The photos and video below show an ERTL tractor trailer I converted to 'Streets today. It runs very smoothly from a scale 15 mph up to faster than I want to try, and climbs 12% slopes with ease. It might actually handle D21 curves (have not tried) but it has no problem with the "D30" curves on my country road. And how ironic that my first satisfactory 'Streets tractor trailer is a Whole Foods truck - our household doesn't seem to be able to survive without a trip there at least once a day.
My wife laughed when I said this conversion is amazingly simple to do. She said I spent three years and countless failed experiments finding out how to do it right: but that is the point, once you find out what works and what doesn't, you can reduce it to the right simple steps, and it is easy and quick: this took four hours start to finish. I explain how at the end. The only thing left to do is to bolt the trailerbody onto the trailer chassis - I left it loose this afternoon in case I had to adjust gears or something but it ran perfectly forever. I may be a tiny bit crooked inthe video.
I'm having serious computer problems and have not been able to view the video I'm posted on my computer, so I am loading it direct from the camera and hope it is good. It's running at a scale 75 mph, I'll probably run it usually at a scale 50 or so.
What I have learned: my "formula" for very satsifactory tractor trailers.
- drive the front axle of the trailer (by which i mean the front of the two in the rear of an 18-wheeler;s trailer, or in this case, the only one)
- use a monstrous can motor with a big flywheel - the biggest you can find. Keep in as low as you can: a high center of gravity can kill good performance
- use diecast vehicles and all the weight you can - traction is the key, and weight gives that. The big motor can move the weight, no problem.
- with a big, big motor, you don't need a gearbox for good slow speed running. Big can motors run at about 40% of the RPM of the tiny motors in 'Streets vehciles, so just using the big motor affects a 2.5:1 change in gear ratio, and they can loaf at low speeds and stillprovide all the torque the vehicle needs.
- with the big flywheel, perfect electrical connectivity is not needed (it rides through even one-second lapes in power without noticeable slowing) so you don't need to pickup power from all axles (I had built 18-wheelers with five center pickups and pickup for all five axles, a real pain requiring lots of time. This tractor trailer picks up power from the four rearmost wheels (two of which are traction tires with less than perfect connectivity) and has only one center pickup. It runs quite well in spite.
- Note again I converted the ERTL tractor un modified except for changing the front axle/wheels to a 'Streets axle and bolted the front inch of a WBB Ford van 'Streets chassis to the rear - in the exact spot the ERTL rear axle went.