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Discussion Starter · #1 ·
Hi everyone,

I have been reading for a while, but wanted to finally register so I could start asking some questions and getting feedback

In true DIY fashion, I have a completely self-built Lotus 7 replica (aka 'Locost') that is street legal, but its primary use is Autocross. It is presently powered by a Yamaha R1 engine, and I would very much like to do an electric conversion at the end of the 2022 season (Not going to do it this season as our club's insurance has stated they will not allow any EVs to participate this year, so it'll be a fall/winter project). Not really concerned about range, so I'm probably going to be looking for the lightest battery that can supply the needed voltage and current. The car weighs 1200 lbs as it sits now, and I'd be happy if I could keep it within ~100 lbs or so of that weight. Some rough math tells me the ICE components coming out should be weighing in around 325-350 lbs.

Right now I'm favouring the Hyper 9 motor, but need to figure out a gear reduction. If I were to connect it straight to the driveshaft, even with the tallest available gears in my rear diff, it would have a theoretical max wheel speed of around 150 mph, haha. The other option I would really like to explore is a Leaf EM57, but I don't think I can feed it enough voltage without going with a much heavier battery, and the same issue of gearing still applies.

Anyway, I hope to be an active member and look forward to doing my first ev conversion!


Pic of the car:
Tire Wheel Vehicle Car Sky
 

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Think Duncan one of the admin here does Autocross in a Lotus 7 replica?
Later floyd
Yes I do
Its not very fast - but that is because of the driver!
This is my thread

The thread takes you through over 10 years of me making mistakes and changing things

I'm using an 11 inch Hitachi forklift motor - no gearbox - and most of a Chevy Volt battery

With 1200 amps and 340 volts .....

Its a bit too heavy at 800 kg - I overbuilt it a bit too much

Great fun on the Autocross and embarrassed a few people at the drags - 12.2 seconds and 109 mph

If I was starting again I would be seriously thinking about a Leaf (or Tesla) drive unit in the back -
but I would probably stick with a Chevy Volt battery as its quite light for the voltage and the power you can get out of it
 

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Right now I'm favouring the Hyper 9 motor, but need to figure out a gear reduction. If I were to connect it straight to the driveshaft, even with the tallest available gears in my rear diff, it would have a theoretical max wheel speed of around 150 mph, haha.
Okay, but for autocross why would you choose the tallest gears? "Tallest" means least reduction ratio, so highest road speed for a given motor speed. For performance you want the shortest gearing that allows the vehicle to reach the required top speed.
 

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Discussion Starter · #5 ·
Yes I do
Its not very fast - but that is because of the driver!
This is my thread

The thread takes you through over 10 years of me making mistakes and changing things

I'm using an 11 inch Hitachi forklift motor - no gearbox - and most of a Chevy Volt battery

With 1200 amps and 340 volts .....

Its a bit too heavy at 800 kg - I overbuilt it a bit too much

Great fun on the Autocross and embarrassed a few people at the drags - 12.2 seconds and 109 mph

If I was starting again I would be seriously thinking about a Leaf (or Tesla) drive unit in the back -
but I would probably stick with a Chevy Volt battery as its quite light for the voltage and the power you can get out of it
Hey, yeah I took a look at your thread and watched some of the videos. It looks like a blast! I agree a MR setup with a Leaf or Bolt drivetrain could be pretty awesome. Not enough room to fit it back there in a book size Locost frame, unfortunately. Unless you ran it backward and solved the oiling issues, maybe. Nonetheless, I don't think I want to explore that too much for this build.

Good tip on the Volt batteries, those look pretty promising. 3 of the 48v modules in series would get me to 144v (perfect for the hyper 9), and if I ran them in 3s2p it looks like the current output, capacity, and weight would all be about right?


Okay, but for autocross why would you choose the tallest gears? "Tallest" means least reduction ratio, so highest road speed for a given motor speed. For performance you want the shortest gearing that allows the vehicle to reach the required top speed.
Brain fart, shortest was what I meant. The car uses a narrowed Ford 7.5" out of a Ranger, so chosen because it would easily accept Mustang disc brakes and much lighter than the more common 8.8. So the shortest gears I can get for it seem to be 4.56. After a ton of looking around, I am tempted to just direct connect it to the rear end with a set of 4.56 gears and see how it feels. The wheel torque is still higher than the R1 engine* across the entire speed range. Next step is to look at how best to attach a driveshaft without adding unacceptable levels of radial or thrust loads to the motor shaft...

*Adjusted for my altitude, and using the current 3.45 gears
 

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Hi Zeig
I'm a bit (a lot) scathing about the Hyper9 - seems like a lot of money for something that is not as good as a forklift motor

I paid $100NZ for my first motor - $150NZ for my second motor and $200NZ for my spare

My overall belief is that the old DC motors (forklift) are great for a cheap and cheerful build
I give up two things -
(1) Total motor life - I will need to change the brushes eventually
(2) Re-Gen
For a Locost and using it on the track - I don't think either is important

If you want to go a step up from there the you should go straight to a motor and inverter from a production EV

With a DC motor you can stuff a ton of current into it and get oodles of torque - as the revs rise you do need more volts

I'm running 84S - 300v - 340v at the moment and I'm trying to fit the last module which will make it 96S - 350v -400v

As far as final drive is concerned I have a Subaru LSD - 4.1:1 - I'm looking at changing it for a 3.9:1 diff
Direct drive just a short propshaft
I have got effectively excessive torque at Autocross speeds anyway - But I would like a wee bit more speed at the drags

Volt Modules
I am very cruel to my Volt modules - but even hitting 1200 amps they only have about a 20% sag
If you do go for a low voltage (144v) setup I suggest using 3 modules only - and setting up a quick change setup
Keep the other modules back with the trailer and fit them after the first set is down a bit
That will save about 60 kg - well worth it
 

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Discussion Starter · #7 ·
Oh, wow, that is good performance indeed! I guess I didn't realize you could extract so much more power than what's on the nameplate. Need to do more reading and some calculations, if possible. Are there any good reading materiels that you'd recommend?
 

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Oh, wow, that is good performance indeed! I guess I didn't realize you could extract so much more power than what's on the nameplate. Need to do more reading and some calculations, if possible. Are there any good reading materiels that you'd recommend?
There is a long thread on the motor section about forklift motors - worth a skim

The basic thing is that the motor is rated at a certain power for an hour - my motor is 10 kw
That is at 1400 rpm
So at 2800 rpm and the same current - the heating will be the same but the power wil be double
AND I'm shifting twice the cooling air - so I can afford twice the current - so four times the power

But I'm not hitting high power for an hour - I'm hitting high power for a few seconds
So 40 times the power seems to be OK

I did melt one motor - but examining the damage I think that I had put a scratch in one of the windings and it had failed from there

Two things
They have stopped using DC motors in forklifts - you need to grab some NOW
The controller I used is no longer available - I would LOVE to replicate it but I don't have the electronic skills
You can still get a "Zilla" but its expensive -
 

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Discussion Starter · #9 ·
Awesome, thank you! Yeah I found that thread and have been reading. I do need to get a better feel for how to estimate how much I can extract from a given motor with a given battery, but I will keep reading. Always good to have multiple options on the table. I also grabbed an ebook called "Build your own electric vehicle" that was recommended by Thunderstruck - looks like it has some great theory in it. Looking forward to learning more!
 

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... I agree a MR setup with a Leaf or Bolt drivetrain could be pretty awesome. Not enough room to fit it back there in a book size Locost frame, unfortunately. Unless you ran it backward and solved the oiling issues, maybe.
The Bolt drive unit - like some others - is coaxial, meaning that the axle line runs right through the centre of the motor shaft...so it doesn't need to be turned around to fit, as a Leaf drive unit might need to be.
 
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