Andrew Wowk wrote on 12/01/06 12:43:
Jeff,
What is your target speed range? Speed takes power no matter if you
have a transmission or not. A 1-1/2 hp motor can only produce about
1119 watts continuously, and mabe as much as 1.5x more for all
practical purposes "continuously" (depending on heat dissipation and
size of motor), and 2-3x more peak.
For a permanent magnet motor, torque varies directly with current,
and speed varies directly with voltage. Heating losses vary with the
square of the current. This means that what you are really trying to
do with a transmission is allow the motor to run at a higher voltage
and lower current for a given power output to improve efficiency, and
reduce heating losses.
Heating losses are directly porportional to armature resistance. A
larger motor has a lower armature resistance and can handle higher
amounts of current while still running efficiently. What follows
then, is a way to get a similar benefit to having a transmission is
to use a larger motor (or two motors).
Also what can be done to get a similar advantage to a transmission is
to get a higher voltage motor or over-voltage the existing motor. If
the existing motor is over-voltaged it will have higher continuous
power capability, and will run at a higher voltage and lower current
for all speeds (provided you gear it to where the vehicle would have
the same top speed as it would while running at a lower voltage,
meaning you'd need to raise the gearing).
Regards, Andrew
Wow, so many good questions in such a short time! I was just hoping for
at best one response (positive or negative) within a week....
Ok, here goes. I'm putting all my replies to the present questions in
this response to keep them in one place for the moment.
What is your target speed range?
We're talking lawnmower-type speeds, 4 wheels, and front-wheel drive.
It's not a motorcycle at all, but I'm hoping to use motorcycle tech.
0-6mph
0-4.5mph
0-3 or 3.5mph
0-2.5mph (would be nice)
0-1.25 or 1.5mph
4 or 5 speeds would be ideal
This would not be an on-road vehicle, though it would have lights and a
horn.
A 1-1/2 hp motor can only produce about 1119 watts continuously, and
mabe as much as 1.5x more for all practical purposes "continuously"
(depending on heat dissipation and size of motor), and 2-3x more
peak.
Right, and this would pretty much overkill for my purposes. Power is
likely be 3 Group-24 batteries, but 3 Group-27's are a possibility if I
can get a compact enough transmission/motor combination. The overall
layout is very fluid and subject to change depending on how things would
fit together.
The reason I had asked about motorcycle transmissions is because of the
multiplicity of speeds, and the fact that the stuff I looked up online
showed a lot of ball-bearings and needle bearings being used rather than
plain bearings. I need to keep the effiencies up if I can. Other reasons
are that they run in oil rather than grease (important at low temps),
and can handle high RPMs with no problems, and the ease of shifting.
For a permanent magnet motor, torque varies directly with current,
and speed varies directly with voltage.
Which is important for me, and it makes regen braking easier.
This means that what you are really trying to do with a transmission
is allow the motor to run at a higher voltage and lower current for a
given power output to improve efficiency, and reduce heating losses.
True.
[EMAIL PROTECTED] wrote on 12/01/06 10:57:
In my mind the ideal (street) transmission for an electric motorcycle
is a small version of a Harley style stand alone belt driven
transmission. It would use a belt drive from the electric motor to
the transmission and enable either a chain or belt final drive.
That's one idea I was considering.
Another possibility is using the front differential from a 4WD ATV
coupled to an ATV or motorcycle transmission. I would have to greatly
change the suspension and tire size. I'm concerned that it might not be
compact enough though.
Why not use a lawnmower transaxle? A little too wide and they always
seem to use worm gears. Hydraulics are out.
BFRListmail wrote on 12/01/06 05:41:
Hi Jeff,
Not really an expert on motorcycle transmission, but the first thing
that comes to mind is, I assume you don't want to clutch it? That
would leave out a lot of transmissions. I'm thinking some of the
smaller kids type motorcycles run without a clutch. My brother old
Honda CT70 comes to mind. Only 3 speed though. Do you want electric
upshift and downshift as well?
Later,
Darin BadFishRacing
A clutch is just fine. Actually, I'd have to have it in case something
broke down and everything had to get pushed. I would use a small
actuator for that, and a solenoid for the actual up/down shift.
Coordination at-speed is not required. I'd probably bring the whole
thing to a stop before shifts.
So, what is this mysterious vehicle?
It's an indoor-outdoor wheelchair. :-)
I need it to be able to pull a small trailer (up to 300-400 lbs) both on
the sidewalk and off-road. I need to be able to plow small amounts of
snow. I need to be able to push a gas-powered mower deck, amongst other
chores.
Jeff
