Torque of onewheel motors
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I'm not sure those numbers are correct. Seems high.
The amount of torque will vary depending on speed. The nice thing about electric motors is they produce max torque at zero rpm and generally the curve is pretty flat until about 2/3rds of the rpm range when it drops away
This prob lines up the the rpm for pushback.Because of the typical torque curve shape, peak mechanical power (750W or 1hp) will occur up highish in the rpm range.
Power = torque x speed
Blah blah.....sorry I'm going all engineer on you.
Based on the board being able to 'lift' or rotate a board with say 100kg on the front footpad at about 25cm from the axle to the centreline of the front foot. That is:
100kg = 980N @ 0.25m then the motor is developing about 250N.m, but probably a bit less than that.
If it was developing any more, nose drags wouldn't be possible unless you are really heavy and have your front foot hanging off the front pad.
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@stinkyface This makes way more sense... kinda. It looks more right at least. Might explain why my attempts at recreating the numbers years back seemed waaaaay off.
Now I feel like some actual science needs doing. We need to make a Onewheel Dyno lol
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@lia said in Torque of onewheel motors:
Now I feel like some actual science needs doing. We need to make a Onewheel Dyno lol
Timing is good for this, lately I've been working on a similar question for another project. If we can measure the acceleration doing a nose drag (time to cover 10 or 20m) then we can calculate the torque pretty easily. Human Dyno! Anyone with fangs want to give it a run?
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@stinkyface here's a question for you: is there a peak power for a onewheel?
the human body can only withstand so much force, so its reasonable to ask: how much is too much?
XR's got what plants crave!
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@notsure And yet another question, what amount of torque/power would it take so the board could totally prevent nosedives? With enough pushback, a person would basically have to purposely fall off the board if they leaned too far, but the board would stay balanced.
GT-S > GT > Pint X > XR > +
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@onedangt i think it increases with speed? so at 30mph, it would need enough to accelerate the board forward and rider upward, fast enough to overcome a heavy lean. i think 10hp is scary af to have whirring openly next to my droopy pant legs.
i think one of the reasons a ow is as safe as it is, is because its not so powerful a human can't overpower it.
im not worried about my xr ripping foot off if i catch a pant leg. worst case is im riding commando back home.
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@notsure said in Torque of onewheel motors:
@stinkyface here's a question for you: is there a peak power for a onewheel?
Yes, if you are talking about mechanical power (the relationship between torque +speed).
Electrical power is different and it is possible to pull full electrical power from a standing start and hold it at full power as you accelerate. Electrical power = volts x Amps, so no relationship to speed or torque.
The reason the two power types can coexist and still be true is to convert electric power (Watts) into mechanical power (also in Watts) there is an efficiency applied to the electrical power to get the output mechanical power. At low rpm the motor efficiency is crap and it gets better as you approach peak mechanical power where it will be ~95%
Not sure @NotSure 🙄 if that's where you were heading and apologies for the technobabble.
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@stinkyface i was referring to the mechanical force applied by the apparatus, and the power required to do so.
the premise is that there is a max amount of force a person can apply to an object in a controllable manner. The human body exerts a certain force when jumping vertically.
the maximum amount of acceleration such an action can induce represents an upper limit as to what a person can physically produce in response to a stimuli.
so if a motor is capable of imparting an 'impulse' exceeding that threshold, the result will be impactful!
i think a standing jump can exert as much as 3 g's on the body. thats a lot of force! more than enough to accelerate u up a hill.
XR's got what plants crave!
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An interesting issue brought out!
I never understood N.m solely just by it's calculation basis. Always felt like there should be smth more to take into account. But that's been my own incompetent raw guess.
The creators of SuperFlux hub motor claim: "> 50Nm (more that twice compared to the original 5" Hub motors). ..... These are real world numbers and not exagerrated confusing HP numbers." Dunno what are their reasonable means to confirm such statement.
Feeling like we need @Lemur input here paired with @stinkyface knowledge. -
@onedangt said in Torque of onewheel motors:
@notsure And yet another question, what amount of torque/power would it take so the board could totally prevent nosedives?
Good question and not too hard to approximate an answer. Leaning fwd a loooong way, your centre of gravity could be as much as 1m in front of the axle, so the motor would need to produce about 1,000N.m of torque to prevent you leaning further forward. Those are pretty big numbers and I suspect the tyre would just lose traction.
People quoting power as the be all of nose dives is misleading. Torque is what the rider feels as acceleration. Lets say my really rough numbers earlier are true and the little XR can produce 200N.m of torque. I'm putting a 144V 110kW electric motor into a car conversion and it only produces 220N.m of torque, but it does rev to 8,000rpm. The XR motor is a low speed high torque electric motor.
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@notsure said in Torque of onewheel motors:
@stinkyface i was referring to the mechanical force applied by the apparatus, and the power required to do so.
the premise is that there is a max amount of force a person can apply to an object in a controllable manner. The human body exerts a certain force when jumping vertically.
I think we'll find that the XR is only capable of about 0.1 - 0.2g acceleration in std form. The magic formula to get from torque to acceleration is Force = mass x acceleration and the torque / wheel radius = Force. The mass bit is why lighter people can generally accelerate faster with the same driving force. Pretty sure we black out at 9g (according to Top Gun!). F1 cars accelerate at 2g, but brake and corner up to 6g.
If a board could exert anywhere near even 1g, your front leg would give way. Would be a wild ride! 😂
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@stinkyface yeah its an intersting thought experiment. i think that perhaps with more power comes a need to buffer that power. at some point u'll get diminishing returns wherein ur buffering most of the power just to make it useable. so given that, i think there is a "peak" onewheel power. would suggest its not a linear scale for performance; its a logarithm.
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Thanks guys, I'm trying to use 4 of them to build a 4-wheel drive vehicle. I like that the motor is inside the wheel, it helps with the center of gravity. With planetary or just regular brushed motors I have to mount the motor on top of the wheel and use a chain or timing belt to drive the hub connected to the wheel. Usually I use low RPM brushed motors which have higher torque, but I had assumed that these would have high torque also since one of them can hold a person.
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@wheelngear neat!
