The Real Deal

Filed under: Random Musings — Chris at 5:00 pm on Tuesday, January 10, 2006

Sometimes it’s helpful to take a step back, stop obliviously patting yourself on the back and take a look at what you’re really doing and how it compares to what other folks are doing. Helps keep you from getting a swelled head unless you really deserve it.

I like to think of what I’m doing as building a sort of hotrod pickup truck. Or as first suggested back in 1998 by the GhiaMonster’s Steve Marks, a “wattrod”. Although a lot of the techniques involved are unique to a high-performance vehicle with an electric powerplant, most of the real work is typical hotrod stuff. Identify the stock parts designed for fabrication economy and driver comfort, which will fail under extreme stress, and replace them with stronger and more expensive parts that won’t. As much as I’d like to think I’m doing something unique, the reality is that most of this is stuff people have been doing for decades.

So let’s pick a standard with which to compare my efforts here. Being no expert at all and having no real insights as to what qualities such a standard should possess, I’ll pick an S-10 project I randomly stumbled on via Google. Now this project may or may not be exemplary of the highest levels of the art; it might be fairly average in the scale of what folks have done to their cars in the name of quick acceleration and high style — I honestly don’t know. But to someone with a background as non-automotive as mine, who only a few years ago found a high sense of accomplishment in changing my own motor oil, a project like this puts this fellow among the pantheon of car-hacking gods. Looking at what he started with and how it finished, one cannot be unimpressed. Merely on the basis of the effort and skill involved in its construction, whether you agree with its aesthetics or not, this is one sweet vehicle. Will the Ohmbre be this awesome?

The short answer is “Um … Sure.

The more detailed answer we’ll explore here is “Absolutely not, for the following reasons.” My honed HTML coding skills will now impress you with some more bullets.

  • Talent. I don’t want to dwell on this, but we need to get it out of the way. This guy has it. If I attempt my own paint job for example, the truck will invariably end up bar-coded in drips and runs, perhaps some in paint colors I don’t even have. It’s only a question of the viewing distance from which the result would look respectable, and I’m not betting on anything closer than twenty feet.
  • Design goals. This at least sounds a little more legitimate, but may in fact be a bargain with mediocrity. I’ve chosen to make the Ohmbre into a street/strip high-performance demonstration vehicle, which will involve a mixture of features that don’t entirely fit in the domain of racing. Notice here the tubs for the wheels and rear axle. Also note how the fuel cell is placed behind them in the bed. All together, this means that the vehicle is no longer useful as a truck — it’s now a full-blooded two-seat dragster in the shape of a truck. My goals include retaining the bed and the use of the truck to haul large items, so this level of modification will not be a possibility for me.
  • EV-specific compromises. The fact that this vehicle will be battery powered introduces a major source of design compromise, especially given that this will be a converted gasoline-powered vehicle, not one designed entirely to be electric. Fitting batteries is a task that requires locating space for them. Rectangular space, the sort that’s really hard to find in quantity within the rounded envelopes of today’s cars and trucks. And a high-performance vehicle like mine which is to store a large quantity of batteries, obviously needs as much space as I can find. One of the reasons pickup trucks make ideal conversion platforms is the high availability of such space between the frame rails under the bed. Forward of the rear axle, batteries can be stored in boxes mounted to either side of the driveshaft. So, the S-10 is a particularly good platform since its frame is spaced wide — wider than the Ford Ranger, for example. This means however that modifications like this narrowed frame, built to provide more width under the bed for huge drag tires, will not be an option. If my tires are to be any wider than the wheel wells, they will have to stick out, or I will have to flare the sides of the bed.

So there are some limitations — some naturally occurring and some arbitrarily self-imposed. Still, my primary goal is to develop a vehicle that will be somewhat useful in light duty, which I will enjoy driving, and which will provide a “test bed” for further developments and an effective and positive conversation piece with which to introduce to others the possibilities of minimally-polluting transportation. And I think I’ve got a better than average shot at pulling that off.

4 Comments »

20

Comment by Tom Kirkley

January 13, 2006 @ 1:17 pm

Chris,
Just a short note to let you know I e-mailed the owner of the S-10 you refer to above, and he thought it was cool! That S-10 is running low 7’s with a hurt engine, just think what it will do with a healthy engine.
You might need to run a 275 series Drag radial to have a little traction, they may require a small tub to fit. If you are hitting them with 900+ lb-ft of motor torque they may just go up in smoke, so by two set at a time.
Keep up the good work!

21

Comment by Chris

January 13, 2006 @ 2:14 pm

Wow, cool! Thanks for making the connection there.

Honestly though, while I’m seriously concerned about getting the power to the ground, it’s more due to my lack of available width for decent tires (since I can’t really narrow the frame or do tubs), than for the actual torque that the rear wheels will see — at least for the time being.

Although a transmission is among my plans for the future, not having one to begin with significantly reduces the final torque. The torque from the motor itself will be just crazy according to my projections, but it won’t be multiplied before going to the rear end. I have a 4.11 gear set for the rear, but this is still the equivalent of about “3 1/2th gear” compared to stock. Bear in mind though, my friend’s MR2 with half the available amps and an 11″ motor, can bark the tires in 4th with warm batteries — or “will again” anyway, once we rebuild the poor abused tranny. :o)

For what it’s worth I have a crazy idea for a motor hack that might provide me with a significantly lower “gear” in an electrical sense, beyond what’s available even with this motor’s dual field. But it’s a long shot and might not even work (or might damage the motor, etc).

For the time being though, assuming a continuous motor torque of 1100 ft-lbs at 2000A (which I think is conservative), you’re looking at a total 4521 ft-lbs at the rear axle. 2260 per wheel. Respectable, but not really that much I think, in the context of drag racing.

The good news is that I’ll be able to hold that torque continuously from 0 RPM to wherever the knee in the graph ends up as the controller exits motor current limit — and not knowing quite where that’s going to be is part of the fun of being a seat-of-the-pants early adopter.

22

Comment by Ryan

January 15, 2006 @ 10:44 am

Just put some 26×10.5×15 ET Streets on it. If they can fit in a Mustang’s tiny wheel wells, I’m sure they will fit on your truck.

http://www.mickeythompsontires.com/strip_et_street.html

That tire has the most traction of any DOT tire’s. Or use a 28″ tall tire or taller for even more contact patch..

23

Comment by Chris

January 15, 2006 @ 11:26 am

My chosen ratio is based on a 30″ outer tire diameter, which is what you see in the pictures, on the rear wheels at least. The front tires are a weird size, a little smaller in diameter. When I had to change the rear tires to get the truck to pass inspection (back when I was still driving it), no one in town had tires like what were on the truck.

So, I’m hoping to find something in that size. Initially I’d like to get something that will fit the wheels I already have (which are 15 by 8.5). The 30″ ET Street tires on this page are for 10″ wide wheels, I don’t know if 8.5 would be too much of a stretch to be safe.

Ultimately though, it looks like these tires are the way to go. I like that they use tubes, so I can get the PSI nice and low without worrying about losing air. Also nice that they’re wrinkle wall. Until I can justify the cost of new wheels though (which will have to be after the truck is on the road), I’ll go with the BFG or Nitto drag radials.

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