Motorized Mechanical Drive (pusher trailer)

[jimbo69ny]

Hey Everyone,

I was at a car show last week in NY and I met a very nice guy who travels the nation showing his red Dodge Daytona that he electrified.

I was talking with him and he told me that he met a guy at a show out west, I think he said Arizona, who had a new body style Rav ev with a custom trailer that he built out of an old VW bus. The trailer supposedly recharged the cars battery as well as provides propulsion for the vehicle, which in theory could happen through regen. With a flip of the switch he would turn the VW engine on and it would propel the vehicle forward. He wasn't sure how the driver controlled the throttle.

The guy I spoke with claimed that he was positive that it was a new body style Rav, that it definitely was a custom vw trailer and that it pushed the car forward. He was certain. I have no idea if any of this is true but thought I'd ask on here. Have any of you guys out west ever seen or heard of this car?

 

[fooljoe]

I've heard of a guy in OR who used the front half of a VW Rabbit as a pusher trailer. It's a VW, and it's out west, and the same trailer could be used to push any EV, so it's conceivable "Mr. Sharkey" has upgraded to a Rav4-EV. The idea of a pusher/generator trailer for long trips has been discussed at length since the days of the old Rav4-EV. I'd love to see such a thing available for rent, but many EV "purists" pooh-pooh the idea.

 

[TonyWilliams]

I've heard of a guy in OR who used the front half of a VW Rabbit as a pusher trailer. It's a VW, and it's out west, and the same trailer could be used to push any EV, so it's conceivable "Mr. Sharkey" has upgraded to a Rav4-EV. The idea of a pusher/generator trailer for long trips has been discussed at length since the days of the old Rav4-EV. I'd love to see such a thing available for rent, but many EV "purists" pooh-pooh the idea.

Why not a battery pack trailer? There's a German company working on that.

I don't see it becoming a commercial success, but if I had a spare RAV4 EV battery on a trailer, it could back up my house and extend my car when I need it.

I can put a JdeMO on both for those rare dual CHAdeMO locations.

 

[fooljoe]

Why not a battery pack trailer? There's a German company working on that.

Well I can think of a couple reasons... An extra battery is going to cost much more than a motorcycle engine, and you only double your range rather than completely remove the range limitation (unless they have swapping stations en route as ebuggy proposes, but now an already costly and slow to develop idea is just getting costlier and more delayed.) But it'd be great to have a marketplace with both types available - batteries if you only need to go a little farther and/or can swap it or fast charge it on the way, and if you can charge for sure at your destination, or an engine for a longer road trip with no reliance on the immature charging infrastructure.

And before everyone chimes in with "just rent a gas car", of course that would make sense in many cases. But if you'll be at a destination with charging available the appeal of having your own EV with you grows with the length of time you'll be staying there. Think going off to college, summer home, week-plus long vacations, moving and not having to have your EV shipped, etc.

And before "just get a Volt" - the appeal (especially if the hypothetical trailer is a rental) is having a hybrid only when you want it and a pure EV (with much more EV range) the rest of the time.

 

[fromport]

Why not a battery pack trailer? There's a German company working on that.
I don't see it becoming a commercial success, but if I had a spare RAV4 EV battery on a trailer, it could back up my house and extend my car when I need it.
I can put a JdeMO on both for those rare dual CHAdeMO locations.

http://nomadic-power.com/

Looking at the size of that trailer, I doubt they could fit 85kWh of batteries in it & a full BMS.

I love that idea though to double it as a emergency backup source.

where to find an inverter from 400 V dc to 240V AC though ?

 

[TonyWilliams]

Why not a battery pack trailer? There's a German company working on that.
I don't see it becoming a commercial success, but if I had a spare RAV4 EV battery on a trailer, it could back up my house and extend my car when I need it.
I can put a JdeMO on both for those rare dual CHAdeMO locations.

http://nomadic-power.com/

Looking at the size of that trailer, I doubt they could fit 85kWh of batteries in it & a full BMS.

I love that idea though to double it as a emergency backup source.

where to find an inverter from 400 V dc to 240V AC though ?

Step down the 400vdc to 48vdc, and there are lots of choices. Won't Sunny Island do this?

 

[fromport]

Step down the 400vdc to 48vdc, and there are lots of choices. Won't Sunny Island do this?

Sure, I've got 2 outback's that could work together and generate 2x120V or 240 when synced.
But I think 1 converter from 400V DC to 120/240 ac would be more economic.

 

[Tadol]

Aww, come on - the obvious solution is to just buy a second Rav, and tow it behind the first one, but set to regen. When the first one gets too low, swap 'em - a sorta EV leapfrog -

 

[jimbo69ny]

Aww, come on - the obvious solution is to just buy a second Rav, and tow it behind the first one, but set to regen. When the first one gets too low, swap 'em - a sorta EV leapfrog -

Haha I love it! I'm definitely going with that option.

 

[michael]

I personally know a guy who has built a pusher trailer for his RAV 4 EV out of the rear half of a regular VW beetle. He has frequently used it to go between Utah and Los Angeles. This isn't third hand, it's for real.

Basically, he tows the rear clip. When it's time to cross the desert, he puts it in gear and starts up. The throttle is wired wide open. He has an ignition kill switch at the driver's position, otherwise the VW is simply pushing, pushing, pushing.

Once he arrives at his destination city, he disconnects the trailer and EV's

 

[jimbo69ny]

How does he adjust his speed if its wide open?

 

[michael]

He told me he either gives a little throttle or a little brake as needed. I don't recall whether he put the car into D or B. Basically, it like going down a 1000 mile long grade....modulate speed with the throttle or regenerative braking as required.

Obviously, you don't want the friction brakes to engage. At that point, I assume he would hit the ignition kill switch to the VW engine. He also was looking into the ability to modulate the throttle remotely, but I think the VW engine was just about right to keep him going a normal highway speeds. A little throttle or regen braking on the RAV gave him the flexibility to control his speed.

The biggest problem seemed to be durability of the VW engines.

In effect, it's like old WWI airplanes with "blip" throttles.

 

[jimbo69ny]

Interesting. That seems risky but I get what you are saying.

So in that situation you would have to save a little charge so when you turn the VW ICE off, as you slow down in traffic or for a stop sign etc, you could propel yourself using the Rav battery. Then flip the switch and turn the VW ICE back on as you are speeding up again.

In his design the driver would need to be very hands on. It would really be best to use it while on a long road trip. Which makes me wonder, I wonder what the top speed could be.

I wonder if it possible to do this with a more energy efficient/reliable motor.

 

[evdrive]

Interesting topic. I like the idea of renting the 85kwh nomad trailer. That sounds perfect especially if it has chademo quick charging.

Towing a rav 4 sounds ridiculous but intriguing at the same time. My max range thus far was 150 miles freeway speed at 50mph with 8 miles remaining including a huge summit and a bigger decent. I wonder how far you could tow another rav at 50mph. Seems like the law of diminishing returns applies here. If you could only go 75 or 80 miles on a charge it wouldn't make sense.

 

[michael]

Interesting. That seems risky but I get what you are saying.

So in that situation you would have to save a little charge so when you turn the VW ICE off, as you slow down in traffic or for a stop sign etc, you could propel yourself using the Rav battery. Then flip the switch and turn the VW ICE back on as you are speeding up again.

In his design the driver would need to be very hands on. It would really be best to use it while on a long road trip. Which makes me wonder, I wonder what the top speed could be.

I wonder if it possible to do this with a more energy efficient/reliable motor.

Actually, as I understand it, the RAV battery will in many cases be charged up by regen, unless of course he wanted to go faster than the VW engine would propel him for a long period of time. It just depends on whether his average power requirement is more or less than the engine provides.

And yes, I believe he used it exclusively for long distance runs, not in traffic.

And yes, I think another engine would have a lot of advantages. The VW engines are old and actually not that easy to find these days based on what he told me. I was thinking maybe a modern motorcycle engine which, in fact is what BMW uses in the I3. Something in the order of 30-40 HP should do the trick I would think.

 

[jimbo69ny]

Correct, not only would you be moving forward courtesy of the trailer you would also be regening.

Would a motorcycle engine be enough to push you forward in a Rav? If so, at what speed would it be I wonder.

This would definitely be something I was interested in if it could be built for a couple thousand bucks. But the more fuel efficient of an engine sure that price would jump.

 

[michael]

I think so.

If the Rav uses 300 wH/mile at 60 miles/hour, it uses 0.3 x 60 = 18 kWh/hour, or 18 kW

18 kW is 18/0.746 = 24 HP. So something in the range 30-40 HP is about right, should be plenty.

I'm not a motorcycle guy, and manufacturers don't seem to list HP rating, but there's a list of dyno test results here

http://cyclehp.com/?page=chart

And it would seem 40 HP is easily achieved. A Honda Goldwing seems to have several times that, for example.

Honda also makes 688 cc industrial engines that put out over 20 HP, so what would be needed seems readily achievable.

http://engines.honda.com/models/series/v-twin

I imagine even something like that would be good for 55 MPH. Looks like they cost in the $1300 class and weigh around 100 lbs. zoom zoom zoom

 

[fooljoe]

I think so.

If the Rav uses 300 wH/mile at 60 miles/hour, it uses 0.3 x 60 = 18 kWh/hour, or 18 kW

18 kW is 18/0.746 = 24 HP. So something in the range 30-40 HP is about right, should be plenty.

Don't forget that you need to push the combined Rav+trailer, not just the Rav alone, so the Rav's efficiency numbers don't apply. Still, it's probably true that you can get away with a pretty small engine since you can use the Rav's powertrain to supplement for periods of higher power demand like accelerating from a stop, passing, and hill climbing.

I'm beginning to think this pusher concept is actually a really cool idea, and I like the idea of using a larger-style trailer like the bus too, as that extra storage and possibly sleeping accommodations could be a great benefit for longer trips even without the range-extending properties. Think a small Airstream with an engine.

Battery trailers certainly sound cool too, but realize a simple pusher trailer is probably up to 2 orders of magnitude cheaper to get set up, and the only modification needed to the Rav (or any EV, for that matter) would be installing a hitch. A battery or genset trailer, on the other hand, requires modifying your EV to tap into the HV lines, which could conceivably have safety / warranty violation issues, not to mention standardization problems if the trailer's meant to work with different types of EVs. The only problem with a pusher trailer is working out the control system, but that seems fairly easily accomplished.

 

[jimbo69ny]

Yeah I agree. I think it would be really cool.

 

[rickrides]

Legal???