I can see this topic has been dredged from the ancient past...
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Originally Posted by LostCause
Issues that come off the top of my head include:
1.) Lower efficiency
While motors (especially the AC variety) tend to have very linear torque curves, they have a speed of most efficient operation. Using a hub motor, which almost certainly means it will be direct drive, forces the motor to operate under a much wider speed range. Generally, the faster the motor turns, the lower its efficiency due to friction.
Many of the top solar cars use direct drive hub motors, though. I've forgotten the motor brand, but it is extremely expensive for its output and extremely efficient.
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Since efficiency is lower at higher speeds, it seems to me like hub motors have the advantage in that regard, because even the 8" trailer wheels on the trike kit of my Burgman, which are far smaller than most car tires, are only about 2,000 revs per mile at a quick guesstimate, (I don't know the exact circumference of the tires), which is much lower speeds than I've seen for ANY central motor in ANY design so far. This seems to me like a much narrower speed range, really. Especially compared to the Tesla, with it's 13K redline.
Quote:
Originally Posted by LostCause
2.) Higher Unsprung Mass
Hub motors are physically attached to the wheels, increasing their weight. From a performance and design perspective, lowering the unsprung weight to sprung weight ratio is desirable. Heavy wheels exert large forces on suspension members, causing their required strength (and thus weight) to increase.
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That I can see as being a concern. My primary focus with hub motors is reducing un-needed weight from the car as a whole, and when I take a light truck like a Chevy S-10, and start weighing out the components, it starts adding up REALLY fast. I bought some lowering spindles for a truck I had once, and each one was 20-30 lbs. EACH. Then you had the weight of the brake disc, (which I thought was undersized), plus the brake caliper. With only 180hp on tap with the stock V6, I can't imagine putting 50hp at each wheel would add a significant amount of weight if it were to replace redundant components, drive shaft & drum brakes in the rear, spindles, discs & calipers in the front. Even better would be to integrate the motor into the rim itself, saving yet more weight, and eliminating a (granted no longer common) point of failure.
Quote:
Originally Posted by LostCause
3.) More Complex Drivetrain
Some high-end electric cars, such as the Tesla Roadster, use hub motors. The average DIYer most likely shies away from the technology because it is easier to drop in an engine replacement than redesign the drivetrain. Axles would have to be lost, kingpins and steering knuckles redesigned to accomodate the motor and its wiring, and special rotating electrical contacts fabricated to power the hub motors. While it is not impossible, hub motors probably rate low on the cost/benefit ratio list.
- LostCause
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Incorrect as has been stated in this thread. Also, rotating electric contacts?
Has no one ever heard of stationary-winding motors?
As for cost/benefit, ANY retrofitting is low on cost/benefit by nature. Even just replacing the engine with a motor. But as for mass production, the reduction in the numerous little parts that exist between engine and wheel is a massive savings for any high-volume auto manufacturer.
Really, as far as things go, I see hub motors as having the most pro's and fewest cons, of ANY electric design.