The highest Liner speed of chains

[Dualsaber]

I was staying all night calculating......

Has any team ever trying to mount a spocket directly on the crankshaft?

We are a team from Fsae-China.

We are try to make a 2-level direct chain dirve,for a 32kw engine.But when I went into calculation,I found that the liner speed of our 1-level chain is up to 50m/s at 8000rpm.A Chinese engineering manual using a formula v=?z*n*p?/60,000.For that Liner speed?even a silence chain won't work.

But I know that a KF1 or KZ1 or whatever a racing kart would have a rpm up to 10000 plus and a engine up to 30kw plus.And they use small chains.Why? That's the part I can't understand.

So what exactly is the limit of the Liner speed of chain drive?Anyone have an idea?

[Kirk Feldkamp]

Is there a transmission in the system? You need to look at what your resultant tire speed will be for a given RPM and gear ratio. Better yet, calculate the thrust forces available at the tire patch as a result of your powertrain system for your entire speed range. I think you'll find that the linear speed of your chain is significantly slower than you're anticipating with a properly specified system. That said, generally it's the load limits (don't forget to use a safety factor) that dictate what chain you use. KZ1 and KF1 have very high revving and low torque engines (and tiny tires), so the chain loads are relatively low compared to FSAE.

[Dualsaber]

Thank you kirk.

I understand this but we are using DIRECT drive.No gear box,No CVT,Only chains.

The load limit is not a problem.What will happen if the rpm of the spocket goes too high (about 8000rpm)? Resonant vibration?Will the drive spocket break apart?

The engineering manual we use only tells us that the roller chain has a liner speed limit of 15m/s but didn't say why and what will happed if we exceed that speed.

=_,=

[woodsy96]

We are try to make a 2-level direct chain dirve,for a 32kw engine.But when I went into calculation,I found that the liner speed of our 1-level chain is up to 50m/s at 8000rpm.A Chinese engineering manual using a formula v=?z*n*p?/60,000.For that Liner speed?even a silence chain won't work.

But I know that a KF1 or KZ1 or whatever a racing kart would have a rpm up to 10000 plus and a engine up to 30kw plus.And they use small chains.

If you look back at the old Formula A motors they were running a lot higher than 10,000rpm, generally about 20,000rpm for the old rotary valves and screaming reids. As far as I am aware they used to run bog standard 0.219 pitch karting chains. I am pulling numbers out of thin air here but I think they were looking at about 25hp for about 150kg ish.

The KZ1/KZ2 on the other hand generally used a motorcycle chain and were driven through a gearbox, hence the bigger gears were running at a much lower speed and higher torque. The class weight when I ran KZ2 in New Zealand was 170kg and my understanding is they were about 45hp.

I think that part of the maximum speed might come down to manufacturing tolerances and the balancing of gears. The tiny front sprockets of a Forumla A motor mightd not have as many issues with poor balance at high RPM (because the eccentricity and mass of the gear might only be small). However a gear big enough to drive 32 kW might be more likely to have significant enough eccentricity ana lot more mass to bend a crankshaft at higher RPM.

Have you asked the manufacturers directly about what the limiting factors are for chain speed or advice on how to go about selecting a suitable chain?

[Kirk Feldkamp]

Originally posted by Dualsaber:
I understand this but we are using DIRECT drive.No gear box,No CVT,Only chains.


You're planning to have some sort of clutch in there, right? You're going to have a very tough time at an autocross style event if you don't!

I don't want to tell you how to engineer your car, but it might be a worthwhile activity to look around for a better engine than a 32kW unit with no transmission or clutch. There are many many choices out there, most of which are more desirable right from the start. Do a little analysis of the force (at the tire patch) vs. vehicle speed characteristics for your intended single speed layout, and then compare it to what's possible with a multispeed gearbox. The results will make you think twice. I'm all for simplicity and ease of use, but the level of the FSAE competition is certainly not on the order of 'beginner kart'.

-Kirk

[Jersey Tom]

The limit of linear speed is approximately 3*10^8 m/s.

Hope this helps.

[Mehul Botadra]

Originally posted by Dualsaber:
Thank you kirk.

I understand this but we are using DIRECT drive.No gear box,No CVT,Only chains.

The load limit is not a problem.What will happen if the rpm of the spocket goes too high (about 8000rpm)? Resonant vibration?Will the drive spocket break apart?

The engineering manual we use only tells us that the roller chain has a liner speed limit of 15m/s but didn't say why and what will happed if we exceed that speed.

=_,=


You might even wanna invest some in your crankshaft bearings! They're gonna get screwed bigtime with the amount of torque coming in from the direct drive.

[Dualsaber]

Originally posted by Kirk Feldkamp:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dualsaber:
I understand this but we are using DIRECT drive.No gear box,No CVT,Only chains.


You're planning to have some sort of clutch in there, right? You're going to have a very tough time at an autocross style event if you don't!

I don't want to tell you how to engineer your car, but it might be a worthwhile activity to look around for a better engine than a 32kW unit with no transmission or clutch. There are many many choices out there, most of which are more desirable right from the start. Do a little analysis of the force (at the tire patch) vs. vehicle speed characteristics for your intended single speed layout, and then compare it to what's possible with a multispeed gearbox. The results will make you think twice. I'm all for simplicity and ease of use, but the level of the FSAE competition is certainly not on the order of 'beginner kart'.

-Kirk </div></BLOCKQUOTE>

Sorry, My mistake.We have a centrifugal clutch (wet type).And the “direct drive” I'm saying means No transmission. About the poor engine we have,we are ”ordered“ to use that carp[32Kw,70kg,originally using CVT(rubber belt)+MT(2 gear),single cylinder 500CC,single cam,4 valve].We have to cut the weight and trying to use a more direct powertrain.

And finally, I gave up the idea of using chain drive for crankshaft output,Gears instead.Of course the final drive is still chain drive.

[Dualsaber]

Originally posted by woodsy96:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> We are try to make a 2-level direct chain dirve,for a 32kw engine.But when I went into calculation,I found that the liner speed of our 1-level chain is up to 50m/s at 8000rpm.A Chinese engineering manual using a formula v=?z*n*p?/60,000.For that Liner speed?even a silence chain won't work.

But I know that a KF1 or KZ1 or whatever a racing kart would have a rpm up to 10000 plus and a engine up to 30kw plus.And they use small chains.

If you look back at the old Formula A motors they were running a lot higher than 10,000rpm, generally about 20,000rpm for the old rotary valves and screaming reids. As far as I am aware they used to run bog standard 0.219 pitch karting chains. I am pulling numbers out of thin air here but I think they were looking at about 25hp for about 150kg ish.

The KZ1/KZ2 on the other hand generally used a motorcycle chain and were driven through a gearbox, hence the bigger gears were running at a much lower speed and higher torque. The class weight when I ran KZ2 in New Zealand was 170kg and my understanding is they were about 45hp.

I think that part of the maximum speed might come down to manufacturing tolerances and the balancing of gears. The tiny front sprockets of a Forumla A motor mightd not have as many issues with poor balance at high RPM (because the eccentricity and mass of the gear might only be small). However a gear big enough to drive 32 kW might be more likely to have significant enough eccentricity ana lot more mass to bend a crankshaft at higher RPM.

Have you asked the manufacturers directly about what the limiting factors are for chain speed or advice on how to go about selecting a suitable chain? </div></BLOCKQUOTE>

Thanks
I find that our limitation is the packaging.A big spocket makes a lot of problem for Suspension design.
I think the speed limit is really about the pitch, 0.219 is very small and the weight chain is low.So they could travel faster,and cause a little centrifugal force in high rpm.Also smaller pitch make the spocket smaller?the liner speed reduced also the eccentricity is not a big problem as you say.

[TorqueWrench]

To be honest with you, I think the loss in tractive effort from a direct drive with centrifugal clutch is going to greatly outweigh the savings in rotating/vehicle mass and efficiency (the Achilles' Heal of CVTs unless tension is set up right).

Its easy to do a plot of vehicle speed vs engine speed and see which setup gives you the most time in your powerband across the ranges of speeds you operate in on the track. This is why transmissions were created in the first place for cars. From doing this myself with track testing data and gearing data taken off a stock bike for competition in 08, I can tell you that a properly tuned CVT actually can beat a stock sequential box in this respect.

The only upside I can actually see to running a single speed is that CVTs are a bear to tune (one of the guys in our shop declared it "black magic"). Some clutches are easier to tune than others, but how much you can dial it in is normally inversely proportional to this. Simplest way to do it is with a stop watch. Best way is to data log engine speed, jackshaft speed, and time since launch. You can calculate wheel speed, CVT ratio, and longitudinal acceleration from this and detect wheel/belt slip at the same time.

EDIT: If I am reading this right, you have a manual transmission and CVT on the engine by default? Only reason I would even consider keeping the manual is if the rang of the CVT wasn't large enough to cover your range of speeds on the track. What that needed range is is up to you to calculate.

EDIT 2: If you are dead set on going without a transmission and you cant get a single stage chain to do it, you can always use a jackshaft and use two reductions. Downside is reduced efficiency, but it may help the packaging problem.

[Dualsaber]

Originally posted by TorqueWrench:
To be honest with you, I think the loss in tractive effort from a direct drive with centrifugal clutch is going to greatly outweigh the savings in rotating/vehicle mass and efficiency (the Achilles' Heal of CVTs unless tension is set up right).

Its easy to do a plot of vehicle speed vs engine speed and see which setup gives you the most time in your powerband across the ranges of speeds you operate in on the track. This is why transmissions were created in the first place for cars. From doing this myself with track testing data and gearing data taken off a stock bike for competition in 08, I can tell you that a properly tuned CVT actually can beat a stock sequential box in this respect.

The only upside I can actually see to running a single speed is that CVTs are a bear to tune (one of the guys in our shop declared it "black magic"). Some clutches are easier to tune than others, but how much you can dial it in is normally inversely proportional to this. Simplest way to do it is with a stop watch. Best way is to data log engine speed, jackshaft speed, and time since launch. You can calculate wheel speed, CVT ratio, and longitudinal acceleration from this and detect wheel/belt slip at the same time.

EDIT: If I am reading this right, you have a manual transmission and CVT on the engine by default? Only reason I would even consider keeping the manual is if the rang of the CVT wasn't large enough to cover your range of speeds on the track. What that needed range is is up to you to calculate.

EDIT 2: If you are dead set on going without a transmission and you cant get a single stage chain to do it, you can always use a jackshaft and use two reductions. Downside is reduced efficiency, but it may help the packaging problem.

Yes,I do make a polt of Vehicle speed vs engine speed using different ratios.I found that the traction force that our engine could provide is far below the tire's(Hoosier tire) capacity. So we chose to use direct drive with clutch.I guess is the best way for power-lack cars, cutting wight comes first.

We find and guy who is expert in scooter,after carefully investigate the rubber belt CVT, he says the design is a total failure, wrong pulley wight?wrong belt length and so on.Make it work well means to rebuild one......and we don't have that time and money.

Thanks for your advice anyway.I check your team's website.I don't understand why you are using a solid rear axle.Yes I know that fine tuning will make great difference.But~.....still don't get it.

[TorqueWrench]

You have a PM with the reasoning for the solid rear simply not to derail this thread.

I would double check your calculations on tire force. 43HP is about what our team had last time we went to competition on Hoosiers and I have telemetry showing wheel spin. Although that is going to be dependent on where your torque comes in (mine was low down), I would still run them again.

The belt length simply determines center to center distance, which is something that is simply a design constraint. The weights in the pulley are fairly cheap to manufacture (we have some made of steel and some out of something else a lot heavier). If it really is a complete redesign though and you are tight for time, don't write it off for future years as it will definitely benefit the team and is a good design project.