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Re: Limited slip freewheel by StefanN
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Author Topic: Limited slip freewheel  (Read 1006 times)

Adrian

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Limited slip freewheel
« on: 23 July 2020, 11:04:38 pm »
Stefan, you might be interested in the work I have been doing on my Renault. I had a bit of a problem with the chain coming off at Stretton and with dreadful understeer because of the solid axle driving both wheels.
I don't want to drive/brake just one wheel either and was pondering what can be done when Rhys told me about a simple device he made for his son’s go-kart many years ago. His design used a friction material between two discs, one attached to the free turning wheel hub and the other attached to the driven axle. It worked very well.
I spent ages trying to develop the idea into something that might work on my Renault, without the need for chopping the back-end about to fit additional bearings and all that goes with that.
I came up with a design but, knowing nothing about friction materials I got in touch (via Google) with a guy called John Price who owns a company called 'Industrial Friction Materials Ltd.' in Cardiff. Not quite next door.
He and I spoke on the phone at length and I decided to go and see him.
He has lots of experience and assured me that the design would work well. He is happy to make all the parts required. 
Rhys popped in today and I showed him my developed design. I said I thought many cyclekart owners might like one (if it works of course) but he pointed out that most cyclekarts have 25mm diameter axles and that the pit-bike wheels are very popular too and that they might struggle with a 30mm diameter axle and he's right.  I have a set of pit-bike wheels which are destined for my next cyclekart so I drew up the hub to see how I might be able to adapt the design to suit them on a 25mm diameter axle.
After a lot of head scratching, we came up with a design that will work for this combination but by now it was tea-time and time to go home so a drawing ‘proper’ was not finished.
I have just caught up with this topic and your Bugatti’s problem with understeer.
Since the Bugatti has a 25mm axle and pit bike wheels I thought I might share this with you now rather than just make one for me some months in the future.
The design will allow you to install the ‘Diff’ without changing any part of your Bugatti’s construction. If you are interested, I can get the necessary metal parts laser-cut and the friction material bonded in place. I’ll try and get a drawing done tomorrow and I’ll post it here.
I still have some design work to do on the compression spring (rate/size) but that’s about all.
If it works as it should, I’m sure other members of CycleKarts GB might well be interested too.
Cost is not a lot but the price will drop if we can do a batch of ten.
This is a ‘not for profit’ idea of course and my objective includes doing it for as little as possible.
 
« Last Edit: 27 July 2020, 07:43:39 am by StefanN »

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StefanN

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Re: Limited slip freewheel
« Reply #1 on: 23 July 2020, 11:34:50 pm »
Sounds interesting.  Looking forward to seeing the design.

Adrian

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Re: Limited slip freewheel
« Reply #2 on: 25 July 2020, 09:05:52 pm »
The drawing (I hope) shows the design for the pit bike wheels and 25mm dia axle.
For this application, the mounting lugs are on the outside. The drive comes in from the right.
I'll make a separate topic for this so everyone should see it.

Adrian

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Re: Limited slip freewheel
« Reply #3 on: 25 July 2020, 09:18:05 pm »
This is the original design for the Renault. It has a 30mm axle.
The positions have changed but the theory is the same.

sylvaman

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Re: Limited slip freewheel
« Reply #4 on: 25 July 2020, 10:06:41 pm »
Are we saying this will only work on the pit bike wheels ,  Different construction on Honda type wheels ?

I ask this as i am picking up some Kart parts in a couple weeks  :), including wheels and not sure what they are yet.

Adrian

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Re: Limited slip freewheel
« Reply #5 on: 26 July 2020, 11:04:13 am »
I would get the honda wheels anyway. I havn't got any to work out a method for them but as they are so popular, I will do as soon as I have one to measure up. I think they will be very similar to the Pit Bike ones anyway.


sylvaman

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Re: Limited slip freewheel
« Reply #6 on: 26 July 2020, 09:08:49 pm »
Thanks Adrian.  Will do .

Chris

StefanN

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Re: Limited slip freewheel
« Reply #7 on: 27 July 2020, 07:58:32 am »
Fabrice has been using a similar concept with a different friction material.   He’s shared his details on the French CK site:  http://www.cyclekart-fr.com/forum/index.php?page=post&ids=5480

Quote
[We] used a plastic disc (POM or Polyacetal but not Nylon or Teflon)
This disc is placed between the axle plate and the wheel hub, then tightened enough so that the wheel cannot turn "by hand" but only with the weight of the Ck, the centrifugal force and the difference in radius between the INT and EXT wheel....
In fact we say "freewheel" but it is wrong !! it has to be as little as possible otherwise there are a lot of effects in the steering wheel (imbalance) during acceleration and when braking.

You will probably have to put a bolt at the end of the axle to constrain the wheel and prevent it from being "too loose" or if you use a circlip you can add spring washers like on my wife's Ck ( view the photos)

RhysN

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Little French

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Re: Limited slip freewheel
« Reply #9 on: 28 July 2020, 08:10:28 am »
Hello

Yes, RhysN had spoken at the time of a friction part to reduce the "undesirable effects" of a freewheel!
I used his idea with a POM washer I had available. This plastic is easy to machine, not too expensive and avoids damaging the hub.
Aging is mandatory, growing up is optional .....

RhysN

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Re: Limited slip freewheel
« Reply #10 on: 28 July 2020, 08:17:33 am »
How time flies!
I have just realised it's almost 25 years since I used this on the go kart for Sean, and that wasn't the first time I used it!

StefanN

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Re: Limited slip freewheel
« Reply #11 on: 28 July 2020, 09:03:58 am »
That's interesting Rhys.   How was the hub supported on the axle in your original design?   What was the fibre washer pushing against in the hub?   I notice the new design that Adrian has posted has changed a little and wonder why given the original worked so well across such a large power range.   Do you have any photos of ones you built on vehicles?

RhysN

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Re: Limited slip freewheel
« Reply #12 on: 28 July 2020, 09:19:14 am »
Hi Stefan, remember when photos were not digital? :) This was all done long before digital cameras, so, no I have no pics from back then. TBH I would be surprised if I ever took any, didn't see the need to document stuff I did.
When you ask about how "the hub was supported on the axle" I'm unclear on what you are asking. If you mean the wheel, it was a relatively close fit on the axle. If you mean the drive hub, it was keyed to the axle. If I were doing it now with a different style of wheel I would have bushes, not bearings as they are too free, in the bearing cavities as Adrian has drawn.
It has become more sophisticated as there is a need to match to the different wheel designs (Pitbike, Adrian's artillery and the Honda), and my "back of an envelope" designs don't seem to cut it with the 21st century.
My original just had a steel washer against the wheel, but the man Adrian spoke to felt the need to use high carbon steel which introduced another level of sophistication.

Adrian

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Re: Limited slip freewheel
« Reply #13 on: 28 July 2020, 11:21:51 pm »
He did Rhys, high carbon steel is necessary apparently if you are using the friction material he suggested because it has a coefficient of Friction of 3.5 and it would rip chunks out of mild steel. I am being guided here by someone who knows about this stuff but I am going to do that sum, the one that tells you how may rpm the inside wheel turns on the axle on say a 25ft radius corner.
I'll bet it's very few.
I have some questions brewing and I need the answer to that sum. If it's very few, like 2rpm say, then sureley nothing is going to rip chunks out of mild steel?

Adrian

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Re: Limited slip freewheel
« Reply #14 on: 28 July 2020, 11:48:28 pm »
At 15mph on a 25ft radius corner the rpm difference between the inside and the outside wheels is 2.33. Now my sums are a bit iffy but thats about what I thought it might be.
Makes you think. Would a friction disc turning against a steel plate at 2.3rpm do any damage at all?
I dont think so but it has to last for years so I'm going for it.
Tomorrow I will order the discs and the friction materials for the 30mm diameter design for my Renault.
Then I should have nothing to concern my little brain with other than how fast can I get round Stretton now?