Garden Railway Forum

ge_rik wrote: ↑Sun Apr 16, 2023 9:37 am
Didn't the de Wintons have fly cranks? Wouldn't that solve your problem of driving the unpowered axle?

Yes they did, but I'd be concerned about quartering going out ( or getting it in in the first place!), without doing some 'proper engineering'

philipy wrote: ↑Sun Apr 16, 2023 9:54 am

ge_rik wrote: ↑Sun Apr 16, 2023 9:37 am Didn't the de Wintons have fly cranks? Wouldn't that solve your problem of driving the unpowered axle?

Yes they did, but I'd be concerned about quartering going out ( or getting it in in the first place!), without doing some 'proper engineering'

I used fly cranks on my latest motor block - primarily because there wasn't room for Delrin chain and sprockets. Like you I was a bit apprehensive at first, but they turned out to be a lot easier to model in 3D printing than I expected.

Firstly, I decided to use grub screws and square nuts to hold them in place. The smallest I could find on eBay were M2.5. You might be able to find smaller elsewhere

I then drew the fly cranks to accommodate them
I'd hoped that 2mm holes would be sufficient to hold a 2mm crank pin (2mm bolts with Allen key heads - eBay once more) in place, but I found I needed to reinforce the back of the cranks with a locking nut to stop them unscrewing.
The concept of "quartering" is actually quite flexible. Whilst a precise 90 degree angle is probably more essential for a live steam loco, it seems as if there is a lot more leeway for our electrically powered models. As long as the opposite cranks are roughly at 90 degrees but more importantly are aligned with each other on each side, then it works.

Rik

Thanks Rik, thats all interesting and I confess I hadn't thought of that, but its certainly another option to look at.
I've just done a quick look round and I can find M1.6 grub screws and hex nuts, but the smallest square nut I can see are M2. I guess a tiny touch of glue would hold a hex nut in place.

I found that the forces exerted when trying to tighten the grub screws tended to make the necks of my FDM printed fly cranks delaminate, but I found that printing them with 100% infill discouraged this. I've not tried resin printing them as I figured they might be too brittle.

Rik

Very nice!