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I just graduated university with an engineering degree and will hopefully start working as an engineer in the automotive field sometime soon. Still applying to jobs lol. I have been thinking about building an electric race car to compete with. Mostly to learn more about electric cars and motorsports, have fun, hone my skills in programming, and learn new skills like fabrication, calibration, car setup, and such. I've done a fair amount of research but I'm starting to hit a few walls and need to talk to people you have more experience.

After reading some of the Sticky thread "I want to build an EV! Where do I start?", I'll try to hit all the basics with the highlights of the main idea I'm thinking of.

  • Racing in SCCA or NASA. NASA races seem to be about 30 mins long, not sure on SCCA. Heard about EVSR racing in SCCA on the East coast but don't know what class and will eventually be reaching out to him.
  • Starting with a Honda Civic EG hatch. Good, reliable, cheap parts, good shape, lightweight, but mostly cause I like the look of the car and I've always wanted one.
  • Running an axial flux type motor, or something similar, around 150-250 kW, through a quick change differential on the front axle (keep it simple for Version 1, maybe later go to rear wheel or all wheel drive). Quick change diff for several reasons. One, it would allow quick and easy changing of final drive ratios at a track. I found you can get ratios that range from 2 all the way up to 9. This also allows for a wide range of motor selection.
  • RMS motor controller as I'm slightly more familiar with them.
  • Moving the front brakes inboard. This will lessen up unsprung weight and allow for hard brake lines throughout.
  • Batteries are a little more of a question mark. I'm not sure whether Model S battery modules will work. I like the cooling potential though. I'm also thinking about LiFePO4 batteries as I'm familiar with the chemistry more and like the safety and power density. But I'm worried about cooling. I want to brake with mostly the motor so the batteries need to take a high current charge as well as discharge.
  • Still working on whether I'll do this for Version 1 but thinking of going with unsprung aero as well. Have a couple of ideas on mounting that I'm taking from Formula SAE cars. But will have to see what limitations I'll have on the classes of NASA or SCCA.
  • Same goes for suspension. Would like to do push or pull rod with heave dampening but not sure on doing this for Version 1. Depends on time and budget.

So to answer the questions from the Sticky thread:
-Skills: I have mild skills on auto mechanics (do my own car work most of the time). And have a good set of tools. But no fabrication experience. I am also an engineer with programming and CAN experience.
-Range: Looking at just completing a single race on one charge, about 30 mins of racing. But for future, I would like to create a quick change battery and go endurance racing.
-Performance: I'm not sure. Would like to be competitive but don't know what class I would be allowed in. Under the current rules I think I can only race in Super Unlimited in NASA as it seems to allow electric and open rules. But they are super quick. I'm thinking about initially shooting for Civic Type R or other FWD hatchbacks as my target, since I will start out as an electric FWD hatchback.
-Money: Kind of up in the air but I will kind of guess max around $100k but minimum of $30k. I know the motor and controller will be about ~$10k each, quick change diff about $3-5k, and batteries can be anywhere between $5k and $50k. BMS, wires, contactors, etc I know will be an extra couple $1,000s, but the fabrication and labor is the real mystery (suspension, mounting brackets, spec roll cages, welding, etc.). This will be a serious project for me, both learning and fun.
-Parts: None so far. Keeping my eyes on the classifieds for any EG hatch shells in good condition as that will be the first part I buy; a car or shell to start stripping down.

Sorry for the long post and I know I have a lot more questions but first I would like to get your thoughts on my current project idea, motors for extended racing, and batteries for high power and charging? Thanks for any help you can give me.
 

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It sounds like a fun project.

What i've read about building a race car, the first item to select is the wheel size and tires. This sets the axle height and other geometric parameters of steering and ride height will be determined around that.

Also the tire width or contact patch will determine the torque limits and power requirements, and the diameter will give you the revs per mile.

From that you can calculate the motor and gearbox combination to make the torque and speed for the longest straight at the track venues.

Now it gets to an iteration of solutions for weight and aerodynamic loads, how much battery (voltage and current) for the motor windings and gearing to make the required torque and RPM. You can push the envelope in whichever parameter will optimize your desired performance parameter (range, speed, torque, weight, cooling or not, etc).

Take a look and read thru Ripperton's electric track bike thread, it is one of the most viewed of any on this forum.
 

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Discussion Starter #3
It sounds like a fun project.
What i've read about building a race car, the first item to select is the wheel size and tires. This sets the axle height and other geometric parameters of steering and ride height will be determined around that.

Also the tire width or contact patch will determine the torque limits and power requirements, and the diameter will give you the revs per mile.
Interesting, haven't thought of that too much. So I just looked up GTE Pro car specs from WEC and they use 18" as well as Honda Type R TCR (touring car) and they use 18". The Civic Si TC uses 17". So I would say my max is 18" and also probably one of the most popular so lots of cheaper spares possibly. But when I look up Spoon and other racing Honda EGs I see 15", 16", and some people run 17". So not really sure. It seems everyone suggests going with the smallest wheel possible for lighter weight and less rolling mass and inertia, as long as it clears the brakes. Good thing is I'll be moving the front brakes in-board and the rears can be on the smaller size. So maybe 16" or 17" since they seem more common than 15". Thoughts?

As for tire width I really wouldn't know. I don't know that much about setting up cars. I also think there is a limit depending on the class, but not sure. Any suggestions? I guess I can start to work on some basic Excel code to calculate numbers from the wheel to the motor with different variables to change like tire size, final drive ratio, top speed. The only issue is I don't know the total weight of the car to figure out the normal force and therefore the friction force on the tires. Guess I can work on an assumed weight range; best case, worst case.

From that you can calculate the motor and gearbox combination to make the torque and speed for the longest straight at the track venues.
Yeah I've been thinking about that a lot lately, in terms of looking at top speeds of hatchbacks like Golf Rs in SCCA at the end of a straight to determine the gear ratio based on the torque curve of each motor. Most motors I've looked at have max torque from 0 to some RPM anywhere from 25% to 75% of max RPM depending on motor voltage. So thinking of picking a top speed and picking an RPM of 10-20% above the rpm where max torque starts to drop off. That will get my the diff ratio with a set tire diameter. So I still have a little power and top speed left even at the end of a straight rather than running out of steam before the end of the straight. But I'm not sure on how to select the tire wall size after I get the wheel diameter so I can get the tire diameter. Any thoughts on tire wall size and how selecting that can affect handling?

Now it gets to an iteration of solutions for weight and aerodynamic loads, how much battery (voltage and current) for the motor windings and gearing to make the required torque and RPM. You can push the envelope in whichever parameter will optimize your desired performance parameter (range, speed, torque, weight, cooling or not, etc).
I've been avoiding it but I just might have to write an optimization program and figure out all the cost functions for each parameter. I've been avoiding this because I'm afraid the best solution will be the costliest, like running an 800+V system which I didn't want to for the first version. And as for aerodynamic loads, I have NO idea what a good goal is. I want to do just a simple flat floor, simple rear diffuser, rear wing (single, maybe double element), simple flat front splitter, and maybe canards. But don't know what kind of downforce numbers I should aim for.

Take a look and read thru Ripperton's electric track bike thread, it is one of the most viewed of any on this forum.
I'll definitely have to check them out. I know bike racing is very different from cars when it comes to calculations, just cause they are soooo much more efficient, lighter weight, better cooling, etc. But maybe I can get some insights.

Thanks for your thoughts and help. It helps to talk to someone (type this out) and think out-loud, made me think about how to progress that I didn't think about before.
 

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Hi
30 minutes is a very very long time
It will be incredibly difficult and expensive to have a competitive electric car for that period

You would be much better off concentrating on the time trials or sprints or hill climbs where a "run" is less than five minutes

Longer events mean a huge battery and an uncompetitive car

It's fairly easy to build an EV with 500 hp - but that would be 400 kw and a 30 minute event would need 200 kwh - or well over a ton of batteries

The limitation is the batteries!

With a five minute event that drops to 30 kwh - and you save a huge amount of weight

I can do five short "runs" on a charge - not six! - about 8 minutes - but I only have 14 kwh and the events I enter are relatively low speed - the longest straight is 200 meters - I hit 100 mph - before having to brake savagely for the next chicane
 

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Discussion Starter #5
Hi
30 minutes is a very very long time
It will be incredibly difficult and expensive to have a competitive electric car for that period

You would be much better off concentrating on the time trials or sprints or hill climbs where a "run" is less than five minutes

Longer events mean a huge battery and an uncompetitive car

It's fairly easy to build an EV with 500 hp - but that would be 400 kw and a 30 minute event would need 200 kwh - or well over a ton of batteries

The limitation is the batteries!

With a five minute event that drops to 30 kwh - and you save a huge amount of weight
I have considered time trials and will probably do a few events as shakedown for when the car is running. Hill climb would be fun too. But my ultimate goal (Version 2 or 3) is endurance racing, with battery swapping.

I'm not sure your math works out though. While yes a 400 kW at 30 mins is 200 kWh. But that is assuming you are at full throttle, 400 kW for the entire race. If you look at the Italian Grand Prix circuit, F1 spends about 70% at full throttle, and that's nothing but straights and chicanes. But something like the Monaco circuit is only 34% of the time. So there is a lot of time off throttle and/or regenerating while braking.

I'll also be shooting for 150-250 kW for the motor. A video recently surfaced with a Tesla Model 3 Performance doing a track day for 30 mins solid and lost 250 miles of range. So a 4,000 lbs vehicle with 340 kW running continuously for 30 mins only used ~78% of its 75kWh pack. Also Formula E run 250 kW for 45-50 mins, albeit all on street circuits, weighting 1,800 lbs (so a little bit lighter), and only use 54 kWh batteries.

A guy made an open top prototype car running in SCCA on the East coast and he says he does 30 mins races with a bit to spare and is competitive. I don't know how big the pack is, or how much the car weights, but he is running 180 hp.

In summary, I'm pretty sure I can run for 30 mins with a pack less than 75 kWh. The trick will be balancing enough batteries so have the power and range, but not too much it weights too much.

Hope I didn't come across as mean, just checking the math out. Also it caused me to do more research and found out some more things I didn't know (like how little you are on throttle for a street circuit), so it still helped me, thanks.
 

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The race sanctioning body and class that you choose is extremely important. They all have extensive sets of rules, and most are based on the assumption that some variation of the stock engine will be used, so an electric conversion will usually be either illegal or impossible to assess against the rules. They also tend to have many rules about tires, so picking a size and designing around that could easily lead to an illegal vehicle if you don't consider the rules when making the choice.

This is all substantially easier (but still not trivial) if you target solo competition instead of fender-to-fender racing, because solo series tend to have a class to accommodate almost anything.
 

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  • Running an axial flux type motor, or something similar, around 150-250 kW, through a quick change differential on the front axle (keep it simple for Version 1, maybe later go to rear wheel or all wheel drive). Quick change diff for several reasons. One, it would allow quick and easy changing of final drive ratios at a track. I found you can get ratios that range from 2 all the way up to 9. This also allows for a wide range of motor selection.
I like the idea of a quick-change final drive unit, but I don't understand why the plan is specifically for an axial-flux motor. In addition to being what seems like an unnecessary restriction, those motors tend to be short (axially) but large in diameter, which will place the bottom of the motor far below the axle line, to the point of potentially being a ground clearance concern.
 

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  • Moving the front brakes inboard. This will lessen up unsprung weight and allow for hard brake lines throughout.
I suggest learning from the experience of generations of race car designers and racers over decades: no one uses inboard brakes because they are not worth the problems that they cause.

  • Same goes for suspension. Would like to do push or pull rod with heave dampening but not sure on doing this for Version 1. Depends on time and budget.
Pure race cars do routinely use inboard suspension units actuated by push or pull rods, but they do it to leave aerodynamic tunnels clear inboard of the wheels. The Civic will not have aerodynamic tunnels, so I see no point in the added complexity of an inboard suspension. Inboard suspensions in cars without the aerodynamics to need them are usually made visible, which is a hint that they are there to impress other people with the "race" tech in the vehicle, rather than for any functional purpose.
 

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The energy requirements

F1 cars are not on "full throttle" for most of the time because they have oceans of power

With less power you will be on "full power" for longer! - so you may use less total energy than a more powerful car - but it will not be as much less as you think

If you have serious amounts of grip then you will use MORE energy on a lap than you will if you don't

The Tesla Model 3 may have used 60 kwh in a half hour of practise - but a car with similar weight and more grip will end up using MORE energy

Your lighter car but with tyres and suspension optimised for grip may well use MORE energy

I would also agree with Brian about push/pull rod suspension - the main advantages come from aerodynamic improvements and you do need to know what you are doing

I remember a friend bought a single seater with push rod suspension and it felt awful!
When I did a quick analysis it had been done as "monkey see monkey do" - it had FALLING rate suspension and bad geometry
We fixed it by moving a suspension pickup point and designing a new pivot lever
 

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Discussion Starter #11
While the energy requirement for anything more than a short sprint might be manageable, cooling (of both the battery and the motor) is potentially a problem as well. I'm not saying that it can't be done, just that you need to pay attention to this issue.

The experience of this race team should be interesting to you:
Tesla Powered Cobra Race Car
Modified Bolt Pack for Tesla Cobra EV Race Car
Yes that is what I'm most worried about. That is why I'm looking at motors, motor controllers, and batteries with liquid cooling.

OMG thank you for those links. That is why I'm on this forum. Reading their posts, so detailed, really helped and gave me a lot of perspective and ideas. Like I said, I'm in the planning and design stage right now, never thought of the Bolt batteries. I thought about the Model S modules but was worried about the cooling. I would love to use the Model 3 modules but I don't think they will work size wise. They seem very long but haven't found too many people who have taken them apart and used them in other projects. I'm definitely going to try to reach out to them.

The race sanctioning body and class that you choose is extremely important. They all have extensive sets of rules, and most are based on the assumption that some variation of the stock engine will be used, so an electric conversion will usually be either illegal or impossible to assess against the rules. They also tend to have many rules about tires, so picking a size and designing around that could easily lead to an illegal vehicle if you don't consider the rules when making the choice.

This is all substantially easier (but still not trivial) if you target solo competition instead of fender-to-fender racing, because solo series tend to have a class to accommodate almost anything.
Yes I completely agree. That is why, as of today, I've reached out to both the SCCA and NASA to see what they may say about possible classes. Seeing how EVSR races in SCCA, I reached out to him today as well about what class he runs and what were some of the SCCA requirements. I hope that if I get an exception, it will be to put me in a class with similar HP rather than the open/unlimited classes that have much faster cars in them. Once I hear from them I can start working on with any tire, suspension, or aero limitations.

I will consider solo competition possibly as a testing area but the ultimate goal is fender to fender. I see enough examples of it that I know it's doable.

I like the idea of a quick-change final drive unit, but I don't understand why the plan is specifically for an axial-flux motor. In addition to being what seems like an unnecessary restriction, those motors tend to be short (axially) but large in diameter, which will place the bottom of the motor far below the axle line, to the point of potentially being a ground clearance concern.
Axial-flux mostly due to the amount of work and research I did on them for a school racing team I was a part of (electric land speed car). I have been thinking about the ground clearance. I thought I could maybe rotate the diff and motor assembly about the axle axis, essentially tilting the motor up to clear the bottom of the car. I'm sure that will make the subframe more "interesting" as the mounts are now at more of an angle. Any thoughts? I also like the efficiency and power density of those motors and from what I can tell they have better cooling designs (as well as less thermal mass).
 

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I suggest learning from the experience of generations of race car designers and racers over decades: no one uses inboard brakes because they are not worth the problems that they cause.
So I'm curious about what kind of problems they cause. I know a lot of people don't do it mostly cause there is no room with an engine taking up most of the space. I've been reading about it and I know you have the half-shaft absorb some of the shock from braking , causing a slight delay in pedal feel. I figured that could be solved by using carbon fiber drive shafts, which I was considering anyway. I also know cooling can be a challenge but with regen braking the brakes wouldn't be as heavily used as well as I would make sure there are cooling duct for them. What other problems have people had??

Pure race cars do routinely use inboard suspension units actuated by push or pull rods, but they do it to leave aerodynamic tunnels clear inboard of the wheels. The Civic will not have aerodynamic tunnels, so I see no point in the added complexity of an inboard suspension. Inboard suspensions in cars without the aerodynamics to need them are usually made visible, which is a hint that they are there to impress other people with the "race" tech in the vehicle, rather than for any functional purpose.
Funny I actually thought of doing tunnels in the car like the Nismo LMP race car a couple of years ago. But I have a tendency to over think sometimes on the first iteration. A couple things I thought:
-I figured it would give me more control over angles and geometry
-More dampening options. I really like the idea of heave dampening, which I could still do with a pushrod attached to a conventional double A-arm suspension
 

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Which school and car?
Embry-Riddle Aeronautical University. Our project was called Eagle Work: Advanced Vehicle Lab. It's a student designed and built vehicle to break a record by going 250+ mph. It uses A123 26650 Lithium Iron Phosphate cells. For a few years I was the battery team lead. I helped design the battery pack. It's only 12.4 kWh but enough to run twice, required for official records. It uses two YASA motors driving the front wheels with two RMS PM150 motor controllers. They had a couple set backs so they probably won't run till next year. Here's a link to our website: http://www.eagleworksavl.com/
 

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I would love to use the Model 3 modules but I don't think they will work size wise. They seem very long but haven't found too many people who have taken them apart and used them in other projects.
Like the earlier Model S and X, the Model 3 pack is as long as can be fit between the axles. The unique thing about this design is that there are only four modules (the largest modules of any production electric car) and they are all the full length of the pack (two longer modules in the middle and two shorter ones on the sides to fit as the pack curves around the wheel wells), and since the car is large the pack is long. I have seen a couple of teardown videos, but have not heard of anyone using these modules at all. There would be very few vehicles not designed to use these long modules which could accommodate them.

That is why, as of today, I've reached out to both the SCCA and NASA to see what they may say about possible classes. Seeing how EVSR races in SCCA, I reached out to him today as well about what class he runs and what were some of the SCCA requirements. I hope that if I get an exception, it will be to put me in a class with similar HP rather than the open/unlimited classes that have much faster cars in them. Once I hear from them I can start working on with any tire, suspension, or aero limitations.
The difficulty for the sanctioning bodies is that engine rules exist both to limit the cost of preparing a car, and to level out competition. It would be difficult to define limitations for an EV which would make it comparable to any specific engine type and size, and it would be reasonable for competitors in the class to be concerned that a well-funded team could beat them simply by paying a lot of money for a lot of power in an EV. This is the sort of issue which has been key to various non-conventional engine designs being banned from various types of competition.

Since it is routine in amateur racing for different classes of cars to run on the track at the same time, classification is mostly about fair competition rather than putting the closest competitors together on the track. Expect to run with much faster cars, whether or not your results are being compared. In our nearly stock Honda I experienced extreme BMWs and Corvettes blowing past me like I was in first gear on a freeway. :eek:

I will consider solo competition possibly as a testing area but the ultimate goal is fender to fender. I see enough examples of it that I know it's doable.
I think that's an excellent idea. :)

Axial-flux mostly due to the amount of work and research I did on them for a school racing team I was a part of (electric land speed car). I have been thinking about the ground clearance. I thought I could maybe rotate the diff and motor assembly about the axle axis, essentially tilting the motor up to clear the bottom of the car. I'm sure that will make the subframe more "interesting" as the mounts are now at more of an angle. Any thoughts? I also like the efficiency and power density of those motors and from what I can tell they have better cooling designs (as well as less thermal mass).
I certainly understand working with what you know... but you should be aware that no one uses axial-flux motors in production.

Yes, if ground clearance is an issue rotating the assembly around the axle line a few degrees might be all you need; subframe design shouldn't be a problem with that. You can even flip the whole thing over (input shaft over the diff instead of under it), but with flipping or even any significant rotation keep in mind that the final drive unit still needs to lubricate properly, and that's based on gear oil sitting in the bottom and being drawn up by gear rotation. For the motor, check if there are angle limits due to thrust limits on the bearings.

I doubt that there is any efficiency difference between state-of-the-art axial flux and radial flux motors. The major EV manufacturers have spent billions of dollars between them developing motors, they mostly build their own motors to suit their specific desires, efficiency is critical to them... and none use axial flux.

Thermal mass is not such a bad thing in an automotive motor. Power demand is highly variable, and high thermal capacity smooths out the peaks, in the same way that a massive brake disk can handle an extreme braking demand better than a light disk which needs to dissipate heat as fast as it is generated. A land speed record car is unusual in that it uses full power (or as much as it can within traction limits) continuously for the entire run without a break to cool down; a road race car gets a break every few seconds.
 

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  • RMS motor controller as I'm slightly more familiar with them.
Embry-Riddle Aeronautical University. Our project was called Eagle Work: Advanced Vehicle Lab.
...
It uses two YASA motors driving the front wheels with two RMS PM150 motor controllers.
I didn't catch the "RMS" reference the first time, but now I realize that's Rinehart Motion Systems. You should be aware that they are now the inverter part of Cascadia Motion, a division of BorgWarner.
 

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Inboard brakes
So I'm curious about what kind of problems they cause. I know a lot of people don't do it mostly cause there is no room with an engine taking up most of the space. I've been reading about it and I know you have the half-shaft absorb some of the shock from braking , causing a slight delay in pedal feel. I figured that could be solved by using carbon fiber drive shafts, which I was considering anyway. I also know cooling can be a challenge but with regen braking the brakes wouldn't be as heavily used as well as I would make sure there are cooling duct for them. What other problems have people had??
That's most of it. Some production designs from back when they were used (primarily the Jaguar IRS, which itself belongs in every automotive museum and on no cars which are actually driven) were very difficult to service. Also, the cars which can use inboard brakes (because they are not production-based and so not limited by modification rules) usually have aero tunnels and the brakes need to be kept out of the tunnels.

Inboard suspension
Funny I actually thought of doing tunnels in the car like the Nismo LMP race car a couple of years ago. But I have a tendency to over think sometimes on the first iteration. A couple things I thought:
-I figured it would give me more control over angles and geometry
-More dampening options. I really like the idea of heave dampening, which I could still do with a pushrod attached to a conventional double A-arm suspension
Inboard mounting of the spring and damping units doesn't change the arm geometry at all. The travel of the spring/shock relative to wheel travel can be tweaked with linkage design, but directly acting on the hub or a suspension arm works fine - there's no need to introduce a bunch more parts to tweak that.

Yes, if you want to link the sides in interesting ways (more than just a stabilizer bar) a linkage that brings the sides together is an advantage. This seems like a good thing to do on a later vehicle, years from now.
 

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Discussion Starter #18
The energy requirements

F1 cars are not on "full throttle" for most of the time because they have oceans of power

With less power you will be on "full power" for longer! - so you may use less total energy than a more powerful car - but it will not be as much less as you think

If you have serious amounts of grip then you will use MORE energy on a lap than you will if you don't

The Tesla Model 3 may have used 60 kwh in a half hour of practise - but a car with similar weight and more grip will end up using MORE energy

Your lighter car but with tyres and suspension optimised for grip may well use MORE energy

I would also agree with Brian about push/pull rod suspension - the main advantages come from aerodynamic improvements and you do need to know what you are doing

I remember a friend bought a single seater with push rod suspension and it felt awful!
When I did a quick analysis it had been done as "monkey see monkey do" - it had FALLING rate suspension and bad geometry
We fixed it by moving a suspension pickup point and designing a new pivot lever
Good point about the more grip = more energy usage. And yeah you're right about more power = less time on throttle. Guess it depends on the type of track. VIR (Virgina International Raceway) or COTA (Circuit of the Americas) will definitely be more on throttle but smaller local tracks might be less.

Yikes, falling rate is not good. Yeah if I do a push-rod I will be designing it VERY carefully. I'll look more into that to see what I can do with the current suspension setup.
 

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Discussion Starter #19
I didn't catch the "RMS" reference the first time, but now I realize that's Rinehart Motion Systems. You should be aware that they are now the inverter part of Cascadia Motion, a division of BorgWarner.
Yes I'm aware. I still view them as RMS. Lol, I still call it Winston Cup Series instead of "Insert Current Cell Phone Network" Cup Series.

Like the earlier Model S and X, the Model 3 pack is as long as can be fit between the axles. ... I have seen a couple of teardown videos, but have not heard of anyone using these modules at all. There would be very few vehicles not designed to use these long modules which could accommodate them.
Yeah, I'm waiting for someone to try to use it to see any issues. Not that many on the market either. If I place it where the passenger seat was I would have from the firewall back to the bumper and I could stack the 4 modules on top of each other. I would have to measure it but it could possibly fit. Might mess with left to right weight balance.

This is the sort of issue which has been key to various non-conventional engine designs being banned from various types of competition. ... In our nearly stock Honda I experienced extreme BMWs and Corvettes blowing past me like I was in first gear on a freeway.
Yeah that's why I'm searching for a racing body that will allow it. Good thing is every group seems to be "kinda" working on rules for electric. I think one is trying to create a production electric class. Lol, yeah I like multi-class racing. Guess could always just sign up for Super Unlimited or something similar and just compete with whoever I'm similar in speed with. That way I can still run and still have fun.

I certainly understand working with what you know... but you should be aware that no one uses axial-flux motors in production.

Yes, if ground clearance is an issue rotating the assembly around the axle line a few degrees might be all you need; subframe design shouldn't be a problem with that. You can even flip the whole thing over (input shaft over the diff instead of under it), but with flipping or even any significant rotation keep in mind that the final drive unit still needs to lubricate properly, and that's based on gear oil sitting in the bottom and being drawn up by gear rotation. For the motor, check if there are angle limits due to thrust limits on the bearings.
...
Thermal mass is not such a bad thing in an automotive motor. Power demand is highly variable, and high thermal capacity smooths out the peaks...
So yes not in high volume production vehicles because of costs. But in low volume production like Koenigsegg uses them in the Regara (YASA P750s with RMS PM 150s) as well as I think Rimac (not sure though). They are also used in a couple of race cars like half of the Formula E cars and the VW ID.R and in a few electric airplanes (not prototypes but ones that are meant for production). For me it is the power density mostly. The smaller size and weight for the same power is big for me. Guess you are right they are similar efficiency on a motor level.

I didn't think about lubrication. Good to hear about the sub frame shouldn't be too bad, but yeah I'll have to reach out and ask the diff companies about their limits. Haha, I did think about rotating 90 degrees so the motor is on top. Would look kind of funny. I'll get back to everyone once I find out.

Guess you're right for daily driving, having more thermal mass. It seemed like that was one of the problems with using a Tesla drivetrain in a high-performance application that once all the thermal mass heated up, the cooling capacity couldn't keep up with it. So a smaller motor with less mass and a similar cooling capacity would not have as much heat soak issues. That was my train of thought.

Inboard brakes

That's most of it. Some production designs from back when they were used (primarily the Jaguar IRS, which itself belongs in every automotive museum and on no cars which are actually driven) were very difficult to service.

Inboard suspension

Inboard mounting of the spring and damping units doesn't change the arm geometry at all. The travel of the spring/shock relative to wheel travel can be tweaked with linkage design, but directly acting on the hub or a suspension arm works fine - there's no need to introduce a bunch more parts to tweak that.

Yes, if you want to link the sides in interesting ways (more than just a stabilizer bar) a linkage that brings the sides together is an advantage. This seems like a good thing to do on a later vehicle, years from now.
Hmmm, didn't think too much about servicing. If I go the inboard route, I will have to keep that in mind. Route lines for easier bleeding, make sure I have clearance for pad changes, etc. Another reason I forgot to mention that helped justify my plan was the Renault Megane RX by Prodrive. The drivers said that the steering feel was much improved. Along with other benefits specific to rally-cross like less debris.

Now that I think about it you're right, no geometry changes but relative position and velocity to wheel travel can be changed. Yeah guess could leave heave dampening to later iterations. I know I have a problem of over engineering things.
 

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Taking an existing car and modifying it - working with all of the compromises the engineers put in there for a petrol engine and for passengers is kind of not as much fun as simply building yourself a car

Mine is a road car that gets used on the track - if you are willing to use the Colin Chapman (Lotus) idea of more is less then it's probably easier and more satisfying to build yourself a car - could be a single seater - or a two seater -
Than to modify an existing road car

If you haven't already seen them look up "Locost"

Building your own car means that you can make all of the decisions about batteries right at the start

If/when I do build again I would like to use the "folded composite" technique for my chassis
 
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