# Ideal motor for power bursts to move car



## nchaud (Jun 19, 2012)

Hi all

I'm new to this forum and it's good to be here.

I was hoping for some advice about a small project.

I'd like to push a standard 2-Litre car at ~5mph for 10 seconds at a time but all the battery packs/motors that are for EV- conversion seem to be overkill but at the same time, I don't want to buy a motor for a golf cart motor if it won't do the job.

Would be grateful if you could help me figure out which motor to use and also what batteries would be good for it. Please try keep the language simple so a layman can understand it 

Thanks!


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## nchaud (Jun 19, 2012)

Also, it won't interfere with any of the existing car mechanics - will operate almost independently perhaps sticking out at the back driving a dedicated wheel behind the car.


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## pedm (May 2, 2011)

nchaud said:


> Hi all
> 
> I'm new to this forum and it's good to be here.
> 
> ...


Hi nchaud!

What is the weight of your car?

It is a hybrid conversion project? Or BEV (Battery Electric Vehicle)?


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## nchaud (Jun 19, 2012)

pedm said:


> Hi nchaud!
> 
> What is the weight of your car?
> 
> It is a hybrid conversion project? Or BEV (Battery Electric Vehicle)?


It's about 3500 lbs; it's not a conversion project as such but it would just be an additional motor strapped to the back of the car that has maybe 1 or 2 small wheels that literally push it up to ~5mph


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## Ziggythewiz (May 16, 2010)

Practically any motor designed for an EV could handle that, provided you have the proper gearing, etc. What is the intended purpose?


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## dragonsgate (May 19, 2012)

5mph isn’t much of a power burst. Is this an electric pusher trailer for stop and go traffic trying to save a little gas on acceleration from the lights? If so I would think you need something that will get you up to at least 30mph or more. The car weighs in at 3,500lbs adding another thousand pounds minimum for electric motor and batteries plus trailer weight equals 4,500lbs. Let’s bring it up to 5,000 pounds after you get behind the wheel with a passenger and a bag of groceries. You can find a good forklift motor to handle that. In my opinion you can never have too much power so do not underestimate your needs.


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## EVEngineeer (Apr 11, 2012)

Lead acid batteries are cheap, but heavy. Lithium batteries are expensive, but lighter weight. What is your price range for your project? That would help everyone figure out what you want. Motors can cost $0-5,000.


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## nchaud (Jun 19, 2012)

@dragonsgate, actually this is just during heavy traffic - e.g. when there's a highway accident and there's long tailbacks, i just want to use this to push the car up to a max of 5 mph so I was hoping for something much lighter than 1k lbs ! 

So if we restrict this scenario to a max speed of 5mph with minimal acceleration required, what's the lightest/cheapest motor/battery combination that I could install on my car?

Thanks for the replies !


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## Woodsmith (Jun 5, 2008)

I can see your plan.

In similar situations I have allowed my car, with the ICE off, to roll if there is a little gradient, or where the law allows and I have been standing beside my car getting some air I just push it a little once in a while.

Unless you have the need to do that very often I am not sure how worthwhile it would be to have a system attached to the car to do that.

If the wheels of the device are on the road then they will need to be able to spin up to the full speed of the car otherwise they will need a method for raising and lowering them to the road surface.
You could look at those trailer movers used at camp and caravan sites, a pair of driven wheels with a tow ball on top. Maybe one of those could be adapted to the task.









There are also motors to drive the wheels, that could work.










I can imagine, if it is a front engine rear wheel drive car then a motor on the propshaft/driveshaft to the rear axle would be an easier proposition.

An Agni95R may be able to spin up to the high speed needed and present little drag and weight when not in use. It would draw high current to move the car at low speed though.

Alternatively a geared motor doing the same job would draw less current moving the car but it would need a freewheel, or sprag clutch, to prevent it from being overspeeded by the propshaft. That would mean no high speed reversing though.

Maybe a motor with a loose belt drive to the tail shaft of the trans or the nose of the diff. The belt tension could be pulled tight with a lever or pneumatic cylinder when drive was needed.

This is all getting a little away from the EV scene though, but still an interesting idea.

Do check the legality issues where you are, just in case there are any issues.



Maybe more ICE car manufacturers should have low power electric drive for maneuvering and parking as a matter of course. I'd like it as an option.


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## dragonsgate (May 19, 2012)

I kind of had a fleeting thought of a friction wheel against the tire like the ones used on bicycles. It is called chicken power. No reflection intended toward this project. It would be hard to get enough pressure between the tire and drive wheel with out a lot of extra time and expense. A small electric powered wheel to push the car could work but there might be some problems to work out. The motor setup will be a lot lighter than the vehicle it is pushing so there might be a traction problem. Add that to the fact that the wheel will most likely be positioned at the rear of the car in the center touching the road where all the oil and gas blow by from other cars is deposited adding to the loss of traction. Anyone who has ever ridden motorcycles for any amount of time will testify that the center of the road can be very slippery. Especially at intersections on a hot day. A hydraulic arm to press down on the electric drive unit transferring some of the vehicle weight might help but again there is the extra expense plus the added weight of the hydraulic unit. Also keep in mind that in order to cut weight you use to small a motor it will burn out in a short time. My contention is if you are going to take the time and money to build something do the job right the first time. The odds are that if you cut corners and build something barely adequate it will not be long before you will wish it was more powerful or faster. There was a PT Cruiser with an electric pusher trailer in this forums garage section but I couldn’t find it.


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## Woodsmith (Jun 5, 2008)

dragonsgate said:


> I kind of had a fleeting thought of a friction wheel against the tire like the ones used on bicycles. It is called chicken power. No reflection intended toward this project. It would be hard to get enough pressure between the tire and drive wheel with out a lot of extra time and expense.


This is where I was thinking with the caravan/trailer mover.








This type fits at a suitable place ahead or behind the trailer's road wheel and is activated to press hard on the tyre and then drive it in either direction.

I am sure it could be fitted to the wheels of a car and the activation can be automated from the cockpit and then remote driven. Many of these things have a remote handset for moving caravans and trailers about.





I reckon I could make one of those but with a quicker engage/disengage process and also no need for independent wheel control.


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## muffildy (Oct 11, 2011)

that caravan mover is really slow; its rated for 28cm/s which is less than 1 mph.
if your car has a differential it would be relatively easy to attach a small motor to it using a belt; that way you would already have gearing for the motor so a lower HP one would be required.


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## Woodsmith (Jun 5, 2008)

It is slow isn't it.
I'm sure 'we' could build a streetable version with a bit more poke!

The built in, motor on the diff or drive shaft, would be idea in my mind though.


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## gonzogogo (Jul 6, 2009)

Another option may be just to use your starter to move car.
Disable engine start (additional switch or something)
Upgrade or fit additional battery
Existing starter probably will die soon, so upgrade starter, maybe fit beefer starter from start-stop car?


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## Arch (Aug 21, 2011)

Woodsmith said:


> It is slow isn't it.
> I'm sure 'we' could build a streetable version with a bit more poke!


And when you've got one that can power your caravan up to 50 or 60 mph, you don't even need the car! 

Interesting idea. The great thing about our electric truck at work is how easy it is in stop-start traffic...


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## ruckus (Apr 15, 2009)

Simple. Just buy my hybrid conversion kit (patent pending). We switch your alternator with a brushless permanent magnet motor. In 'regen' mode it acts as a regular alternator. In 'power' mode it adds 20hp to your car. In 'mpg' mode it takes cheap grid electricity and uses it to dramatically increase your mpg, regardless of the vehicle you drive.

Cheers


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## Ziggythewiz (May 16, 2010)

nchaud said:


> @dragonsgate, actually this is just during heavy traffic - e.g. when there's a highway accident and there's long tailbacks, i just want to use this to push the car up to a max of 5 mph so I was hoping for something much lighter than 1k lbs !


I don't think you'll accomplish anything with this scheme. If you're in heavy traffic you can't exactly shut your ICE off, and if it's idling anyway, it would use no more power to go 5 mph.

As for the battery's required, a single 12V marine battery would probably be plenty, or maybe even a 8V GC battery. You could probably use a contactor instead of a controller, but as mentioned by others you'd need a motor that can take your max RPM at whatever gearing you setup, or a means to push it into the ground. Total system would probably be around 150-250 lbs plus the wheel/gearing assembly.

A tow hook on the guy in front of you would be easier.


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## PStechPaul (May 1, 2012)

For a 3500 pound vehicle on a 5% grade you need a force of about 175 lb. If the tires are 24" dia this is 175 lb-ft torque. 5 MPH for a tire that is about 6 ft circumference is about 73 RPM. So the power needed is 73*175/5252 = 2.4 HP. The torque on the driveshaft for a 3:1 rear is 58 lb-ft and 220 RPM. If you can mount a 12" dia pulley on the driveshaft and a 2" dia pulley on a motor, that would be 1320 RPM. 

Of course this assumes you have a RWD and a driveshaft, but the same principle might work on a FWD if you can get to the half-shafts of the axle. And in any case you will need to rig up a way to tighten up or loosen the V-belt for the pullies, as is done for garden tractors.

I have seen some 3HP DC motors out of treadmills for sale on eBay for under $100. They might be 90 VDC (but may run on 48 VDC) so you would need four batteries. Using 100 A-H deep cycle lead acid cells that will cost about $400 and weigh about 200lb. A controller might be another $100, or you could build one.


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## nchaud (Jun 19, 2012)

dragonsgate said:


> A hydraulic arm to press down on the electric drive unit transferring some of the vehicle weight might help but again there is the extra expense plus the added weight of the hydraulic unit. Also keep in mind that in order to cut weight you use to small a motor it will burn out in a short time.


 
The hydraulic arm got me thinking but then I need power and yep, it would add some serious weight I'd have thought. Instead, I'll try some sort of mechanism to latch the wheel in place.

I'll go out and do some field testing on the slipperiness of the middle of the road - it's a factor I would never have thought of . Thanks !


@Woodsmith, that caravan mover is pretty interesting - it's another potential solution. There's possibly other vendors that sell the same thing that goes faster - call for some Googling I thinks

@gonzogozo, I was thinking of hooking into the starter to move the car too. How'd you imagine this working? What would the battery drive when the engine is off?


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## nchaud (Jun 19, 2012)

Also, taking inspiration from airplanes, how about 2+2 mini wheels on either side of the car about an inch off the ground that will come down simultaneously and drive it forward, controlled by a switch in the dashboard?

That way, it'll require 4 motors that would be small enough to perhaps fit under the car?


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## PStechPaul (May 1, 2012)

If you can rig up a tow bar you might be able to make a trailer with powered wheels. It could act as a regenerative brake on downhill and push the car during stop and go traffic jams. I think they make trailers which reduce the drag on the hitch, but generally you don't want the trailer to push the car at highway speeds. But it might be OK with the engine off and on slight inclines.

Here's one for bicycles: http://electricbicycletrailer.com/

And here is a discussion with some examples for cars:
http://ecomodder.com/forum/showthre...ev-pusher-trailer-make-conventional-2975.html

This looks cool:
http://www.jstraubel.com/EVpusher/EVpusher2.htm


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## CrazyAl (May 9, 2011)

gonzogogo said:


> Another option may be just to use your starter to move car.
> Disable engine start (additional switch or something)
> Upgrade or fit additional battery
> Existing starter probably will die soon, so upgrade starter, maybe fit beefer starter from start-stop car?


Is the beefier starter you are referring to the Belt Alternator Starter (BAS) as found on a 2009 Chev Malibu?
http://alternativefuels.about.com/o...bu-Hybrid-/Malibu-Hybrid-motor-alternator.htm

A slight variation to Woodsmith's idea is perhaps a pulley on the tailshaft and have a belt to the BAS (with the BAS installed under the car). Just check local laws on legalities on this type of mod and if insurance company is happy to insure a car with this type of mod.


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## dragonsgate (May 19, 2012)

Here are a couple more ideas and some questions. I take it you run into a lot of slow traffic. Is this on your commute to and from work? How far do you usually drive under these conditions? Do you want to do this to save gas? Is your car an automatic transmission or stick? If it is auto you could have some problems pumping fluid backwards if you turn off the engine. It has been my experience while driving in heavy traffic that the flow might go at about 5 mph for a while and then speed up to 25 to 30 for a distance and then drop back down. That is one reason I earlier suggested that whatever you build should be able to push you at least 30mph for some leeway in fluctuating speeds so you did not have to keep switching back and forth from one drive to the other.


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