Hub Motor Idea

[APL]

The cycloidal reduction is a very cool idea! I haven't seen that one yet, but it looks to be very robust, witch is what
we want to see in cycling. Planetary gears don't give me any confidence.

(Can a cycloidal gear reduction be changed very much? Just curious.)

One thing I might suggest is to attach the spokes to the axle flanges instead of the rotor diameters. Axial rotors don't
like side loads very much.

I might also try to make the stator section as narrow, and as large of a diameter as possible. This allows for more coils,
more speed reduction, and more torque. Unfortunately more stator flex too, so there are limits, but being an air core
has the advantage here.

The Bionx D500 motor is an example of some of these ideas. But since things have to fit between the spokes, then that
becomes a problem too. (there are wider rims though)



Trying to keep all this and a cassette between the rear dropouts can be the biggest pain of the design sometimes.
Using a flat stator wind like the Marand motor style may save some space too, although might not be as easy to wind.

Keep up the good work! Your off to a great start! :thumb:

 

[DesignCycle]

APL thanks, some great suggestions. Yes the cycloidal design seems much more robust than tiny nylon gears, some people have raised concerns about the necessary tolerance but I think it should be totally achievable. There are videos of 3d printed cycloid gearboxes on Youtube which seem to work adequately, and I can't imagine tolerance can be very tight for that.

Cycloid reduction ratio is determined by the number of teeth or 'lobes' on the cycloid wheel, the outer ring has the same number +1. I chose 12:1 partly because it worked out nicely with standard size bearings to form the outer ring gearteeth. Higher reductions require either smaller gearteeth (can't go much smaller using bearings as teeth) or a larger ring (increasing overall size). It would be possible but another possibly easier way to adjust the torque ratio might be to change the turn count on the coils.

The flat stator wind is very interesting. There have been a couple of people attempting to do a PCB stator which is a cool idea but I think in practice the thickness of traces on a PCB is far too thin, would require many many turns giving a crazy high rotor speed.

 

[Chalo]

The cycloidal reduction is a very cool idea! I haven't seen that one yet, but it looks to be very robust, witch is what
we want to see in cycling. Planetary gears don't give me any confidence.

I guess the ubiquitous use of planetary gears in both internally geared bicycle hubs and traditional automatic car transmissions isn't enough to give you any confidence.

Maybe I should point out that neither of those things is known to use cycloidal reduction.

 

[DesignCycle]

There aren't many things which use axial flux motors either. Both are underexplored mechanisms. The exceptional torque density of axial thrust motors may prove to be the key to electric aviation.

 

[spinningmagnets]

The Tangent Ascent 6000W mid drive uses a cycloidal reduction. Either 20:1 or 40:1...

Theres a review on electricbike.com with pics of the insides.

Axial flux vs Radial...if the width and diameter are fixed, the radial (like our DD hubmotors) has a lot of unused space near the center.

An axial can have the stator coils and rotor-magnets shaped to use the entire face of the airgap with active motor components.

Then you stack more stators and rotors until you reach the proper width...so they can have exceptional power capability per volume.

The half of the motor that is near the center does not have as much leverage as the outer half, but...every bit of magnet and copper that can be added will help power density

 

[APL]

I guess the ubiquitous use of planetary gears in both internally geared bicycle hubs and traditional automatic car transmissions isn't enough to give you any confidence.

Automatic auto transmissions giving me confidence? No. Love the way they work.., hate the way they don't last. To be fair
though, it's more clutch band than planetary related. But they also have more area and weight to work with, and circulating
oil cooled systems. Not the best comparison.

Internally geared hubs "can" be trustworthy, but not always, I've repaired my share of Sturmys. Depends on the quality of
the parts and specific design I guess. (Fast moving planetary gears generally have more resistance.)

The cycloidal reduction seems more robust to me, and maybe even thinner,.. looks like it could be good choice for this motor.

 

[TorontoBuilder]

Well I don't think it's been done. It's a dual rotor axial flux motor with twin offset cycloid gear reduction. The cycloid gears use bearings as gearteeth to transfer the torque with minimal friction. It fits in a 135mm dropout with a 9 speed cassette.

Cycloid reductions have been done... axial flux motors have been done... it is assured that someone has put the two concepts together. A google search "cycloid gear reduction axial flux" confirms this

 

[DesignCycle]

But not for bike hub motors. Also mine is somewhat unusual as the offset cycloid gears are either side of the motor rather than on the same side.

 

[Chalo]

You should let the guys over in the 3D printing thread try to convince you that your widget can be 3D printed from plastic in wasp-like fashion. I mean, technically they'd be right, as long as you didn't try to run it.

 

[mxlemming]

I don't see any reason not to 3d print it. It'll run if it is a good concept and design and you can probably replace the structural bits with laser cut sheet or CNC bits later.

You could probably build a working hub for less than 1k. High power and sellable no. Presentable to investors? Sure

 

[spinningmagnets]

Id love to see a life-sized unit 3D printed.

Quite a few issues can be sorted out in V2 and V3 before you spend money on laser-cut metal.

Ive seen engineers on ES provide free stress and design analysis if enough initial effort is shown.

Lebowski posted how to DIY an axial motor, and its brilliant.