[428RC]

Hi, I am a Mechanical Engineer by trade and somewhat weak in my knowledge of electrical components. I would like to understand the options and capabilities of adding electric motor/motors to a car I started many years ago. the car is a 1962 corvette, however I had a tube chassis built and the suspension and drivetrain from a 1999 corvette was added. I would like to understand some general options to see what is the best path to explore. My understanding from doing some reading is that there are a lot of ways to accomplish the same things, each with good and bad. so let me first list what I think are major paths with the hopes that some of the more experienced builders can get me started down the right path of investigation.

Obviously with a corvette i would like to get good performance, similar to the 1999 in stock trim. I dont need or want a race car, but would like it to have respectable power.

In case someone is not aware, the 1999 corvette has an independent rear with a transaxle, the transmission is attached to the rear differential and the motor is attached through a long tube from the front. My car has the manual 6 speed, and an automatic is also available. I am looking for some pictures of my specific frame but I have not found them, sadly the car is buried right now so i wont be able to show much of its construction until I am ready to start. For reference the frame was built by SRIII motorsports about 15 years ago.

1. I see a lot a Tesla big and small rear motor conversions, this seems economical but I am not sure how well that will fit on my rear subframe without a lot of reconstruction.
2. I see that there are many large DC and AC motors like a warp9, warp11, warp13. I could either attach this directly to the front of the differential or to the front of the 6sp transmission, however the best fit by far would be to eliminate the transmission.
3. reverse, is it costly to use the electronics to reverse, or does having a transmission simplify/cost reduce enough to justify the transmission?
4. can you get Tesla performance from the warp type motors?

sorry, I know these are very general, but this is my basic understanding so far. Thanx for your time and patience.

 

[428RC]

here is a quick sketch using a view from SRIII webpage. this is the chassis I have.

 

[brian_]

For anyone who doesn't remember the exact years that Corvette generations changed, 1999 (the chassis components donor) is a C5.

 

[brian_]

2. I see that there are many large DC and AC motors like a warp9, warp11, warp13. I could either attach this directly to the front of the differential or to the front of the 6sp transmission, however the best fit by far would be to eliminate the transmission.

All of the WarP motors from NetGain are brushed series DC motors... essentially the same as old industrial equipment such as forklift trucks.

If the motor you choose with the voltage you have available from the battery configuration that you choose can provide enough power over a wide enough speed range, you don't need to shift between different gear ratios; almost all production EVs have only a single gear ratio. Regardless of the number of ratios, the overall gearing needs to put the motor at a suitable speed for all road speeds. For typical EV motors that is a much higher ratio (more reduction, "shorter" gearing in traditional automotive terms) than the final drive (ring and pinion gearing at the differential) can provide, so an additional reduction gear set is used; some motors are suitable at low enough speed that just the final drive is enough.

3. reverse, is it costly to use the electronics to reverse, or does having a transmission simplify/cost reduce enough to justify the transmission?

The contactors (relays) to reverse a brushed series DC motor are not unreasonable, and any AC motor reverses with just a software command in the controller. If you keep the transmission with a DC motor you can use the transmission for reverse, but reverse certainly doesn't justify a transmission in my opinion.

4. can you get Tesla performance from the warp type motors?

No.

 

[428RC]

Thanx, I am thinking the Tesla Large rear drive unit would be good, a lot of power. the cost difference seems to be reasonable to jump from the small to the large. I will need to crawl under the frame and see if the size is manageable. trying to add a reducer to the C5 diff, or keeping the 6spd seems counter productive...... how many Tesla battery modules would be needed for say 150 miles range with the Tesla large drive unit? I am also thinking to use the Volvo electric PS pump to drive theC5 steering rack and a hydro-boost, is this an efficient system or would it be better to go with the direct electric assist steering and an electric brake booster, in terms of efficiency, I was really wanting to keep the C5 rack and pinion and the hydro-boost seems like a freebee at that point. This keeps the C5 systems and feel more original. Also SRIII did a fantastic job setting up the C5 rack with zero bump-steer so I want to keep that rack, not sure if forcing a power rack using a steering shaft booster would be good for the power rack either.

 

[brian_]

1. I see a lot a Tesla big and small rear motor conversions, this seems economical but I am not sure how well that will fit on my rear subframe without a lot of reconstruction.

The combination of the motor and transaxle (where the transaxle, as always, is the transmission plus differential) is commonly called a "drive unit".

Tesla drive units are fundamentally just like almost every other modern EV: transversely mounted motor, fixed ratio reduction transmission, and differential. They are popular because they have been hacked to be controlled without all of the rest of the EV's original electronics. One problem mounting the traditional Tesla drive units (from the Model S and Model X) is that the motor is behind the axle line - that's great for a Porsche 911, but not for the structure of most cars. The Model 3 rear drive unit has the motor ahead of the axle line (and a more modern motor design), so it might be a better alternative.

Some EVs have coaxial drive units, in which one side axle shaft runs through the hollow motor shaft, placing the motor directly on the axle line, which might be good for fitting everything in... but unfortunately that makes them relatively wide, forcing the use of short axle shafts.

The other commonly used EV drive unit, mostly because it has been in production for so long, is the Nissan Leaf. You would need the highest-power version (from the recent version of the Leaf with a 62 kWh battery), or an earlier unit modified for more power, to get the performance that you're looking for.

 

[brian_]

I am also thinking to use the Volvo electric PS pump to drive theC5 steering rack and a hydro-boost, is this an efficient system or would it be better to go with the direct electric assist steering and an electric brake booster, in terms of efficiency, I was really wanting to keep the C5 rack and pinion and the hydro-boost seems like a freebee at that point. This keeps the C5 systems and feel more original.

Direct electric systems would be more efficient, but I don't think either steering or brakes use enough energy for this to be important.

You might consider mixing solutions, using a direct electric brake assist (typically the Bosch iBooster) to avoid the noise of a vacuum pump or complication of a hydroboost, but an electric pump for the hydraulic steering to keep the same steering feel (and to reduce cost).

 

[428RC]

thanx, I will do some searching on the bosch steering. from a quick review this looks pretty nice and cheaper than the hydroboost solution. how is its electronics integrated? does it need a CAN bus signal or can it operate stand alone? looks like they are in a lot of new models including Tesla and Honda


I found a guy on another forum who is making a control for the Volvo power steering to make it react to need as it is meant to work but I have not talked to him yet. that seems to be a good solution to keep the C5 rack

 

[brian_]

trying to add a reducer to the C5 diff, or keeping the 6spd seems counter productive...

If you use a separate motor (instead of a complete drive unit) with the original final drive, you could possibly get the advantage of retaining the Corvette's original electronically controlled limited slip differential... although that would be an electronic control system management challenge. EV drive units generally have open differentials, depending on individual brake application for traction control, and I don't know if anyone has kept that working in a conversion. There are Quaife ATB limited-slip differentials available for some drive units, typically the Teslas.

 

[brian_]

thanx, I will do some searching on the bosch steering. from a quick review this looks pretty nice and cheaper than the hydroboost solution. how is its electronics integrated? does it need a CAN bus signal or can it operate stand alone? looks like they are in a lot of new models including Tesla and Honda

Do you mean the Bosch braking? Yes, the iBooster is very common. As much for the humour as the technical information, here's SuperfastMatt's take, with an answer to the control question:
Inside Tesla's Brake Booster. And How To Use It On Any Car.

 

[57Chevy]

You'll be disappointed with anything less than Tesla LDU Sport. It is a sports car after all

 

[428RC]

You'll be disappointed with anything less than Tesla LDU Sport. It is a sports car after all

I am still pondering this. to be honest I have only ever driven this car when it had the original 327, powerglide, manual drum brakes and skinny 6 inch tires, so my expectations are it will improve no matter what but more horsepower is always welcome if I can swing it. I think I will start with whatever large drive unit I can get to keep initial cost down, I think I can always swap in a sport one later without oo much changing and sell the first one to offset? I hope this is true anyway. I am considering if it makes sense to try to buy a wrecked model S, not sure if the EV guys are not gobbling those up but maybe I might be able to get an older one

 

[428RC]

Do you mean the Bosch braking? Yes, the iBooster is very common. As much for the humour as the technical information, here's SuperfastMatt's take, with an answer to the control question:
Inside Tesla's Brake Booster. And How To Use It On Any Car.

great info thanx, and yes I did fast forward.......

 

[57Chevy]

If you have the funds and the yard space you can buy a wreck, nick the motor and whatever you need and onsell what you don't. The battery is the primary value item and you can get the motor etc for free effectively. Be aware of older cars and flooded ones, the LDUs are weak in a few areas so high mileage is not ideal unless you can see the LDU revision code. I think after rev Q is ok, about 2017. Lots of older cars got factory replaced due to faults. I'm doing a Trifive with two LDU Sport motors I got from wrecks.

Plan your control system up front as it will save a lot of hassle later on. The open source gear is only really suitable if you like to get down and dirty with the very inner workings of it. Not suitable for someone who wants to build a car and go driving as it is not particularly robust and there is very limited product support. Get what you pay for etc. The aftermarket is slowly coming around to this and there are a few proprietary controllers out there now, some using the Tesla logic board, others replacing it entirely. The cost is not that bad if you aren't forced into buying a recycled drive unit off the electronics supplier- then it can be fiendishly expensive.

There are LDU cad models online now so building a cad mock up is relatively easy. I bought a Chinese 3d scanner and scanned the frame and firewall etc so have a good setup going. I'm also fitting the Tesla suspension, brakes, iBooster, ABS etc in as well

 

[428RC]

If you have the funds and the yard space you can buy a wreck, nick the motor and whatever you need and onsell what you don't. The battery is the primary value item and you can get the motor etc for free effectively. Be aware of older cars and flooded ones, the LDUs are weak in a few areas so high mileage is not ideal unless you can see the LDU revision code. I think after rev Q is ok, about 2017. Lots of older cars got factory replaced due to faults. I'm doing a Trifive with two LDU Sport motors I got from wrecks.

Plan your control system up front as it will save a lot of hassle later on. The open source gear is only really suitable if you like to get down and dirty with the very inner workings of it. Not suitable for someone who wants to build a car and go driving as it is not particularly robust and there is very limited product support. Get what you pay for etc. The aftermarket is slowly coming around to this and there are a few proprietary controllers out there now, some using the Tesla logic board, others replacing it entirely. The cost is not that bad if you aren't forced into buying a recycled drive unit off the electronics supplier- then it can be fiendishly expensive.

There are LDU cad models online now so building a cad mock up is relatively easy. I bought a Chinese 3d scanner and scanned the frame and firewall etc so have a good setup going. I'm also fitting the Tesla suspension, brakes, iBooster, ABS etc in as well

I think I will have a while to plan. I am a planner at heart and by trade so I want to try to hash out the best approach. I have access to CREO and Solidworks so I will likely model anything up I can and I have some CNC to make brackets and such. I have some EE contacts as well so I was hoping there was a stable open source control electronics out there. the cost of going to an EV retrofitter or even buying one of their converted drives looks cost prohibitive, but I know guys who can take a schematic or gerbers to finished PCBA's. If one of the resellers will sell the boards separate that would be preferred but I imagine their business model is such that they want to provide the whole retrofitted DU. So in the end I am hoping the maturity of the open source will be enough to make a good driver. I have a good sized yard and some workspace so I can dismantle a car to get parts, I just need to evaluate the best approach first.

which scanner did you get?, I may need to scan my frame as it is a one off, I had SRIII narrow the rear c5 cradle as I am loath to add flares on a 62. So this cradle may not be wide enough for the tesla LDU.

 

[remy_martian]

The problem with a Tesla donor is it makes a C5 a pig for weight (if you use all 16 battery modules) and handling.

The 57 Chevy was a pig from the factory and drove like a truck, so there it doesn't matter...
😂

You're the ME, or used to be before you became a bureaucrat....you need to figure out if the chassis designers were relying on the C5's torque tube setup structurally. It may crack your fiberglass body if you take the torsional rigidity out of that frame by ditching the torque tube.

 

[428RC]

The problem with a Tesla donor is it makes a C5 a pig for weight (if you use all 16 battery modules) and handling.

The 57 Chevy was a pig from the factory and drove like a truck, so there it doesn't matter...
😂

You're the ME, or used to be before you became a bureaucrat....you need to figure out if the chassis designers were relying on the C5's torque tube setup structurally. It may crack your fiberglass body if you take the torsional rigidity out of that frame by ditching the torque tube.

tube chassis, torque tube is moot, and the batteries will be under the floor. I do not plan to use 16 packs but it remains to be worked out.

 

[remy_martian]

Wow - you are pretty rusty in your structural. That "tube chassis" is essentially a flat plate. The fact it's made of pipes means nothing.

There's no roof or anything of large section that's triangulating against twist. That torque tube is the primary reaction force against twist. Pull it and you may have a wet noodle on your hands.

There's also NFW you're getting batteries under the floor in that chassis without completely chopping it up and redoing it. Is that your plan?

 

[428RC]

ask nicer, and we can discuss, otherwise I will no longer reply to your comments.

thanx

 

[57Chevy]

If one of the resellers will sell the boards separate that would be preferred but I imagine their business model is such that they want to provide the whole retrofitted DU

Yes they do, you don't have to get headlocked into somebody else's value chain. I have chosen AEM because the VCU can run up to four inverters (I only have two) and the control board inside the LDU replaces all the Tesla logic so traction control can work properly etc. It is very under developed in terms of support right now as it only came out last year, I'm hoping they are going to do a more formal release shortly with documentation and firmware updates. The hardware is very good which is the main thing, the rest will come into shape over time.

So in the end I am hoping the maturity of the open source will be enough to make a good driver

The price premium for gear from an aftermarket vendor will be quickly used up if you blow up the power stage trying to get the open source kit reliable. One mouse click in the wrong place and now you are up for another inverter unit. This is why you'll have to get down and dirty with its inner workings, your ability and skill setting it up is the only thing keeping it alive; any misunderstanding or incorrectly set parameter can end up with smoke and loud noises.

which scanner did you get?

I got a Thunk3d Fisher, I don't know if they still make it but there is a newer equivalent unit out. The online prices were halved when buying directly from the maker a few years ago. Not the best quality and very obviously hand made but it has performed flawlessly for everything I needed it for. The software is somewhat non-intuitive as expected but you get used to it. For the price it is very good value for money compared to the professional grade equivalents. One issue is that it requires a Nvidia 2GB or greater graphics card as that is where the grunt work is done. Nothing particularly uncommon but something to think about when looking at total cost

Dumb idea, if you have the chassis etc there, could you noodle print an LDU and offer it up? Big FDM printers are about, a low density print wouldn't be that expensive particularly if you have one available through work. Could quickly rule it in/out for fit. For my front DU I have to run the inverter separately as the frame rails are too narrow, so that is an option I guess. Not ideal but workable.

ask nicer, and we can discuss, otherwise I will no longer reply to your comments

You met the resident troll. Some people just don't get it; the difference between being and engineer and being an asshole is quite a lot. Perhaps a little less alcohol in the evenings might reduce the tendency.