Hello again thingstodo,
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Originally Posted by thingstodo
Hi
The inside wheel should have more torque, since it has more slip. Breakdown torque on an induction motor is 3.5 - 4 times rated torque ... but each motor seems to have it's own base speed. We have ACIM on all of our equipment (at work) and changing out a motor DOES change the speed that the motor runs when lightly loaded. Loaded - it's only a few rpm.
But if the inner wheel is pulling hard the outer wheel should be OK going along for the ride?
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Hmm.
With an "auto-locker" (Detroit, Lock-right, etc.) in a corner, the inside wheel drives around corners when there's good traction and low throttle input. The outer wheel unlocks and freewheels faster than the ring gear, clicking past the dog clutches in the locker. Hit the gas and break traction on that inside wheel, the locker dog clutches lock and instantly slams the torque available to the outer wheel. Usually breaking traction on it, causing that end of the vehicle to slide out. On slick surfaces, this happens a lot easier - so you coast around corners.
The "higher torque available to the slower motor" issue could cause similar behavior. The inside wheel gets more torque because it is slipping more than the outside wheel (assuming both motors are loaded, so both are going slower than commanded speed), while the body rolls away from said wheel, unloading it. Once the traction drops below what is needed to keep the tire from slipping due to torque, it lets go. No max overspeed, because AC, that's nice. The whole vehicle slows down a bit since it isn't being driven by that wheel anymore. Now the outside wheel is going even slower than commanded, so slip goes up. Thus torque goes up. Traction is higher than it was on the inside (all else being equal, body roll will do this), so it takes longer to let loose, but when it does, now both wheels on that end of the car are spinning and it's sliding out. Again, this would probably happen faster on slick surfaces.
The point being, without an "open" differential, when one tire lets go the other gets the rest of the torque, making it more able to break traction. Hmm. Maybe slap pulleys on either side of a "truetrac" geared limited-slip differential, and run without a pinion or ring gear at all? I wonder if that'd allow the proper torque biasing.
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My existing/planned setup is only RWD. A warp9 DC motor coupled to a 2002 Honda civic gearbox ... and obviously a DC Controller. I am planning to use it as a Side by side Quad/offroad buggy. Top end or redline (5500 motor rpm) in second gear would be in the 50 mph/80 kph range.
Going to 4 of these motors, one per wheel, driven by one AC controller and battery pack would be great for traction and control. The tires on it give about 1000 revs per mile. 1000 rpm on the wheels = 60 mph. So if I went for .. 20 mph? .. that's 333 rpm. And if I limited to 3000 motor rpm ... I could go as high as 9:1. I have read elsewhere that anything more than 3:1 would require 2 stages, which complicates things.
Belt slip may be bad. I am thinking $10 belts and single drive pulleys. I guess I am assuming that the belt tensioner would let the belts slip if you go over the rated torque? Maybe that's a bad assumption.
Sounds expensive. Maybe I should look around for a spare belt?
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I think you missed my point - it's a glorified fan belt. Nothing too special. It'll cost more than a "plain" fan belt, but it should be pretty common. You still don't want it to slip. The tensioner just keeps the "slack" side of the belt from flopping around. If you want reverse and/or regen braking you will want a "set the tension by setting the distance between the pulleys" setup, else the belt will always slip on reverse and/or regen as the slack swaps sides. A really strong tensioner could work, but might need to be impractically strong to function properly, leading to too much side load on the pulleys.
Check the Gates website, there's a nice pdf in there somewhere for their toothed belt drives, including power calculations, pulley diameter ratios, etc. Higher "gear" ratios are only a problem due to the physical space they require for the larger diameter pulley.
In any case, unless you want to run leading and/or trailing arms (think motorcycle rear suspension) on both ends, you'll need CV jointed half-shafts to bring the power out to the wheels. You may be better off with one motor and the driveline out of something like a Subaru or a 4x4 ATV. Used LEAF motor? Car-part has them as low as $445. More than 4x $85, but you get to use existing driveline parts...