[Closed] Any mechanical designers in today?

I'm at work so can't spend much time on this, but couple of points-

How old is your daughter/how large is the load?

The force from the hub is now cantilevered instead of being simply supported at both ends - the axle has to be much harder. An old 20 mm though hub might be up to is with a steel axle. The clevis for the axle to fit in to would have to be quite wide to carry the moment from the axle. How wide is the mount for a Lefty?

The disc would be susceptible to contamination from oil on the chain.

You want a simple sliding/swinging dropout - there's loads of these around to [s]copy [/s]take inspiration from.

Have you seen Rob English's [url= http://www.englishcycles.com/custombikes/project-right/ ]project right[/url]?

I think he custom made the rear hub and axle but it might give you some ideas. He's only got a front brake so that could be an option for you.

Forgot to ask, why not an ebb?

like this

same principle , this does 40 odd mph axles are 20mm but press fit fronts have only 20mm engagment in a plate but its a heavy press fit

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It seems generally accepted that the drive cog and and wheel itself should be split across each side of the swing arm. That way, under drive, the pull of the chain on one side, is balanced by the resisting grip force of the tyre - making the net twisting of the axle on the swing arm much more balanced. So you diagram would read from left to the right

bolt - hub - disc - arm - freewheel - bolt

I'd also agree with the comment of an EBB. A sliding dropout is reducing your ability to stop cantilevering of the axle - it simply cant be supported all round if there is a cut out of the support. It also means you dont need to have sliding mounts for the brake caliper either.

I'm with fisha, split the disc and freewheel either side of the swingarm. Think Ducati 916 swingarm for example.

Again, ebb would solve the chain tensuonung issue.

As a separate issue I didn't see mentioned in a skim-read through the above, be wary of having something oily right next to, or in the centre of a brake disc. You're going to have to keep the chain very clean or provide some means of catching the tiny oil droplets flung out from that chain, or otherwise protecting the disc, to keep the pads from becoming contaminated very quickly.

Sorry!

As a separate issue I didn't see mentioned in a skim-read through the above, be wary of having something oily right next to, or in the centre of a brake disc.

[url= http://singletrackworld.com/forum/topic/any-mechanical-designers-in-today#post-8227872 ]

The disc would be susceptible to contamination from oil on the chain.

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😉

What about a left field idea, as someone else said I'd be concerned about grease/oil from the chain and freewheel contaminating the disc so with that in mind what about going belt drive which would also reduce the danger of any finger/spiky cog interaction.

Secondly instead of having the freewheel at the rear ,have a fixed cog/pulley at the back which should be easier to mount and figure out how to have a freewheel mounted on the chainset instead.
For a small child the gearing shouldn't be too much of a issue.

Millyard racing did something like this

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You can also buy (or you used to be able to) trials bikes that had the freewheel on the crank. Monty probably make them

Thanks for the responses, some useful things to thing about.

How old is your daughter/how large is the load?

She's a slight 5yo, 16.5kg at the mo.

The disc would be susceptible to contamination from oil on the chain.

Indeed, hadn't thought of that. Belt drive might be the way to go..

Forgot to ask, why not an ebb?

Will look into that.

like this

Yeah, that's the sort of idea. Is there just a bolt going through the hub?

split the disc and freewheel either side of the swingarm

That could work. I was thinking of having the swingarm on the right side but could do left with brake left. Only issue could be the exposed drive on the right?

what about going belt drive

Looking into that now.

the freewheel on the crank

THat's also an option. Just found these....140mm arms, standard freewheel fitting: http://www.tartybikes.co.uk/cranks_pair/jitsie_forged_kid_cranks/c514p13254.html

Have you actually done any calculations of force then? She might be slight, but if the parts are designed to be supported on both sides then you really should establish that the forces in this usage case are comparable.

Having the brake and the drive on opposite sides of the arm will help the forces, but one of them will be much more exposed to damage and possibly snagging fingers. If you put the drive on the hub and the brake outside, it would be easier to enclose/guard the brake somehow and have the drive protected inside the arm. The main problem with this is that the axle then has to rotate in the swing arm, rather than being rigidly fixed/pressed in place.

Could you used a fixed sprocket at the back, and move the disc brake to the cranks?! It would simplify your back end loads, but there are downsides to having a disc by your ankles. Not sure if you could apply a brake to the chainring, but have the cranks on a freewheel. I guess your daughter doesn't want a fixie?

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Kids and disc brakes.
Finger chopper off-ers

Hub coaster brake? Then you just need to make the drivetrain work...

Giant did a folding bike a few years ago called the 'Halfway' that had monostays front and rear, might be worth tracking one down or doing some research on them.
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Thats a mike burrows designed giant i think. Ask him?