High torque motor at 0rpm (stalled)

[scm007]

Are there any motors that can generate 50Nm of torque in a stalled or 0 rpm state? I guess this would be a direct drive gearless motor? How would this work with a gearbox?

 

[Hillhater]

Many motors can do that....but not for long as all the energy is being converted into heat and few motors can dissipate heat fast enough to prevent damage.
A high reduction gearbox. (100;1) would be better with a low power (0.5Nm) motor, which would have much less energy to dissipate
If you really want to just “Hold” 50Nm @ 0rpm there are better solutions than a simple motor...
..but i suspect you want more than just 0rpm ?

 

[MadRhino]

You would need a thousand pound and a freaking steep slope to stall a big DD hub fed 20 kw. :

Mine digs the ground throwing 4 inch rocks 50 ft behind, then spins off its tire when I try climbing too steep.

 

[AHicks]

You would need a thousand pound and a freaking steep slope to stall a big DD hub fed 20 kw. :

Mine digs the ground throwing 4 inch rocks 50 ft behind, then spins off its tire when I try climbing too steep.

Maybe some details about the bike you are thinking of, with some details regarding "your bike" to provide some relevance?

Otherwise, it sounds like a lot of pie in the sky....

 

[MadRhino]

You would need a thousand pound and a freaking steep slope to stall a big DD hub fed 20 kw. :

Mine digs the ground throwing 4 inch rocks 50 ft behind, then spins off its tire when I try climbing too steep.

Maybe some details about the bike you are thinking of, with some details regarding "your bike" to provide some relevance?

Otherwise, it sounds like a lot of pie in the sky....

Your ‘pie in the sky’ is redundant old sh*t already. You find that everywhere on ES for a decade. The receipt is simple and well described in so many building threads. You need a big DD hub motor around 30 lbs, a powerful controller that feeds +200 A, a dozen bricks of quality RC lipo, and a good bike to fit them on.

 

[AHicks]

You would need a thousand pound and a freaking steep slope to stall a big DD hub fed 20 kw. :

Mine digs the ground throwing 4 inch rocks 50 ft behind, then spins off its tire when I try climbing too steep.

Maybe some details about the bike you are thinking of, with some details regarding "your bike" to provide some relevance?

Otherwise, it sounds like a lot of pie in the sky....

You find that everywhere on ES for a decade. The receipt is simple and well described in so many building threads. You need a big DD hub motor around 30 lbs, a powerful controller that feeds +200 A, a dozen bricks of quality RC lipo, and a good bike to fit them on.

Many of the notes written here, with honest questions, are written by folks who haven't been around for 10 years, or 5 even. They're newbies! If they had been around for a while, MOST of those honest question would already have been answered quite a few times.

My point is, bad or misleading information is often worse than none.

 

[MadRhino]

My point is, bad or misleading information is often worse than none.

It is only simple truth. A search will give you choice of building threads for a fast and powerful bike, even if you are here 5 minutes. The ‘newb’ is asking if high torque is possible. I simply answer it is with a big DD hub, which he had guessed already. Bad? Misleading?

 

[scm007]

To be clear this is not for an ebike but since you guys are the electric motor wizards I thought this would be a great place to ask! I'm looking for basically a configurable torque motor that can output between 1 - 50Kn of torque at stall without burning up. I'm trying to DIY a version of the Tonal fitness system (www.tonal.com). I believe they are using differentials and gears to output their torque but a big brushless motor with a big ESC would be much simpler and would drastically reduce wear. Any recommendations?

 

[MadRhino]

You mean you plan to workout against the motor and never let it spin? No way. You need the differential and gears because a motor need to spin, otherwise it is only building heat. There are ways to avoid the differential and gears yet letting the motor spin, but no way you can keep it stalled. And, IMO you don’t need a motor for the purpose that you are seeking. Magnets alone would suffice, for an example, and then electricity or heat wouldn’t be a concern.

 

[scm007]

How can you make a system without a clutch that enables the motor to keep spinning while the system itself is stalled? Also regardless of whether the motor is spinning if the entire physical system is "stalled" wouldn't the heat generated be more or less the same? And the motor would be spinning during the negative of the exercise but it would be stalled or rotating backwards when the user is pulling against it.

All you could do is distribute it more evenly? Magnets would be interesting if it worked, however I don't see how you would be able to configure the pulling force electronically. What did you have in mind?

 

[MadRhino]

An electric motor does convert energy to force and movement, and its efficiency determines a part of energy that is lost (converted to heat). If there is no movement it does convert energy to force only, very inefficiently thus most of the energy is converted to heat.

The movement and force of a motor can be converted to force alone while maintaining its efficient rotation, making and maintaining air or oil pressure for a simple example.

Permanent magnets have a magnetic force, and are rated according to the amount of force, or amplitude of magnetic field that they are capable of. By moving magnets closer or further from ferrous metals, or from each other, we can vary the force that they deploy in attraction or repulsion. That simple explanation should be enough to let you imagine the numerous methods that can be engineered to use this force to produce variable load and progression required for the purpose of a workout machine.

 

[scm007]

I don't see how a magnet would be able to exert a constant force across the entire linear motion of the machine? The force is proportional to the distance so you need some sort of magnetic rail like in a maglev train?

 

[MadRhino]

A hint?
The magnets don’t have to be fixed. They can be moved with the action of the machine, and the distance of other magnets or ferrous metal can be adjusted to create and vary a linear or progressive resistance to movement.

 

[MadRhino]

This is true and practical with any other force. Most of workout machines are working against the force of gravity. Some even use magnetic force already. Some are using force of inertia, etc..

 

[MadRhino]

The only good reason to use a motor for the purpose of a workout machine, is to convert the energy deployed by the user of the machine, to produce electricity.

 

[scm007]

So, without weights how is it that the user will be able to generate electricity via a motor while maintaining the feel of say 200 pounds worth of weight? I don't see how this is possible.

 

[HrKlev]

I am by no means an electric motor wizard, but I do have an electric power steering system on a race car that is stalled a lot of the time without burning up. Its a really simple system with just a 0-5v signal from a torque sensor controlling a brushed 12v motor via a programmable syren controller.

I havent looked at the links, but sounds like pretty much the same as a power steering system, just doing the opposite thing....

 

[MadRhino]

So, without weights how is it that the user will be able to generate electricity via a motor while maintaining the feel of say 200 pounds worth of weight? I don't see how this is possible.

You adjust the restriction via Amp demand to the motor, just like regen braking. The force deployed by the user to spin the motor is then converted into watts, minus the efficiency loss inherent to any energy conversion.

 

[MadRhino]

The small motor of your power steering system is governed by a controller that feeds it the power required by the signal. When it is not spinning, it is not stalled, but stopped by the controller that is not feeding it anymore.

 

[amberwolf]

So, without weights how is it that the user will be able to generate electricity via a motor while maintaining the feel of say 200 pounds worth of weight? I don't see how this is possible.

You can look up "dynamometer" or "dyno" projects, to see how a motor is used to put a specific load on another motor (or in your case, on a person's input into the machine).