DC Motor Sizing Help For Electric Trike?

[smcallis]

Hey guys, I'm working on a little project building an electric recumbent trike, I'm designing for a maximum weight (including rider) of 300 lbs and I'm looking for a top speed of 30mph, the wheels are going to be standard bike wheels, 28", I can handle building a controller and all the accessory electronics, but, being a computer engineer, I'm a little out of water trying to figure out the physics and sizing a proper motor (or dual motors) for the job, can someone help me out with this?

 

[abeltio]

just thinking out of the box and not doing too many calculations... a 50cc scooter will do about 50mph... and that motor is about 3KW
google for motor, speed and cc (50cc, 75cc, etc)
may give you a fair idea of what's being used by the industry.


saludos.
a.

 

[GregLocock]

Check out the recumbent solar bikes for a better estimate, but I'd guess 800W should be sufficient, if you have a decent nosecone.

The equation is

power=v*(m*g*gradient+crr*m*g+1/2*rho*Cd*A*v^2)/efficiency

all in SI units

m is mass
g is gravity
crr is about .005-.007 for typical bike tyres
rho is 1.2
A is going to be about 0.5
Cd is probably 1 if you have no fairing, 0.5 for a reasonable looking nosecone, down to 0.2 for a beautifully made full enclosure with the right shape. If you get really good you might see <0.1
v is speed

You'll need a transmission to get the speed of the motor to match the speed of the wheels.

You may be dissapointed with the hill climbing performance if you don't have gears.




Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[aamoroso]

There is an excellant company in Syracuse that makes a nice motor for that application.

Advnaced DC Motors


We used motors from advanced to power the golf carts shown at the top of the page here:
Planet Electric

We could actually get these close to 50 mph with the gear technology and battery technology we were developing. The golf carts load was about 600 pounds empty I believe.

 

[smcallis]

Yeah, I found some electric scooters and did some rough math which suggested 750Watts, so you 800W estimate is very good, and I'll be sure to check out those motors, thanks guys!