# Are axial flux motors suitable?



## kennybobby (Aug 10, 2012)

Need more information to determine this.

How quickly do you require to accelerate up to top speed? How fast to travel up the 30 degree slope?

What size tires?

Do you have a datasheet for any of these motors of interest?


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## Madmonkeyrtu (Jul 11, 2018)

kennybobby said:


> Need more information to determine this.
> 
> How quickly do you require to accelerate up to top speed? How fast to travel up the 30 degree slope?
> 
> ...


Acceleration isn't required to be quick, 10 seconds is fine if not slower

Travelling up the slope can be done at a crawl, but it will need to start from stationary.

The tire size we are hoping for will be pretty big, we have got 20" hubs so with tires it will be approx 28". Haven't actually got tires yet so can't be exact.

I was looking at https://www.lynchmotors.co.uk/pdfs/lmc-lem-2x2.pdf

and http://www.saiettagroup.com/products/ 
(In their FAQ they provide a calculation for 'is our motor suitable' asking for you to times weight by speed (momentum?) and comparing it to a figure of 30,000. I don't suppose anyone knows what that 30,000 is and how it relates to their motor?)

Like i said before we would be looking at a fixed transmission with a high ratio.

With regards to batteries we were going to use 4 x 12v 70AH as we can get hold of some. I know this will not provide a decent range but for our purposes that should be fine.

If you need anymore info let me know and thank you


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## Duncan (Dec 8, 2008)

Hi
Sounds like you need a forklift with bigger wheels 
So why not go that way?


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## Madmonkeyrtu (Jul 11, 2018)

Okay for some reason my whole previous reply has never appeared.

Acceleration isn't a priority, 10s is more than adequate, if not slower

The speed up the slope can be done at a crawl, but it will need to start from stop

The tires are large, we have 20" hubs so the full tire size will be approx 28"

Here are two of the products i have been looking at, will hopefully be using a fixed transmission with a large ratio

http://www.saiettagroup.com/products/

https://www.lynchmotors.co.uk/pdfs/lmc-lem-200.pdf

quick note, on the saietta FAQ they have a section for 'is our motor suitable'. They ask you to times top speed by weight and compare it to a number of 30,000. Does anyone know what this 30,000 is or how it refers to their motors? My only thoughts are it is somehow related to momentum because of the speed x weight.

Batteries we are hoping to use 4 x 12v 70AH(ish), i know this will not provide a large range but for our purposes it should be fine.

Thanks


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## major (Apr 4, 2008)

Madmonkeyrtu said:


> ...
> The fact i can run the axial flux motors at 48volts is one of the major draws to me, also they seem to be very easy to package. I understand i will need considerable ratio reduction to achieve my requirements though.
> 
> My worries are that they will still struggle with the low end torque, even with sufficient gearing attached.
> ...


Hi,

I'd stay away from PM motors, axial or radial. Look at a robust series wound motor such as used in forklifts. 48 volt systems are common with those. 

Regards,

major


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## Madmonkeyrtu (Jul 11, 2018)

Hi there,

Why would you stay away from permanent magnet motors? I have been told that with the rare earth magnets in them they are quite good.

Doing a quick bit of reading myself i see that series wound should have the lower end torque i am after, but i thought that the permanent magnet motors were generally more efficient and by using gearing i should get that lower end torque.


thanks


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## rmay635703 (Oct 23, 2008)

Even though ac motors can potentially spin more rpms in general.
at 48 volt you will 
1. need a very large ac motor to perform the same duty cycle as a smaller series model
2. To have adequate starting torque, you Likely will have very limited top speed/rpm without shiftable gears 
(ac motors need very high voltages to have any power at higher rpm to even start performing like a series motor)

Your usage case is the definition of a standard series wound application 

Lastly cost, to make an ac system work correctly with your requirements and constraints will be an order of magnitude more expensive than series wound and even then given the low voltage likely operate in an inferior way

So the payback on the “efficiency “ is likely not there , especially at 48 volts where an ac motor is less efficient


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## major (Apr 4, 2008)

Rmay, I am quite sure the motors he is considering are commutator/brushed PM motors.

For traction applications, the PMDC motor has proven less than durable and often experiences failure early on. The ACPM or BLDC with sophisticated controllers can avoid those problems. For heavy vehicle propulsion, motor overload is fact of life. Your money is wiser spent on the brute force wound field machine.

major


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## kennybobby (Aug 10, 2012)

*Back of the envelope calculatus eliminatus*

Looking at the LEM sales brochure there are two 48V motors.

Using the "technical data" for the model 127 (8.55 kW rated power) you would need about a 10.5:1 gearbox to run the 4400 lb vehicle at 20 mph.

Acceleration @Peak Rating:
It will require 400 Amps to accelerate up to 20 mph in 10 seconds with this motor and gearbox combination, which is the peak current and power rating of this motor.

Acceleration @Rated Current:
It would take 215 Amps for 19 second acceleration to 20mph, and would require 52.4 Volts to the motor, so the gearbox would need to be higher ratio to get back down to the 48 V pack.

The question would be if a 70 A-hr pack can provide/survive very long with these kind of loads and how much voltage sag will result. The sag would limit the ability to reach the speed also.

Constant speed @ 20mph:
The motor would draw about 55 Amps on flat smooth road. Same comment, how long can 70 A-hr pack run at 55 A draw, and how much sag.

So it might be possible/feasible to use one of these motors with the right gearbox and pack combination, but this doesn't account for any losses. You would need to allow for friction, gearbox and controller efficiency. Nor does it consider the hill climb case.


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## Madmonkeyrtu (Jul 11, 2018)

rmay635703 said:


> Even though ac motors can potentially spin more rpms in general.
> at 48 volt you will
> 1. need a very large ac motor to perform the same duty cycle as a smaller series model
> 2. To have adequate starting torque, you Likely will have very limited top speed/rpm without shiftable gears
> ...


I am actually looking at 48v DC system but i think what you say is correct with that a standard series wound application is more suitable.

@major: what do you mean by BLDC? Im guessing PMDC ACPM is permanent magnet Direct current and Alternating current permanent magnet.

@kennybobby: Could i have the equations you are using to get your answers?
I have been using the rpm=(mph x ratio x 336) / Tire diameter to get my ratios and i get 10.8 as the total.

Thanks for everyones help so far, i think the answer is that an axial flux motor wouldn't be suitable and that i definitely should be looking at a series wound motor instead. Are there any brands and/or 48v dc motors you would recommend me looking at?
The M1002 seems to keep on be popping up but it has very similar kW to the axial flux motor.


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## major (Apr 4, 2008)

BLDC = Brushless DC. Armature coils on stator with field magnets on rotor. No brushes. Position sensors with electronic commutation. Typically 3-phase. Really AC but not sinewave.


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## major (Apr 4, 2008)

1C on chosen batteries gives ~3.5kW. Actual if lead-acid is more like 2kW. So like a 8kW continuous rated motor seems overkill. Especially with series motor. Check out D & D Motors. Contact them for recommendations.

major


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## kennybobby (Aug 10, 2012)

28" tires @ 20 mph => 245 RPM.

127 motor rated speed is 2592 rpm, this ratio looks like greater that 10:1 and less than 11:1, so i said ~10.5:1.

back of the envelope this is close enough to your formula with 10.8 :1.


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## Madmonkeyrtu (Jul 11, 2018)

Okay thank you very much for all the help guys. I will contact the d & d motors this week and see what they say.

I don't suppose there are any good places you know off to contact in UK/europe though? Much cheaper on shipping if i can find something uk based.


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