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Old 04-02-2017, 04:33 AM   #32 (permalink)
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Adding these electric motors to the back wheels of my FWD gas car?

Originally Posted by jray3 View Post
On projects like this I'm not worried about synching up the electronics between engine management and motor control. The engine will behave like it's going downhill. (Just like operating my ICE pusher trailer behind an EV.) The electric rear axle could be completely independently controlled, preferably with a hand throttle, or if off the same accelerator pedal; through a master switch to enable/disable the Warp drive.

However, I think this car will be too difficult mechanically. On any car it is difficult to put one series motor on each rear wheel unless they are offset by using a gearbox, as there's not enough width for two motors, half shafts, and CV joints, let alone at the right angles. Putting a differential beneath a body that wasn't designed for it might be doable if you don't mind a big hole in the floor.
Also, this dual rear motor approach with one per wheel has been oft discussed, but very rarely implemented on a DIY EV. As I recall, the Tropica was then only series-motored 'production car' to do it, and not particularly well at that.
Polychain belts and their cogged pulleys are noisy.

I'd still love to french a motor into the driveline of a pickup one day. That would be much easier.

Hi Jay, Its good to see you here. I've been out of this stuff for a while. What ciano22 wants to do is totally doable. He even showed pic up under the car and all the worries I would have are alleviated.

First I want to state that I am not so up on joining yet another forum. Too many over the years got me too many house projects that have got me in trouble with the spousal unit. But EcoModder sounds like a cool one to me and right up my alley as a Certified Energy Manager.

Next I want to say that its good to see other EV (and NEDRA) guys on this forum. If there EVer was an ecomodder it has to be an electric vehicle guy. Maybe Jay has told what he gets for GGE. For me its about 100 MPG on my truck. But thats an analysis based on current cost of gas. Price of gas goes up my GGE goes up too :-)

And now to get to ciano22 project. Its totally doable. I'm going from memory but I thought you said the Impala makes 327 ft-lbs torque. And that you want more than that to the rear wheels to get the car moving. I can tell you than my 1978 Pinto with two WarP 9" motors puts 1500 ft-lbs to the Dyno. That is likely way more than you want to put what I think your desires are. So don't be sold on bigger is better and try to stick 11" motors up under the rear end.

9" motors may be more than you are looking for. And for your budget doing dual 9's will put you slightly over your $10k budget because you also have to consider the motor controller and batteries.

Now for batteries you don't really have to go too big because you are just wanting the motors for accelerating from slow speed. Aside from what many might think it does not take that much energy to accelerate a car to 60 mph compared to what it takes to just drive it for 10 miles (at that same speed). Think about it 180 HP for 15 seconds compared to 10 HP for 600 seconds. Although not really a unit of measure, it is in my mind. 2700 HP-seconds or 6000 HP-seconds. Its the same amount of energy. So you say the car makes plenty of HP at speed. That means it makes enough to slowly charge the 2700 HP-seconds you wasted accelerating at a high rate over the next few minutes. So really the Hybrid approach is a good idea. And it works the same way for other hybrids.

So the question you have to ask is how much "extra" torque do you need? As I said my twin 9" motors make 1500 ft-lbs. Although torque tapers off quickly with RPM, that's where a good string V* just getting up into its HP band would be useful.

If you want 3000 ft-lbs go with dual 11" motors.
If you want 1500 ft-lbs go with dual 9" motors.
If you want about 1000 ft-lbs go with dual 7" motors.
You could probably even get 600 extra ft-lbs with dual 6.7" motors salvaged directly off an old forklift.

The problem with the "differential movement" fixes itself with two motors wired in series from the same controller. Imagine if you were to mount two motors on top of a straight axle of a front wheel drive car. Put a gear inside the hub and mount a series would DC motor to it with about a 3:1 gear reduction. With the motors in series they will always have the same amount of current (and voltage) when they are turning the same RPM. BUT, if one starts to slip and the RPM is faster, the back EMF on the motor will drop. The other motor with the slower RPM and higher back EMF will have a higher power split from the batteries. With the same current flowing through them, the motor with the higher Back EMF on it will pull more power. Higher back EMF X same current is > than Lower back EMF X same current. So its a natural Differential action.

So the long and short is that what ciano22 wants to do is readily possible. You just have to figure out how to mount the motors to an axle that connects the two rear wheels. If as he says he wants to start with smaller motors he could do that. Two 6.7" motors cost $600 each. A Zilla 1K costs $2k (I think - its been a while) and 30 XE-16 lead acid batteries cost $3k (LiFePO4 would cost more)(but there are other more power dense Li- based batteries that would be suited to just jump starting). I have the idea on how to do that if he wants to contact me off list. I won't share the details until we get a working model, which I have been thinking of doing lately on my 7.3L Powerstroke Diesel. :-)

The guys at NetGain which makes the WarP motors have a kit for that by the way.

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