After a bit of a recess I've dragged out my Waverley and I am a bit puzzled about which size of pulley and belt to link motor to drive shaft.   My intention is to fit a 4mm shaft across hull with one link via belt to an MFA919d which has a shaft size of 6mm.  Paddle wheels will be either made from copper or plastic sheet.

Any info on pulley sizes much appreciated.

The main thing I'd want to know is which version of the MFA 919D you've got, as they come with several different gearbox ratios, which will make quite a difference to the pulley sizes required.

For example, if it's the 50:1 version, the output is around 316 RPM at 12V, so a 20-tooth pulley on the motor and a 32-tooth pulley on the paddle shaft would bring that down to roughly 200 RPM unloaded.

There was a previous discussion on the forum at My first paddle steamer project - PS Waverley  which suggested around 291RPM was potentially the correct RPM depending on your exact scale.

I'd probably use a toothed timing belt, with a 6mm bore pulley on the motor and a 4mm bore pulley on the paddle shaft. The difference in shaft diameters isn't an issue.

I'd aim for around 150–250 RPM initially, depending on the size of the model and paddle wheels, then adjust from there. You can fine-tune the speed with your ESC.

Do you know which gearbox ratio your 919D has, and what scale your Waverley is? That would help narrow down suitable pulley sizes.

Cheers,

DG Jnr