The limits of torque production for a given weight of motor
- Thread starter Miles
- Start date
speedmd
10 MW
John in CR said:
This is exactly why I think we need to establish what is needed for bottom end torque as well as top rpm suitability. A small motor will be fine in most situations if you can wind it up and gear it low. We need to weight the bottom end requirements if we truly want to find a more universal configuration - solution for a direct drive configuration.
John in CR
100 TW
Miles said:
I love hubmotors, but know better than to get into that comparison. The magnetic working area still has to be supported just as rigidly, so doing it at a larger diameter has to weigh more assuming equal materials...or are the real limitations the same as those encountered when trying to come up with a practical hubless wheel?
speedmd
10 MW
Miles said:
Understood. Better to keep this thread to finding some golden rule of length to diameter if possible.
John in CR
100 TW
speedmd said:
LOL, that's not going to happen.
Hillhater
100 TW
Miles said:
Gearbox weight ? Why
I thought you were "simply" going to see if (for example) that Astro could be reconfigured to produce 100NM at 500rpm for the same 2kg (?) weight of "active" materials ? At similar efficiency levels ?
And if not, what are the issues preventing it
Then maybe assesing the practical issues of such a configuration ?
Hillhater
100 TW
But do you know the max potential torque or the limiting reasons using available tech ?
Hillhater
100 TW
.? I thought that was the objective of this thread...without the constraints of being a hub motor ?
PS ..what happened to the hub motor project ?...no posts in 18 months ?
PS ..what happened to the hub motor project ?...no posts in 18 months ?
speedmd
10 MW
Miles said:
Your simulations on the ultimate hub were showing some impressive specific torque values. Active weight was in the 2.5kg range. No way a small astro style motor would come close to the calculated torque without a gear box and its associated weight.
Ignoring the weight and torque loss of the gear reduction does simplify the problem but also reveals an obvious logical limit to the idea of simply increasing the diameter to trade torque for speed using a given weight of active material & supporting structure (packaging): 2kg of motor clearly cannot produce infinite torque being infinitely great in diameter as the packaging would have to be infinitely strong.
Therefore, I think there must be an optimum diameter to optimise torque output per unit weight of motor, dictated by the strength of the available packaging material, after which a gear reduction possibly becomes the better solution. That point would be affected by the weight and efficiency of the reduction, hence those variables get thrown back into the mix.
Why do engineering problems always have to be a mess of compromises?
Therefore, I think there must be an optimum diameter to optimise torque output per unit weight of motor, dictated by the strength of the available packaging material, after which a gear reduction possibly becomes the better solution. That point would be affected by the weight and efficiency of the reduction, hence those variables get thrown back into the mix.
Why do engineering problems always have to be a mess of compromises?
Hillhater
100 TW
Punx0r said:Ignoring the weight and torque loss of the gear reduction does simplify the problem but also reveals an obvious logical limit to the idea of simply increasing the diameter to trade torque for speed using a given weight of active material & supporting structure (packaging): 2kg of motor clearly cannot produce infinite torque being infinitely great in diameter as the packaging would have to be infinitely strong.
Therefore, I think there must be an optimum diameter to optimise torque output per unit weight of motor, dictated by the strength of the available packaging material, after which a gear reduction possibly becomes the better solution. That point would be affected by the weight and efficiency of the reduction, hence those variables get thrown back into the mix.
Why do engineering problems always have to be a mess of compromises?
I think you are jumping a few steps there..
Why not First see what can be done with "2 kg of ACTIVE Materials"...find the limiting factors
. Then review what that means in practice when you consider the "packaging ?
IE..throw some random test numbers into the mix... 0.5m, 1.0m dia air gap ? ...what does that give us with 2kg AM's ?
"Shake the tree" until something falls out ?
Hillhater
100 TW
Interesting Miles.
Does that imply that is viable ?...or is there any issues you see in those results ?
Is the 20A an input parameter to maintain a 1kW power rating ?
What would be the amp limiting factor, and what would be the result ?
Does that imply that is viable ?...or is there any issues you see in those results ?
Is the 20A an input parameter to maintain a 1kW power rating ?
What would be the amp limiting factor, and what would be the result ?
We could certainly double the amps. How much further beyond that depends on the ability to shed heat.
20 amps was a guess to achieve peak eta. I was lucky
All the parameters were guesstimates. Still a lot of tweaking to be done.
Looks like we can get 50Nm continuous from 2kg of active materials, though...
This slot pole combination gives us 3 layout symmetries which will help distribute radial forces.
Winding distribution factor is 0.953
LCM is 1836 so, not a lot of cogging.....
20 amps was a guess to achieve peak eta. I was lucky
All the parameters were guesstimates. Still a lot of tweaking to be done.
Looks like we can get 50Nm continuous from 2kg of active materials, though...
This slot pole combination gives us 3 layout symmetries which will help distribute radial forces.
Winding distribution factor is 0.953
LCM is 1836 so, not a lot of cogging.....
Interesting simulation
Comparing to the Astro:
The simulation has 23Nm at 400rpm for 1000W input (I assume that is continuous, as based on 80°C winding temp?). The Astro would be 5.2Kw output.
Does the ~2T flux density of the simulation indicate its already close to its peak torque?
Comparing to the Astro:
Miles said:
The simulation has 23Nm at 400rpm for 1000W input (I assume that is continuous, as based on 80°C winding temp?). The Astro would be 5.2Kw output.
Does the ~2T flux density of the simulation indicate its already close to its peak torque?
Oops, posted at the same time. Since it's clearly not near saturation, how would it perform at 4 or 5kW input? If the torque can be quadrupled it would hit the Astro plus gear reduction target. Well, minus the packaging...
Astro state the 3220 is at 90% efficiency for 4.2kW continuous output.
I'd hope that equal or better heat shedding for a physically larger motor wouldn't be too hard to achieve
Astro state the 3220 is at 90% efficiency for 4.2kW continuous output.
I'd hope that equal or better heat shedding for a physically larger motor wouldn't be too hard to achieve
Miles said:
Ok.
My understanding of motor design is that power production is a function of active area and magnet speed. Active area gives torque. Magnet speed supplies the necessary angular speed to produce power.
Bigger diameter: more magnet speed - more power.
Bigger active area: More torque
As in: more RPM -> more magnet speed -> more power. As in: Wider stator and magnets -> more torque -> more power.
Proposed case: Take one motor. Change one parameter, change everything else - does the results match up?
I'd like to entertain this, but I am not able to do the FEMM analysis - so I'll start with a proposed method.
1. Find a suitable hub motor.
2. Design another hub motor with different parameters, but same performance.
3. What material is needed to achieve this?
4. Does material/performance match?
A test:
1. Selecting Crystalyte HS3540 ish.
Active area: ~220mm diameter, Stator height: 40mm. Total active area ~27 646 square mm.
Max RPM: 350 RPM
Keep RPM constant.
2. New hub motor. Slimline rimalichious hubmotor. Diameter 550 mm. The question now is the new active area needed to match performance?
taking regard to T=k*D^2*L. T=Torque, k = constant, D=Diameter, L= Length; I'm going to take a (wild) guess at what new active area is needed.
550/220=2,5.
2,5^2=6,25.
27646/6,25 = 4400.
New active area: 4400 square mm.
Motor magnets and stator width: 4400/(550*pi) = 2,5 mm
Remember RPM is constant. As the magnets in the new design has a 2,5 better lever arm than the HS3540 - only 0,4x the force must be generated by the magnets.
3 and 4. "What material is needed to achieve this?" and "Does material/performance match?"
How thick must the magnets be?
How thick must the stator be?
How much copper is needed?
Will the simulation even match the original motor performance?
My intuition tells me the calculations in nr 2 is wrong - but from my moderate experience with BL motors i think that my intuition is wrong. (My intuition tells me new motor active area should be divided by 2,5). Would be cool if someone would entertain the groundwork in this post and finding the fault(s).
Hillhater
100 TW
TS,....did you read the thread title ?
The objective is to see how much torque can be produced from a given weight of active materials .
The objective is to see how much torque can be produced from a given weight of active materials .
speedmd
10 MW
Are we just looking for max torque? It is the power band that is key IMO. If you have enough torque, you can effectively create acceleration. Being able to do this efficiently throughout the design speed range is what determines a motors worth. Thinking that a Broad/ large Area under the torque- rpm curve is key. Not sure what we should do on limiting to one design frequency/ design rpm/ turn count etc., or if that matters at all in just rough size comparisons.
Hillhater
100 TW
One parameter at a time.
So , aim for Max torque,...then look to see what the implications are in terms of efficiency, power, rpm range, etc etc. ?
So , aim for Max torque,...then look to see what the implications are in terms of efficiency, power, rpm range, etc etc. ?
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