Rear Sprocket discussion

[Mikeyt46]

There is a sprocket design that has been brought to the attention of our team. and has risen discussion

http://www.kushsprockets.com/sprockets

the idea being that on road bikes inside the rear wheel has bushes to limit the shock through to the rear wheel from the sprocket.

2 sides of the discussion have been raised

1 being that the sprocket will be good for FSAE use as it will potentially mean smoother gear changes and pulling away, this can create faster gear changes and maybe create more driver confidence. it also means less stress on components. maybe a good idea for testing and driver training when the driver is not suited to the car yet.

2 the other side of the discussion is that the cushioning will mean a loss of power to the driven wheels due to the compression of the bushings. this will also create a less responsive throttle. the weight of the item and complexity also mean that it will be weighty and costly (nearly $100 australian $ im assuming)

it would be interesting to hear what views you all have on this

Discuss http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[JWard]

Regarding your second point, I don't think you would see a noticable difference in throttle feel. The 'play' created by the compression of the polymer between two events like mid corner part throttle to eventual WOT would be a couple of degrees, that compression will be over atleast one revolution of the tyres which just wouldn't be noticable enough IMO.

Great for singles though... Might absorb some of the angular velocity change over the course of a 4 stroke single cylinder cycle? Good for all round drivability

I would also like to see some data on how it affects a gear change, that's where I imagine the largest benefit to be? That and gear wear?

Not many reviews of the new model online, not with any significant miles on anyway. In general people sound like they love them - "improved cruising and seamless gear changes" are the most common comments. Sounds like a good deal if you can package it on your diff. Only other comment is people seem to have a hard time getting hold of them as it's a new model and I imagine the company's priority is honoring the lifetime guarantee to owners of the mk I?

What's the weight difference btw?

Also... buy one and let us know how you get on! http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Adambomb]

1) Regarding smoother gear changes, I think it would be great for downshifts. Upshifts generally don't seem to be a problem, assuming you're doing it right...

2) Regarding "loss of power:" Again, as JWard mentioned, this will occur over a couple degrees, at which point it will have settled into compression. Do an energy balance on that...it ain't much. And if it were truly "absorbing" power, it would get really hot, no?

As for throttle response, it's a double-edged sword. Drive an FSAE car around at part throttle. For those who aren't experienced at driving an FSAE car at moderate speeds, chain slack typically causes it to buck like mad. This would fix it. Again, if you think you can "feel" a change in throttle response because of this, I want what you're smoking. http://fsae.com/groupee_common/emoticons/icon_wink.gif

So because of that, this is something I always thought would be cool to implement, again it's really just a copy of what they've done in the rear hub of sportbikes for YEARS. This looks like an ingenius solution that would be very easy to implement.

[AxelRipper]

The issues with it as I'm currently seeing:

1.) With a steel outer ring, dampers, and aluminum center, how much weight gain will you see over a standard 7075 sprocket

2.) What are the advantages over, say, a slipper clutch.

3.) The only 3 sprocket sizes to chose from are 41, 45, and 50.

It seems like it might be a good idea. Would be interesting to see how one would actually work, and <STRIKE>if it would hold up to the increased traction of a FSAE car compared to the dirtbikes.</STRIKE> EDIT: Looking a bit more, seems that these are FOR dirtbikes on the street.

[Z]

"Cush-drive" is generally a good thing, especially with big singles, as noted above.

Disadvantages are more places for failure, very slight extra cost and weight, and as noted above... But there is an easy Plan B, namely just swap with conventional sprocket.

Similar results can be had from "rubber donut" CVs (only one required per side), suitable spring loaded chain idler pulleys (interconnected top and bottom), or conventional solid steel driveshafts (rather than large diameter CF tubes - "We use them because of their superior stiffness...")

Z

[Steve Slowboy]

I built a similar cush-sprocket for my OMS Hillclimb car a couple of years ago!

"ovalled" the mounting holes in the sprocket, and then turned up some steel tubes which were set into the oval holes with 2-part potting compound (had a bit of give). One side of which was against the diff drive flange, and on the outer side turned up a steel ring that held the sprocket within. So that the sprocket could rotate against the diff (albeit a very small amount and against the rubber) - could have used stepped fasteners instead of the inserts.

Worked a treat at reducing chain-stretch but no idea if it helped traction or hindered throttle pick-up or anything else.

Sorry - hard to explain - I have a couple of photos but no idea how to attach a picture.

Steve