Saturday, February 14, 2015

Now With Two Working Axles!

This will probably be the last post for a while on the tiny Hudson-Hunslet locomotive I've been building but before I show you the current state of affairs I thought a quick recap was in order, especially for anyone who has joined us part way through.

In the break between Christmas and New Year I came across a set of scale drawings for the small 24HP diesel locomotive produced by the Hunslet Engine Company and distributed by Robert Hudson Ltd. As the Robert Hudson works at Gildersome were probably the closest narrow gauge tracks to have existed to where I grew up I thought having a go at building a locomotive they sold seemed like a good idea. While I was able to fairly easily turn the drawings for the body into a 3D model and to produce some nice looking renders I didn't initially know how I was going to be able to power the model.

Given that it has a tiny wheelbase (2' 10" on the prototype so just 11.33mm on an OO9 gauge model) and I wanted to produce a cabless version I couldn't find a suitably sized motor bogie I could use, so I decided to try and print the chassis as well as the body. I printed the body using the FUD material from Shapeways and this turned out nicely. The first attempt at a chassis I printed in the hard wearing nylon material (black strong and flexible) that Shapeways also offer. Unfortunately while the dimensions etc. of the printed chassis seemed right, I was unable to actually get it to work.

While the first chassis didn't work I did learn a lot and received a lot of helpful feedback. Most of the feedback suggested that I alter the chassis so that I could fit brass bearings to support the moving parts. While this sounds like sensible advice I didn't want to sacrifice the shape of the chassis I'd designed (it would need to be bulkier to have room for bearings) as this would compromise the final look of the model. The solution I settled on was to have the chassis 3D printed in brass.

After a few initial teething problems I managed to get the printed brass chassis up and working, albeit directly connected to a power source. By the time I'd wired the chassis up so that it would collect power from the track one of the worm gears had come loose and so the front axle wouldn't turn, although the power from the rear axle was enough to make it move very slowly along the track. And that brings everyone up to date.

While the current version is still just a prototype and the next version will be improved, mostly to make assembly easier, I still wanted to see if I could make this version work properly. So yesterday I completely stripped down the chassis and re-built it. To avoid getting glue into the bearing surfaces (like I did the first time) I took a razor saw to both worms to cut between the teeth until a small hole appeared through into the central shaft hole. I then reassembled the chassis without using any loctite on the worms, which meant I didn't get any into the bearings. Once everything was in position I then added loctite through the small holes I'd cut which fixed the worms in place. Unfortunately I managed to somehow destroy the motor I was using (I'm not sure how, maybe I pulled too hard on one of the wires and broke something inside) so had to swap it for a spare, but after re-assembly I ended up with..... two working axles.

So there we have it, I've managed to design, have printed, and assemble a complete and working locomotive! It is still a prototype though so next I'm going to tweak the chassis to make it easier to assemble, make a few minor changes to the body, and I need to draw up the artwork for etching the remaining body panels. All this will take some time, hence there probably won't be a post on this topic for a while, but I've proved that the idea works and I've already had a number of requests to turn it into a kit!


  1. Wonderful. I bet you are happy with it now.

  2. I'll take my hat of to your achievement and downright determination. It must be very satisfying to have made the model and the rails. Good luck with the next bit.

    1. I think determination is definitely the right word. There were a couple of points (like gluing it solid for the third time) when I almost gave up, but I'm glad I persevered. As you say seeing it run also on track I built is very very satisfying.