Springs

[squirrel_hunter]

Let me prefix this with, any indication or suggestion that I am any sort of a mechanical engineer is fake news and propaganda. 

Anyway, I've been making my own rearsets for my YSR project and have hit a spring related problem. I need an expansion spring to return the rear brake lever to rest so thought the simple option was to buy one of those generic sets of springs such as this and see what fits. From that kit the closest I have is the following:

Its about 12.5mm long at the body without any tension, with 7.5mm diameter coils, and 0.5mm wire thickness. it fits nicely, though needed better loops or hooks at the end. Fitting it gave me some idea of how it would work. The only problem is the spring is not strong enough. It can just about return the lever to rest when off the bike but when fitted does't have the force to snap back. 

I've had a little look around and calculating spring rates appears to be like voodoo to me so I'm not sure where to go as I only have a requirement of "that but stronger", so hopefully someone can give me a pointer of what I need to do next... And don't worry about the defects in the rearset shown, this is my 'D' set prototype that I can try things out on as I learn how to do all this stuff. Also the distance from centre to centre of the mounts are about 36mm at maximum rest and 52mm at full extension, though I doubt we'll see those numbers in operation as there is a cam and drum brake adjustment to close those numbers out, not sure if that helps?

So any suggestions of how to workout what spring I need and where to get one from would be much appreciated?

[martzxr]

This is how we've done it on the race bikes, would that work for you?

[lorenzo]

10 minutes ago, martzxr said:

This is how we've done it on the race bikes, would that work for you?

Where are you getting that kit from?

[Superdunc]

lots of people use remote control car springs, for the mc pushrod design.

To the OP, try a thick O'ring instead of a tension spring.

[martzxr]

26 minutes ago, lorenzo said:

Where are you getting that kit from?

Just something my team mate made up, simple cup with a hole in it made on the lathe

[Toneale]

43 minutes ago, lorenzo said:

Where are you getting that kit from?

I use one of these on my fireblade. 

Works really well.

 

[Swarf]

2 hours ago, martzxr said:

This is how we've done it on the race bikes, would that work for you?

That reminds me, need to make one of them. 

[squirrel_hunter]

Thanks all for the suggestions. That rear brake return spring is a cool idea, but unfortunately won't work for me as its a drum rear brake. 

The oring or the RC Car spring is an idea I'm going to pursue as I know a couple of guys who play around with those things...

[Mark/Foggy]

Rubber bands are good, Honda Louth used to use cut up inner tubes for years.

O Ring idea is a very neat solution, you can get little nylon wheels off of the GHay and make something that will last well.

Edited August 11, 2020 by Mark/Foggy
More detail

[Mark/Foggy]

I run 3.5 diameter O rings for this sort of thing which is plenty elastic. Little wheels come in various diameters of RV applications and usually available for a 4mm band so you can run a little off centre line and not wreck them regularly.

[blow_away]

https://www.flexosprings.com/

I normally go here and ask, and they work it out for me.

[Adam]

 

[hawkati]

On 8/10/2020 at 11:01 AM, Toneale said:

I use one of these on my fireblade. 

Works really well.

 

Is it adjustable for compression damping?

[Toneale]

49 minutes ago, hawkati said:

Is it adjustable for compression damping?

You just need to get your foot calibrated. 

[squirrel_hunter]

11 hours ago, Adam said:

 

This has crossed my mind, but I'd prefer to get something off the shelf at this point. I've got lots of other bits to make such as the petrol tank, and front brake conversion, so time spent is a bit of a consideration. This Old Tony's videos are great though. 

One of the RC boys pointed me in the direction of a supplier that they've used so ordered a small sample and one of the others has offered a test fitting of what he has so I've got a few options now...