Parkour on a bike: freewheel or not freewheel?

Phil Pilgrim (PhiPi)

This is strictly a mechanical engineering query. Watch this video:

····vimeo.com/4207784

Now, try to answer this simple question: does his rear wheel freewheel or not? Some clips seem to indicate yes; others, no. Frankly I'm stumped. Can it be switched on and off? Perhaps someone more experienced with this style of biking can shed some light on how these bikes are equipped.

Yeah, I know: what does this have to do with the Parallax forum? Except that it's populated with smart, interesting people who know stuff like this.

-Phil

beebs

Hi Phil,
A lot of these guys use special freewheel hubs on the rear to accomplish these stunts.
Braking is done with the hand levers.
I had not seen this guy before.
Just incredible.

Phil Pilgrim (PhiPi)

Beebs!

Welcome back to the forum! It's been awhile!

In a couple segments, he seems able to pedal backwards. In others, he's rolling forward without pedaling. Hence my perplexity. But, all engineering questions aside, his skill really is mindbendingly amazing.

-Phil

kwinn

It is possible to have a hub mechanism that allows pedaling in both directions and free wheeling.

Beau Schwabe

Wow!... back in the day, I was notorious for being able to ride a continuous wheelie EVERYWHERE, I just loved doing it and did, everywhere I rode... it was not uncommon for me to ride a sustained wheelie from the swimming pool all the way home or vise versa... about 3/4 a mile through streets including twists and turns.

Amazing!

As Beebs says, braking is done with the hand levers, and can even be obscured in a 'throttle style' hand control rather than a 'grip style' hand control. When I was doing it you only had back pedal braking.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Phil Pilgrim (PhiPi)

kwinn said...
It is possible to have a hub mechanism that allows pedaling in both directions and free wheeling.

Okay, so how does it work? Is there a hand lever for a clutch?

And what permits the handlebars to turn 720 degrees and still have a cable that goes to the rear wheel? (The front wheel I can understand.)

I guess I need to visit the local bike shop...

-Phil

Searider

Perhaps he has different rear hubs/wheels that he changes out depending upon the type of tricks he is planning on doing. As for brakes. I saw one solution were the hand cable accuated a ring on the handlebar hub and another cable went from the rear brake to a rink that was interlocked but could roate around the handbar ring. Hope this makes sense.

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Searider

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Phil Pilgrim (PhiPi)

Hmm, yeah, the ring thing does make sense.

-P.

W9GFO

Haven't seen one but a friend once described something like a swashplate that allowed for multiple handlebar rotations.

Rich H

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The Simple Servo Tester, a kit from Gadget Gangster.

John R.

For what it's worth, my take is that this is a relatively standard rear sprocket (freewheeling capable). At about the 3:40 and 5:00 minute marks, when he appears to be pedaling backwards, it is the momentum of the bike moving backwards, and with a normal freewheeling sprocket, he would have to let the pedals turn "backwards" in order for the rear tire/wheel to rotate backwards.

Amazing rider. I'd like to know how many times he banged the jewels...

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John R.
Click here to see my Nomad Build Log

Phil Pilgrim (PhiPi)

Okay, if you think he's not pedaling backwards, watch this one at about the 2:07 mark:

vimeo.com/4474629

-Phil

Beau Schwabe

Phil,

360-Deg cable detangler (aka Gyro)
www.parktool.com/repair/readhowto.asp?id=144

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

kwinn

Pardon the poor quality diagram, but paint is not great for detailed mechanical drawings. I hope it is clear enough to show the basic idea.

Normally the pedal pin is hexagonal or octagonal and the tolerances are much closer in the actual mechanism but I hope this will do for an explanation. Basically as the pedals turn in either direction the inertia of the rollers will cause them to lag behind the rotation of the pedal pin and they will get wedged between the inner wall of the hub and the pedal pin. Friction will keep them there unless the force is removed from the pedals. Springs are used to pull the rollers in towards the center of the pedal pin.

Forgot to mention that centrifugal force will also force the rollers out against the hub and the friction from that will also cause them to lag behind the rotation of the pin and aid in wedging them in place.

Post Edited (kwinn) : 3/10/2010 12:12:34 AM GMT

Phil Pilgrim (PhiPi)

Beau,

Thanks for the link. It can't get any clearer than that!

Kwinn,

That diagram makes sense. Thanks! Just to clarify, though: coaster-brake hubs have a radial tab that affixes to the frame to provide a fixed mechanical reference for backpedaling to apply the brake. Does the forward/reverse freewheel hub require something similar? Or is engagement entirely dependent on centrifugal force?

-Phil

John R.

Phil Pilgrim (PhiPi) said...
Okay, if you think he's not pedaling backwards, watch this one at about the 2:07 mark:

vimeo.com/4474629

-Phil

Again, for what it's worth, I still believe it's momentum and balance providing the backward movement, and when you move a bicycle backwards, you have to allow the pedals to move backwards.

If you have a bike handy, push it backwards and see what happens with the pedals.

On the diagram Kwin posted, what would keep the pins/rollers from "jamming" in place while the outer wheel was "coasting" or "freewheeling"? At any one moment, half the pins will have gravity pulling them down to the "wrong" corner when coasting.

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John R.
Click here to see my Nomad Build Log

Phil Pilgrim (PhiPi)

John R. said...
On the diagram Kwin posted, what would keep the pins/rollers from "jamming" in place while the outer wheel was "coasting" or "freewheeling"?

I think that's what the springs he mentioned are for.

But looking at the film again, you may be right about reverse momentum vs. pedaling in reverse.

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 3/10/2010 5:13:41 AM GMT

kwinn

Please note I said it is "possible" to have a hub mechanism that allows pedaling in both directions and free wheeling, not that that is what was used on the bike in the video. I have seen the mechanism used on a conveyor where it was possible to manually move the belt in either direction when the motor was stopped, and the motor could also drive the belt in both directions. From viewing the video it seems as if something similar was used on that bike.

@John R. Thats why there are springs to hold the rollers against the pedal pin when it is not turning. As long as the pedal pin is stopped or turning very slowly the rollers would be held in the center of the flat portion.

@Phil The mechanism was a bit more than just springs. There were 8 rollers around an octagonal pin or shaft and they were held in place by a plate on each end of the shaft. Those plates had 8 slots that allowed the rollers to move radially out from the shaft, and the plates could rotate slightly in relation to the shaft. I can try to draw a simple diagram if my explanation is not clear.

Not sure how brakes would be done on this mechanism except that pedaling in the opposite direction would work to slow you down. Pedals would turn though.

Post Edited (kwinn) : 3/10/2010 5:36:10 AM GMT

Phil Pilgrim (PhiPi)

Apparently there is a "freecoaster hub" that engages only when actually pedaling forward. When rolling backward, the pedals don't rotate. The G-Sport version of this hub can be modified (by removing a pin) to allow it to engage when pedaling either forward or backward, but to freewheel when the pedals are stationary. Frankly, I don't really understand the mechanism, but it's talked about by the guy who invented it in a video available here:

www.free-coaster.com/html/g-sport.html

Fast forward to 5:24 for the beginning of the description.

-Phil