Arlo1 said:
HP will only go down as you add more paracidic losses and drag to the system. Torque will be multiplied!liveforphysics said:Arlo1 said:
The advantage of a rear-end, is you can put a 6:1 gear ratio in it, and spin the motor 6x faster than wheel speed, and only need 1/6th the motor size/mass/weight to equal the same power of a direct drive setup.
But yeah... you're right, I have 100 other projects to handle before that... lol
Ok so that number of 6 times depends on the actual gear ratio you use. So if you used 4:1 rear end gears it would be 4 times. And because its being replaced by two wheel motors then it would be only 2 times in a rear wheel drive or it would be the same in a 4 wheel drive vehical!liveforphysics said:Ehh, problem is, they still have to be 6 times bigger for the same amount of torque delivered to the wheels.
The 10% power you'll lose in the rear end will be way more than worth it for the ability to get the motor into an efficient RPM range sooner.
Remember, all motors are 0% efficient at 0rpm, and then climb up from there.
Going with a rear-end like this does not make it a reliability concern. It will hold everything you can throw at it to run 5's in the quarter. That should be good enough.
Very cool!
Arlo1 said:
This is a good way to do things--it's worked for almost all of my projects and hobbies, and indeed much of my daily living stuff.methods said:
Your still going to be at 0% effieiency with either design at 0 rpm. And the rpm of the motor will be depending on the design so if you have a motor wound for 1000 rpm at 100 volts it will be in its efficiency at the same time as one wound for 6000 rpm 100 volts and geared down 6x In the end the diff ends up being a drag on power and dead weight and in the case of good suspension a terable design. ( ok for drag racing but not as good for the rest)liveforphysics said:First, powering the front wheels on anything fast that has the rear wheels powered is useless. (front wheels should be in the air on anything RWD and fast)
Second, the torque production is very much related to motor physical size. Even if you have a magic motor and controller that has infinity current and current handling, and infinity cooling, you are still bound by the strength of the magnets in the rotor to push your field against (and by stator tooth flux saturation etc). When you're looking to push a motor hard for racing, you have defined torque limits based on the size of the flux area, so if you want to match a geared motors torque, you gotta get that flux gap area physically as large as the size increase to match the geared motors advantage to equal the torque and power.
It's why a little geared hub can be 5lbs and match the torque of a 15lbs direct drive hub.
Torque * RPM = power. Anything you can do to get that RPM up is a good thing. Direct drive hubs means the first part of the track is going to be at like <5-10% efficiency, and off the line you're at 0% efficiency. You could spend those same amps and voltage into something that gets into an efficient RPM range 1/6th sooner with a rear-end, and get to use a lot lighter and more compact high RPM motor to milk power from.
Plus, for me, I've broken every sort of CV shaft and diff and axle and suspension control arms and suspension mounts on the chassis etc.
Just knowing you can spend just $3k to permanently end all those types of failures makes me froth at the mouth for building a sick RWD electric dragcar, where your only concern becomes burning up motors and controllers, rather than breaking the drive-train AND motors and controllers.
Arlo1 said:
jondoh said:
But don't you have a lil lecky car of some sort Luke -->
Is there no limit to which they will go?
AussieJester said:
methods said:
8) LOL! 
