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Learning how to build Lotus Seven replicas...together!
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PostPosted: January 19, 2020, 9:24 pm 
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Location: San Diego
Major Parts List (costs exclude tax):
Tesla Model S FDU 1035000-00-F with full length HV cable, throttle pedal, brake switch $2,500
Tesla Model S front left axle (x2) $450
Tesla Model 3 rear uprights (x2) $240
1", 1.5", 2" 16ga steel tubing $150
1" x 0.095" DOM steel tubing $84
Open Source Logic Board $400

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Autobahn Used Tesla Parts, El Cajon, CA - very honest, helpful.
Belmetric - metric fasteners
McMaster-Carr - everything else
Leaf Sales, Chula Vista, CA
Industrial Metal Supply
Online Metals
Good-Win Racing, Chula Vista, CA
EVBMW - Damien Maguire




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Well, I decided to pull the trigger with my second locost build, a decade after the first. This will be a Haynes Roadster sized build with a Tesla Small Drive Unit. Up to 300 hp depending on battery arrangement, 248 lb-ft of torque. I will copy the first build but modify the build with a few minor changes. Here's the first build, pictured yesterday as I left to go pick up the Tesla drive unit:
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Here is the new drive unit:
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Martin


Last edited by hassleweed on March 29, 2020, 11:07 pm, edited 3 times in total.

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PostPosted: January 19, 2020, 9:30 pm 
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The drive unit is a front unit from a 2016 AWD Model S. It will fit well with the standard Haynes dimensions, but first order of business is the purchase of an alternative bracket you see in the photo above on the far side. As far as I can tell, the bracket used on the Model X has less of an offset. The motor is the same. The bracket will arrive on Friday so we'll wait and see. If it has less offset I'll gain an extra inch or two to play with on the passenger side.
Martin


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PostPosted: January 19, 2020, 11:19 pm 
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Interesting.

Using a Tesla battery then I'm assuming. Curious what the range will be like on such a light, yet aerodynamically awkward car.

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PostPosted: January 20, 2020, 1:06 am 
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My research suggests that in order to go lightweight with enough voltage to run the Tesla motor I need to avoid the Tesla batteries and go for something like LG Chem modules. Range is not a priority as I plan to try and focus on this being a quick autocross car. It will be interesting to see what I get out of a 16kwh pack. Probably 30 - 50 miles. Might go further in reverse with aero playing a factor!


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PostPosted: January 20, 2020, 11:25 am 
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I'll be watching your build closely! I've been mentally rolling around the idea of an electric scratch-built car, but (currently) feel that it doesn't work economically (unless an electric drivetrain falls in your lap). My current hang up is "what does an electric version get me that a gas one doesn't?", and I don't really have an answer. I'm very impressed by the Performance Model 3, but it's 4000 lbs of weight to lug around corners, which in my mind makes it inappropriate for extensive cornering (though I do wonder how it would do at the Virginia City Hill Climb...).

That said, for a specific venue, such as autocross, it makes a lot more sense due to its low noise and low range requirements, but since I no longer do autocross, that advantage is lost on me. Your project should be very revealing as it's on the cutting edge (as these things go) and will probably get you into some magazines. FWIW, I'm got a thread on my builders' forum where we're discussing the merits and costs of just such an endeavor - http://www.midlana.com/forum/viewtopic.php?f=30&t=1055

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PostPosted: January 20, 2020, 12:42 pm 
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I'll be following this new build with interest, Martin. The electric "bug" hasn't bitten me yet. I'm still happy with fossil fuels, perhaps because I'm approaching "fossil" age myself.

I wonder if California will require that you have a noise generator? As a cyclist, I can tell you electric cars are the most feared - you can't hear them until they run over you [LOL].

Best of luck,

Lonnie

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PostPosted: January 21, 2020, 9:29 am 
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A young fellow named David Marcus that has autocrossed a Tesla Model 3 with us at SGMP won his class at the SCCA National Championships. Heavy batteries and all, he out ran the rest of the class, which I'm told included a Lotus and several "M" series BMW's. Given an overall lighter car to tote around and lighter batteries, it should be a little (silent) screamer!

:cheers:
JDK

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PostPosted: January 23, 2020, 10:36 pm 
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KB58 wrote:
I'll be watching your build closely! I've been mentally rolling around the idea of an electric scratch-built car, but (currently) feel that it doesn't work economically (unless an electric drivetrain falls in your lap). My current hang up is "what does an electric version get me that a gas one doesn't?", and I don't really have an answer. I'm very impressed by the Performance Model 3, but it's 4000 lbs of weight to lug around corners, which in my mind makes it inappropriate for extensive cornering (though I do wonder how it would do at the Virginia City Hill Climb...).

That said, for a specific venue, such as autocross, it makes a lot more sense due to its low noise and low range requirements, but since I no longer do autocross, that advantage is lost on me. Your project should be very revealing as it's on the cutting edge (as these things go) and will probably get you into some magazines. FWIW, I'm got a thread on my builders' forum where we're discussing the merits and costs of just such an endeavor - http://www.midlana.com/forum/viewtopic.php?f=30&t=1055


Thanks Kurt. You are right about performance/cost. It is not the deciding factor for me, although I am aiming for a pretty tight budget. It is the flat torque curve bug that has got me, the lack of attention-grabbing noise, and the desire to learn something new. I am a firm believer in continually learning but I need a decent incentive to do so! I also had a rough year last year, and just like my first build, this project will be good medicine.

As to the performance characteristics, I have thought a lot about what the end goal is to be. My rough calcs indicate that I can build the car within 1,400 lbs. That's just 50 lbs heavier than the first build, with 2.5 times the HP and 2+ times the torque. The weight wil be rear biased. Range will suck at between 30 and 50 miles. But that is what I am conceding for an agile electric car (as opposed to the dragsters so far).

Thanks for the comments and the link to an interesting discussion.
Martin


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PostPosted: January 23, 2020, 10:39 pm 
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Lonnie-S wrote:
I'll be following this new build with interest, Martin. The electric "bug" hasn't bitten me yet. I'm still happy with fossil fuels, perhaps because I'm approaching "fossil" age myself.

I wonder if California will require that you have a noise generator? As a cyclist, I can tell you electric cars are the most feared - you can't hear them until they run over you [LOL].

Best of luck,

Lonnie


Lonnie! Great to hear from you. It's got to have been nearly 10 years since we met! A noise generator might be a lot of fun...so many options to choose from! I promise it'll be worth getting run over.

I've checked in on your build from time to time, a work of art!
Best
Martin


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PostPosted: January 23, 2020, 10:41 pm 
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GonzoRacer wrote:
A young fellow named David Marcus that has autocrossed a Tesla Model 3 with us at SGMP won his class at the SCCA National Championships. Heavy batteries and all, he out ran the rest of the class, which I'm told included a Lotus and several "M" series BMW's. Given an overall lighter car to tote around and lighter batteries, it should be a little (silent) screamer!

:cheers:
JDK


You got it JD! That's what I've been craving. A torque monster following Colin Chapman's principles as far as possible.
Cheers
Martin


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PostPosted: January 23, 2020, 11:30 pm 
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Well the first experiment has been completed. The passenger side mounting bracket from the Model X arrived. In the photo on the left is the original Model S bracket, the right is the Model X. You can see the Model X is "shallower", offering a narrower overall drive unit, however the orientation is a little different, putting the rear mounting hole lower on the chassis. Not sure if that will be beneficial or not at this stage. I tried flipping the Model S bracket over, but sadly the bracket clashes with the motor housing.
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PostPosted: January 24, 2020, 12:42 am 
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https://www.youtube.com/watch?v=krD4hdGvGHM

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PostPosted: January 24, 2020, 10:42 am 
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B85 wrote:

:D


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PostPosted: January 25, 2020, 10:46 pm 
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Today was a productive day. I built half of the build table. Why half? I only had enough steel to make half, and I think I will be spending a lot of time fabbing up the rear end where the drive unit will be, so a 4ft x 4ft work surface will be plenty for now. I also have a space issue in the garage so I built the table tall enough and wide enough to drive the front 2/3 of the original 7 under it. The next project involves continuing to make wall cabinets to get stuff off the floor. You'll note the plywood has the chassis layout from the original build.
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PostPosted: February 4, 2020, 10:29 pm 
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So things are starting to get interesting.

First up, axles. I bought two Model S axles from my supplier with the thought of having someone shorten them. What kept bugging me though was that if the axles become "consumables" to torquey torture, then having to have specially made axles would be a killer. I happened to be looking at aftermarket axles (which are now available) and remembered that the front motor is not centered in the Model S, therefore the front left axles are shorter - 4 inches shorter. My supplier had a pair and kindly agreed to swap them (+ cash as they are in high demand). So it looks like hub face to hub face dimensions will be around 60 inches.

Secondly, the Model S hubs are 5x120mm bolt pattern which is not great for wheel options. With the NC Miata at 5x114.3mm, it was a nice surprise to discover the Model 3 is the same 5x114.3mm. But will it fit the Model S axle? After much eBay reverse engineering via photographs, it looked like the Model 3 hubs have the same splice count as the Model S. So I took a $70 gamble and ordered one through eBay. It arrived and slid on just perfect on the Model S axle...with one minor issue. It would not slide on all the way as I believe the Model S hub is wider:
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After pondering what to do I searched for a spacer/bushing that would work to fill the gap with the backside of the hub and the outer end of the CV joint. I have ordered what will look to work - an inner race for a bearing. I'll report the success or otherwise of that effort.

Lastly, I built a cradle for the motor on Sunday that holds it as near-as-damnit in the orientation it will be in the car, matching the orientation from the Model S:
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After assembly I decided to try fitment of one of the axles. This was a heart-sinking moment. The front motor, as mentioned earlier, does not sit central and it therefore has a short 'stub' axle held by a bracket on the right side. When I tried to install the left side axle, it clashed with the cast nubs that hold the bracket on. What's worse, it looked to clash with a bolt flange right next to the differential. However, it did look like the CV casing was machined just enough to bypass this, but I wasn't sure. After nervously filing down one of the nubs enough to get a feel for if the axle would fit or not (damaging the nub would result in the motor case being worthless to anyone else), I took the plunge and pulled out the sawzall.
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Thankfully....:
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Meanwhile, at the front end, NC Miata spindles have been sourced and are on their way. I really hope I can figure out ball joints and rod ends for them.

Later
Martin


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