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Old 08-08-2020, 09:46 PM   #1 (permalink)
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Traffic Jam Motor

Hi, anyone investigated the feasibility of installing a small electric motor on one of the back wheels of a front wheel drive car? The back wheels of my car freewheel independently of any power train. I'm wondering if anyone has designed a sprocket that bolts on behind the wheel and goes to a small electric motor driven on a chain to drive the car at speeds between 5 and 10 mph in heavy traffic in an "engine off coast" situation. Ideally the sprocket will have a freewheel or overrun clutch just to protect the motor at high speeds where it's not needed. A solar panel on the roof could charge the battery. You probably wouldn't need more than a kilowatt motor just to get the car moving in low speed stop and go, where a petrol engine is puttering along doing next to nothing and the car is not moving fast enough to make use of the engine's minimum fuel consumption. It seems there is little point in making the car extremely heavy just to get it slightly better at handling traffic jams, so a small motor and battery would suffice - maybe even an e-bike battery or two.
I thought of the idea when in really low speed traffic jams I could just open the car door and scoot the thing along with my foot, rather than having the engine puttering along all the time or turning it off and on an excessive amount of times. But due to the angle of my leg I can't get much power down, not to mention it looks ridiculous.

I'm wondering how feasible it is. It seems like an easy mod if you can custom design a sprocket to go on the rear wheel with a built in overrun clutch. Clearances might be an issue though depending on the car. I'm a complete mechanic novice so it's unlikely I'd be trying it but it's an interesting concept IF you can get the chain not to rub against sprocket parts. Otherwise a specially designed rear wheel with gear teeth on an inside rim that also freewheels might be needed.

As for the freewheel, I'm assuming the car does not need to be reversed at excessive speeds which could damage the motor.


Last edited by CeeforCitroen; 08-08-2020 at 10:01 PM..
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Old 08-09-2020, 12:07 AM   #2 (permalink)
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There have been a few conversations on ecomodder about using Hub motors for similar project. I don't recall anyone bringing up a chain and sprocket arrangement, but it wouldn't surprise me if it's been discussed here. I'm sure it's been done. I kind of feel like I saw somebody with a pickup truck on YouTube wants to it done something like that maybe for regenerative braking. But I don't recall for sure.
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Old 08-09-2020, 12:21 AM   #3 (permalink)
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A motor driving both rear wheels can be used, and it has already been deployed to production cars.
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Old 08-09-2020, 05:57 AM   #4 (permalink)
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I'd imagine a production car would employ a more elegant solution than one that would require you to drive with the engine manually off for maximum benefits, though it could have an auto stop like in a Prius. I mean you could use it with the engine on but the whole point is to avoid having to putter the engine along at low speeds. If the engine uses almost a litre an hour doing nothing (probably less in my 1.1l citroen C2) then at speeds of 5 mph you can only get 5 miles per litre. Turning it off and on is annoying in traffic which randomly starts and stops and puts more wear on the starting system.

I've had downhill traffic queues which are easy because you can just turn the engine off and roll. I don't recommend this in a higher speed area with lots of hazards because the brakes become stiff after a while and whilst they still work you have to push a lot harder. I'd imagine an elderly woman would have a hard time stopping unless she pulls the handbrake.

Uphill queues are annoying because of multiple hill starts. I typically leave a gap of a few cars and roll up in first gear (I drive a manual) and repeat. There is no real effect holding up traffic with this unless there are multiple lights in which case I wouldn't bother as leaving a gap wastes light cycles. Even in this situation they would require a stronger motor and more battery capacity, maybe even a two speed hub gear, though a high torque motor would handle some incline okay.

Of course, my e-bike kit is coming soon so I will be the most efficient person on the forum!
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Old 08-11-2020, 07:08 PM   #5 (permalink)
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Of course, my e-bike kit is coming soon so I will be the most efficient person on the forum!
Sez Mr. Two Posts.

Welcome to Ecomodder.

What you are asking about is a through-the-road hybrid. Why not a golf cart motor?
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Old 08-11-2020, 07:16 PM   #6 (permalink)
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Quote:
Originally Posted by CeeforCitroen View Post
I'd imagine a production car would employ a more elegant solution than one that would require you to drive with the engine manually off for maximum benefits, though it could have an auto stop like in a Prius. I mean you could use it with the engine on but the whole point is to avoid having to putter the engine along at low speeds.
Reminds me of the way the Peugeot 3008 and CitroŽn DS5 Hybrid4 operated.
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Old 08-12-2020, 08:39 AM   #7 (permalink)
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That setup with the golf cart motor looks cool - driving a back axle. Does each have an independent freewheel? A free wheel is mandatory (unless it's a central hub motor) or else the motor will probably be destroyed spinning several times its rating when driving 60+ mph. Also, the moving parts would sap more energy than you'd save.

Of course my car has no official back axle in the driving sense. It is just a cross bar to strengthen the back and is not even in line with the centre of the wheels. The wheel hubs on the back just free wheel independently, though are obviously connected to the braking gear and bearings. I have no drive shaft that I can apply power through.

As for being the most efficient on the forum - I think a solar e-streamlined-shell- recumbent would be the most efficient. A weird quirk is that e-bikes are lower carbon emissions than pedal power. First of all, human muscles are about 25% efficient e.g. similar to an internal combustion engine (against the 60-90% efficiency of an electric motor). Unless the other person is eating anyway and letting themselves get fat - until the extra energy use of daily activities surpasses the cyclist. Cycling would use extra food, by the time you've farmed the food, packaged the food, kept the food cold in store fridges (Though refrigeration is going to be an energy cost anyway, I've been in one where all the open fridges were enough to provide AC for the store! Assuming the heat from the back was vented outside), bought the food, processed the food, cooked the food, washed the dishes, showered your increasingly sweaty body more often than you'd otherwise have to, washed your sweaty clothes more often than you'd have to, then the electric wins by a large milestone. Though it likely still beats the car by a large margin. Unless you are a raw vegan who eats home grown food and takes cold showers.

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Old 08-12-2020, 10:37 AM   #8 (permalink)
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If you talk about details like that have you considered what it takes to make the battery you are using? or the materials that your bike is built of? Or even the manpower required to manufacture those materials?

Plus the whole human efficiency argument is almost non-sensical. Most people have everything listed atleast a little in their lives and adding a little extra doesn't add as much as the initial useage. I get most of my exercise by cycling anyway, so for me using an e-bike would negate that benefit I am getting. Arguing is pointless without any numbers though. Once you get a Mi/Kwh number post it up and we can compare it.

To get back on topic:
I have been considering adding a small go kart engine to the rear axle of my car to use as a highway cruiser. I was going to get a knuckle, hopefully from the awd previous generation of my car, if not then just knuckles from the front of another fwd car so that I can use a cv axle to power the wheel. It'd be one wheel drive, but as with any open diff it should be fine. Any way I evaluate it it just isn't as cost efficient to go with electric drive. Not quite the same as what you are proposing in this thread though.
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Old 08-12-2020, 01:50 PM   #9 (permalink)
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RWD low speed EV

Quote:
Originally Posted by CeeforCitroen View Post
Hi, anyone investigated the feasibility of installing a small electric motor on one of the back wheels of a front wheel drive car? The back wheels of my car freewheel independently of any power train. I'm wondering if anyone has designed a sprocket that bolts on behind the wheel and goes to a small electric motor driven on a chain to drive the car at speeds between 5 and 10 mph in heavy traffic in an "engine off coast" situation. Ideally the sprocket will have a freewheel or overrun clutch just to protect the motor at high speeds where it's not needed. A solar panel on the roof could charge the battery. You probably wouldn't need more than a kilowatt motor just to get the car moving in low speed stop and go, where a petrol engine is puttering along doing next to nothing and the car is not moving fast enough to make use of the engine's minimum fuel consumption. It seems there is little point in making the car extremely heavy just to get it slightly better at handling traffic jams, so a small motor and battery would suffice - maybe even an e-bike battery or two.
I thought of the idea when in really low speed traffic jams I could just open the car door and scoot the thing along with my foot, rather than having the engine puttering along all the time or turning it off and on an excessive amount of times. But due to the angle of my leg I can't get much power down, not to mention it looks ridiculous.

I'm wondering how feasible it is. It seems like an easy mod if you can custom design a sprocket to go on the rear wheel with a built in overrun clutch. Clearances might be an issue though depending on the car. I'm a complete mechanic novice so it's unlikely I'd be trying it but it's an interesting concept IF you can get the chain not to rub against sprocket parts. Otherwise a specially designed rear wheel with gear teeth on an inside rim that also freewheels might be needed.

As for the freewheel, I'm assuming the car does not need to be reversed at excessive speeds which could damage the motor.
I've read of AWD vehicles, in which the driveshaft was interrupted to the rear wheels, and an electric motor added to power that axle, independent of the remaining FWD. Probably mated directly to the yoke on a cradle attached to the differential.
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Old 08-12-2020, 05:33 PM   #10 (permalink)
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The forum seems to have eaten my previous reply. Anyways, what M_a_t_t said.
Quote:
Of course my car has no official back axle in the driving sense. It is just a cross bar to strengthen the back and is not even in line with the centre of the wheels.
Citroen C2 have a twist beam rear axle? Right? Amirite?


insideevs.com/news: ZF Presents Its Electric Advanced Urban Vehicle

With twin motors you get torque vectoring. My previous reply explained the spur gear differential in the golf cart axle.

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