custom geartrain to adapt 20 to 50kw in car

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cheapcookie   10 W

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custom geartrain to adapt 20 to 50kw in car

Post by cheapcookie » Jun 24 2018 5:11am

Hello, I have a few questions regarding installing a motor sized from a Motoenergy to something like a Zero in a Volvo RWD wagon.

Theses motors seem to top at 6k RPM, and have from 40 to 80 Nm of rated torque.

The stock vehicle has a 3.69:1 first gear, and a weight of approx 1400kg, wheels about 40cm.
Eventually gutted the Volvo would be easily in the 600kg range, removing seats, glass windows, maybe doors.

I don't need to go much above 50mph at all, this is to go to the post office and back.

What of theses following options would be most reasonable ?

I could couple the motor directly to the transmission.
I could couple the motor with additional reduction to the transmission. (baldor type helical gearing from 2:1 to 5:1, sold by electricmotorsports.)
I could make my own belt drive to connect directly to differential and get rid of transmission and engine.)

If done some calculations.
ecalc.ch only has hobby motors.

http://robotics.ee.uwa.edu.au/theses/20 ... per-ME.pdf
This research paper that I found on endless sphere talks about power and torque requirements for both a ICE car and a collegiate racing kart.

phate   10 W

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Re: custom geartrain to adapt 20 to 50kw in car

Post by phate » Jun 24 2018 6:50am

cheapcookie wrote:
Jun 24 2018 5:11am
The stock vehicle has a 3.69:1 first gear, and a weight of approx 1400kg, wheels about 40cm.
Eventually gutted the Volvo would be easily in the 600kg range, removing seats, glass windows, maybe doors.
You're forgetting about the final drive as well, which is between ~3.3:1 and 3.9~ depending on what model the car was originally.

So really your first gear would be more like 12:1 or 14:1. A motor that size would certainly move the car, but you really would want either something larger, or use more than one of them just so you aren't beating on the motors quite so hard.

Also, I'm not sure how easily you could get a mostly-functional Volvo 240/740/940 wagon down to 1400kg.

cheapcookie   10 W

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Re: custom geartrain to adapt 20 to 50kw in car

Post by cheapcookie » Jun 24 2018 5:58pm

Thank you, mostly functional is not what I am going for, I will try to get rid of as much stuff as possible, will have to see about power steering.
The car would probably be left with one seat, windows replaced with polycarb...

phate   10 W

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Re: custom geartrain to adapt 20 to 50kw in car

Post by phate » Jun 25 2018 3:35am

Edit: my apologies for switching back and forth between lbs and kg. I'm in the US and tend to think in terms of lbs.
cheapcookie wrote:
Jun 24 2018 5:58pm
Thank you, mostly functional is not what I am going for, I will try to get rid of as much stuff as possible, will have to see about power steering.
The car would probably be left with one seat, windows replaced with polycarb...
When I said "mostly functional", I meant "mostly recognizable as a car that could be taken on the street. My point with this upcoming wall of text is that your weight savings estimates are WAY off.

I really do not know how you intend to get a 740(?) wagon rolling shell down to 600kgs (1400lbs) before you stuff it full of batteries, let alone with motors/batteries. I can see somebody getting a 740 street car down into the low-3000lb range, which means if you pull all the doors and leave an interior with a single racing bucket and no dash, you can probably get into the high 2000lb range, or low-mid 2000lb range once you pull the engine out.

Budget street/autocross build of a 740 wagon, with 250-300lbs of weight reduction:
https://grassrootsmotorsports.com/forum ... 804/page1/

Here's some info about weight reduction measures that were done to get 200kg's off a 740 turbo race car.
http://www.ovlov.net/page.php?page_name=tips

You can absolutely get a bunch of weight off the car, but you're not getting away from the fact that the body of your chosen donor vehicle has a LOT of very thick steel that you are not going to want to cut out. If you started with something front wheel drive, you could get it a lot lighter (since you don't have to worry about the rear axle/diff and driveshaft).

A Volvo 240 Group A race car weighed around 1050kgs (~2300lbs) in race form, with steel body panels that had been acid dipped to make them thinner (along with stock-shaped but thinner hood and trunklid panels) and an aluminum roll cage. Pull out all the cage and racing-specific safety equipment, and you can probably get it under 1000kgs (2100-2200lbs, approximately the weight of a stock early 90's honda civic). This is what a factory-backed racing team could was able to make out of a 242 turbo, which weighs around 3000lbs, not a 3700-3800lb 740 wagon.

Remove the engine and whatever accessories they kept on the race car (call it 350lbs), the doors (the race car already had lighter doors, so 30-35lbs each) and you're around 1700lbs (7-800kg) before you start loading it up with batteries/motors/controller.

----------------------------------------------

Let's say we started with a different donor.

If you started with a small-to-medium sized japanese front wheel drive sedan, you can get things quite a bit lighter. Because I'm a honda nerd and can find that info more quickly, a 1994/1995 Honda Accord LX sedan weighs 2800lbs with a full (cloth) interior, and power windows/locks (the EX weighs more because sunroof and power seats). 4th gen accords (90-93) are boxier and not quite as aerodynamic, but weigh about the same. Personally, I'd really like to convert an old 87-91 prelude with 4 wheel steering at some point in the future.

Here's some of the component weight info for a 4th gen accord:
http://www.cb7tuner.com/vbb/showthread.php?t=10770

Starting with a 2800lb car, you can relatively easily get it down around 2500lbs before you've even made the thing uncomfortable (still have stock front seats, doors, airbags, power windows, full interior ahead of the B-pillar, stereo, etc), let alone questionably-street-legal. There's another 50-ish lbs there if you replace the stock front seats with lightweight buckets. Replace the rear glass with fixed lexan and remove the window regulator and tracks/supports for another 25-30?lbs or so. Get lighter wheels and you can absolutely get one of these into the 2300-2400lbs (under 1100kg) range without ruining it. At which point it'll be a fun little car to bomb around town with (at stock weight they handle pretty nicey, a 400lb diet makes it accelerate/brake/handle much better).

I've seen people get them down to 2100 and change for racing.

As far as stuff you don't need for an EV, the engine with all manifolds will be another 250-300lbs, fuel tank is like 20lbs (plus figure another 60lbs of fuel from the above weights), exhaust is probably 30-40lbs, and you're probably going to be between 1800-2000lbs. Pull off another 200lbs for race mods that would make it unsafe for street use. And I guess another 30-40lbs each if you really want to drive around with no doors, which will destroy aero and might not be legal where you live. Now we're starting to get closer to your original target weight. The transaxle weighs another 80lbs, but I'd leave that in place because it's going to be very useful.

Then it's just a question of how many batteries you want to stuff into this thing.

cheapcookie   10 W

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Re: custom geartrain to adapt 20 to 50kw in car

Post by cheapcookie » Jun 25 2018 4:21am

Thanks a lot for bringing me back to planet earth.
Honestly I was thinking more of 700kg when posting this.
I do realize its a steel chassis, despite not being a petrolhead.

Thanks alot for the links again, great stuff, thanks even more for the words.

I pretty sure I didn't mention range at all, but my requirement is 5-10 miles in a very urban setting with AAA in case shit happens.

All I really need is 20-30mph and torque for hills.

I need really power dense batts, lead acid could work honestly (maybe not lol).

Hope your motorbike goes along as well as my dreams ;), cheers.

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