(Kinda) Pusher Trailer - New Idea
 

One of the problems with classic pusher trailers is that they can be unstable while pushing the vehicle, especially when turning, and especially single wheeled trailers. So, would it be possible to have a trailer with an engine that uses a flexible driveshaft to drive the rear axle of the towing vehicle?

I got this idea when looking at city busses in Warsaw, some of them are articulated, with the engine in the very rear (behind the third axle) driving the middle (second) axle, with the articulation between them.

So here is what we'd have: An EV, with electric motors driving the front wheels and a diff axle in the rear, plus an aerotrailer with a small engine. For city driving with no trailer, the diff axle would freewheel. For long distance trips the trailer would be hitched up and the a flexible driveshaft would connect to the differential. The engine in the trailer would be sized to just barely push the car up a slight incline at highway speeds, with a 3 speed transmission (with clutch) geared to hit the efficiency sweetspot at 45mph/70kph (in 1st gear), 55mph/90kph (2nd), 65mph/105kph (3rd). Higher speeds and hill climbing would be helped by the electric motor. Lower speeds would be in pure electric mode. Of course, there would also be a small generator for charging.

The downside of this is the extra weight and drag of the diff axle when in EV mode, but this should be made up for by stability when towing at speed. So would this work?

I like the gear ratios.

Can you build a cheap, telescoping driveshaft that transmits 15-30HP despite large trailer articulation angles, trailer pitch, and body roll? It sounds complicated and problematic. You couldn't put it on the vehicle's centerline, because that's where the trailer coupler goes.

Mr. Sharkey reports that stability is not an issue with a VW Rabbit engine pushing a VW Rabbit EV, but he probably only operates at low speeds.

It's an interesting idea, but I can't picture how you'd make the driveshaft flexible enough. I think there are better alternatives.

I have given the driveshaft some thought, but I admit that I've never indulged in fooling around with that kind of stuff, so I don't know what the limitations are. One of the things that come to mind is a mechanism for steering the rear wheel(s) of the trailer, allowing it to articulate less in a turn. Also, the really sharp angles between the car and trailer happen only when maneuvering at low speeds, when the car is in EV mode and the driveshaft would not be spinning anyway.

We had lots of PTO driven stuff on the farm and it had to transmit pretty good amounts of power, sometimes through pretty obtuse angles. And the shaft was directly above the hitch on centerline.

Some farm PTO shafts also telescope when needed. I am thinking of a hay baler, high rpm and torque.

Piwoslaw: I would find a farm parts store and wander in and look around, you might come up with some ideas and price ranges.

sorry for the double post

Oh, but I'm not planning on building it! I just got a terrific idea and tossed it up for others to grab. Wouldn't want it to go to waste in the dark, forgotten regions of my dark, filthy mind;)

Well then someone who would build it can wander through a farm store :)

I like looking through hardware stores and farm stores, I come up with lots of ideas that I will never use.

Hensley Arrow makes a hitch that transfers the "effective" hitch point forward as far as the axle. It is not the same as a leveling-hitch. It uses a system of cams. I have never seen it. It is used when towing a big RV trailer. That might solve your handling challenge.

I would rather tow the trailer and send electricity to the electricity bus at the front axle. The idea of extra parts and weight does not appeal to me.

My understanding of articulated buses with the engine in the rear is that it is the rear axle that is powered, not the middle. Pushing loads on the front chassis are handled with active hydraulic rams between the front and rear chasses.