Here's a drawing of the chassis frames. Apologies for the quality!

The chassis sides were made from .025" brass strip, chosen over .016" to make filing easier and for a larger bearing area for the front axle.

Spacers for the EM loco are Gibson and for the the OOn3 version I made my own from strip, 7.5mm wide.

Bearings again are Gibson and are only fitted to the rear driven axle, small bearings on the OOn3 and large bearings on the EM version. (Gibson do 2 sizes of 2mm bearing).

Note the compensation bracket, this is fitted between the frames on the centre line. I soldered it in before the front axle holes were slotted. It was made slightly too large, then filed down until the axle just touched it to set the ride height.

The 7mm dimension from the frame top to the axle centre line was a bit of a guess, if anything it was slightly too small becouse I figured that it would be easy to add a shim between the chasis and body if the loco sat too low. Seems to be ok though.

The wheelbase is set at a prototypical 21mm.

Before I started cutting metal I made a paper template to test the design and make sure that the gearbox would fit.

Just to recap the motor is a Mashima 1015 fitted with a Mainly Trains 1/2dia. flywheel driving the rear axle through a High Level Slimliner Compact+ 54:1 gearbox. A Mashima 1020 would also fit if the flywheel was left off and the shaft shortened. Even though the 1020 would be more powerfull I wanted smooth running so I went for the smaller motor and flywheel combo.

Axles are 2mm silver steel from Squires and wheels are Gibson 10mm disc.

Today some brass arrived in the post so the OOn3 version now has a footplate, but more on that next time.