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T-Bucket inspired tandem seater with a roof

3383 Views 7 Replies 3 Participants Last post by  Darxus

Years of my babbling about vehicle design: - includes a video loop panning around this car.

This is more simple and fun than my previous plans. I guess I want to show people that electric cars can be fun, to encourage them to switch. Plus, have a fun car, that I understand and can fix every last bit of. And enjoy the process of making it.

I'd appreciate all kinds of feedback.

I realize this is an ambitious project, likely to take years. I'm planning to weld the frame myself, and I haven't even welded.

NetGain Warp 9 motor: $2,074 (just behind rear axle)
Soliton 1 controller, 1,000 amps continuous: $2,899 (behind rear axle)
48 160ah prismatic lithium cells, 144v = $9,627 (front, yellow block)

Lots more than I'd like to spend. I think I'll save buying those parts till the end.

Those three components plus the driver are positioned so that the weighted average of their locations is centered between the two axles. For 50:50 axle balance, therefore balanced steering at the limits of traction. (Passenger will bias the weight toward the rear. And of course there's all kinds of stuff I haven't accounted for.)

One of my higher priorities is being able to spin the tires. But I want to bolt the motor directly to a rear differential, so I'm a little concerned about having enough torque without a transmission.

Motor goes up to 5,000 RPM. The most reduction I've seen in a diff is 4.9:1, which works out to 96mph max, which sounds fine to me. Does that leave me enough torque to spin the tires from stopped? I'd prefer more gear reduction. 5.9:1 would give me a max of 80mph. I wonder how NetGear feels about doing different windings for more torque (more winds and fewer turns = more torque).

This bug has the same components (slightly smaller pack), can spin the tires, and will go 90 miles when babied. But has a transmission. But probably also weighs more?

I really don't want a front bumper, but that seems to be required by New Hampshire law. Although it looks like they can be very minimal, like a bit of 1" thick pipe. I was thinking about putting bumpers on the fronts of the fenders, since the nose doesn't stick out past them. But I think it might be better to extend the body out past the fenders, and put something like 1" thick by 4" tall rubber across the front. I'd really like ideas here.

Looks like all New Hampshire law relevant to titling a car is here:

I need to work out the suspension details (arm angles). I'm thinking dual wishbone, with push-rods to cantilevers to inboard coilovers (formula 1 style). I'd like to get the uprights / knuckles (and disc brakes) from a junk yard, but needing to attach fender supports might require fabricating them.

How should I do the windshield wiper? Windshield is an inconvenient shape. I could get the thing to rotate the right way with two rods attached at wider points at the base.

Which kind of welding should I use? For a square tube space frame. TIG is sexy, slow, and expensive. Stick... would probably work just fine?

I'm thinking of pivoting the hood and the canopy both just above where the firewall would be, between the driver and battery pack. Make the whole front end pivot up, for easy access.

I know I could really easily significantly improve the aerodynamics, especially at the front end. (I know about laminar vs. attached flow, and Sears-Haack bodies.) But... I keep coming up with stuff that's insanely difficult to make, or ugly. I like the way this one looks. Gives me shivers.

How does this have anything to do with a T-bucket? Take a T-bucket, remove the bucket / seating. Add tandem seating and a full length body. Add a roof. Replace Model T frame with space frame. Convert to electric. (I still need to lower the seating position because there's no-longer a drive shaft in the way.)

My last ancient thread, never built anything.
I need to re-read that, lots of good stuff there.
Stuff in that thread was structurally complicated and efficient. My new one is structurally much simpler and more fun.

So much to learn.

I've been doing my modeling in blender, which is free. I wish solidworks wasn't $4,000.
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Tires in the model are 245/75-17, apparently common on light trucks in 2012.

Go modern - stick a Leaf motor unit in the back and use Leaf cells

That is what I would do if I was starting now
You smoke tires in a bug because they are generally only 175 to 195 wide.

A ford diff can be had up to almost 6 to 1 with aftermarket richmond gears.

New Hampshire might have a class of vehicle normally called replica, or get it titled in a state that allows one-offs and import it in.
I'm feeling really discouraged. I don't feel like I can make this work (not look dumb) with a front bumper. And that seems like a really unfortunate reason to give up on this. I'd really like suggestions.

And I'm also really concerned about having enough torque, without a transmission, even with an ideal differential gearing. Without spending a lot more money on components.

Hmm, I bet it would work to add another motor ($2,074), double the pack voltage, and halve the amp hours. This page says Warp 9s can't take more than 144 volts, so doubling pack voltage, and running them in series, so they get the same voltage (and amperage) makes sense. And the Soliton 1 can handle that.

And I bet if I want to do each motor driving a drive shaft independently (instead of a mechanical diff), I don't want to be using NetGain motors, because they behave slightly differently depending on the way they spin? They at least recommend different brushes depending on rotation. Are there motors better suited to that?

You smoke tires in a bug because they are generally only 175 to 195 wide.
I was thinking about asking the guy with the bug what gear he was in and trying to work out his total ratio, but figuring out contact patch size would clearly also be important, thanks.

A ford diff can be had up to almost 6 to 1 with aftermarket richmond gears.
Oooh, that's great info, thanks. They apparently do up to 7.17:1:
And they do 5.71:1, which works out to 82.4mph, which is perfect as far as I'm concerned! And just knowing that ratio exists allows me to search for other things providing it. Here are nine differential gear sets in 5.71:1:

New Hampshire might have a class of vehicle normally called replica, or get it titled in a state that allows one-offs and import it in.
I've read through a lot of the law, which I linked to in my first post. Replicas don't seem to get much more leeway: "(b) All replica antique vehicles shall comply with the laws, rules and the manufacturer's specifications of the passenger vehicle chassis on which they are based."

But I could use a Model T frame, just like an actual T Bucket, and get those benefits. I think. Ugh. Those frames are terrible - practically four square tubes welded together. Oh right, they're not even tubes, they're three sided channels (no bottom).


Go modern - stick a Leaf motor unit in the back and use Leaf cells

That is what I would do if I was starting now
Thanks. That's about what I've been looking into, due to reading through your thread. I've been having difficulty finding Leaf batteries available though. I wonder if that's because of Nissan's plans to collect them to build household batteries.
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Bumpers (simple rubber, seems to be adequate for NH law). What do you think I should do about this?

I tried modeling two Warp 9s, but that much weight behind the rear axle is really tough to balance.
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First ignore the voltage limits on the DC motors - they are not relevent

You can get a ton of torque out of a DC motor
My car is 900 Kg with me in it, 55% of the weight on the rear, 215/45/17 tyres, 4.1:1 Diff, direct drive - no gearbox
And I can smoke the rear tyres!

I am assuming that you intend to build something lighter! - so you will need less torque
Thanks Duncan. I guess I haven't been thinking about yours because we don't know the official specs of the motor. But it's probably mostly a matter of amps + efficiency, and a warp 9 is probably not substantially less efficient than yours.

You have 1200 amps, I'm planning on 1000. You have smaller contact patches. But I'm planning on more gear reduction, and I do hope to end up with a lighter car.
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