Why not more direct/shaft driven cars?

[Beast]

Wondering why there was only 4 or 5 cars at last years competition using an ATV diff.?

Seems like an easy way to save time designing and save weight.

What's the biggest issue with it?

Weight distribution from engine rotation.
Sourcing an ATV diff.
Gear ratios.
Strength.
Packaging engine into chassis.
Designing/making a driveshaft.
Clutch style diff.

Just seems like there must be something wrong with if 95% of the teams use a chain.

[Beast]

Wondering why there was only 4 or 5 cars at last years competition using an ATV diff.?

Seems like an easy way to save time designing and save weight.

What's the biggest issue with it?

Weight distribution from engine rotation.
Sourcing an ATV diff.
Gear ratios.
Strength.
Packaging engine into chassis.
Designing/making a driveshaft.
Clutch style diff.

Just seems like there must be something wrong with if 95% of the teams use a chain.

[gug]

dont worry about 95% of the teams using a chain. its more like 97% dont use a cvt, but we are still going to use one. there are so many possibilities for doing something different in fsae, half the time people dont take the more unusual choices because they dont have the time/manpower to research and prove the idea. everyone knows a chain, has seen one work before, and there is loads of experience with them.

but with your idea in particular, could you outline the exact benefits? is that weight saving off a torsen? i dont quite know how an atv diff works.

- if it isnt coming, you need a bigger tool.

[Ben Beacock]

We used a suzuki vinson 500 diff last year.

Sourcing the diff is a bit of a problem and can be expensive to buy. However:
-Gear ratios work out great (3.6:1)
-Packaging is dead simple
-Weight was about 18lbs without driveshaft and input brake rotor/hat
-Our driveshaft was a 75mm long cylinder with splines cut straight through it (the diff and engine splines match)
-strength wasn't an issue at competition

We did however, blow the unit apart after the competition. After about 10 minutes of test driving(and therefore sticky tires) we switched drivers. Being a new driver, he didn't take up any slack, revved it up and slammed it into 1st and dropped the clutch at the same time. Broke the pinion, ring gear and blew the side out of the case half. On top of that, we were running the engine with the throttle bodies and no restrictor.

If anyone is planning on running this diff, we will likely be designing a new ring and pinion out of a stronger material, and designing a shorter, lighter case (since we need 2 of them)
We might be able to make a few extras if anyone is interested.

Ben Beacock
Co-Manager
2004 Gryphon Racing - University of Guelph

[Beast]

I believe most ATV differentials are a clutch pack style limited slip and weight ~12-15lbs for the diff, housing, seals etc.

[Angry Joe]

Simple = good

Chain drive is simpler than shaft drive

http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

The difference between racing and a crack addiction is that racing costs more and has a more adverse affect on your social life

Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[All Wheeler]

Ben,
I'm interested to know what kind of material you are looking at using for your crown wheel and pinion. I assume that contact stresses are the greatest concern here, unless you are hardening the living daylights out of your material. An excessively hardened material would explain the blowing apart under impact loading. Also, what criterion are you using to come up with ratings for these gears.
We have done a little gear design here at Newcastle, and have been using infinite fatigue life under maximum torque loading and equivalent impact loading for our design. Consequently our gears are a little larger than we would like them to be. When we get a bit of data on gear loads, it may be possible to apply Miner's rule of cumulative damage or something like that.
Doug
douglas.teyhan@studentmail.newcaslte.edu.au

[Ben Beacock]

We're looking at 8620, case hardened to 58-60 Rockwell at a depth of 25 thou. We're more interesed in a cheaper gearset, since the one from suzuki only comes with the diff attached. We can probably make it for 1/4 of the price it would cost us to get it with the diff.

Ben Beacock
Co-Manager
2004 Gryphon Racing - University of Guelph

[A Reinke]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Chain drive is simpler than shaft drive<HR></BLOCKQUOTE>

but when it comes to packaging a rear end for a chain drive, it is NOT a simple task.

[JG_GRYPH]

how would you know that chain drive is easier if you havent done shaft drive. We did it last year as Ben was pointing out and I found that when our design changed to shaft drive it was one of our best decisions last year. It eliminated a lot of headaches that need to be designed around.

Jeremy Goertz
University of Guelph
Formula SAE

[Angry Joe]

It's two sprockets and a chain. You can't get much simpler than that. As far as packaging, it wasn't much of an issue for us.

The difference between racing and a crack addiction is that racing costs more and has a more adverse affect on your social life

Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Daves]

Chain:
Advantages:
"¢ Do not have to remove differential to install or reinstall.
"¢ Simple alignment.
"¢ Reliable. No slipping.
"¢ Engine sprocket already made.
Disadvantages:
"¢ Marginally less efficient than belt.

Shaft:[/]
Advantages:
"¢ Reliable.
Disadvantages:
"¢ High cost due to many new parts.

[B] Belt:
Advantages:
"¢ Marginally more efficient than chain.
Disadvantages:
"¢ Only works with a small range of tensions.
"¢ Possibility of slipping when driving in rain.
"¢ Must remove differential to install or reinstall.

Gears (transaxle):
Advantages:
Disadvantages:
"¢ Places engine mass over the rear of the car, creating difficulty attaining 50/50 weight distribution.
"¢ Parts must be high accuracy for alignment.

http://www.letu.edu/formula

My Formula Photos & Links (http://what3542.5u.com/dave/fsae/formula_photos.html)

[Angry Joe]

You forgot one for driveshaft, fabrication time. That alone would be a turn-off for me...

The difference between racing and a crack addiction is that racing costs more and has a more adverse affect on your social life

Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Matthew]

who says you NEED 50/50 ??

http://fsae.com/groupee_common/emoticons/icon_wink.gif

-Matthew Hetler
hetl0020@umn.edu

[Ben Beacock]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Angry Joe:
You forgot one for driveshaft, fabrication time. That alone would be a turn-off for me...
<HR></BLOCKQUOTE>

Last year's driveshaft was a 1-3/4" dia bar, 3" long, bored and then splines cut straight through. It just happened that the splines on the input to the Suzuki diff are the same as the splines for the Suzuki GSXR sprocket. Man, did we get lucky there. http://fsae.com/groupee_common/emoticons/icon_cool.gif

Ben Beacock
Co-Manager
2004 Gryphon Racing - University of Guelph