Ben Nelson's Electro-Metro Build thread

[Tango Charlie]

72 volts, baby! Woo Hoo!
Very, very, very cool.
(dress decorum aside.)

I can't wait to see what your range is. Any calculations?

[bennelson]

Hey Baerfoot,

It's been a while since I checked your build blog. Thanks for the ideas.

One thing I found out on this car is that since it doesn't have air conditioning, all the holes are still there in the firewall for it, but they aren't used. They just have little plastic plugs in them.

Pop those out and you have a pre-made hole for running wires into the engine compartment!

[MazdaMatt]

Re: brakes.

I highly recommend doing some research into a non-power brake system. It is a simple matter of master cylinder and pedal pivot point. A sketchy system is okay for 'go' but not for 'stop'.

[johnmyster]

My '90 Supercharged Thunderbird used an electric pump and accumulator system to get power brakes without using vacuum. Supposedly Toyota has used those in recent history, for instance on a '05 4-Runner.

Perhaps a non vacuum assist master cylinder (race car supply) could be improvised.

Air brakes? Anybody?

[bennelson]

Well, since the car originally had power brakes, I will try my luck with home-brewing up an alternate source of power vacuum.

I have at home right now:
a coffee can
electrical tape
caulk
an aquarium air pump and hose

Think I can rig up something with that? It will be just like that scene in the movie APOLLO 13 where they have to jerry-rig the CO2 scrubbers....

[johnmyster]

Well,

My memory is rusty, but I think vacuum boosters work because they have vacuum on BOTH sides of the diaphram. Then, when you push the pedal, you allow atmospheric pressure to push against the back side. The harder you push, the harder you spring-load the inlet regulator, and the more pressure the side facing you gains. That's the "squshing" sound made when you tap the pedal - air rushing in on your side.

Maybe you could more easily have power assist by using compressed air. Think about it. The vacuum system works with less than 15 PSI of differential. With a few old freeon tanks at 120 psi, you could probably do quite a bit of braking if you only needed 10 or 15 psi of pressure on your side. You'd recharge on air at the same time you recharged your batteries.

You'd be a ground breaker if you figured out how to do this. The booster system itself is pretty simple. If I had junkyard resources, I'd start tinkering with one myself.

I'm just thinking that an electric pump is going to be a bad way to spend your watts. And if you had to do it on-board, it'd be better to have a compressed air pump than a vacuum pump.

They guy on here with the beetle could even use compressed air from his spare tire - an old VW joke...

[bennelson]

Hey Johnny,

I had kinda thought about some of those same things.

If you have a little air tank, it would be a great way to store up air while recharging, then use it to run the brakes while charging.

I had to look up power brakes on "howstuffworks.com" to finally get how they really work - and it's the atmosphere pushing that really does the hard work.

If I could replace that will compressed air, that should work fine.

I am just playing around with it right now.

(The caulk seals on the coffee can is drying right now...)

[johnmyster]

Seriously Ben,

If you figure this out - even if you have to have a local handyman help you weld up a modified vacuum booster - this could be your big contribution to EV conversions. You could supply these bad boys to conversion types pretty easily. If you figured it out on a metro and for a S10, you'd have most of the EV conversion market covered. Plus, if people don't have engines under the hood, they'd have plenty of room to mount up your booster/master cylinder unit in other types of vehicle.

Oh I wish I had a shop. I'd grab a booster from the Pick-A-Part tomorrow and get on this. An "air over hydraulic" setup - where you actually have a mechanical linkage present for backup.

I can store 10 atmospheres in a tank pretty easily - but you can only store one atmosphere of vacuum. That's the huge advantage. You could regulate down to 10 psi of line pressure and probably get significant use out of the thing. If not, a pressure switch turns on a small pump and spends a few watts to get you back up to pressure. Air compressors that guys use for airbagged suspensions on cars are pretty affordable and built to make 150 psi or more. Plus, that market would be an easy source of 5 to 10 gallon tanks - which, you have plenty of room under your hood for.

This is the type of thing that Mullet or Schultz could bang out in a jiffy.

[metroschultz]

Whadya say JM?
Weekend project in 2.5 weeks?
I may go to Pick-N-Pull this weekend and see what they have for boosters.
I have tanks and a regulator.
Hmmmmmmm
S.

[bennelson]

I experimented with a coffee-can vacuum canister and aquarium air pump for my electric car power brakes.

See the results below!

YouTube - Electric Car Power Brakes Experiment