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Discussion Starter · #1 ·

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No experience with the suppliers. The three major stumbling blocks to hub motors, as I see them:

1) lots of unsprung weight
2) having to control multiple motors with multiple controllers leads to a more complicated setup
3) no gearing means your motors are going to need a very specific torque band to get you to the speeds you want to go. I'd want to see a detailed torque band spec sheet before investing any money
 

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Discussion Starter · #3 ·
No experience with the suppliers. The three major stumbling blocks to hub motors, as I see them:

1) lots of unsprung weight
2) having to control multiple motors with multiple controllers leads to a more complicated setup
3) no gearing means your motors are going to need a very specific torque band to get you to the speeds you want to go. I'd want to see a detailed torque band spec sheet before investing any money


Thanks good input.

1. Weight, doesn't the batteries weight help towards unsprung weight issue?

2. What we are thinking is processor controlled, I come from a robotics background so that is not bad. But the cost for multiple controllers is an issue.

3. don't the motors have built in gearing in the wheels? What you say about torque spec is still true.
 

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Thanks good input.

1. Weight, doesn't the batteries weight help towards unsprung weight issue?

2. What we are thinking is processor controlled, I come from a robotics background so that is not bad. But the cost for multiple controllers is an issue.

3. don't the motors have built in gearing in the wheels? What you say about torque spec is still true.
I'm not sure what you mean about the weight. The batteries are going to way the same, whether the motor is being held up by the suspension or not.

#2 sounds like it is surmountable for you, good for you on that one. I think the average DIYer would probably be out of their league on that.

The motors usually do have built in gearing, but even then, it's a specific gear. The last one I looked at was a fixed 5:1 I think, which gives you a pretty slow top speed. With a fixed gear, you're going to sacrifice acceleration or top speed, no matter what, but it would really depend on the motor specs as to whether the performance would be acceptable for a given vehicle.
 

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No experience with the suppliers. The three major stumbling blocks to hub motors, as I see them:

1) lots of unsprung weight
2) having to control multiple motors with multiple controllers leads to a more complicated setup
3) no gearing means your motors are going to need a very specific torque band to get you to the speeds you want to go. I'd want to see a detailed torque band spec sheet before investing any money
1) Well you don't have to mount the wheel motor inside the wheel do you? Why not mount them next to each other back to back where the front differential would be on an AWD car...you can have half-shafts come from the motors and connect to the front wheels as normal AWD works

2)multiple motors may be able to share controllers, but maybe not, so it may be a bit more complicated in that respect, but less complicated when comes to transmission adapting and shift timing, clutch/ no clutch, Battery pack location, weight of transmission, etc... additionally they can all feed form a central battery source, so its different yes, more complicated than another DIY EV, I don't know 100%.

3) The link below lists the motors as having 380NM but that might mean 2x, since they are trying to sell 2 motors. Still if you were to build an AWD car, 760NM is enough torque..

http://www.alibaba.com/product-free/105699534/e_Car_10_15kw_Hub_Motor.html
http://www.evworld.co.nz/magnetronic-technology/

I emailed the company about the peak power output, hopefully its something like 30kw peak, 10kw cont....in which case with 4 motors AWD, 120kw 760NM, something doesn't seem right, I guess I will just wait for the response...

Keep in mind Ev-propulsion.com has a wheelmotor for a motorcycle available...they could be used on a light car experimentally....;)
 

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Discussion Starter · #6 ·
I'm not sure what you mean about the weight. The batteries are going to way the same, whether the motor is being held up by the suspension or not.

#2 sounds like it is surmountable for you, good for you on that one. I think the average DIYer would probably be out of their league on that.

The motors usually do have built in gearing, but even then, it's a specific gear. The last one I looked at was a fixed 5:1 I think, which gives you a pretty slow top speed. With a fixed gear, you're going to sacrifice acceleration or top speed, no matter what, but it would really depend on the motor specs as to whether the performance would be acceptable for a given vehicle.
What I meant, the batteries weigh a lot thus account a lot to help offset unsprung weight issue. But hey I am not a ME I am an EE programmer.

I too have concerns about being one speed. The ME guys were not as much, we will see.

My neighbor approached me knowing my work in robotics about making an ATV with wheel motors. He invests in companies and knows how to make money (unlike me). I said I would explore what it would take and put together an engineering team to look at it. It is fun just exploring and we may put together a proto type with him funding it, if nothing else it will be a learning experience.

BTW one year we built a robot with omni wheels, these wheels will drive you forward but also will slip sideways. The robot had four independent wheels and motors each being at 45 degrees to each other. This thing could drive sideways any direction and rotate as you drove forward etc. The math in the controls systems was a challenge. It was beautiful to watch.
 

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Discussion Starter · #7 ·
1) Well you don't have to mount the wheel motor inside the wheel do you? Why not mount them next to each other back to back where the front differential would be on an AWD car...you can have half-shafts come from the motors and connect to the front wheels as normal AWD works

2)multiple motors may be able to share controllers, but maybe not, so it may be a bit more complicated in that respect, but less complicated when comes to transmission adapting and shift timing, clutch/ no clutch, Battery pack location, weight of transmission, etc... additionally they can all feed form a central battery source, so its different yes, more complicated than another DIY EV, I don't know 100%.

3) The link below lists the motors as having 380NM but that might mean 2x, since they are trying to sell 2 motors. Still if you were to build an AWD car, 760NM is enough torque..

http://www.alibaba.com/product-free/105699534/e_Car_10_15kw_Hub_Motor.html
http://www.evworld.co.nz/magnetronic-technology/

I emailed the company about the peak power output, hopefully its something like 30kw peak, 10kw cont....in which case with 4 motors AWD, 120kw 760NM, something doesn't seem right, I guess I will just wait for the response...

Keep in mind Ev-propulsion.com has a wheelmotor for a motorcycle available...they could be used on a light car experimentally....;)
Thanks this was helpful, let me know what you find out.

Doug
 

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I think so; otherwise it is not a wheelmotor. It becomes a motor coupled to the wheel.
What I meant about not having to use the wheel motor inside the wheel is that you benefit from reducing un-spring weight that way while not requiring any gear reduction because the wheel motor is designed to operate at a direct drive rpm range...So I guess I should have said a "motor with a wheel motor rpm range" But thanks for pointing that super important point out.:rolleyes:
 

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Not ALL EVs..... Doesn't the BMW Mini EV use wheel motors? it is plenty road capable and does have 4 wheels.
I believe you are thinking of the old PML Flightlink prototype, which never lived up to their hype by the way.
Enertrac has a nice wheel motor for use in motorcycles so it was designed to take the abuse of that application.
http://www.enertrac.net/
Four of them might work in a small car, I know they are using two of them as inboard, (not in wheel), motors for a Miata I believe.
I did see a prototype, Michelin maybe, that actually used a gear reduction unit with an in wheel motor system. However that takes a way some of the simplicity of a direct drive in wheel motor and you may as well use an inboard mounting and save the unsprung weight.
 

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I believe you are thinking of the old PML Flightlink prototype, which never lived up to their hype by the way.
Enertrac has a nice wheel motor for use in motorcycles so it was designed to take the abuse of that application.
http://www.enertrac.net/
Four of them might work in a small car, I know they are using two of them as inboard, (not in wheel), motors for a Miata I believe.
I did see a prototype, Michelin maybe, that actually used a gear reduction unit with an in wheel motor system. However that takes a way some of the simplicity of a direct drive in wheel motor and you may as well use an inboard mounting and save the unsprung weight.
But it did exist prototype or not, it was a fully functioning ev with four wheels using wheel motors.
 

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What I meant, the batteries weigh a lot thus account a lot to help offset unsprung weight issue. But hey I am not a ME I am an EE programmer.

Unfortunately, it just does not work out that easily. If your unsprung weight is high, you have to work it out via suspension design and this has practical limits, particularly when you consider the reality of driving on, well, all types of roads from rough to smooth and in all types of conditions, surface friction coefficients etc...

Just step away from the physical mass of the motor and wheel assembly for a moment, but don't forget that putting the mass of the wheel moor out there means beefing up the control arms / strut rods and of course the carrier / spindle assembly if on the front or an IRS setup. All that aside, you are very likely going to end up with an unconventional suspension design; one that either relies on very high spring rates or perhaps a complete change of the chassis that may or may not work well with your battery pack.

You can go torsion bars, but your chassis has to be designed to resist the flex induced by the fixed end of the bar. You can use a transverse spring assembly (al-a Corvette) which can be very nice, but you are going to be facing some big issues in getting the spring loading to work well with the unsprung load plus you will have to figure out how to get all of that shoehorned into a chassis where you pretty well need a lot of flat space to put a battery pack.
Maybe you can put the spring / damper set above the load. That would work if you are doing it in a really tall vehicle where your spring fixed end is high enough to give you adequate jounce travel and avoid coil bind- and don't forget, your spring wire diameter is going to be pretty big due to the high rate required by the high unsprung mass, so your coil height in bind is therefore longer and all of this gets even taller.

If you are driving only on dry pavement that is really smooth, then you probably will not worry so much about unsprung weight until you look at another factor which is the gyroscopic force that you will have in the armature and housing. You are going to feel that as counter input in the steering system, so that too has to be engineered out. Perhaps a mix of high scrub radius and a very heavily restricted feedback loop or some tuning of the spool valves in the steering servo can would help, but it is not going to be easy to overcome it completely. This is particularly true if you want to sell it to the masses who are accustomed to driving a very mature design in their mass produced car / truck / SUV.

I am not saying this cannot be done. I am saying it is nowhere near as easy as just overloading the sprung weight in hopes that a change in sprung / unsprung ratio will fix the problem. I am sure that with enough time, funding and tools, this can be overcome or at least brought under control to a safe and suitable level.

If I were challenged to do it, I would look at trying it on a pickup truck or van first. The heavy live rear axle setup and big 'ole diff setup in the center- those are pretty heavy and maybe if you are really savvy, you could work in hub motors on a beam axle setup that would give you RWD. All that work and expense and headache to get you to a point where you are probably not as good as a cheap LSD and a single motor without all the control issues.

Also, a note about shopping Alibaba.com - note that most of the vendors are not manufacturers, but trading companies. The one highlighted on that search is really into the metal door business. I have lived here in China for more than 10 years and elsewhere in Southeast Asia for several prior to that. My experience is, find the right supplier, not the supplier you can find right now.

Phase
 

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But it did exist prototype or not, it was a fully functioning ev with four wheels using wheel motors.
Just because it moved around doesn't mean it was a fully functioning EV. If it couldn't handle the demands of normal daily use then I don't consider it fully functioning.
 
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