A Technical Question

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RevDon

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I came across this forum quite by accident while researching automobile-based EV's, and I've been pleasantly surprized by the technical and mechanical pioneering that goes on here :D Going through Ypedals battery battle, watch Beagle build his scooter from scratch, not to mention Fechter's controller rebuilds - it's all very impressive :!:
So I figure this is the group to help me understand the differences and limitations of certain components, namely wheelmotors / hubmotors. In the automotive realm, the wheelmotor, as used by PML Fightlink: http://www.pmlflightlink.com/ is high performance and capable of regenerative braking. From what I've been able to gather from this forum, regen braking is of little use on lightweight EV's such as bikes / trikes using hubmotors. Is this a size / mass issue, or does it have to do with the components themselves (controllers included) and how they work? I realize that an auto platform allows for more weight for things such as onboard computers, more / bigger batteries and such.
What got me thinking about this subject is the sprung / unsprung weight issue. The wheelmotors used by PML are comperable to the weight of the brake components they replace. Even so, I think that if you moved the wheelmotors inboard, mounted the stator to the frame and drove the wheel from the rotor via a driveshaft / CV joint, it would be even more efficient :idea: Am I just grasping at straws here, or am I onto something, and if so, could it translate to lightweight EV's using hubmotors :?: Or am I just plain nuts :wink:
 
We have a technical section...

(you should copy what you wrote and delete this thread and make a new one there)
 
safe said:
We have a technical section...

(you should copy what you wrote and delete this thread and make a new one there)
Click to expand...

There's an E-Bike Technical, but not an EV Technical, other than battery, and I want to get answers from both sides.
 
It'd make the suspension perform better, but I don't see how it would make things more efficient. If anything going through a universal joint is going to make it less efficient.
 
Hey Rev,

It's debatable. Might be long-term testing will tell us more. The difference may be close enough to call it a wash.

The wheelmotor generally reduces weight and drivetrain losses, but it does get a beating and generates losses through vertical movement.
 
I also had doubts about unsprung weight and duplicating motor and drive components at each wheel. I did a little reading about PMLs approach and found that the weight penalty is just 2 kg compared with a conventional wheel assembly. The regen system also provides all the braking, so you'll notice in some of the press photos for the mini that there is a wedge under the wheels to stop it rolling away. They're still working on the handbrake, which is required by law. Putting all the drive components in the wheels also means easy access for maintenance or replacement, as well as freeing up a lot of space for the battery pack and storage space.
This approach still needs some development, but it seems to me it'll open up a whole new range of design possibilities.
 
I was remembering the old Jag XKE rear suspension, where the disc brakes were on either side of the differential, before the drive axles, and that's what got me to thinking......
 
At the two extremes size wise- monster trucks use a similar braking system, and so do a lot of little power sports vehicles.
 
There was a thread that I put together a while back where I actually went through the calculations about braking using regen. You have to be able to increase the magnet strength about 8 times higher than in the forward direction to get the braking power you need.

So this means that if you are going to do this (eliminate the brakes) then you need to think in terms of the Induction motor design.

:idea: Think Tesla Motors...

That way you can modulate the braking force by increasing or decreasing the magnetic field strength of the motor.

With a typical permanent magnet motor the braking force would be fixed and pretty limited.

(not enough to do the job)
 
I ran regen braking on my Zappy scooter. It was more than enough to make the belt skip over the teeth. The belt was the limiting factor.

Try rolling downhill with a hubmotor and short out all 3 phase wires at the same time and tell me there's not enough braking. :eek:

I like regen. I think all controllers should at least have it as an option.

It loses any advantage if your on a lightweight bike on flat ground. Add weight or hills, and the advantages grow.

My Honda Civic Hybrid uses regen braking. At 70,000 miles now and the front brake pads look practically new. I think the brakes will outlast the rest of the car at this rate.
 
:arrow: It depends on how you do your calculation...

A dragster was once predicted to have a minimum 1/4 mile track time because you can only accelerate at a maximum of the force of gravity. Since then they've beat that because the rear tires expand when they spin and that raises the motor creating an effective extra type of downforce. On top of that they also use downforce from the wind at higher speed. So today they can actually do the 1/4 mile faster than gravity... which is amazing.

:arrow: Back to our reality...

If you want to deal with brakes that can produce a skid on the FRONT tire of a bike or front wheels of a car then you ideally need to produce a full "1G" worth of braking force.

Since most of our motors produce well less than it takes to propel a dragster in the forward direction then you will have a huge difference between the peak performance of acceleration verses braking.

So it all depends on how "real world" you want to crunch the numbers. If you want to compare high performance vs high performance then you need a ratio that matches the acceleration vs the braking.

In such a case it's really hard to get a 1 hp forward direction motor to be able to achieve the 8 hp of braking force to stop a regular electric bike. I'd have to run the numbers again to look at cars.
 
those Jag rear ends are great. I've been hoping to find one for my MG for a while. they realy improve handling.

but not efficancy. having 2 CV joints between the motor and the wheel would cost you 5-10% efficancy. a total rethink of the CV design might improve that, but you'll still end up losing efficancy for the sake of improved preformance.

I think it might be possable to build a true hubwheel, were the motor is the wheel, with no extra parts, eliminating the weight of things like rims, lignits, axles, brake calipers, rotors, pads. if it was built like the wheel Micillin prototyped a while back, you could eliminate the suspension and tire, too.

As for Regen braking, its a great idea, and works great on high mass to power ratio vehicles, but on a bike, not so much. even with the other tech problems Regen has on an Ebike, you can only recover that part of the energy lost due to accelerating the mass, and then only part of it. thats great when you have a large mass moving at high speed, and having high kenetic energy, but on a bike, there just isn't enough energy to convert back to electricity.
 
hub motors in light EV's would be great. there has been one japanese EV minivan that used hub motors.

i agree if we could design replacement hubs that had electric motors, it would make electric conversions extremely simple - 4 hub motors replacing the car hubs, wire them up and mount some batteries and controllers.

in the christmas holidays i might have to take the wheels off my car and have a lookies at how it could be designed.
 
Rassy said:
I may be missing something here, but I don't see why an "automotive" type hub motor could not have a disc brake rotor as part of the assembly, even bolted on like the bikes.
Click to expand...

The automotive wheel motors are used for regenerative braking, very effectively so, that a disc brake is redundant and unnecessary.

Don
 
RevDon wrote:

The automotive wheel motors are used for regenerative braking, very effectively so, that a disc brake is redundant and unnecessary.
Click to expand...

I guess I wasn't clear, I am all for the regenerative braking, but what about when you need to hold a full stop on a hill, etc. Also, a parking brake that can be locked on without using up your battery or having to block your wheels would be nice. :D
 
RevDon said:
Rassy said:
I may be missing something here, but I don't see why an "automotive" type hub motor could not have a disc brake rotor as part of the assembly, even bolted on like the bikes.
Click to expand...

The automotive wheel motors are used for regenerative braking, very effectively so, that a disc brake is redundant and unnecessary.

Don
Click to expand...

The reason why brakes are in the wheels is for heat transfer. Putting a motor in a wheel is a nonsense (for a car). It is exposed to water, theft(!), shock, vibration, and is very exposed in case of a crash.
Unsprung weight will also be much higher. If a wheel motor is strong enough to brake a wheel whitout generating high heat, it is much better to located it under the hood (less unsprung weight, shorter electrical cables, possible water cooling, crash protection).
A good combination would be to include disc brakes just next to the motor under the hood: with regen, they will generate much less heat and dont need to be out in the wheel. Hand brakes would then be no problems too.
 
The reason why brakes are in the wheels is for heat transfer. Putting a motor in a wheel is a nonsense (for a car). It is exposed to water, theft(!), shock, vibration, and is very exposed in case of a crash.
Unsprung weight will also be much higher. If a wheel motor is strong enough to brake a wheel whitout generating high heat, it is much better to located it under the hood (less unsprung weight, shorter electrical cables, possible water cooling, crash protection).
A good combination would be to include disc brakes just next to the motor under the hood: with regen, they will generate much less heat and dont need to be out in the wheel. Hand brakes would then be no problems too.
_________________
OLIVIER

Please see:http://www.pmlflightlink.com/archive/news_mini.html
 
Please see:http://www.pmlflightlink.com/archive/news_mini.html[/quote]

I am not sure I believe everything they say... Their motors develop 750 NM of torque each ? :shock: Thats 550 ft-lbs. A DC motor that develops about 200NM costs about 5000$, do the math. They also say 400A at 350 V. :shock: That is 140 KW per wheel, or 560 KW total. This is the equivalent of 1000 e-bike hub-motors...
I think the only benefit of hub motors for cars is in the ease of conversion from ICE to E.
For a bike with no suspension and low speed it makes sense. For a scooter it is just ok. For a motorcycle it already does not make sense anymore.
 
yeah i agree. this jap thing had that style of setup - it still had the brakes etc, just the motor was in the actual hub (thing that holds the brake rotor on.

that way u still had a choice of aftermarket rims and brakes (important to some people)
 
To Olivier,

While I agree that PML's numbers seem unrealistic, there are at least a couple of other companies attempting to use their motors. See these links...

http://www.lightningcarcompany.com/

http://www.zapworld.com/electric-vehicles

I was looking into the motors for an electric motorcycle. Found a couple of websites saying the motors were going for nearly $20k because they were still being hand made. Too rich for my blood.

JJ
 
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