Author Topic: Playing around with a rear axle  (Read 91 times)

Jimr1999

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Playing around with a rear axle
« on: 26 Jan 23, 09:38 am »
Morning all.
This is a short video of me playing around with a design for a rear axle.
The reason I am posting it is because, like all things, it is probably not new and, therefore, if someone has had a go at this before, you can point out the pitfalls of the design. All comments welcome, positive or negative.  :) (I always miss something)

... You can lead a horse to water, but a pencil must be lead.

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StefanN

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Re: Playing around with a rear axle
« Reply #1 on: 26 Jan 23, 11:18 am »
I love the experimentation.

I guess you have thought of this, but I'd make sure the transition from the 17mm to the larger diameter is well radiused to minimise stress concentration.

The unknown for me is whether 17mm will be strong enough.  The rear axle takes an unfair share of the weight and it's not cushioned by a spring, so peak forces will be much higher than the fronts.

Are the axles surface hardened?   If so, machining will have reduced that.

Certainly an interesting idea.  Having four wheels set up the same* would be an improvement.  The oilite bearing approach works because there's so little rotational movement between the axle and the wheels.

An alternative approach would be to find 35/25 bearings and use these front and back - but so far I think we've struggled to find these at an affordable cost.  Or, we make a wheel specifically for cycklekarts and we can choose the bearing size - it'll be more expensive than a pit bike wheel mind.

*I have seen people cutting the lugs off the front wheels to improve the look which would make them not interchangeable.  I've left mine on thinking I might use them to attach fake brake drums.

Jimr1999

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Re: Playing around with a rear axle
« Reply #2 on: 26 Jan 23, 12:03 pm »
Thanks for the reply Stefan, the radius was on my mind, but as I need a spacer washer between the axle and the bearing face to minimise the possibility of the outer race of the bearing rubbing on the axle I could not easily accommodate it. The Gemini front stubs also are not radiused to the  larger dimension as the bearing seats onto this section so this gives me a little hope. Driven, they will be using the Kart hub as an inner support on the 30mm section and both bearings as an outer. Undriven they will be on the 17mm bit solely but without the torque forces from the axle so like the front to an extent, but as you say - with the extra load and no springs.
I worry a little about the stress on it too. But the axle was almost for nothing, with the hubs and sprocket / brake carrier and in the interest of experimentation I think I will give it a go. If it fails, it could be painful. there are a number of "front wheels coming adrift on a cyclekart" videos around so I think this is a possibility, although most of them seem to blame bearings binding and the spindle twisting off the kingpin carrier.
The axle was not apparently surface hardened as it turned on the lathe the same all the way through
Jim
« Last Edit: 26 Jan 23, 12:05 pm by Jimr1999 »
... You can lead a horse to water, but a pencil must be lead.

RhysN

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Re: Playing around with a rear axle
« Reply #3 on: 26 Jan 23, 02:23 pm »
I too like the experimentation, and have similar concerns to Stefan, but have an additional thing for you to consider.
When Graham Hill still had bearings in his non driven wheel, it was very apparent that under  acceleration the car was pulling one way  (towards the "bearing wheel". ) Under braking the opposite occurred. Only under neutral throttle was the car running straight. On reflection my ERA so long ago did the same.
I know that replacing the free running bearing with bushes made this a huge amount less apparent.
We must avoid torturing our brains with false problems, it occupies but it can annoy. In jest!

Jimr1999

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Re: Playing around with a rear axle
« Reply #4 on: 26 Jan 23, 02:40 pm »
Thanks for this Rhys, interesting, I wonder if it was the increase in friction to the bushes that helped or some other factor?
... You can lead a horse to water, but a pencil must be lead.

RhysN

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Re: Playing around with a rear axle
« Reply #5 on: 26 Jan 23, 08:58 pm »
My belief, based on back to back experience, is what I said previously.
We must avoid torturing our brains with false problems, it occupies but it can annoy. In jest!