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Conclusive proof gearboxes are awesome.
- Thread starter Teh Stork
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liveforphysics
100 TW
onloop said:
For the purpose of adding loss needlessly? Why not choose a motor wind that suits your needs on whatever pack voltage you've got?
macribs
10 MW
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I guess because he is so limited by space, as he was asking for his electric skateboard.
Not much room to change batteries to bigger pack, and probably also very limited range of motors that will fit into his skateboard regime.
And I can certainly see the need to up the voltage for such a specific application. For a bike it would be easier to just get the correct parts that meets your need - cause there is always room somewhere to add a little extra. But on a skateboard not so much.
O/T:
Not much room to change batteries to bigger pack, and probably also very limited range of motors that will fit into his skateboard regime.
And I can certainly see the need to up the voltage for such a specific application. For a bike it would be easier to just get the correct parts that meets your need - cause there is always room somewhere to add a little extra. But on a skateboard not so much.
O/T:
On a side note, if you got deep pockets or money left on your credit card and really need more fun in your life get the Baja Board. 4wd with 1 rc motor to each wheel, and air shocks. They say it is like snowboarding an endless descend.[youtube]slLHy4NlOvQ[/youtube]
liveforphysics
100 TW
macribs said:
You still will have the lightest smallest most power dense system by not choosing to add the losses pointlessly of a boost converter.
boisrondevens
100 W
liveforphysics said:Wind it as a single turn motor, perhaps HVH style bar-in-slot winding like the modern Remmy stuff used in the Volt and others.
Then the weak-link is no longer the motor, it is in finding a controller with the capability to drive it to it's potential. Make that controller, and you can stay in non-lethal voltage ranges, have your brutally delicious and extremely efficient low-RPM torque cake and eat your high RPM's power needs too.
I was reminded of this thread after Miles recently commented on a motor design with a comment about the eddy current losses of the winding. If I understood it properly, it was that a large, solid copper wind would suffer very high losses. That was what made me think of this discussion involving single-turn windings.
So, what is the relationship between winding eddy current losses and construction/dimensions of the winding in a PMDC motor? What I've read on Google was about transformer, which I'm not sure is the same, and also said that laminated windings suffered increased eddy currents and inductance.
That was in the context of an air cored motor, though. With an iron core, eddy currents induced from any stray flux would be minimal. 'Skin effect' eddy currents, from the AC field, would be the same in either case, I think.Punx0r said:
Thanks for the clarification
I think it was skin-effect eddy currents I was reading about in the transformer-related information.
So there really is no inherent penalty for a very low turn motor apart from the size of the phase wires and the burden placed on the controller?
I think it was skin-effect eddy currents I was reading about in the transformer-related information.
So there really is no inherent penalty for a very low turn motor apart from the size of the phase wires and the burden placed on the controller?
The skin depth roughly limits the width of the conductors.
In SMPS transformers the flux swings from full positive to full negative with a frequency of 20kHz to 2MHz or so. The skin depth is half a millimeter down to less than a tenth, in that span.
In motors the full flux swings with the electrical frequency of the motor, which typically is 50Hz-1kHz (there are some variations proportional to switching frequency on top of that, but small). The skin depth is 2-10mm in that span.
In SMPS transformers the flux swings from full positive to full negative with a frequency of 20kHz to 2MHz or so. The skin depth is half a millimeter down to less than a tenth, in that span.
In motors the full flux swings with the electrical frequency of the motor, which typically is 50Hz-1kHz (there are some variations proportional to switching frequency on top of that, but small). The skin depth is 2-10mm in that span.
liveforphysics
100 TW
If the mass of this mechanism were instead added in the form of a bigger radius of iron and copper to a direct drive motor, it would yield similar results, but in a way that improves continous power.
macribs
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I do agree, but sometime realestate makes it hard to fit everything into a frame. And I think for maybe a mid drive real estate can be a big issue. I mean if you crave more power then say Astro 3220, where do you go? Revolt 160? That is a step not only in power but also in size. Might be hard to fit to a frame. But a 3220 + a smesh possible used as a "variable jackshaft" might fit.
Smesh has a loud mouth, and claims higher efficiancies then other gears I've seen. Wonder if their claims are valid or just marketing BS?
Smesh has a loud mouth, and claims higher efficiancies then other gears I've seen. Wonder if their claims are valid or just marketing BS?
speedmd
10 MW
Formula E is playing with a bunch of different tranny setups this season. Some 2, 3, and 4 speeds racing each other. Not sure if any are going single speed yet. Will be interesting how that all shakes out.
Right. What value does the added mass bring compared to its equivalent in a larger motor? What are the drawbacks?liveforphysics said:
Although it's a separate argument, the same applies to adding an extra reduction stage.
What happens if you include the gearbox in the jackshaft of the extra reduction stage? Does that change the equation?
What other advantage can you get out of the mass added by the gearbox?
These are the figures for my own motor and gearbox design.
Motor weight 1.5 kg
2 speed gearbox weight 1.0kg
Items needed to use gearbox as jackshaft (including pulleys for 4:1) 0.4 kg
Elements of gearbox solely related to use as variable gear 0.6 kg
Elements of gearbox related to use as jackshaft 0.4 kg
Weight of 2 speed drive complete 2.9 kg
Weight of single speed drive complete 2.3 kg
What are the other benefits of the added 0.6 kg?
- Integral freewheeling
- Potential to easily switch between freewheeling and regen. for lowest gear.
Gearbox ratios 1:1 and 2:1
Reduction ratio on first stage 4:1
It's worth the weight but is it worth the effort?
Motor weight 1.5 kg
2 speed gearbox weight 1.0kg
Items needed to use gearbox as jackshaft (including pulleys for 4:1) 0.4 kg
Elements of gearbox solely related to use as variable gear 0.6 kg
Elements of gearbox related to use as jackshaft 0.4 kg
Weight of 2 speed drive complete 2.9 kg
Weight of single speed drive complete 2.3 kg
What are the other benefits of the added 0.6 kg?
- Integral freewheeling
- Potential to easily switch between freewheeling and regen. for lowest gear.
Gearbox ratios 1:1 and 2:1
Reduction ratio on first stage 4:1
It's worth the weight but is it worth the effort?
motomoto
1 kW
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I know I am bringing up a 'controversial' subject, but it's not. Luke's obsession with copper and magnet weight always
being superior to the weight of steel gears is not correct. All the 'waste' of the extra weight and the drag of gears meshing
and bearing losses is nothing compared to the real waste. The waste of amps needed to do the job because of not having the proper gear ratio. That's it. The waste of amps needed to do the job because of the lack of having the proper gear ratio.
You're climbing a hill with your one speed Luke special and it takes 300 amps, or you could switch to the
proper gear and use only 50 amps to do the same thing. The waste is not having the proper gear and wasting your battery.
I am not saying Luke will not save us all by creating some miraculous battery technology because he probably will. I am just saying
that the physics in the real world of uphills and downhills and limited battery capacity, a proper gear change is negligible
and necessary.
being superior to the weight of steel gears is not correct. All the 'waste' of the extra weight and the drag of gears meshing
and bearing losses is nothing compared to the real waste. The waste of amps needed to do the job because of not having the proper gear ratio. That's it. The waste of amps needed to do the job because of the lack of having the proper gear ratio.
You're climbing a hill with your one speed Luke special and it takes 300 amps, or you could switch to the
proper gear and use only 50 amps to do the same thing. The waste is not having the proper gear and wasting your battery.
I am not saying Luke will not save us all by creating some miraculous battery technology because he probably will. I am just saying
that the physics in the real world of uphills and downhills and limited battery capacity, a proper gear change is negligible
and necessary.
liveforphysics
100 TW
motomoto said:
Not how it works my friend.
There is no penalty in power consumption to not have a tranny, it's actually less power drawn off the pack being wasted heating gears to chaffe against eachother.
hydro-one
10 kW
you cant waste amps . its not a unit of energy. at 500 amps u would be going ten times as fast up the hill (lukes kickass bike ) the 50 amp nancy bike with gearbox is creemping up like a winch lol 
liveforphysics
100 TW
motomoto said:
If you have sufficient design liberties with the electro mechanical machine, it's impossible to match the efficiency potential with any topology involving additional power loss.
motomoto
1 kW
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I guess all your motors are at peak efficiency at all RPMs.
All the motors in the real world have an efficiency curve through the RPM band.
It's simple math to run the motor in the efficient area of the graph to not waste power. The drivetrain losses are minor. Losses from running
in poor performance RPM areas is many times greater.
Man, I don't know about you smart guys.
All the motors in the real world have an efficiency curve through the RPM band.
It's simple math to run the motor in the efficient area of the graph to not waste power. The drivetrain losses are minor. Losses from running
in poor performance RPM areas is many times greater.
Man, I don't know about you smart guys.
liveforphysics
100 TW
motomoto said:
That graph is of a terrible motor.
Every motor starts at 0% efficiency at 0rpm, because there is no work being done until you've got rotation.
However, it's possible for the whole meaningful area under the curve from just above 0rpm to look fantastic with a good motor design.
