Building an Electric Autocrosser-Winter is boring

[twinch]

I've been thinking about this for many many many years since graduating college, and now is the time to start the design. In fact I actually started buying the frame materials when I lived in the states, but I moved back here before actually starting things. I want to build an open wheeler with electric power. I have good connections for the electric motor expertise, but as for building the body I'm winging it.

First things first. the frame. I wish to do this all from scratch(yes, I know this is going to be an endeavour) but i will be giving myself about 10 years from start to finish.

The suspension is a formula type A arm setup, but the rear will have the motor attached to the trailing arms.

My first question is...Is this frame over kill or do you think I could give up some structure to lighten it up more? For scale the tires are 205 50 15.

http://farm6.static.flickr.com/5020/5445614297_50628f6d2a.jpg

Here is the rear setup. I'll probably go with 2 struts and shocks, but that right now is not important. The electric motor has not been planned yet, but it will be part of the trailing arm suspension. I may even have the motors in each hub of each tire. I guess I could even go 4 wheel drive.

http://farm6.static.flickr.com/5213/5445610933_9b8c192404.jpg

The battery packs will be placed in the rear and under the seat to push as much weight to the rear over the rear axles.

http://farm6.static.flickr.com/5016/5446209596_96b6fd92c1.jpg

Right now I'm using magic steering inputs, kind of like a Nintento Wii steering wheel. It's to iliminate the need for a steering rack and column. :)
http://farm6.static.flickr.com/5171/5446209366_a988142d9e.jpg

[Snizzoop]

YES! I think an all electric open wheel autoslalom car has the potential to decimate all!

I would definitely want to go AWD. I would definitely want to have some YAW sensors, wheel speed sensors, etc...and some super fancy computer to control it all. With the torque of the electric motors, and controlling each one independently, it would be pretty cool to get the two outside wheels driving the car through the turn.

Since it only has to run for a minute, you shouldn't need TOO much juice. I think regen would be high on the list to reduce the need for more battery packs.

Also, I think some wider tires would be necessary. 255-40-13 sounds about right. :p

[darcyw]

your driver weighs like 100 lbs at most to help offset the monumentally heavy batteries i imagine.

wicked cool design, though. what program did you design that in?

as for snizzoop's comment on traction control, i just recall reading about an aftermarket "soft" traction control system on the s2ki.com forums.

darcy

[twinch]

Thanks for the ideas. Because it's an autocrosser I would not need massive batteries. Intact I might be Able to get away with something like 50lbs depending. There are so many options I could use. There are even high discharge bAtteries thAt can discharge all of their power in a short period of time which means POWER! Even today I was talking to a co worker who is a remote control plane and helicopter instructor who was showing me electric motors that replAce 100 cc gas engines for 1/2 scale planes. Give me one of those per hub and I have over 50 horses and oodles of torque at my disposal.

Darc the program is 3d studio max 2009 with final render.

[GordRoss]

Cool,

What about using a stock formula car chassis (like a formula ford)? It would give you ready made brakes, front suspension, bodywork etc. It would get you on the track faster (but may be less fun/challenging to build)

Depends on your goals I guess

Cheers

Gord

[karmaboy]

Cool project.
Ever consider finding a old Formula SAE chassis...might be the perfect foundation.
Have a look at Dennis Palatov's site...some very interesting insight into chassis design.
http://www.dpcars.net/

K

[twinch]

Karmaboy...That is one inspirational site! I've only gone through a few pages and already I have some new ideas.

Well, having a ttc commute gives me some time to contemplate things and I think I'm going to one up my original idea. A new frame is going to be designed, however, because my skills are more in touch with carpentry. I'm thinking a birch frame. The price is good, it's one of the strongest hardwoods with some elasticisity, and it's easily available, plus, who has built one that is on the track? The frame will have to be closer to a boat or airplane but I think I can adapt it to be a sort of hybrid of a traditional metal car frame and a boat frame.

Another benefit to wood is if there is ever any damage it's a lot simpler to repair.

As for purchasing a frame, I think I would rather make it from scratch because of the challenge and satisfaction of doing it. It gives me a project to work on. The Sentra is almost where I want it after I redo the suspension, and after that, it's just a matter of maintenance on it and no more new projects for it other than the odd thing or 2, or 3...

[twinch]

Well a new direction with the frame and suspension. I'm going to go with more of a standard setup with both front and rear independant, and I will be going with hub motors for each tire with a controller. All wheel drive baby!

Obviously the steering rack and column are just mocked up, but I would like to either just get one from a recked car and modify appropriately.

I'm still not sure about the suspension setup considering the hub knuckle would be a lot of fabrication. I'll have to see once I talk to the electric guy and see what would suit it best.

The tires I moved up to 225 45 15 sizing.

http://farm6.static.flickr.com/5256/5474908512_11fde8af73.jpg
http://farm6.static.flickr.com/5098/5474312363_1e5b13faf8.jpg
http://farm6.static.flickr.com/5011/5474908662_6d6a323858.jpg

[thgear]

are cars made from wood allowed in motorsports? :confused:

also if you are going to be building an AWD car you're either going to sacrifice center of gravity (since you'll have to sit above the driveshaft)

or put the driveshaft to either side, but then you're stuck making the diffs work.

i think for a garage project you should stick to RWD, and put your ass as close to the ground as possible.

[Burnsey]

Since it only has to run for a minute, you shouldn't need TOO much juice. I think regen would be high on the list to reduce the need for more battery packs.

Very cool idea. You should be able to calculate exactly how much battery power you'll need once you know your motor horsepower. Speaking of motors, you'll also have to consider gearing and RPM, as most commercially available motors may not spin fast enough if you use direct drive.

Regen will be tricky though...maybe find a wrecked Prius and hack away :p

Start a blog and keep us posted. ;)

[MazdaMatt]

are cars made from wood allowed in motorsports? :confused:

also if you are going to be building an AWD car you're either going to sacrifice center of gravity (since you'll have to sit above the driveshaft)

or put the driveshaft to either side, but then you're stuck making the diffs work.

i think for a garage project you should stick to RWD, and put your ass as close to the ground as possible.

Serge... 21st century here... no drive shafts or diffs. The motors are IN the wheels.

Burnsey - no need for gearing. Hub motors exist exactly for this purpose.

Twinch - check the chinese industrial supplier websites for a hundred options for hub motors. Most are for bikes/scooters/motorcycles, but you could probably find something that will work. Many of them also do custom designs.

[thgear]

Serge... 21st century here... no drive shafts. The motors are IN the wheels.

that can't be very fast.. can it?

in that case why is the seating so high the diagrams, you should be design a system where you're laying down then like those solar powered cars they had in the 90's

[~[MPR]~]

To start off, awesome idea! :cool: I hope you go through with this and make it a reality. There are lots of people who would love to see this and I think it would really start to turn heads to electric power for the performance-oriented individuals who are stuck on the mentality that all electric cars are slow...lol.

Hope you don't mind some constructive critisism. ;) This is just a few things I've notice from your inital designs where I believe there could be some significant improvements:

-Center of gravity
-Driver position
-Wheel base and track(width)
-Drive train layout
-Smaller wheel/tire size

I believe your goal is to keep it as small and light as possible. However I think the design would benefit from making the wheel base a bit longer and with a wider track(width). In doing this, you'll be able to lower the drivers position to a go-kart like ass dragging position. This will significantly drop the center of gravity and result in a more 'stable' layout.

You may have to play around with driver position in accordance to the size, shape and location of the battery pack. In keeping the car as light as possible, using a battery that would last the day may end up needing to be bigger than necessary. Having two or three battery packs that will last 2 or 3 runs and could be changed out quickly (and charge while not being used) will also help keep the weight down. But that is something you'll have to figure out later on.

I would also use a much smaller (13" or so) rim size with a wider tire. This will keep the cost, weight and rolling resistance at a minimum. You don't want to waste any more power on spinning the tires/wheels than you have to.

For suspension, you may want to adapt or mimick the front and rear sub-frame/suspension modules from a miata or other similar small car with front and rear fully independent suspension system with already excellent geometry.

As for drivetrain, I would assume you'd run the motor at 1:1 directly to the wheels. RWD is typically ideal, though there is the option to go with AWD. You could go with hub-mounted motors, allowing for more freedom of chassis design/layout as you wouldn't have to worry about where to route the axles etc. Hub mounted motors would also allow for a really effective AWD system with a sophisticated traction/stability control system. You could also run one single motor in the rear with an LSD to drive the rear wheels, with a 2nd motor setup up front to drive the front wheels. Or just one motor driving the rear wheels as a mid-rear layout. Lots of options! lol... :D And here's a cool idea, you could use the motors as brakes to re-capture energy back into the batteries to increase their range/run time... (regenerative braking)

So to sum up basically, if you lengthen and widen the car a bit, shrink the wheel/tire size and lower the drivers position as low as possible (keep the overall center of gravity as low as possible), I think the chassis design can be simplified, lightened and yet retain it's strength and optimise it's function.

This is a really cool project and I hope you are able to build it. It's a great idea. I think it would be very competitive and really turn some heads. Keep the ideas coming and keep us posted! :)

[twinch]

Thanks for the comments and kind words. Constructive critism is always welcome because I'm basically doing this while learning on the way.

Anything to do with electric motors and what is available is where I need a lot of information as I am still really learning about this.

I'll definately going with a smaller tire and longer wheelbase. I was thinking that exactly during my last redesign and it will be incorporated with the next design concept. As for driver position, the batteries will be located under the drver seat and the idea of interchangeable smaller battery packs is a great idea. I'll probably go that way. It'll need some fiddling around to lower the centre of gravity the best I can.

I'm going to eliminate anysort of driveshaft from the motors so it will either be rear wheel, or all wheel hub motors. I'm hoping that instead of an LSD I am that there is some programming that can be done to mimick one using the motors instead. Again, I'm going to have to talk to my electric motor guy in Montreal, but if there is anyone on here that has extensive knowledge of electric motors and how best they can be used I'd love the insight.

I am also considering to start a blog with this. Anyways, the next concept will be up in a couple of weeks.

Thanks again to everyone's input

[Snizzoop]

It might be better to mount the motors on the chassis, and run a short drive shaft to the wheel. Motor on the hub = more unsprung weight, and we know how much we love unsprung weight.

Oh, and with respect to the issue of driving the wheels directly, I think you'd be good to go. If I recall correctly, 1800RPM is a common "max" RPM for electric motors. Using 225/45/13 tires as an example (circumference ~ 1675mm), you would end up with a top speed of 180km/h. That's WAY more than enough for autoslalom.

What you LOSE by direct driving the wheels is the torque multiplication factor of a gearbox. You will need to find a fairly high torque motor in a small package...that will be the tough part I expect.

[~[MPR]~]

Thanks for the comments and kind words. Constructive critism is always welcome because I'm basically doing this while learning on the way.

Anything to do with electric motors and what is available is where I need a lot of information as I am still really learning about this.

I'll definately going with a smaller tire and longer wheelbase. I was thinking that exactly during my last redesign and it will be incorporated with the next design concept. As for driver position, the batteries will be located under the drver seat and the idea of interchangeable smaller battery packs is a great idea. I'll probably go that way. It'll need some fiddling around to lower the centre of gravity the best I can.
I'm going to eliminate anysort of driveshaft from the motors so it will either be rear wheel, or all wheel hub motors. I'm hoping that instead of an LSD I am that there is some programming that can be done to mimick one using the motors instead. Again, I'm going to have to talk to my electric motor guy in Montreal, but if there is anyone on here that has extensive knowledge of electric motors and how best they can be used I'd love the insight.

I am also considering to start a blog with this. Anyways, the next concept will be up in a couple of weeks.

Thanks again to everyone's input

There should be plenty of room either just behind the drivers seat and or right beside the drivers seat. You could either off-set the driver slightly to one side to compensate for the mass of one battery pack or use two battery packs, one on either side of the driver. In any case the batteries should remain as low and centrally located within the chassis as possible. Driver position should be considered as more important to "get low" than the batteries, due to the shape and mass location of the human body. (and since the driver will weigh more than the batter pack, most likely...lol).

One option for drive train could be to get you hands on a small, lightweight transversed transmission from a FWD vehicle. Either get one that already has an LSD differantial in it (like integra GSR/Type-R etc. or??). Pop the case off, remove all the guts and gears and adapt the motor to drive the differential directly. That way you'd keep the unsprung weight down, have minimal drive-train loss and LSD.

Can't wait to see your next design concept! :)

[max attack]

The minimum wheelbase is 80" under the casc ruleset so there's no need to have your feet tangled up in the steering/suspension components.If you went with a motor in each wheel how would it work with essentially a locked center/front/rear diff?.Normally not well if starting out with a conventional awd car and lock the diffs.
There's options for the steering rack,if you budget is big look at sports racer stuff-you can have it built to your specs for rack travel and width for bump steer.If your like me and no budget look at off road buggies,you just to find one that you can make work.The one I used for my build had slightly less rack travel than I was looking for but the price was right,has a center pinion,it isn't heavy and lock to lock is 1 turn.It was intended to be used for rear steer spindles but I used front steer miata parts,just had to simply flip it upside down and put it where I needed to get the correct orientation.
The narrower the track the more important roll control becomes,wide track means a slower car thru the slaloms though so a comprimise needs to be found.I simply went with a miata stock hub to hub as it saved costs by using factory cv shafts.
For the body I suggest building the car and getting it driving and work the kinks out 1st,once thats outa the way than deal with the body.Ideally get it driving in 1 season and then work on the body the next winter.
My car has a body on the inside of the tubing,looks ok and was pretty easy to build but for higher speed events the drag is probably horrific.I've build a complete composite car in the past and didn't want to get bogged down with that sticky(and far from cheap),itchy and stinky part of the project.Once I finish up with the chassis sorting this coming season I MIGHT consider spending the winter building the bucks,moulds and parts to enclose the chassis.
Btw don't set too tight of a schedule,building from scratch is a TON of work,I was a madman on mine with most nights and weekends in the shop and from 1st tube to driving it was 8 months.

Have fun,can't wait to see what you come up with.

[Marsh]

Couple of comments:

1st - Tom is right. There is a minimum wheel base in the rule book. That model looks a little too small to me. An old FSAE car is not legal for CASC autoslalom unless it is completely legal to the FSAE rule set it was built for, including 600cc gas engine and 20mm restricter. An electric FSAE car is simply not competition eligible.

2nd - All cars must have body work up to the drivers waist. It doesn't have to be fancy. It doesn't have to protect anything but the driver, but it has to be there.

3rd - Correct on the un-sprung mass issue. Motor-in-the-hub is a packaging and efficiency thing. It destroys handling. A chassis mounted motor would be preferable. Although one front and one rear would work well (remember there is no limit what so ever on the number of engines in the CASC-OR autoslalom Modified rules)

As a steward I would also expect to see a protective layer (preferable metal) between the batteries and driver (same as I would between fuel and driver).

[MazdaMatt]

Serge, hub motors can be incredibly powerful. There was a british mini with 150hp PER WHEEL, 4wd.

Also, torque is a NON issue with electric motors. They have a perfectly flat POWER band - you do the math and figure out the torque at 0RPM. (hint, you can't hold that motor). This also means that there is no need for a clutching mechanism at all.

Max - there are no diffs.

Unsprung weight is definately an issue. When I've considered doing this my thought was to have the motors mounted on the pivoting axis of the suspension with a short shaft to the wheel. The motor then pivots as the suspension moves instead of moving with it.

However, you may need to do the math on the motors - you get more bang for your buck (weight, space, cost, torque) with a larger motor. You can get double-shaft motors, but that won't allow you to the traction control that you're after. You could feed a motor at each end into an LSD, though. If you did this, just size the rear motor 2x the size of the front.

The considerations for this project are endless, so the top priority should be to avoid analysis paralysis. Consider the motor layout options, the drive wheel options, pick one and run with it. Lowest cost and easiest build would be a RWD single-motor through an LSD.

[MazdaMatt]

This will answer a LOT of questions... What's your budget?

[twinch]

Sorry haven't had a lot of time to respond to things.

My budget, right now, I have no budget. I still have a lot of reserarch to do about what things actually cost especially the motors. Custom racing steering racks are definately out of the equation, I'm still hoping for a junked one that can be cut and chopped.

I have been thinking about the unsprung weight and I'm going to try and figure out a design that would work.

The only reason I have the feet dangling out the front was an aesthetic reason. For some reason I really like this look. Silly, but I think I'm going to try and keep it, I may just extend the back to increase the wheelbase by 19 inches. We'll see how it looks.

I agree that it can be paralyzing analyzing any design, and I think it will be that I choose one thing and go with it.

As for the rule violations this design has, I have some design changes in the works to to rectify them. All barriers will be added later once the design is closer to being established.

The reason why electric is the best in my opinion especially for autocross is the the flat torque curve of the motor as Masda Matt made a mention to.

It may be this weekend now that I can talk to my electric motor guy.

I tell you, I wish I had unlimited funds and had no need to work, because work is totally getting in the way of me doing this. :)

[MazdaMatt]

Careful, that's a flat POWER band, not torque band. Very high torque at the start that drops off as you reach top speed. Yes, work and money sure do get in the way of life, don't they?

MOtors are not terribly expensive. A few hundred dollars. Batteries are the killer. You'll probably want about 5k in batteries for this thing.

It would be good to read up on how the electric drag racers are getting massive amperage out of their batteries. Autox is closer to drag racing than road racing or street legal cars in that regard. More current = more torque.

[max attack]

Serge, hub motors can be incredibly powerful. There was a british mini with 150hp PER WHEEL, 4wd.

Also, torque is a NON issue with electric motors. They have a perfectly flat POWER band - you do the math and figure out the torque at 0RPM. (hint, you can't hold that motor). This also means that there is no need for a clutching mechanism at all.

Max - there are no diffs.

Unsprung weight is definately an issue. When I've considered doing this my thought was to have the motors mounted on the pivoting axis of the suspension with a short shaft to the wheel. The motor then pivots as the suspension moves instead of moving with it.

However, you may need to do the math on the motors - you get more bang for your buck (weight, space, cost, torque) with a larger motor. You can get double-shaft motors, but that won't allow you to the traction control that you're after. You could feed a motor at each end into an LSD, though. If you did this, just size the rear motor 2x the size of the front.

The considerations for this project are endless, so the top priority should be to avoid analysis paralysis. Consider the motor layout options, the drive wheel options, pick one and run with it. Lowest cost and easiest build would be a RWD single-motor through an LSD.


I know there is no diffs,jeesh I guess I'm new to this car stuff.

Would adding power equally to all 4 wheels at the same time in a corner not cause a problem due to the differing speeds traveled by each side of the car?.

[max attack]

I have to admit I have 0 interest in electric power,beating a dead horse imo untill there's a way to make the batteries light,compact,affordable and last long enough make it worthwhile.Having said that,without the work by people to figure that stuff out we'd still be racing horse and buggies.
How much does the motors and batteries weigh?,just curious as I have no idea.For reference the R1 engine in mine weighs 145lbs complete with fluids and makes 150hp stock,I suspect that ratio of weight to power is damn hard to beat with electric motors and the batteries to make it move.

[MazdaMatt]

For power/wgt you'll never beat a cumbustion engine with a chemical fuel source... unless someone starts building nuclear. However, the drag race guys are really moving. There's a bike that's done 7.7 quarter and a cars breaking 100mph in the quarter.

As for the 4 motors and 4 wheels... remember, you're 100% in the demain of electronics. You can turn each of those wheels at exactly the speed they should be turned at with millisecond accuracy. A motor controller could sense steering angle, and even slip if you wanted to hook up the right sensors, and adjust the current going to each wheel-motor accordingly.

Also of note, when you see the rating of a gas engine, you know what the HP curve looks like - it only has that power at ONE rpm reading and it is lower everywhere else. How much lower depends on lots of stuff, but a 4-banger is usually MUCH lower when you go +/- 25% from that peak RPM. An electric motor has a completely flat power curve from 0RPM up to its maximum rating. So if you're looking at area under the curve, a 145hp gas motor will be MUCH lower than a 100hp electric.

[MazdaMatt]

http://www.canev.com/KitsComp/S10Kit/S10-Kit.html

Here's an example of a regular street vehicle. S10 + 10k buys you 75mph+ top speed and 40-60 mile range. Most of the cost is batteries, the controller is a good chunk of it and the motors are cheap, relatively speaking. The motor offered there seems to be the status quo in electric conversion, the Warp 9".

[~[MPR]~]

Sorry haven't had a lot of time to respond to things.

My budget, right now, I have no budget. I still have a lot of reserarch to do about what things actually cost especially the motors. Custom racing steering racks are definately out of the equation, I'm still hoping for a junked one that can be cut and chopped.

I have been thinking about the unsprung weight and I'm going to try and figure out a design that would work.

The only reason I have the feet dangling out the front was an aesthetic reason. For some reason I really like this look. Silly, but I think I'm going to try and keep it, I may just extend the back to increase the wheelbase by 19 inches. We'll see how it looks.

I agree that it can be paralyzing analyzing any design, and I think it will be that I choose one thing and go with it.

As for the rule violations this design has, I have some design changes in the works to to rectify them. All barriers will be added later once the design is closer to being established.

The reason why electric is the best in my opinion especially for autocross is the the flat torque curve of the motor as Masda Matt made a mention to.

It may be this weekend now that I can talk to my electric motor guy.

I tell you, I wish I had unlimited funds and had no need to work, because work is totally getting in the way of me doing this. :)

I'm not saying with your current design you would not be competitive, but I am saying the design would not be optimal in terms of weight distribution and location of center of gravity. These things are very important when it comes to performance. It's mere physics.

I realise there is a 'look' you're after, but is autocross about cool looking cars? I hope you don't take this the wrong way, but I think if you want this to be a strong competitor and perform to your expectations, you need to not worry so much about aesthetics at this point. Instead I'd consentrate on optimizing the weight/weight distribution/center of gravity/overall setup first and foremost.

[dubya_rx]

http://www.autoblog.com/2011/03/04/video-translogic-takes-the-all-electric-z-kart-for-a-spin/

[twinch]

Dubya RX-So bizarre. my body just sent me that link to that electric car.

MPR-No offense taken by your comments. Everyone has opinions and what you says makes total sense. I am going to try and stick with my design, but if it looks like it can't work, I would sacrifice aesthetics. But I think that this frame might be able to work. I'm actually going to try and incorporate the Miata Suspension.

So I have created a blog page. It's just in the works, and I'm just learning how to do it. Here is the link. There is nothing yet there really except for a cover page, but I'll get to it with a whole bunch of silly sketches that I started since the beginning of this adventure, way back in 1999.

http://e-crosser.blogspot.com/