Ideas for a powered trailer.

[Clev]

The three factors that affect a car's towing capacity are power, braking and weight. Power and braking you can handle on the trailer end, but weight (specifically, the frame and mounting points for the hitch) would probably be an issue. Even if you perfectly balanced the trailer to have little or no tongue weight, a too-heavy trailer might still tear off the rear of the car if the weight shifts.

How much weight are you thinking about hauling, and are you talking about the Commutacar specifically? Does it even have a solid metal mounting point?

As for a pusher trailer, maybe one of those truck-bed trailers? Keep the differential and mount the motor and batteries underneath the bed. It already has brakes and running gear, and those things are always running around, so the cops won't give it a second look (unlike, say, the rear of a Beetle hitched to your car.)

[jray3]

I'd be hard-pressed to think of any vehicle less suitable to pull a trailer than a CommutaCar, so can only say- go for it! I've countered similar doubts in adding a 2" receiver hitch to my electric Karmann Ghia, with the intention of first pulling a genset for range extension, and then a pusher trailer. Of course, everything else on the car was beefed up first, and I'd much rather having more power (or regen) on tap at all times rather than leave it sitting on the trailer 95% of the time... updates soon at the karmanneclectric blogspot. However, I do think that your idea of balanced trailer assist has merit, in that an AC drive could be combined with a surge brake assembly on the trailer tongue, such that the (former) master cylinger piston constantly signals the motor to assist or regen automatically, keeping whatever amount of drag on the tongue that is dialed in via a balancing spring. Some e-bikes do this with pressure sensors, I think in the pedals...

[Clev]

Originally Posted by jray3

However, I do think that your idea of balanced trailer assist has merit, in that an AC drive could be combined with a surge brake assembly on the trailer tongue, such that the (former) master cylinger piston constantly signals the motor to assist or regen automatically, keeping whatever amount of drag on the tongue that is dialed in via a balancing spring. Some e-bikes do this with pressure sensors, I think in the pedals...

Awesome. If I ever had a travel trailer, I'd figure out how to rig up an alternator or generator head to the trailer brake controller to recharge the house batteries while decelerating. Why waste it?

[Ryland]

If and when I do end up building this (I'm not finding any electric golf carts for less then $1,000 right now) I would like it to be a 4 wheeled trailer so non of the trailer weight is on the hitch, this way I could tow it behind any vehicle including a bicycle or my commuti-car, the commuti-car has solid mounting points to the aluminum roll cage that the bumper shocks are mounted to, I have a tow bar for towing this car behind another vehicle that mount on to those points and a trailer hitch could attach the same way only in the rear.
for towing a trailer like this behind a bicycle the sensitivity of the controls would need to be adjusted so it doesn't push you over, but I've hauled adults with my child hauling trailer without issue and a bicycle is going to be going much slower then a car.
At that point, with a 4 wheeled trailer, the big worry would be that the steering is tight and maintained so that you don't have it fish tailing.

At this point this project is more of a big dream then anything else, mostly due to time and money, but I plan to keep my eyes open for good deals on the parts I'd need, or if anyone else wants to take on a project like this I'd be more then happy to give input.

[billyjones]

Many years ago there were tractor-trailers used on the west coast that had pusher engines (gas usually) mounted on the trailers to help push the rigs up grades. In the east, modified pick-up trucks were used to help push the rigs up the grades. Both were fraught with problems in that sometimes the pushing was going on at the same time stopping was being attempted.

Twin engine motor-graders had the same sorts of issues.

That said, work out the controls and it should work just fine. The pushing was never the problem-- the problem was in controlling the pusher. Those old rigs used lots of cables that rusted, got stuck or broke. Modern electronics could eliminate those concerns.

Me, I'm wishing I could afford to replace the rear wheels on my Tercel with hub motors and a few batteries.

[Ryland]

When I figure came up with an idea like this years ago, I thought I was going to have to make all of the controls mechanical and figure out ways to dampen and fine tune them, then I started reading about the programming in solid state speed controllers and all of those issues are solved in the controller settings so by having the trailer powered while you are trying to brake and so on will be taken care of because the braking and the power are all controlled by the same device, the speed controller, there will of course be a manual over ride brake that will cut power to the wheels for when you want to come to a complete solid stop.

[Bob425]

Ryland:

A comment if I may, regarding the inter-vehicle control process.

Presuming that the trailer propulsion can be controlled electronically, an accelerometer can be used to determine the push/pull differential between the tow vehicle and the trailer.

I designed a microcontroller application that uses a three axis (X, Y & Z) accelerometer, in conjunction with a tow vehicle master cylinder’s pressure transducer for our 5th wheel trailer.

As a result and within reasonable towing speeds, the trailer provides its own braking such that its braking rate equals the tow vehicle’s braking.

The microcontroller code can be edited to provide desired relative braking rates and timing.

You may want to consider such a methodology to control the trailer assisting power and also to match its braking rate with the tow vehicle.

Regards,

Bob425

[Frank Lee]

I know! Ride in the trailer and drive it from there!

[bwilson4web]

Originally Posted by Frank Lee

I know! Ride in the trailer and drive it from there!

Various prototypes:

The four-wheel version:


Bob Wilson

[billyjones]

You probably already know this but as a lot of people don't understand braking I thought I'd add:

A common misconception is that the trailer brakes need to apply before the brakes on the towing vehicle. Brakes should work from front to back, steering first, rear wheels on vehicle second and trailer brakes last. Of course, this all takes place in less than a second.

The most common causes of jackknifes are applying the trailer brakes first, only or too much.

Vehicles designed for towing are set us so that this is automatic. Of course, some drivers circumvent this by the use of what is commonly called a trolly brake. The trolly brake only works the trailer axles.

The real reason for the trolly brake is to test the trailer brakes when coupling to the trailer. Many companies spec their trucks (power units) without trolley brakes because many drivers don't understand the real purpose of the trolley brake and cause jackknives they could have avoided with less effort.