Drive Sprocket FOS [Archive]

benko

11-04-2006, 03:46 PM

I was wondering if anyone knew what an appropriate Factor of Safety would be for a 48 tooth drive sprocket made of 7075 aluminum (running a CBR 600 engine). I'm just not sure how low you can go and still be comfortably safe with the design. I appreciate any feedback.

benko

11-04-2006, 03:46 PM

billywight

11-04-2006, 05:21 PM

Yeah, pretty much anything above 1 should work just fine.

Mike Claffey

11-05-2006, 07:19 AM

It obviously depends on your loading model, and how you define comfortable. Without knowing that, its pointless to answer the question. If you haven't built/tested or run the part on a previous car I would go very conservative considering its not something you can afford to have fail. Remmember that no loading model is ever going to be perfect because its a model of reality based on assumptions.

FEA And destructive testing are your friend.

Welfares

11-05-2006, 07:31 AM

Yes, FEA is your friend.

And remember when you're doing your load case, take your worst case as the max grip you can get from your tires, not the max output torque, as you will break traction before all that force can be applied to your drivetrain.

Jersey Tom

11-05-2006, 09:05 AM

Fatigue.. keep that one in mind. Also be pretty careful of alignment when you set your car up. Or else it'll eat up those aluminum teeth.

I'd reccomend a hard anodize on top. MIL-A-8625E, Type III, Class 1 or 2, at least .0020" thick.

benko

11-05-2006, 10:22 AM

Thanx for your replies guys. I have a few designs already in Solidworks and did some COSMOS on it. I applied our worst case output torque at the tires (not torque from the engine); is that the same as what Welfares is saying? I noticed that many motorcycle drive sprockets are made from 7075 aluminum; is it still recommended to anodize this alloy even though it was designed for such applications? Does anyone know if or how you can apply cyclic fatigues in COSMOS? Thanx for the help.

Jersey Tom

11-05-2006, 11:38 AM

Well first you have to know what fatigue loading the sprocket will see.

Motorcycle drive sprockets might be made from 7075 but I bet you anything they have some surface treatment. I would HIGHLY reccomend the hard anodize for wear resistance.

But yea, you can do fatigue analysis in Cosmosworks.

Matador Motorsports

11-06-2006, 01:28 AM

Go through the COSMOS tutorial using a steel fatigue curve since it has a "knee" on the curve, most aluminum alloys don't have that "knee." About the safety factor, since it is a drivetrain component, every time there's a shift in the transmission there will be a shock loading scenario that will break any low safetyfactor just above 1 with time. As far as fatigue safety factor, just aim for a value of 1!

murpia

11-06-2006, 03:36 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Welfares:
And remember when you're doing your load case, take your worst case as the max grip you can get from your tires, not the max output torque, as you will break traction before all that force can be applied to your drivetrain. </div></BLOCKQUOTE>
No, you need to use max output torque. Your drivetrain and rear wheels have inertia, so they can accept more torque than the grip limit by accelerating.
Regards, Ian

Welfares

11-06-2006, 04:17 AM

"No, you need to use max output torque. Your drivetrain and rear wheels have inertia, so they can accept more torque than the grip limit by accelerating."

But surely it is negligible if you design it well enough and make them nice and lite.

Nah, is see your point. I won't mention names, but there was a man who knows about designing race cars, and he said, ever SAE car he had seen had a FOS that was to high.
He was asked "what safety factor should we use"

1

If you design it for the comp, and design it really, unfeasibly well, your car shold have a design life of < 100km. But then we all like to do some testing/ hooning around after the comp. so its not realistic.
Really.
Is it?

In one of the solar car races, there are 3 corners, and there was rumour of a team, who had designed their brake calipers with a fatigue limit of 4 cycles.
Not that i would associate with people from solar car.

benko

11-06-2006, 02:59 PM

I appreciate all your help guys...thanx

benko

11-06-2006, 05:00 PM

Please excuse my lack of knowledge, but does anyone know how to use a fatigue analysis in COSMOS? Is it something you have to choose in the "Study" menu under "Analysis Type" or located somewhere else? Thanx

Iloper

11-07-2006, 07:33 AM

Our sprocket seen in the pic below is designed with a safetyfactor of 1,5 according to the designer. Material is Al 7075, anodized. 520 chain.

http://www.tfd.chalmers.se/~v02jope/drivetrain.jpg

It ran with no problem trough testing and the UK comp. We are putting out 92 Nm torque, 89 Hp.

My impression is that anodizing is not necessary, sinze all of the anodizing is gone on the teeth surface, and the sprocket is far from worn out. Also keep in mind that a formula student car runs quite a short distance compared to a bike, and under quite clean conditions, not like a motorcross.

/Per CFS -06

drivetrainUW-Platt

11-08-2006, 09:16 AM

maybe its because I'm the drivetrain guy, but that sprocket is pure sex.

benko

11-08-2006, 10:35 AM

That is definately a sweet looking sprocket....may I ask how much it weighs?

Ian M

11-08-2006, 12:12 PM

Agreed on the pure sex comment!
That whole rear section is dead sexy!
OK, this is a little off topic but I have been checking the advantages/strength issues with using a 428 chain and 13 tooth front. According to my calculations, (full engine torque with locked rear wheel) there will be a factor of safety right at 1.5. I know this is good, but it kinda scares me. Any experiences of teams using a 428 with around a 4 to 1 final drive ratio would be helpful to calm my worries. Packaging is just so much nicer with the 428 due to the .5" pitch compared to .625"

Analogue

11-08-2006, 04:22 PM

7075 will not take a traditional hardcoat well. Neither will 2024. There are some proprietary processes that claim to be able to do it.

The only anodizing you'll get with 7075 is the pretty color stuff. It's thin, and fairly worthless against anything other than corrosion.

Keith

chavez

11-08-2006, 05:05 PM

92Nm, what is your engine package?

billywight

11-08-2006, 07:41 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">That is definately a sweet looking sprocket....may I ask how much it weighs? </div></BLOCKQUOTE>

Does it matter? It's attached to a 12 lbs diff...

Looks good otherwise though, and the supercharger is a nice touch.

drivetrainUW-Platt

11-13-2006, 02:30 PM

what supercharger is that? Looks similar to Texas A&M's

Ian M

11-14-2006, 05:15 PM

I was wondering the same thing about the supercharger. Who makes that?
Would anyone be interested in an 11-tooth 520 sprocket if I put in an order for 5?

rjwoods77

11-14-2006, 05:47 PM

Looks like a kenne bell/autorotor case.

Iloper

11-15-2006, 01:57 AM

Yea, there realy is no atvantage in having a 125 gram sprocket when you attach it to a 5kg chunk of steel ... but of course every gram counts. except the diff, couse it's just to heavy.

I'ts an Autorotor 1040 positivie displacement supercharger, its good for about 180 hp. Texas A&M is running the same model.

/Per
CFS