[Zieg]

Hi everyone,

I am still in the early planning stages here, but I thought I may as well start a thread to document some of what I'm working on/planning, both for information and feedback.

The car:
-Lotus 7 replica (AKA 'Locost'), built by myself to original book dimensions.
-Currently powered by a 2004 Yamaha R1 motorcycle engine.
-Current weight is about 1200 lbs without driver and half a tank of gas
-Primary use is Autocross, though it is street legal

Goals:
-Safe and well-built EV conversion
-Torque at low speeds but still possible to cruise on the freeway
-Keep reasonably close to the same weight
-Range isn't a huge concern but 30 miles or so would be nice
-Keep costs under $10k CAD?

Here's a photo from last season:

So the car is obviously a front engine RWD layout (I guess, technically the engine is 'mid' since no part of it is forward of the front axle). The rear axle is a narrowed Ford 7.5" out of a Ranger. From what I can tell, it looks like I can get up to a 4.56 gearset for it. It is currently geared to 3.45, which means the engine is running at 6-7000 rpm on the highway (not good) and still doesn't have as much low end torque as I would like. Also, due to the open intake and limited space for a muffler, I am constantly within a decibel or so of going over the noise limit when I get near redline at WOT. The car will do over 60 MPH in first gear, so I rarely even hit second on the courses we typically run here.

Since I will be left without a transmission after the bike engine is out, and to keep weight down, I am planning to go directly from motor to axle with a two-piece driveshaft. I thought long and hard about a DC motor, but decided against it due to a few reasons, including choice of controllers and availability of suitable motors locally.

So I am looking at either a Leaf motor or a Hyper 9. It would be nice to use a Leaf motor for the lower cost, and bonus if I can get the charger to work with whatever batteries I choose. Right now I can't seem to find much info on using the charger, and even less info on using it with a different battery voltage.

And speaking of batteries, I'm leaning towards second gen Chevy Volt. It looks like I could fit four modules in the car - two under the hood and two in the back where the gas tank is now. The Volt battery comes with three 16s modules and four 12s modules, so I can think of two possibilities:
1. Use two of each module size to get 28s2p (actually 4p since each module is internally 2p) (Good for Hyper 9)
2. Use all three 16s modules plus one 12s in series for 60s (Leaf motor would need at least this much voltage)

Since I designed all the suspension and everything except for the basic layout of the 'book chassis', I already had a CAD model to start with. Here's what it looks like with the Hyper 9 and a Spicer PTO u-joint adapter:

And finally, some of my comparisons. I had to go and wrap my head around how synchronous motors work, so hopefully this is right. I would really appreciate some feedback on this! To get the Leaf numbers, I first took the commonly available graph for the 80kW motor and scaled it up to 110kW at the same RPM. I then scaled the RPM for a given torque value, based on going from 360v to 240v.

If I did that all correct, it looks like the Leaf motor would give me better torque up to about 40 mph and then the Hyper 9 takes over. The MPH line assumes 4.56 gears. On one hand, I like the added low end power, but on the other hand, power is only useful if you can put it to the ground. Maybe as a next step, I should make another graph that compares wheel torque instead of driveshaft torque, and play around with different combinations of motors and rear end gears.

And that's about where I am at now. Any input is appreciated. My timeline for buying parts is basically most of the summer, then once this season is over I plan to tear the car down and start the conversion as a winter project.

Cheers!

 

[floydr]

So I am looking at either a Leaf motor or a Hyper 9. It would be nice to use a Leaf motor for the lower cost, and bonus if I can get the charger to work with whatever batteries I choose. Right now I can't seem to find much info on using the charger, and even less info on using it with a different battery voltage.

Is it a level 2 J1722 charging station? all it does is provide both L1/L2 of a split phase system to your charger OBC which charges to Your Voltage. You are in Canada?
level 2 j1722 with the appropriate interface for the J1722 socket such as this one J1772 Active Vehicle Control Module AVC2 - For Public Charge Stations
later floyd

 

[remy_martian]

Hey Mr Excel graphs,

Now do a plot of curves for tire force (assume infinite coeff friction), motor torque, and acceleration (a = F/m) vs vehicle speed. From there a second graph of distance vs speed from a standing start.

Seems geared too tall to me by about 2:1, though it is low mass...or was.

Zero to 100 Kanadian miles /hour in 6 seconds?

 

[Zieg]

Floyd, actually I meant the onboard charger (and whatever controls it). I'm not actually sure at this point where the charger gets its control from. If it's onboard programming or if it just gets CAN messages (which I suspect is the case). I don't need anything fancy though, that's for sure.

Remy, well the tire force graph would look just like the torque curves if assuming infinite traction. 1345 lbs for the Leaf motor and 834 for the Hyper 9 at the peak. Not really an excel wizard but what I came up with is this:

• They both have flat curves up to 30 mph, so assuming infinite traction, no losses etc, the 0-30 is 1.5s Leaf and 2.5s Hyper 9 (ha, yeah right!).
• 30-60 is trickier but if I average the acceleration of the Leaf motor through speed range, I get 2.2s Leaf and 2.5s again for the H9 since it's still in constant torque.
• Total times for both would be 3.7s for the Leaf and 5.0s for the H9.

Where it gets more interesting is 60-80. Using the same averaging of acceleration method, 7.8s for the Leaf and only 5.7s on the H9. Therefore 0-80 is 11.5s Leaf and 10.7s Hyper 9.

Thanks for the idea, that tells a very interesting story! And you're right, the H9 would be better if geared lower..

 

[Duncan]

If it was mine I would cut the back out and put the entire Leaf unit in there -
making up a rear suspension setup would be relatively easy and it should be better than a live axle
I have a subaru rear diff with MacPherson struts - easy to make and works well
That would also give you the entire front engine bay AND the old transmission tunnel area for batteries

Your acceleration times are a bit slow - I'm doing 95 mph in just under 8 seconds

 

[remy_martian]

What's your final drive ratio?

 

[brian_]

So the car is obviously a front engine RWD layout (I guess, technically the engine is 'mid' since no part of it is forward of the front axle).

Yes, "front-mid engine"; Nissan even named one of its platforms FMR in recognition of this configuration.

Since I designed all the suspension and everything except for the basic layout of the 'book chassis', I already had a CAD model to start with. Here's what it looks like with the Hyper 9 and a Spicer PTO u-joint adapter:
View attachment 128742

The motor appears to be in roughly the stock engine location. Can it go further back, in location of a Lotus 7 or Locost (but not this motorcycle-powered) transmission? That would help with space for battery in the front.

 

[Zieg]

If it was mine I would cut the back out and put the entire Leaf unit in there -
making up a rear suspension setup would be relatively easy and it should be better than a live axle
I have a subaru rear diff with MacPherson struts - easy to make and works well
That would also give you the entire front engine bay AND the old transmission tunnel area for batteries

Your acceleration times are a bit slow - I'm doing 95 mph in just under 8 seconds

Yeah, I have been thinking about that. Will continue to keep the idea in mind, but there would also come a point where I decide to build a whole new car a few years down the road. Maybe even something with a Bolt (or Tesla?) motor...

As for the acceleration, I guess it's really coming down to motor kW and gearing.. Though I have been reading about people extracting more power out of the Leaf motors. One option might be to use 4.10 gears instead of 4.56 and plan on upping the current coming out of the inverter a bit.

What's your final drive ratio?

The math above was done assuming a direct coupling to the diff, and 4.56 gears in the diff (though see above for my second thoughts on that).

Yes, "front-mid engine"; Nissan even named one of its platforms FMR in recognition of this configuration.


The motor appears to be in roughly the stock engine location. Can it go further back, in location of a Lotus 7 or Locost (but not this motorcycle-powered) transmission? That would help with space for battery in the front.

Sadly, no. Due to the bike engine layout, I did not build much of a widening into the tunnel - partly to allow myself some more room at the pedal box. The tunnel is very narrow through the middle of the car, widening to the passenger side near the front to accommodate the offset output shaft of the engine. What you see the driveshaft connecting to at the bottom of the screen is the reverse box (necessary to make the car street legal). What I would want to do is mount the center carrier bearing of the new driveshaft to the same place as the reverse box. If it makes sense to do so, I could then offset the motor to the passenger side a couple of inches for better balance, depending on battery arrangement.

Speaking of batteries, are there any other options I should be looking at, other than the Volt? They seem pretty well favored but I'm always open to other possibilities. The brand new 1.6kWh batteries that EV West sells look amazing, but way over my budget sadly.

 

[brian_]

... Due to the bike engine layout, I did not build much of a widening into the tunnel - partly to allow myself some more room at the pedal box. The tunnel is very narrow through the middle of the car, widening to the passenger side near the front to accommodate the offset output shaft of the engine.

That makes sense, but it's unfortunate for this conversion. It is, perhaps, an argument for going for the new build now, whether that has an independent rear suspension and rear-mounted drive unit or the current suspension and a tunnel-mounted motor.

 

[blackterminal]

If it was mine I would cut the back out and put the entire Leaf unit in there -
making up a rear suspension setup would be relatively easy and it should be better than a live axle
I have a subaru rear diff with MacPherson struts - easy to make and works well
That would also give you the entire front engine bay AND the old transmission tunnel area for batteries

Your acceleration times are a bit slow - I'm doing 95 mph in just under 8 seconds

It looks a bit like your car Duncan.

 

[Duncan]

If going for a new car I would make one comment
Battery space is limited - the space between the wheels on each side is completely wasted on a 7
I would be going for a car without that wasted space
You could either put batteries down each "sill" - or move the driver and passenger further apart and put batteries down the middle

Something like this

 

[Zieg]

Yeah, the new car path would most likely be a full body, and hopefully more aerodynamic. Not sure how much I would want to be climbing over a huge sill, so I'd probably prefer batteries down the center.

After some more thought, I'm going to go ahead with a front engine conversion for the time being, and make the new build be a future goal. For the next couple years I would prefer not to start a whole new build due to other life factors, but I can at least start designing something new, completely from the ground up.

Meantime, I phoned a nearby salvage yard and asked about both a Leaf motor and Volt battery they had. Waiting to hear back on whether they can include some of the extra wiring I asked for.

 

[Duncan]

Yeah, the new car path would most likely be a full body, and hopefully more aerodynamic. Not sure how much I would want to be climbing over a huge sill, so I'd probably prefer batteries down the center.

After some more thought, I'm going to go ahead with a front engine conversion for the time being, and make the new build be a future goal. For the next couple years I would prefer not to start a whole new build due to other life factors, but I can at least start designing something new, completely from the ground up.

Meantime, I phoned a nearby salvage yard and asked about both a Leaf motor and Volt battery they had. Waiting to hear back on whether they can include some of the extra wiring I asked for.

With the motor in the front you will not have anywhere near enough room for the batteries
My motor is situated where the gearbox should be - and I managed to fit only 14 kWh of the 16 kWh Volt battery in the engine bay
That is with the battery on the floor - which gives a wonderfully low C of G
You could probably fit a 9 inch diameter motor in your "tunnel" - remember you can lose the clutch pedal so you can afford to move the tubes over a bit

 

[Zieg]

Hmm, yeah it does look like I could offset the tubes but it would be pretty extensive. The inside dimension of the tunnel is 4" now do I guess I'd have to do 2.5" per side if I wanted to keep it centered.

Unfortunately the Leaf motor looks to be a good bit wider, but on the bright side it's also shorter than the Hyper 9. I'm not planning to use all of the cells from the Volt, but it looks like I could put two 16s modules right up front, one 12s beside the motor, and one each of 16s and 12s modules in the back, for a total of 72s without having to mod the tunnel. That arrangement would leave me with about 30 pounds added behind the rear axle compared with a full tank of gas. If I really had to I could move a 12s or a 16s to the back as well, but that would be a last resort.

As far as frame mods go, I did have to offset the motor to the right, so I'll have to model up a driveshaft and see what the u-joint angles look like. Probably going to have to mod the steering rack mounts, definitely relocate the 12v battery, etc. But I think it looks promising?

 

[Duncan]

Hmm, yeah it does look like I could offset the tubes but it would be pretty extensive. The inside dimension of the tunnel is 4" now do I guess I'd have to do 2.5" per side if I wanted to keep it centered.

Unfortunately the Leaf motor looks to be a good bit wider, but on the bright side it's also shorter than the Hyper 9. I'm not planning to use all of the cells from the Volt, but it looks like I could put two 16s modules right up front, one 12s beside the motor, and one each of 16s and 12s modules in the back, for a total of 72s without having to mod the tunnel. That arrangement would leave me with about 30 pounds added behind the rear axle compared with a full tank of gas. If I really had to I could move a 12s or a 16s to the back as well, but that would be a last resort.

As far as frame mods go, I did have to offset the motor to the right, so I'll have to model up a driveshaft and see what the u-joint angles look like. Probably going to have to mod the steering rack mounts, definitely relocate the 12v battery, etc. But I think it looks promising?

View attachment 128788

The trouble is the Leaf motor is a high revving low torque unit - it really wants about an 8:1 final drive

The advantage of the DC forklift motors is that they are low revving high torque units

Your two tubes are at floor level - right?
So the motor is above that level - at floor level the motor is effectively zero thickness

The tubes on my car are too close together to lower the motor into place - so I have to drop the motor into the passengers footwell and then shift it sideways into place

On my car the floor is completely flat with the batteries and motor as low as I can get them
This means that I'm running with soft springs (70 lb/in front 100 lb/in rear) and no roll bars at all and it still only just rolls a tiny amount

 

[Zieg]

The trouble is the Leaf motor is a high revving low torque unit - it really wants about an 8:1 final drive

The advantage of the DC forklift motors is that they are low revving high torque units

Hmm, maybe part of my problem is that I'm not understanding how to estimate power outputs of a DC motor and/or underestimating how much current I can draw from these Volt batteries in short bursts. Looking at the Warp 9 specs they say 100 ft lbs at 500 amps, so I guess I'd be looking for peaks around 1500 amps? And to do that, would I need 3 battery modules in parallel?

I guess the other thing I should look into is how to scale these graphs. A 16s+12s module arrangement would get me like 112v so I think that would be enough, but I don't know how to calculate how much torque I would end up with at a given RPM.

This is the one I'm looking at for reference:

All this is wrong, but I'm leaving it crossed out so people know what not to do!
Edit: Alright, I think I have my head wrapped around it now. All my reading about AC motors threw me for a bit of a loop but it looks like DC is a lot simpler. It looks like if you want more torque at a given RPM, just increase the voltage proportionately. I'm going to go play with more spreadsheets now..

 

[Zieg]

Edit: This is all wrong too, same as above, leaving it here but crossed out.

Alright, gonna need this checked please. I had to sift through a bunch of information that sometimes contradicted other posts, but I think what I figured out was that for a given rpm, if you increase the voltage by a factor of x, the amperage will also increase by x, and the torque produced at that same rpm will increase by a factor of x^2. That last bit, I am least confident in, though, since it was hard to find info about how to compare power levels at the same speed. I whipped up a spreadsheet based on that assumption and checked the power in vs power out and it did seem to follow. I also found updated motor specs from Go-EV (motors made in 2010 or newer) so I plugged it all in and whooooo doggy that paints a very different picture! If this is all correct, then I guess it looks like a no-brainer. I even changed the rear end ratio in the calcs back to the 3.45 it's currently sitting at.

 

[remy_martian]

Hmm, maybe part of my problem is that I'm not understanding how to estimate power outputs of a DC motor and/or underestimating how much current I can draw from these Volt batteries in short bursts. Looking at the Warp 9 specs they say 100 ft lbs at 500 amps, so I guess I'd be looking for peaks around 1500 amps? And to do that, would I need 3 battery modules in parallel?

I guess the other thing I should look into is how to scale these graphs. A 16s+12s module arrangement would get me like 112v so I think that would be enough, but I don't know how to calculate how much torque I would end up with at a given RPM.

This is the one I'm looking at for reference:
View attachment 128807

Edit: Alright, I think I have my head wrapped around it now. All my reading about AC motors threw me for a bit of a loop but it looks like DC is a lot simpler. It looks like if you want more torque at a given RPM, just increase the voltage proportionately. I'm going to go play with more spreadsheets now..

Um...not really.

Voltage is proportional to speed in a DC and Current is proportional to torque.

Back EMF cuts back max current, which is why you increase voltage.

The square law you're seeing is horsepower, not torque.

 

[Zieg]

Um...not really.

Voltage is proportional to speed in a DC and Current is proportional to torque.

Back EMF cuts back max current, which is why you increase voltage.

The square law you're seeing is horsepower, not torque.

dangit just when I thought I was getting somewhere.

Ok, so torque in ft-lbs = HP x 5252 / RPM, right? So let's say we are making 100 hp at 1000 rpm, I plug that in and get 525.2 ft-lbs.

If I double the voltage and double the amps I quadrouple the horsepower? So now we are making 400 hp at 1000 rpm? Plugging that number in gets me 2100.8 ft-lbs, or quadrouple the torque. What did I miss this time? If RPM isn't constant in that squared law, how would you calculate the new expected torque at a given rpm?
Looks like what I missed was that it still follows a constant torque line while hooked up to a typical controller, and just like with an AC motor, the point at which the flat line starts to decay just gets pushed further out when you add voltage.

 

[remy_martian]

Finite Element Analysis to capture the back EMF contribution, if you must calculate.

Easier to bench test.