After I bought my first steam locomotive in 2014, I found Zach's article about the momentum van, and like many, I decided to have a go with a Zecar friction drive. I constructed a goods van freelance from plasticard, scored to give the plank effect, and scaled to suit the Zecar chassis (a bit squat and dumpy), fitted 25mm wheels in place of the supplied ones, and shortened the axles to fit within some dummy axleguards. This was the end result, from below
And viewed side on
I weighted the van with lead sheet to about 500 grams, and also applied some foam packing to the interior to try and reduce the awful whine which emanated from the drive. In trials, I found the results to be variable, and felt that the main problem was the short chassis length, which seemed to make the van work sometimes, but not others (someone earlier identified that the driven wheels need to be located at the locomotive end - not something I had considered when I ran my trial).
Eventually I replaced the Zecar with standard axles, and continue to use the van as a regular part of my stock.
Re-reading this thread a few weeks ago, I noticed that Simon Wood had combined 2 Zecars to make a momentum van, something that I had considered but taken no further when I decommissioned the Zecar unit from mine. Having acquired, some time ago, a goods van (I think an Andel models kit) which proved a poor runner, mainly due to the axle spacing on it and it's light weight, I began to consider a second attempt.
Having kept an eye on Zecars on Amazon over the intervening years, I noticed that prices (from a peak of nearly £30 a couple of years ago), were now more reasonable at about £12. I took the plunge and purchased another (having first made sure I still had the old one safely stored
Not for me the easy route of placing both devices in line, or angled so the undriven axle is within the body of the van. I decided to indulge in some bodgelling, attacked both carcasses with my Dremel, and then very skilfully cobbled the two surviving parts together with some brass plate and nuts and bolts. The axleguards are IP, and the axle stubs are retained in the brass bushes within the guards. so far, it all appears to be smooth running.
This is the stage I'm at at the moment - still to do is - install weighting, add foam insulation for noise suppression, refurbish and repaint. I'll update as it goes.