Unstoppable Geared hub motor!

[The Stig]

This idea is intended to lessen some of the shock load on geared hub motors, when landing from jumps. Like when you don't take your hand off the throttle during a jump and the motor spins up fast in the air, then suddenly tires meet the ground and gears break.:
What if we were to prevent gears getting stripped by connecting heavy SPRINGS to torque arms on the rear axle of a geared hub motor. We would also allow the axle to rotate freely, the rotation limited only by the springs to about 45-90 degrees max! This could vastly improve the reliability and power capacity of geared motors by preventing stripped gears, failed freewheel clutches and failed keyways.

Background info:
I've been throwing around this idea for a while... When you jump bikes with geared hub motors(BMC 600w, MAC), the impact of landing and sudden change in RPMs can destroy gears, this can happen even over little bumps if you don't let off the throttle. Having springs between the torque arms and the frame would absorb the peak forces!
Added Notes:
- Stronger gears have they're problems as I may recall... Aside from metal gears being loud as hell, i think they lead to freewheel failures. The springs would protect the freewheel too. Plastic/composite gears still aren't that tough.
- To allow the axle to twist in the frame, a greased metal on metal bearing will do. we don't mind a bit of friction. Hell we would add a damper if we needed to. If there were some appropriate sealed bearings that will thread onto the motor axle why not.
- This might be a good thing to be built into future motors


Rough concept drawing:

Potential "Leaf Spring" torque arm design. It is a thinner, bendier version of the EVworkslab.com non-flat torque arm

Now all this means that the axle will have to rotate inside the frame. So basically I will have a new set of greased bearings where my dropouts used to be.
My frame would now have 16mm round holes where the dropouts used to be, my motor axle has 14mm(major dia.) threads.
I will machine a collar to slip onto the threaded axle to pick up the radial loads. I will have washers on either side of the frame to allow the axle to twist. The whole thing will be packed with grease, and maybe shielded from the elements.

Heres a sort of exploded diagram of the bearing between the motor axle and frame(plus the torque arm spring, thing, allowing the axle to twist a bit):

I'm ready to test this in a current build! ...with a bit of help fine tuning and finding the parts

Dibs on being inventor of this if it works.

 

[Chalo]

You've created a need for another set of bearings.

 

[dh-paule]

what about stronger gears ?

 

[The Stig]

You've created a need for another set of bearings.

Nah we don't mind the friction. Two smooth round metal surfaces with grease will do.
Some sealed angular contact bearings would be doable on the outside of the dropouts, if you could find some sort of cup to go on the dropouts. This would give more stiffness to the swingarm.

what about stronger gears ?

Stronger gears have they're problems as I may recall... Aside from metal gears being loud, i think they lead to freewheel failures. The springs would protect the freewheel too. Plastic/composite gears still aren't that tough.

 

[winkinatcha]

Hey mate, not to sure if I am getting what you are doing here... is this like a kinda damper so the axle can rotate a small amount before power is applied through the frame, or a way of enabling the axle/motor to include suspension on a hard-tail... My first interpretation was for the latter, in which case wouldn't a full suspension or rear suspension bike be the same thing, only the suspension includes the entire rear end rather than just the motor/axle?

joe

 

[neptronix]

*broken record mode*

Just lower your phase amp to battery amp ratio. This will dramatically reduce the initial torque from a stall, where torque is at it's highest, and these gears are at their weakest.

Some old infineon controllers had soft starts too. That helps as well, to gradually bring the torque on.

Why do something mechanical in a complex way when you can do it simply in an electronic way?

 

[Ypedal]

this is counter productive at the core.. ......

Geared motors are made as light as possible for their intended power, ie . 250/350w, we want to push these motors far . FAR beyond these levels and this is the cause of their failure..

Same thing goes with Direct Drive motors, they are intended for 500/750w, with a bit of fudge / buffer so that we can push them to thermal limits...

geared motors, suffer both limitations, friction, moving parts, plastic gears, damage from shock loads and damage from overheating.. a geared hub motor designed for 5000w wouuld be cool but i dont know of any.

 

[The Stig]

this idea is intended to lessen some of the shock when landing from jumps. Like when the motor is spinning fast in the air and suddenly tires meet the ground and gears break. This might happen a bit between small bumps as well.

ow.. ow... ouch.. ok guys let me know exactly which bits are confusing.. sorry wrote this in a rush. I removed the bragging bit at the beginning so maybe now the idea will get more fair consideration.

*broken record mode*

Just lower your phase amp to battery amp ratio. This will dramatically reduce the initial torque from a stall, where torque is at it's highest, and these gears are at their weakest.

Some old infineon controllers had soft starts too. That helps as well, to gradually bring the torque on.

Why do something mechanical in a complex way when you can do it simply in an electronic way?

yeah... I'm definitely not talking about this failure mode... not the initial torque from dead stop.

 

[neptronix]

Sorry, i jumped the gun on that one as i've stated it about 50 times and had nobody listen :lol:

Okay, as to your idea. There is one big problem with geared motors and taking jumps, that is temporary distortion of the axle during landing, which causes the planetary gear assembly to warp ever so slightly..

Yes, you can try to damper this warping, but i don't know how well that can be done. Your best option is simply to relocate the motor out of the wheel itself. A mid drive setup is best for this kind of duty.

 

[Ypedal]

shock load from high rpm to low on jumps could more easily be dealt with using an internal slipper clutch set to slip at a given torque level.... just my opinion.. not meant to discourage you from proceeding with the project..

 

[The Stig]

temporary distortion of the axle during landing, which causes the planetary gear assembly to warp ever so slightly..

Uh oh... However the failure may be due to a combination of Axle Warp and rotary shock load. And we don't know which is more at fault! So the springs may just do enough to save us from failures


And yeah I like the internal slipper clutch idea but I guess it's never been really necessary in the market for ebike gear motors... doesn't sound like something I could DIY. I'm having hard enough time finding the spring guides / linkages etc...

 

[amberwolf]

If you really want to do something like this, I suggest a half-leaf style spring instead, used as a bendable lever-arm, instead of a coil-spring. Might be easier to implement.

I dunno if it'll actually help the problem for "offroad" situations or curb jumps, potholes, etc., but it could reduce shock-loading of the gears in setups that use hard-start controllers with high phase/battery amp ratios, over-watting them.

 

[adrian_sm]

shock load from high rpm to low on jumps could more easily be dealt with using an internal slipper clutch set to slip at a given torque level.... just my opinion.. not meant to discourage you from proceeding with the project..

Or just use shock spring concept from a clutch. I believe these take the shock loads by creating some rotational give between the shaft and the plate.

 

[neptronix]

Given that there's no extra room inside the hub, i'm not sure how that would be implemented.

This would require some extensive CNC work. If you have the means to do such precision metal work, might as well design your own dual reduction drive and drive the rear sprocket at that point.

 

[The Stig]

Or just use shock spring concept from a clutch.

he he prob not happening but thats an interesting mechanism... You might be able to fit that spring system into the "Planet Carrier" part of the planetary gear system of MAC style hub

There is one big problem with geared motors and taking jumps, that is temporary distortion of the axle during landing, which causes the planetary gear assembly to warp ever so slightly.

I had another thought on this... Maybe the shock rotary load causes some of the axle distorsion.

Regardless, and out of curiosity, where's the evidence that axle distortion causes gear failure or evidence that it is a problem?

 

[neptronix]

Open it up and you will see what i'm getting at. There are various places for the motor to flex during shock loads. The axle is the 'sun' ring in the planetary gear set.

 

[adrian_sm]

Or just use shock spring concept from a clutch.

he he prob not happening but thats an interesting mechanism... You might be able to fit that spring system into the "Planet Carrier" part of the planetary gear system of MAC style hub

Yeah that's the idea. But as pointed out you would need to remake or possibly heavily modify the existing planet carrier/clutch, to incorporate the springs between two plates. There are a few pictures in this thread of the clutch pulled apart. Looks like there might be enough room to do it, but definitely not a straight forward job.

Have a look at the picture below. Imagine the three countersunk screw holes where instead slots, with shoulder screws through them. This gives one half of the sprag clutch a degree of rotational freedom. Then you need to introduce a torsion spring of some sort between the two halves. The clutch used compression springs but other methods would work as long as you balance the forces, and they are strong enough to take the shock load and not have the shoulder screws hit the ends of the slots. If you are lucky you might be able to fit three compression springs in between the new screw slots, with a bit of milling of the two halves of the clutch.

Looks vaguely possible, but I am probably missing something. Would be easier if I had one of these motors open in front of me.

[EDIT] Sorry if this is off topic.

 

[Chalo]

You've created a need for another set of bearings.

Nah we don't mind the friction. Two smooth round metal surfaces with grease will do.

That's a bearing too. A plain bearing makes more sense than a rolling element bearing for something that budges rather than spins. But like any bearing, it presents lubrication, wear, and maintenance issues that must be resolved somehow.

 

[The Stig]

This could increase the performance/usability of BMC motors quite a bit. sounds like something hi-powercycles.com should get BMC to make a prototype of. Lets see what they say.

Or just use a shock spring concept from a clutch.

... You might be able to fit that spring system into the "Planet Carrier" part of the planetary gear system of BMC style hub

Yeah that's the idea. But as pointed out you would need to remake or possibly heavily modify the existing planet carrier/clutch, to incorporate the springs between two plates.

Looks vaguely possible, but I am probably missing something. Would be easier if I had one of these motors open in front of me.

Yeah I don't have any of these motors around me here. I have an older version BMC back in Athens, GR.

it presents lubrication, wear, and maintenance issues that must be resolved somehow.

This bearing would not get much action, should be 5-10 degrees of turning every time your tire gets airborne, or you hit a big bump. I think your makin it out to be more of a problem then it would be. It just needs to stay greased or wax lubed.

If you really want to do something like this, I suggest a half-leaf style spring instead, used as a bendable lever-arm, instead of a coil-spring. Might be easier to implement.

So what kind of style spring do mean? Pic/link/description?

Here is another Idea I like, adding damping to this Sprung Axle concept, with shock absorbing springs http://www.mcmaster.com/#compression-springs/=loxwz5

 

[CogHog]

Cheapest route is electronic. Just put a micro switch on the rear suspension so when it is at full extension the motor is off. You are most of the time sitting on the bike or even the weight of the ebike alone may trip the switch on. Hard tail is another story.

 

[amberwolf]

If you really want to do something like this, I suggest a half-leaf style spring instead, used as a bendable lever-arm, instead of a coil-spring. Might be easier to implement.

So what kind of style spring do mean? Pic/link/description?

I bolded the basic part in the quote above.

Further description is simply half a leaf spring, which is only suported on one end, rahter than both (a full leaf usually has the load in the middle and support at either end). Some bicycle (and other) trailers use this for suspension. At least one build or concept here on ES uses it for rear suspension on the bike itself.

In this case you would have one end of the leaf fixed to the axle, and the other end fixed to the chainstay or seatstay, so that when the axle rotates in your dropout, it bends the leaf spring in the middle, against the force the spring creates.

Assuming that fixing it to the axle is easy for you, then mounting the rest of the spring to the bike should be much easier than fitting in a large enough spring and mounting that between a lever on the axle and the bike frame in some way. In this case, the lever would *be* the spring.

However, another way to do it would be very similar--use a normal coil spring at the mounting point of the bike end of the lever, and the lever attached to the axle in a fixed way.

 

[shock]

What about letting off the throttle when your in the air?

 

[waynebergman]

shock » Fri Mar 01, 2013 5:43 pm
What about letting off the throttle when your in the air?

This takes the fun out of climbing under power and slows you down and it is hard to do as well in a controlled fashion. I also would like to see this issue resolved with the hub motor mounted in the wheel. I have sheared a key doing this in my mac motor and I hope to do a mid drive next bike to help this. Best of luck with your efforts here Stig.

 

[ryanstev]

What about a sensor on your rear spring, so when the spring is fully expanded (when you're in the air) the sensor cuts power?
If you have a hard tail, the sensor can go on your seat, being a sensor you can program a delay before applying power again, eg, half a second or so.

EDIT: Someone already suggested this, ignore my post.

 

[The Stig]

The bike will definitely be full suspension, DH. And yeah I'm seeing that the electronic solution Could be the cheapest and simplest route, if the details work out.... Although the mechanical solution offers better performance.

Cheapest route is electronic. Just put a micro switch on the rear suspension so when it is at full extension the motor is off. You are most of the time sitting on the bike or even the weight of the ebike alone may trip the switch on. Hard tail is another story.

y'all think this would work if I wired it so the micro switch to cut off the throttle? I wonder what type of controller and type of switch this would work best with?