# Crazy idea? - using the EV as a pusher behind an ICE tow vehicle!



## MJ Monterey (Aug 20, 2009)

Cool! A whole new sport...... Trailer burnouts!

My concern with flat towing any competition vehicle is weather it will be in any shape to tow home after the comp. It's competition, stuff happens, things break.


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## DavidDymaxion (Dec 1, 2008)

I towed my electric to rapidly charge it -- it worked well except the motor got hot. When I get my external cooling fan installed it should do better. I did a little calculation, and since the voltage rises under regen, I computed 60% more heat was being dumped into the field windings than motoring! So anyway, be careful you don't overheat your motor if you do extended regen via the tow vehicle. This was with the motor switched directly, a good controller should help prevent too much current to the windings.

Also, you'd need to be careful as a pusher could make the tow vehicle go unstable! 



toddshotrods said:


> My race rod EV project is obviously not the typical daily commuter type project, and will need to be towed to long distance events. In the interest of keeping my carbon footprint as low as possible, and keeping as much money in my bank account as possible, I am planning to use as lightweight of a tow vehicle as possible. I figure the Inhaler race rod is going to be under 1500lbs complete, and my daily driver Accord can actually pull that much weight comfortably around town and at highway speeds.
> 
> The easiest way to keep the weight down is to flat tow the EV (all four wheels on the ground, with a tow bar connecting it to the two vehicle). I remembered reading, from links posted here, about people building pusher trailers. That led me to think, “what if I used the EV as a pusher instead of just dragging around dead weight?” It wouldn’t be used constantly, just for certain high demand situations like climbing grades, and maybe stop-n-go city traffic. Since my motor is a SepEx, I could also use regen like trailer brakes.
> 
> Any reason why this wouldn’t work in real life, as good as it does in my imagination?


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## toddshotrods (Feb 10, 2009)

MJ Monterey said:


> Cool! A whole new sport...... Trailer burnouts!
> 
> My concern with flat towing any competition vehicle is weather it will be in any shape to tow home after the comp. It's competition, stuff happens, things break.


Lol! That's a good point. I would be willing to take that chance though. It's not uncommon to see mega-horsepower vehicles being driven long distances to compete and then driven back home now. Worst case scenario, I would have to find some parts to get it rolling well enough for the tow home, or just pay to have it hauled.





DavidDymaxion said:


> I towed my electric to rapidly charge it -- it worked well except the motor got hot. When I get my external cooling fan installed it should do better. I did a little calculation, and since the voltage rises under regen, I computed 60% more heat was being dumped into the field windings than motoring! So anyway, be careful you don't overheat your motor if you do extended regen via the tow vehicle. This was with the motor switched directly, a good controller should help prevent too much current to the windings.
> 
> Also, you'd need to be careful as a pusher could make the tow vehicle go unstable!


Good points here too. I was thinking more about controls for the EV in the tow vehicle. Gauges to monitor what's going on back there would definitely be a good idea.

Actually, stability was my main concern. The people who built the pusher trailers seemed happy with them, and didn't express any concerns about instability, but it does seem strange to have something shoving you down the road. I am more interested in the EV just compensating for its own weight than moving the tow vehicle though. I would want it to feel like there's nothing back there more than I just tapped the afterburners. Going around curves, in inclimate weather, would be a good example of a situation where the EV would be in standby mode!  Even with the regen on going downhill, I would be more interested in easing the tow vehicle's responsibility of keeping everything under control than pumping massive voltage into the pack.

I guess the key is I like being in control. I wouldn't want the EV controlling my driving. Cool, that you've actually done something like this - thanks for the feedback!


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## Woodsmith (Jun 5, 2008)

Is it even legal where you are?

I know in the UK it would be illegal due to the weights of the vehicles. I also think that there may be some restriction on powered pushers, as a rule, as there are none here except in heavy haulage using 'road locomotives'.

The stability issue is when cornering. The pusher is going to push the towing vehicle's back end sideways instead of around the corner. Also on the straight at speed any deviation, pothole or tramlines in the road is going to cause some very difficult handling.

I speak from experience of having my 6x6 Land Rover towed by a 88" Land Rover. I had a badly leaking crank oil seal that couldn't be fixed on site so we decided to tow it home. I would start up the engine in the 6x6 just to push a bit on hills and at junctions to keep things moving. Everytime I pushed on the A frame, the 88" went sideways depending on the camber of the road and the turn.
In the end we gave up as the lighter 88" just couldn't control the front of my 6x6 when it powered up.


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## Stunt Driver (May 14, 2009)

quite a few people done this already, so not that crazy.
http://www.metrompg.com/posts/phev-pusher-trailer.htm
http://en.wikipedia.org/wiki/Pusher_trailer


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## MJ Monterey (Aug 20, 2009)

O.K. on a more serious note, now that I have had time to ponder. 

Since you are looking to have it mostly cover it's own added loads, How about a push pull sensor in your hitch? Basically put a sensor in place of the "master cylinder" for a hitch used for hydraulic braking on the trailer. Then set ideal parameter to be say min push of 100 pounds during regen. When assisting up a hill, never drop below 100 pound of tug on the hitch. Basically have a +- 100 pound dead spot for hitch tension/compression.

There may allready be somthing like this in the RV arena for electronic brakes. If not you may have another marketable product on your hands!

Have fun,
Jack


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## Woodsmith (Jun 5, 2008)

That is an idea I have been looking at with respect to off road powered trailers and cycle trailers.

With ICE off road trailers I figured on using, say, a VW beatle engine and auto box where the hitch 'pull' pulls on the throttle and the hitch 'push' actuates the brakes. That way the trailer would only need to power its own weight.

For a cycle trailer a small motor, controller and battery could be fitted in the trailer and the potbox attached to the towing arm of the trailer. The towing arm would have a range of movement that would 'open' the throttle on the potbox allowing just enough power to the motor to move the trailer. If the trailer tries to push the bike then the controller will reduce power to the motor.

In these examples there would need to be a small amount of pull on the trailer to make them power so they are always being towed albeit with very little effort.
With your pusher idea, MJ, there would be a constant small amount of push as a helper. That would work too so long as the towing car is still driving. If it was used as a way to avoid using ICE then it would grind to a halt at the first corner.
The idea is basically sound though and no doubt a bit of driver control would also help.


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## Guest (Dec 4, 2009)

I have thought about the push pull type of switch on the tongue of the trailer but worry that there would be a bump jerk effect. How about something like a cruse control . Take a reading of the rpm on the axle of the lead car with a sincere on the axle of the car and send the information to the motor on the pusher telling it how much power it needs. You would need matching tire size and axle dia. on both units. This could be tricky as the trailer will already be going the same speed as the car.
I have been going over and over this in my head for awhile with no clear idea of how it would be applied to the trailer I am building so here's hoping one of you knowledgeable people will come up with something. The only other thing I can think of is to have a separate hand throttle in the cockpit and just feather the trailer speed that way. This would be an added distraction while driving. Ev drivers are distracted enough as it is. I heard someone say they didn’t like riding in a electric car because the driver was always looking at the gages more than the road.


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## Woodsmith (Jun 5, 2008)

I don't know about US trailer hitches but in the UK braked trailer hitches (anything over 750kg) has a telescopic damper to control ther 'push' of the trailer activating the brakes. It stops the on/off bounce and gives a very progressive braking action. I figured that would work just as well with applying power as well as applying brakes.
http://www.towitall.co.uk/trailer_spares/bradley.htm


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## MJ Monterey (Aug 20, 2009)

Woodsmith said:


> With your pusher idea, MJ, there would be a constant small amount of push as a helper. That would work too so long as the towing car is still driving. If it was used as a way to avoid using ICE then it would grind to a halt at the first corner.
> The idea is basically sound though and no doubt a bit of driver control would also help.


Woodsmith, I think we are on the same page but I may not hove expressed my concept well. 

What I want is a neutral area. No braking no pushing. the 100 pound value is arbitrary and not set in stone it is just an example threshold.

When the tow vehicle begins to slow the regen/braking does not turn on until the hitch has 100 pounds of compressive force and turns off if compression drops below threshold.

On the pushing side. I would not have the trailer push until there is 100 pounds of tension in the hitch and stop pushing if tension drops below 100 pounds.

You would also have a speed cut off, no affects below a threshold speed. You would need this to be able to back up any time. Or to stop at a light or park while going up a hill.

What I would be most concerned with is to keep the braking affect consistent. If the pack is fully charged (regen is not an option) how do you keep the experience of the tow vehicle driver the same, especially if/when regen suddenly stops when pack becomes fully charged?


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## Woodsmith (Jun 5, 2008)

I think we're on the same page, MJ. Same idea approached from different requirements resulting in almost the same solution.

With a UK set up I would look at the damper, and a little slack in the control feedback, to provide that dead area to ensure some tension in the hitch.


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## toddshotrods (Feb 10, 2009)

Woodsmith said:


> Is it even legal where you are?
> 
> I know in the UK it would be illegal due to the weights of the vehicles. I also think that there may be some restriction on powered pushers, as a rule, as there are none here except in heavy haulage using 'road locomotives'...


Here in Ohio, I doubt legality would be an issue. Our vehicle code and laws are very forgiving, and cops don't usually bother you unless they see a danger to other motorists.



MJ Monterey said:


> ...Since you are looking to have it mostly cover it's own added loads, How about a push pull sensor in your hitch?...


I actually think that's a good idea. It would take some exerimenting to find the best setup for a given application, but could be a nice setup.

I am looking for a more technologically involved system. Since I will be adding supplemental power via the electric motor, and not an ICE, I should be able to use the controller to easily adjust the amount of acceleration and braking assist. Placing limits on available pack voltage and current would adjust the acceleration, and adjusting the amount of regen would control the braking.

I was just wondering if there were any other serious considerations with the concept itself, beside control and stability.

For people considering building a ICE pusher trailer for their EV, many GM front-drive cars (possibly other makes?) have the entire powertrain mounted to a bolt-in cradle. The lower suspension mounts are usually on this cradle as well. Add upper strut mounts, and a tow ball receiver, and you have a huge head start.


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## Thaniel (May 25, 2008)

Stunt Driver said:


> quite a few people done this already, so not that crazy.
> http://www.metrompg.com/posts/phev-pusher-trailer.htm
> http://en.wikipedia.org/wiki/Pusher_trailer


Those are pusher trailers. A pusher car isn't quite the same thing.

When Towing the bigest issue on tow rating is not getting the mass moving. It's getting it stopped and controling it's direction. Many vehicles that are very heavy and underpowered have HIGH tow capacities. Smaller cars with very large engines never have high tow capacities.

What ever you do just be sure you can get it to stop (from freeway speeds) and turn.


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## toddshotrods (Feb 10, 2009)

Thaniel said:


> Those are pusher trailers. A pusher car isn't quite the same thing.
> 
> When Towing the bigest issue on tow rating is not getting the mass moving. It's getting it stopped and controling it's direction. Many vehicles that are very heavy and underpowered have HIGH tow capacities. Smaller cars with very large engines never have high tow capacities.
> 
> What ever you do just be sure you can get it to stop (from freeway speeds) and turn.


NOt too much different in may case - did you see the expected weight of the EV? Under 1500lbs, and I have towed more than that (actually over 2000lbs) with my car. I had no trouble accelerating and keeping up with traffic, no trouble maintaining 65pmh on the highway, and no problem hauling it all back down. Of course, I allowed extra stopping distances, which is standard procedure with something in tow. This was all also with stock brakes, which I hope to upgrade eventually.

Your comments are duly noted though, because stopping is the most critical need.


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## Thaniel (May 25, 2008)

Ah. Hadn't realized that you are already towing the EV with your current tow vehicle. I probably missed it. Then you are already familiar with it's handling. I think adding the pusher effect would be a good deal then. Properly implemented with the right controls you could indeed get some Hybrid effect


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## Woodsmith (Jun 5, 2008)

I wonder if the steering on the EV would have an effect as a pusher?

How are you towing it? On an A frame?


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## toddshotrods (Feb 10, 2009)

Thaniel said:


> Ah. Hadn't realized that you are already towing the EV with your current tow vehicle. I probably missed it. Then you are already familiar with it's handling. I think adding the pusher effect would be a good deal then. Properly implemented with the right controls you could indeed get some Hybrid effect


I haven't towed this EV yet - the chassis is still under construction. I have towed a trailer with more weight than the EV will have, and I know my car can handle the load easily. I have also flat-towed cars before (with different tow vehicles), as well as pulling trailers a lot, and flat-towing seems to affect the tow vehicle less than a trailer because the weight balance isn't constantly changing with the grade. With a trailer you get more or less weight on the hitch depending on the pitch of the trailer itself. Properly loaded, it's a small effect, but it is perceivable with a lightweight tow vehicle.



Woodsmith said:


> I wonder if the steering on the EV would have an effect as a pusher?
> 
> How are you towing it? On an A frame?


What's an A-frame?  If you're referring to a tow bar that hooks to the frame of the towee, then couples to the ball on the hitch of the tower, by means of a, typically, A-shaped towing device - then yes, I'm using an A-frame. If not, I have no idea what you're talking about.

The slight lateral tug on the front of the frame guides the front wheels. Theoretically, the front wheels should be controlled by the tow vehicle, and the rear wheels by the motor. The only way I can see steering effecting it is if I actually start doing pusher burnouts!  In that case, if the rear end of the tow vehicle slides sideways it could conceivably cause the pusher to push my rear end in the other direction, but it still seems like I should be able to steer my way out of that. Hmmm, sounds like that would be fun to try in a nice, open, wet, parking lot!!!  Seriously though, with just enough power being applied to negate the extra weight of the EV, that shouldn't be a big concern.

If it seems like I am arguing against every point you guys make - I am!  I'm not trying to be a pain, just trying to debate the issue to see if it's a good idea or a death wish.  You guys are raising valid points and actually making me think of a lot of safety factors, plus manual and automatic overrides, that I wasn't thinking of before.

One thing I definitely want is an "OFF" button that I can instantly stop whatever the EV is doing if I feel something isn't right. Another is even with my desire for electronic control of the EV/pusher during towing, I am going to look into using the push/pull receiver to give the EV's controller throttle and brake signals. In other words, rather than being hard-wired to what I do with my feet, the receiver could allow a slight delay that would make the pushing more transparent. It would wait for the EV to start lagging behind before adding supplemental power, and for its momentum to start overcoming the tow vehicles to add regen. That could all be done with software, but it seems like the programming would be a HUGE undertaking! You'd have to factor in speed, overall grade, relative pitch of the two vehicles, throttle input, braking input, blah, blah, blah...


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## Woodsmith (Jun 5, 2008)

toddshotrods said:


> What's an A-frame?  If you're referring to a tow bar that hooks to the frame of the towee, then couples to the ball on the hitch of the tower, by means of a, typically, A-shaped towing device - then yes, I'm using an A-frame. If not, I have no idea what you're talking about.


Yep, that's it.

So long as your EV doesn't exhibit any torque steer and would accelerate straight with your hands off the wheel then it should be ok.
Torque steer from the EV would cause sideways movement at the back of the towing vehicle much like towing a badly loaded trailer down a hill and it starts swaying.

It's good that you are exploring all the possible issues before you do it. Better to find out stuff now then at speed on the freeway.


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## toddshotrods (Feb 10, 2009)

Torque steer shouldn't be an issue. My EV has a solid rear end, that will ultimately have a locking differential applying equal power to each wheel until the situation causes it to unlock and allow varying individual wheel speeds. At the small torque loads that would be applied during towing, it should be a perfectly straight forward push even with different traction available to each rear wheel. Even when punishing the EV at the dragstrip, one of the solid rear's greatest advantages is even power delivery. You do have to compensate for torque reaction in the spring rates, but that's for unloading massive amounts of torque in an instant.

That's a good point to bring up though for people building pusher trailers with front-drive transaxles. Unequal length axles, open differentials, etc in an economy type powertrain setup could result in a substantial amount of torque steer. I can wiggle my Accord around on the road a bit with the throttle, and it has an intermediate shaft that is supposed to balance the torque reaction by allowing equal length drive axles to the wheels.


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## Electric Car-Nut (Jul 5, 2009)

This is an idea that has been proven if driven by an attentative driver.Several ev owners have built gas powered trailers to push their EV for long trips, like to and from college once a year and just drive the EV on campus most of the time. My personal design was a trailer built from the back half of a pickup truck, a short drive shaft leads to the motor mounted at the front of the p-up bed between the frame rails as they start to turn inward to about eight feet past the front of the trailer bed and converge at a conventional rigid trailer hitch, so the hitch is about 12 feet in front of the axle and the "Bed" is 8 ft long and extends 4 ft behind the axle, so the entire rig is 20 ft long. (A little extra long to minimize jackknifing when backing up. The battery pack is located in two groups behind of and ahead of the axle between the frame rails. the controller and charger and various control relays and contactors all go into a box inside the bed at the front or in a box above the motor. a long control cable is run to a box mounted next to the driver. On/Off, Throttle (With a knob...) a monitor display for motor rpm, battery voltage and battery current as an aid to careful EV driving too. The trailer lights are operated by the auto pushed systems and application of brakes for slowing or getting set for cornering cut the motor off in the trailer until the throttle in the pushed car is turned down to stop and then back up to proper power position. The trailer doesn't push the car sideways in a turn. that only takes a couple relays to accomplish. Don't try to make it totally automatic! Note that you idle the pushed car to provide power steering and start out from a stop, and power brakes. And you can carry stuff in the trailer! Just using the electric to cruise boosts mpg to about 100 mpg for 50 miles. you need to keep from over revving the motor even if just pulling the trailer with power off. This is the application I was originally going to use a jeep transfer case for, because that gives two gear ratios, 1::1 and 1::2 and a neutral for highway, city, and coast in neutral, you just pull over to the road side and walk back to change "Gears". I am planning to use these systems to train EV technicians about all the EV components, then sell them at about $10,000. each.


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## Electric Car-Nut (Jul 5, 2009)

There is no reason I can fathom to prevent using a car carrying trailer and replace one axle with a p-up axle and with a motor coupled with a short drive shaft, possibly with a jeep transfer case as a cheep 2 speed transmission and available neutral. I doesn't have to be a pick-up bed...

you can add electric brakes controlled by the driver in the second trailer axle to control the load if it is heavy.
like a tandem axle equipment trailer, or race car hauler.

How about a teardrop trailer for vacations, that is recharged at campgrounds and pushes a tow vehicle like a off road jeep that gets poor mpg but is lots of fun off road.

There are lots of alternatives.


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