Ben Nelson's Electro-Metro Build thread

[bennelson]

I went down into Milwaukee today for the EV build meeting.

There were lots of people there, and most of the work was on Swee's trike.

My car never even made it into the garage. However, both Brian and Tim took a look at my Metro with the idea of trying to figure out how many and where I can cram some batteries through the floor of the car in the back seat.

I think we can fit 7 batteries in a box sunk through the floor. It would be five batteries wide (about 35") with two batteries turned 90 degrees further back.

This should just fit in without cutting into the structure between the rear strut towers.

I should also be able to fit four batteries total in the radiator position under the hood.

That gets me to 11 batteries. I only need to find location for 1 more to get 72V parallel or 144V series configuration.
I think I can put one more under the hood. It would go over the motor in its own custom angle iron rack. Something like this:


Brian has a metal equipment cabinet which would make a great battery box. It would just need to be cut down to fit in the back of the Metro.

It's about time that I get some more power in my garage, so I am planning on adding a 240V 30amp circuit breaker and outlet. That way, other people can recharge EVs in my garage AND I will have a place to plug in welders and plasma cutters that people bring over.

Tom donated a 30amp twist-lock extension cord for me to get started on my 240V garage power.

Now all I have to do is figure out how to trick Brian, Tim, Tom, and Tim to come over to my house, and use all their time and skills on my project.

I am sure promises of Pizza will do....



[EDIT]
Almost forgot! Rich gave me some black coroplast, which should make a fine (matching-color!) belly pan. Tom had a big box of switches and buttons. I grabbed an extra-large button that I plan to paint red and use as my "Push in Emergency" button. It is a momentary-on switch, but I should be able to figure out how to rig it up as a contactor-kill-switch.

Also in that box of switches and things was a control box with a large dial marked "Torque". While the dial did NOT go to 11, I could certainly modify it to do so. I seriously considered grabbing it just to have a giant "Torque-Knob" for my dashboard.

PPS: The recharging energy for my 16.2 mile ride the other day came to 4.69KWhrs. That is about 50 cents of electricity, or 3 cents per mile. It calculates out to 126 MPGe, a little below my average, but still good, considering that it's winter, and I just increased my vehicle weight by 400 lbs!


Here is the button I grabbed from Tom's box 'o parts. It was just dirty plain aluminum.

How did I get it so candy-apple red? That's right, Sharpie® Red marker.

It should make a very nice EASY BUTTON. I just press it, and building the rest of the car becomes very easy.

[Tango Charlie]

Or you could mount it conspicuously in sight of the passenger seat and label it "EJECT".

I'm sorry to see you took the 'mark of the beast' on your left hand, there.

[MPaulHolmes]

That was funny, Tango Charlie!

[bennelson]

Originally Posted by Tango Charlie

I'm sorry to see you took the 'mark of the beast' on your left hand, there.

That's where I mark down my latest fuel economy, so I can't lose it.

Sort of a Polish Palm-Pilot.

[bennelson]

I was able to remove the rear-left spring from the Geo.

The spring when removed from the car is:
11" long
3.75 inches across inside the spring (hard to measure - I measured straight across with the top of the tape touching an upper coil, and bottom of tape to measure bottom coil)

The diameter of the spring itself is just a hair over 1/2 inch. (but less than 9/16)

The outside of the spring diameter is is pretty close to 4.75 inches.

The spring is 7 coils.


Also, I measured the height of the car, and then again after removing 4 batteries, which were pretty much right over the rear axel. The difference in height was 1.5 inches. I figure the weight of two of the batts was on this one spring (the weight of the other two batts was on the OTHER spring)

The batteries weigh 70 lbs each, so that means that 140 lbs compresses this spring 1.5 inches, or roughly one inch per hundred lbs, right?

Here are some photos
http://gallery.me.com/benhdvideoguy#101020

[MPaulHolmes]

To carry more weight, do you just replace the springs with larger diameter ones, or longer ones?

[bennelson]

I have no idea! I am asking you guys!


PS: I just cut a big hole through my car. It's real easy. Drill a couple of holes. Then another one right next to the first to make room for the saw blade. Rip a couple of big cuts with a cordless sawzall. POOF - a hole!

I made it big enough to fit my head through so that I would be able to easily see where things line up above and below the car.

The gray tube is plastic conduit which houses the cables running from the back to the front of the car. I made sure NOT to saw that in half while cutting this hole. (Please note that I did, of course, unplug my battery disconnect for doing this!)

This is an "exploratory" hole in the car. The final cut will be done with a plasma cutter, or at least using a straight-edge. I did NOT want to make too big of a hole right now, but I do need to figure out where the suspension lines up, etc.

Also, I may have to replace rusty brake line or do other work while it is easily accessible.








Now that I think about it, I HAVE built a super-eco-friendly vehicle. Just "Fred Flinstone" your way down the road!

[Tango Charlie]

Originally Posted by bennelson

Ya really gotta stop doing that. It's really really hard to stifle the guffaws that escape my cubicle when you post pictures like that.

Kudo's to you for continuing to fiddle with the Electro Metro to make it better!

[Christ]

RE: Springs

Ben, the spring rates actually get higher when you compress more.. the shorter the height of the spring, the harder you have to push to make it EVEN shorter... When you catch sight of spring rates on aftermarket springs, that's what they're telling you, is the average pressure necessary to compress the spring a given distance.

That said - Your calculation is about correct for what I know of most OEM small car springs... they're never more than 200lb/in.

One thing you could look into is just using springs from another small car that are *slightly* longer, and the car is slightly heavier... that would give you more preload once they're installed. You could also preload your stock springs (insert measured washers above them), but you'd have less travel in your suspension from doing so.

What you're probably going to end up being comfortable with is a set of *GOOD* adjustable coilovers, which you can usually find cheap on places like Craigslist or similar.

You can find very cheap ones on ebay which will last you a good time until you figure out exactly what you want to do weight-wise, they're about $60 shipped. You can get them from a Civic, Eclipse (some), Neon (hint hint stock springs hint hint) and several other cars, as they're "basically" universal blanks that are cut from a 300-400 lb spring stock.

You'll want to pay close attention to your stock ride height though. If you sag too much, you'll need even stiffer springs, or you'll certainly pop your shocks. Running too stiff of a spring will also wear on the shocks, so keep it as light as what will handle your load, or get better shocks. (Koni makes decent shock/coilover kits that will probably work for you if you can do some light modding.)

One thing you can do to make your car feel less "bleh" in the suspension is just to get a slightly stiffer sway bar. This will also help distribute sudden bumps and shocks across the suspension, so that one corner isn't taking all the abuse of a hit, and there's some distance to absorb part of the initial shock.

If you can find cheap progressive rate coils, that would be your best bet... they keep a standard spring rate until they are compressed, at which point the spring rate begins to multiply by a factor of compression. You can tell these springs from others by the winding, as they're not all the same depth/diameter per coil.

I hope this helps a bit, good job so far on the car Ben. Keep it up!

[TestDrive]

Originally Posted by MPaulHolmes

To carry more weight, do you just replace the springs with larger diameter ones, or longer ones?

First so it doesn't get lost in the bloviating -
Ben, have you considered checking the electro-metro's axle weights on a truck scale (local grain elevator will have one) and comparing them with stock metro specifications?

Aside from additional springs (inside current spring, around shock, other), there are four basic possibilities: heavier, longer, tighter windings, variable rate. (You could also have combos like longer and heavier, but we'll kind of ignore that.)

Two times longer fixed rate spring will carry twice as much weight, but good luck fitting it into available space.

Two times heavier (not 2x increase in spring stock diameter, maybe ~1.3x ???) will carry 2x the weight, but will ride like a lumber wagon.

Twice as many windings with same size spring stock won't carry 2x the weight (sagging stress failure) and will ride like a lumber wagon.

A variable rate spring could be made from the same spring stock and it would not carry 2x the weight, nor as much weight as a 2x as many windings spring, but it would not ride like a lumber wagon. Using a slightly heavier spring stock and variable rate windings you can get a spring that is the same length, carries 2x the weight and doesn't ride like a lumber wagon. (Ok, that's an exageration. If it's carrying 2x the weight, it's still going to ride like a lumber wagon, but it will ride better than all the other alternatives.)

For anyone that isn't sure what is meant by variable rate spring, here a picture of a variable rate (top) and a fixed rate (bottom) spring.


Lets assume the springs in the picture are made from the same diameter spring stock. (They appear to be close.)

If 140 lbs will compress that fixed rate spring 1", 280 lbs will compress it 2"; 420 lbs - 3"; 560 lbs - 4" ... The numbers for the variable rate spring would be something more like: 140 lbs compresses spring 7/8" (less than the fixed rate spring as even the loosest windings are tighter), 280 lbs - 1 5/8"; 420 lbs - 2 1/4"; 560 lbs - 2 11/16" ...