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Old 08-25-2009, 09:52 PM   #1
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Questions?? If you were to build an extremely fast car from scratch you would.....

Let me start off with a little background info...

I'm a senior at the University of Kansas majoring in mechanical engineering. For my senior design project, we are converting an abandoned 1974 VW Beetle into a 500 mpg Hybrid. All our testing and theoretical work will be done on the 1/8th scale RC level. This has huge cost and time advantages over the full scale (and all the same concepts carry over VERY well). Testing will be done on homemade inertia dynos, in wind tunnels, stress modeling programs, and of course on the street. There are 6 groups with 4-5 people in each group. Each group is doing something different. Our group is building the fastest car possible Minimum goal is 100mph and I would really like to be in the 135mph range.

Our body will be based around a 2010 Camaro (aerodynamically modified), no salt flat looking torpedo.

My question is, if you were in my position, how would you go about building this car. Everything can either be built from scratch or purchased as "off-the-shelf". We are open to all ideas. Here's a little bit of where I was leaning towards.

Modifying the E-Revo chassis. Using the two motor setup (2 Mamba Monster Combos). Converting it to rear wheel drive only. Smaller a-arm suspension (1/10th or 1/12th scale). Single servo steering (vs. E-Revo dual servo). 2500mAh 6S Lipo packs. Gearing Around 3:1 or 2:1. Thoughts?

Here's a link to our website if anyone is interested (it is currently being updated for the 09-10 team)

EcoHawks.org

And if anyone is interested in sponsoring our efforts on any level, feel free to contact me at [email protected]
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Old 08-26-2009, 01:43 AM   #2
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Are you aiming to get your 1/8 scale model up over 100mph? Or your full-size car?

There hae been a number of speed run contests recently. The master of these is someone called Nic Case. So look at what he has done for inspiration.

Basing a high-speed car on a Revo is a mistake from the start. It's too heavy. A 2wd pan car or a 4wd touring car is a much better basis. But they have little relevance to what you could replicate on an abandoned VW chassis.
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Old 08-26-2009, 02:38 AM   #3
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Hi guys,
Just for your info, I'm no racing expert but i really think your full scale ride really need a lot of work to hit 135mph.
First look at it. Handling really need alot of work. i mean Coil overs and springs are the most important in handling. Your wheels set up is it gona stay the same or are you goin to change??? 20" rims??? Amount of Down force in the front and the rear in stationary and speed? are you going to do anything??? Power to weight ratio???? Gearings??? Engine management example: Dynojet. EFI or Carbs???

For a Fast Car Weight is always a factor... keep that in mind.

And one more question. Is your electric motor since it's going to be a hybrid, going to be able to do that type of power and speed efficently??? no point doing a "10sec Car when it can only run 10sec and after that back to the junkyard.

Well i use to mod superbikes for local club races. 4 wheels still in the learning stage.

Well best of luck.
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Old 08-26-2009, 09:29 AM   #4
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Sorry, guess I should of clarified that a little better.

Full scale goal is 500 mpg. Some are going to say this is unreasonable, and they may be right in the end, but it is what we are striving for. Currently the bug (full scale) is setup with a biodiesel generator and an electric motor. The generator chargers the batteries when the voltage drops and then shuts off. The electric motor powers the vehicle.

The 1/8th scale -- The purpose of the RC scale is to learn and experiement with all the technologies while avoiding paying $50,000 to $60,000 for a battery pack. Each group is going to do something different from this aspect. We actually have a group that is going to attempt to power their RC car with a hydrogen fuel cell. Another group is going to attempt a parallel hybrid.

E-Revo -- The idea behind the E-Revo was to essentially borrow the dual motor setup and the low center of gravity. Our chassis will be a one-off. It will be designed in SolidWorks. Stress/deflection analysis done. Weight removed. Stress/deflection analysis done. Weight removed....and so on. The chassis will then more than likely be cut on a CNC.

So would it be better to stick to a single motor design? is the weight from the extra motor, ESC, and battery not worth the extra power? Again, I'm open to ALL ideas at this point.
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Old 08-26-2009, 09:51 AM   #5
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for a low CG dual motor setup, a custom 1/8 buggy would be better. you have a flat chassis you can bolt two motors two, with some inventive electronics placement you could fit a battery pack either side of the drive shaft. You could then fit on-road wheels, and have lots of traction too.
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Old 08-26-2009, 09:57 AM   #6
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aerodynamics is going to be your friend at that speeds.
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Old 08-26-2009, 10:20 AM   #7
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I understand what your getting at, and where your coming from.

The e-revo is a bad idea for your scaled down version for several reasons. First its not 1/8 scale to a bug, its 1/8 scale to a monster truck. The tire sizes alone will not allow you to reach those speeds.

Dual motors are set up specifically for torque, as in a motor boat scenero.

For example one rc motor spining at 30,000 rpms will have a top speed of say 30 mph.

Two rc motors both spinning at 30,000 rpms will also have a top speed of 30 mph.

The difference is there will be twice the power (torque) to reach 30 mph.

Your best bet (for the example) is to purchase a single motor that is capable of 60,000 rmp, which for all entensive purposes, will go 60 mph.

As for your car.

If your intention is to similuate a VW beetle, buy a pan car, on road plat form. VW beetles are built on a pan platform so your scale replica will start off correctly.

Beetles have torsion bars in front with shocks and springs in the rear, Super beetles have struts and springs in the front, so as long as you have a 4 wheel independant suspension, pan plat form to start with you will be fine.

As for your way to generate electricity to power the motor or charge your existing battery, your on your own for that. All that I can suggest is if you have a 4wd rc plat form to start with, use the shaft from the center diff, that would normally drive the front wheels, to turn your generator.

If you get a belt driven car, use the belt that would power the front wheels to turn your generator.

My suggestion for a car would be use an associated TC 3, TC 4 or TC 5. As its already capable of speeds close to what your suggesting.

A motor capable of those speeds would have to be a brushless 2.5 or 3.5 with the proper gearing and a lipo battery with at least a 35c rating.

Be very careful, as lipo batteries will charge differntly than Nimh batteries. They are also much lighter.

The 2.5 motor, and everything else for that matter would be 1/10 scale not 1/8 when your searching the internet for parts.

Remember 1/10th would be accurate as your replicating 1/10 of a beetle which is smaller than a normal car to begin with.

As for bodies check with HPI. I know they make several late model cars including Mustang and Viper. Not sure about the camaro yet.

Keep in mind as low to the ground as possible as your light, 4 pound car can easily get lifted off the ground at those speeds. Low profile rubber tires, just as on road tires that come a tc5 will be what you need, because they wont "ballon" at high speed.
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Old 08-26-2009, 11:06 AM   #8
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Heres a little more of where we are coming from with the top speed build.

At the end of the project we have to justify our experiment to the advisory board for the department. Therefore we have to have some reasoning as to why we are trying to go so fast (other than its way more fun than building a 10mph solar powered RC car). The justification is as follows...

What are some of the main problems with electric cars and hybrids at the current point in time (full scale)?
No power. No range. Expensive.

So if we can show off this extremely fast RC car, we have blown the slow aspect out of the water. Now we need to do so without giving up range and without spending a fortune to do so. Range is easily overcome by using a larger battery. I mean we could use a 10,000mAh lipo, back the speed controller off a bit and run for a very long time. Obviously the 10,000mAh battery is going to be quite expensive. So its really hard to have two of the above without greatly sacrificing the third. But isn't this the case with full scale technology as well?

As far as the generator idea, that is for the full scale bug. Our power generation is going to come from a small solar filling station that we will design. And yes I am fully aware of the charging features of lipo batteries. We will more than likely be using a Tenergy balance charger ran off a full size automotive battery which is charged by solar panels. That will come much later down the road and is actually pretty easy to design.

So at this point, should we scrap the dual motor idea? Who builds the best 1/8th scale motor/esc setup for top speed? I've heard 2500mAh batteries are going to be the sweet spot for top speed (as far as having enough capacity without weighing a ton). True?
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Old 08-26-2009, 11:11 AM   #9
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Body -- As far as the body goes, the Camaro idea was simply because at full scale the wheelbase was essentially the exact same as the revo chassis. (.5" at full scale and 1/16" difference at 1/8th scale). We are not fully committed to that at this point. Our body will not be an exact replica of the orignial body, simply based off the original. Our body will be sculpted out of automotive modeling clay (just like full size designers do). A resin mold will then be made of this body and placed in the wind tunnel on campus. After computing the coef. of drag, we will modify the body and test it in the wind tunnel again. The process will be repeated until we come up with the most aerodynamic body possible (or as time and funds allow). We will then create a mold of this body and vacuum form it on a table to create our final plastic body.
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Old 08-26-2009, 11:12 AM   #10
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Sounds like an interesting project

I agree with the motor options... you need RPM not torque for top speed (torque for acceleration). Maybe some sort of gearbox would be handy ?

There are RC cars that have exceeded 150mph, a couple have passed 160 - have a trawl through Youtube.


Good luck !


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Old 08-26-2009, 11:28 AM   #11
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If cost of batteries is a problem, you can get two 5000mAh batteries and connect them in parallel. These will cost you about 200$. You can at the moment get about 5300mAh max afaik.

Back to the other problems, speed has been already demonstrated to be easily achieved by electric cars like the Tesla roadster (0-60 in 3.9 seconds is Ferrari F60-Enzo territory), 244 mile range (not sure the Enzo has this kind of range) and you can buy it right now (true, it's 100k $, but hey, it's a sport car and the Enzo would have cost you 6.5 times that when new, and currently sells in auctions for ten times that). The Tesla S though (four door) is only 50k$ and not a lot slower (5.6sec to 60mph) with longer range.

There is also the guy you have over there in California who is drag racing his little Datsun (the white zombie) converted to Lipo power and getting 12 seconds on the qtr mile. Here's his videos:

http://www.youtube.com/watch?v=369h-SEBXd8

Pretty impressive, and he has some decent range too. Not sure how much it cost him, though, and the battery was borrowed from a university department back then. Now, I would imagine you can get them custom made, again not sure about the price. His car though is home made with more or less readily available materials.

Have a look maybe you get inspired.
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Old 08-26-2009, 11:45 AM   #12
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Quote:
Originally Posted by niznai View Post
If cost of batteries is a problem, you can get two 5000mAh batteries and connect them in parallel. These will cost you about 200$. You can at the moment get about 5300mAh max afaik.
Jason at Thunder Power has agreed to throw us a pretty solid discount as a sponsorship. He sent me a full product list that isn't available on the website and they offer a couple of 6500mAh and 8000mAh LIPO packs. I thought I'd throw this out there just in case anyone was interested.
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Old 08-26-2009, 11:56 AM   #13
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Ditch the 2 motor idea. Why add unecessary mass when there are motors that are powerful enough on its own? What you should aim for is an efficient drive train, low weight, aerodynamically balanced for speed and stability and most importantly, cost efficiency and usability if you wanna succeed in this project.

Brainstorm for a little longer before starting out...
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Old 08-26-2009, 12:10 PM   #14
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We are definitely still in the brainstorming part of all this. We actually have until May to have a running RC car. There is still a lot of theory work to be done before anything is purchased or developed.

As far as efficiency goes, I know Castle CLAIMS the Neu-Castle motors are around 85% efficient and some of this most efficient in the world. This is definitely worth testing (and will be tested as soon as the dyno is complete). What other brushless motors are known as being the most efficient?

Is a 6 cell lipo going to be more than enough for what we are going for? or should we look towards more? Say 10 cell?
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Old 08-26-2009, 12:29 PM   #15
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Quote:
Originally Posted by austinitsua View Post
Jason at Thunder Power has agreed to throw us a pretty solid discount as a sponsorship. He sent me a full product list that isn't available on the website and they offer a couple of 6500mAh and 8000mAh LIPO packs. I thought I'd throw this out there just in case anyone was interested.
I was talking about hard cased lipos, sorry I didn't specify. You should think about it becasue Lipos can explode if the membranes are damaged in a crash. I know there are higher capacity batteries, but they're soft case.

Did you check the links I posted?
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