I got used Prius battery packs whenever they were available. A gen one pack has more subpacks, but the size and interlocking feature is different between the first gen packs and the second gen packs. The used packs go for between $600 to $1200 on e-bay. There are 40 subpacks in the first gen, and only 29 in the second gen. The second gen subpacks have higher current internal connections and of course they should be in better shape with less cycles on the newer packs. $600/29 subpacks would put the price per subpack at ~$20.
Of course the shipping is not considered.
$1200/ 29 brings the price to $41 each.
While the e-wheel was a lot of work, I chose that route so that I could easily return the car to stock if it did not work as planned. Now that I see that an small e-wheel can give me a 40+ mile EV range, I would do it all differently.
The trailer concept has a few other issues.
1. side scrub on turns
The caster concept does not lend it self to a simple drive system, while it does work well for passive support.
When I mounted my e-wheel, I got it as close to the rear wheels as possible to allow the wheel to be mounted on a pivot that would only need to move up and down. I determined that at my mounting position, only 1/4 " of side scrub would occur on the sharpest turn that the car would do.This is acceptable, and is what allowed me to mount the thing in such tight quarters. I have only 1/4 " on either side of the assembly. As soon as you move the drive to the rear hitch area, the side scrub on a rigidly mounted wheel starts becoming a big factor, and a simple up down action will not work when you try to turn a corner. This means that you would have to allow a side to side motion of nearly a foot. If the thing also wants to lift off the road, you have a pretty complex attachment system.
2. The down force
Substantial down force is required to get sufficient friction to push the car.
We normally don't give this much thought, since the cars weight is supported by the 4 wheels, so there is plenty of down force. The insight has low rolling resistance tires, and even with all the batteries it is still lighter than most cars. I have 130lbs of down force, which works quite well on dry clean roads,
But If I try to take off from a stop and I am on sand/grave/, wet/ or snowy roads, it just kicks out sand and stones at the poor guy behind me, so I constantly have to be mindful about where and when to use it. Once moving, that issue goes away.
A trailer with 2 wheels, and all of the batteries should make a nice pusher, as it puts a the battery and motor weight on the trailer drive wheels, and with a regular ball hitch also takes care of the side to side motion required.
On the wheel motor concept, I would expect that any reasonably priced wheel motor (is there such a motor?) would have trouble generating the required torque to push a full size car.
This is why most prototype wheel motor cars use 4 motors.
I like the concept of a two wheel trailer with dual motor drive one for each wheel, with some amount of gear reduction to increase the torque to a level that would provide adiquate acceleration.
Lots of things to consider.
http://peswiki.com/index.php/PowerPedia:Hybrid_Adapter
This guy put up a peswiki after reading about my car.
The whole e-wheel assembly weighs about 80 lbs, the batteries are 300 lbs.
I am leaning towards what seems to me to be a better solution.
Say you start with a FWD car, with a trailing arm rear suspension. This would include most modern cars.
You make a custom aluminum timing belt pulley that is made to exactly fit the id of the cars standard wheel rim. It could be tig welded to the rim, and would protrude 1/2 to 3/4" towards the spring. The drive motor would want to be a Brushless motor to reduce the drag when un-powered to a minimum. The body of the car in the rear trailing arm attachment area would be where you would mount the motor, with the drive shaft exactly in line with the rear suspension pivot point. This puts the motor weight on the chassis so it is sprung weight, and only adds a bit of unsprung weight to the existing wheel. The timing belt tension would not change through the full suspension travel, and you can size the motor drive pulley to whatever final drive ratio you like. This concept could be the simplest to do, and it seems to eliminate all of the issues that the e-wheel or trailer have, while also solving the unsprung weight issues that any wheel motor designs would have.
I have the Blue Insight rear end to play with, so I may give this a try if I can find the time, energy and $$ to pursue it.
I have acquired an Insight motor, which may be a nice drive motor for this concept.
http://www.99mpg.com/workshops/mikessaturdayhybri/
I can envision a switchover system to hot swap the Insight drive electronics from the stock IMA motor to the modified IMA rear drive motor.
I did not get the Insight power electronics with the motor, so if anyone has the power electronics from an Insight that they are willing to part with, let me know as I may be interested.