Induction Hub Motors

[fizzit]

I just went to a meeting about the electric Formula car that the engineers at my university plan to build. They said that they plan to use induction hub motors (9 inch diameter) in all 4 wheels of the car, and the car will not have axles. They also said that having these motors would be far more efficient and lighter than having a single motor with transmission, because of the weight and efficiency loss of the transmission. I was surprised because I thought that induction motors had to be spun at pretty high RPMs to get decent efficiency.
What do you guys think about this? Does it sound realistic?

 

[Lebowski]

they must be planning to go fast then

 

[liveforphysics]

Induction motors can be designed to have just fine low RPM torque, it just needs more cooling than a PM because too generate it's torque requires keeping a field moving/slipping through the rotor to generate it's internal rotor currents to drive it's magnetic field. It's never going to match the continuous low RPM torque of an equivalent PM motor for a given amount of thermal budget, but it can match the torque at the cost of just a little more power.

I think rotor mass on the wheel might make the suspension very hard to dial in to work well, but I don't think power density or acceleration needs to be bad just because it's induction over PM. Good induction kicks PM's ass in efficiency for cruising at light loads, which is where most commuter vehicles are being operated, but for a race car, I would think the high percentage of WOT time would justify the PM motor as the logical choice.

 

[Dauntless]

they must be planning to go fast then

Hey, these are students. They need to hear more of your thoughts on that.

I just went to a meeting about the electric Formula car that the engineers at my university plan to build. They said that they plan to use induction hub motors (9 inch diameter) in all 4 wheels of the car, and the car will not have axles. They also said that having these motors would be far more efficient and lighter than having a single motor with transmission, because of the weight and efficiency loss of the transmission.

I assume this is for Formula SAE. You have your website going yet? So many schools have figured out the only way to sell sponsorship of the project is to SHOW they are REALLY working and creating something. You could go to kickstarter, I've seen a number with just a blog which I suspect is more productive because they update what they've done and look legit, etc.

If you have that, link it up here.

 

[spinningmagnets]

What top speed are you planning for?

 

[fizzit]

Thanks for the info, Liveforphysics. I am not entirely sure why they chose to go with induction over PM motors. Unfortunately there's no info yet about the project on the internet.
I'm not sure which specific competition it is, but I know that there are multiple events: an endurance race, a drag race, and an autocross race. They said that they are planning for an average speed of 35mph and a max speed of around 100mph, I believe. I guess the efficiency of the inductance motor would help them out a lot in the endurance race?
They said that they are about to order the BMS and for the batteries they are using Haiyin 6AH LiPo cells that are rated for up to 300A. Apparently the powertrain is mostly worked out, but the suspension/frame design are yet to be figured out. I signed up to help with that part so hopefully I can contribute, even though my major is EE and not ME.

 

[MrDude_1]

When it comes to making a well handling vehicle, the most important thing is suspension.
When it comes to mass effecting handling (aka acceleration in all directions), the largest effect is from unsprung mass.. followed by mass carried furthest away from the CG and moving inward.

In otherwords they're placing the motors and sticking them as far as possible from ideal.

When it comes to Dragracing and autocross at the power levels they can afford, RWD is preferred. If you have AWD, thats nice, but its only a benefit when the front wheels only use the traction not being used to steer... their setup will not be that advanced. In endurance, it doesnt matter, what matters is reliability.


If I was making an electric SAE car, it would be similar to a conventional SAE car... except the single rear motor would be in the center driving the rear hubs via axles. Think of the motor as replacing the output of the transaxle. its just transverse, in the middle. That ONE larger motor, along with some Carbon Fiber driveshafts will promote mass centralization, be lighter, more efficient, and easier to control. Cheaper too.

I wont debate the motor type. To me, thats more of a controller issue anyway. If they want an induction motor, and can control one, more power to them. As someone who judged SAE though, a 4hub motor layout is dumb on several engineering levels.

 

[MrDude_1]

Dammit. I broke my rule on posting here. I'm supposed to be lurking only. Been here for years, and this is the first time someone suckered me out to post. lol.

 

[fizzit]

Well I appreciate that you broke your rule! That is very interesting about the effect that it would have on handling. I guess I figured that unsprung mass wouldn't matter since the tracks are very smooth but I see that it has larger effects than just suspension response. I'm a freshman so I'm not going to tell the seniors who came up with this that their design is bad, but I'll keep that in mind

 

[Stevil_Knevil]

WOW

Got me thinking of an AC Induction, 2-speed geared hub motor..


..ouch 8)

 

[fizzit]

WOW

Got me thinking of an AC Induction, 2-speed geared hub motor..


..ouch 8)

That would be cool. The team is planning on going direct-drive, however. The rotor will also be the rim for the tire.

 

[Dauntless]

. . . . the single rear motor would be in the center driving the rear hubs via axles. Think of the motor as replacing the output of the transaxle. its just transverse, in the middle. That ONE larger motor, along with some Carbon Fiber driveshafts will promote mass centralization, be lighter, more efficient, and easier to control. Cheaper too.

I'd like to think of having a limited slip differential, yet if you read 'The Unfair Advantage' Mark Donohue talks of his solid axle cars and explains a slightly different driving style to suit it. The guy won more than 1/3rd of his starts, etc., maybe he has a point.

http://tncscooters.com/index.php?route=product/product&path=52_55&product_id=61