer with some mechanical experience, but not enough to make a good choice for this design. The assembly would need to handle about 20 HP at up to 3600 RPM.
There has been some discussion in a hybrid/EV group about efficiency of mechanical speed reducers and transmissions. One member claimed it would have only about 70% efficiency. My initial research and common sense indicate it should be at least 90-95% efficient, and I would think it should be nearly 100% efficient in 1:1 ratio (with only bearing friction and maybe some windage).
I would like to be able to obtain a suitable transmission for something like $200 each in moderate quantity. Any suggestions on sources for this?
Thanks,
Paul E. Schoen www.pstech-inc.com
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Well, you needn't pay much attention to him in future.
My initial research and common

1:1 figure 98% -99% for a decent pair of gears, or 98% for a LOW SPEED well set up chain drive. 3600 rpm is probably a bit fast for an efficient chain drive.
4:1, I'd guess low 90s. If you did it with two 2:1 gears in series then 94%, or about the same for a well designed epicyclic.

A worthwhile efficient 20 HP two speed transmission for 200 dollars?
Let me know when you find a source...
Incidentally you must have at least one more reduction between the gearbox output and the ground, why don't you combine them into one box?
Cheers
Greg Locock
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I found a 4:1 reduction drive from www.MatexGears.com that handles 250 ft-lb, for about $350 single piece. It is rated about 98% efficiency. If the input is 3600 RPM motor speed, the output is 900 RPM (about 30 MPH with 24" dia tires) and that is (I think) about 42 HP (250*900/5252). If there is a simple way to bypass the reducer at higher speeds, I would have what I need. Could I slide the reducer off the shaft splines and slide a splined coupler on the shafts to get 1:1 direct drive? This would be similar to the old Sturmey-Archer 3 speed hub in English Bikes. I know you need to remove the driving force when gear changing, but that should not be a problem with a properly designed motor controller.
Paul
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You've made at least two significant errors in that paragraph. Are you sure you know what you are doing?
I am impressed by the 98% efficiency, that is rather good.
Cheers
Greg Locock
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Yes, I later realized that 900 RPM is about 60 MPH.
I figure I will need only about 100 ft-lb on each drive wheel for a total of 200 ft-lb which should push a 2000 lb vehicle up a 10% grade. I would use the reduction drive for up to 15 MPH, where I would like to be able to negotiate a 25% grade, or 250 ft-lb per drive wheel. Of course there should be some safety factors and other considerations. I'm an electronics engineer, but I have some basic knowledge of mechanics and physics. I'm trying to help with reality checks on the forum: http://groups.yahoo.com/group/SmallEfficientVehicles /. The latest weirdness was the proposal that two 2HP motors would be sufficient for a 4 passenger vehicle. I had to jump on that one...
Thanks for the input. I might play around with some planetary gears. I will probably use some timing belts and pulleys I have on hand to make a rough prototype.
Paul
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Hello Paul....we meet again! Anyway, I'm a big fan of wheel motors and direct drives, and I'm aware of most of the shortcomings they have too.....so I won't get into that so much here. But some interesting stuff you should look into would be solomon technologies...they push a wheel motor design for use as direct drive on boat shaft drives using two motors with a planetary gear transmission.....
http://www.solomontechnologies.com/about.htm
If you are simply looking for an "off the shelf" transaxle...then might I suggest these folks!
http://www.imperialelectric.com/cgi-bin/wspd_cgi.sh/WService=imperial/prodbr.html
David

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My senior project in college was basically this application, only with a gas engine.
A single planetary set, with appropriate clutches, can provide two forward and one reverse ratio. We stole one of the sets out of a Corolla transmission, which is good for more than 100 HP, so I'm sure it would stand up to your need. We were using pneumatic actuators, so the whole critter fit in a cube about 10" per side. With hydraulics you could go a lot smaller.
Tom.
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Paul,
In the early 80's, Quincy-Lynn Enterprises, Inc Phoenix Arizona designed several hybids for Mechanix Illustrated magazine. In their "Urba Town Car" design, they coupled a Baldor, 72 volt, 8 hp motor directly to a VW manual transmission stating---"the syncronizers in the transmission will allow you to shift gears without a clutch..." Top speed was 55mph and cruise 45mph--range 60-65 miles on batteries, 100miles with generator on. Mechanix Illustrated Plan No. MI-C-2-81.
Hope this helps.
Tut
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? 2006?5?9???? UTC+ 8??2:56:20?Paul E. Schoen??? ?

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