gearbox weight reduction

[benko]

Can anyone provide information on eliminating 6th gear from the primary shaft and still use the 6th gear/dog on the secondary shaft to deliver the second gear ratio. Are there any drawbacks to this idea? Thanx

[Jersey Tom]

Well it would be nice to know what transmission youre takling about..

Havent pulled apart many bike transmissions, but on the F4i the 5th and 6th gears are on the mainshaft. Just take out the actual gears and keep the dog ring in there to transmit torque to the countershaft.

[Duff]

we run a 4 gear car.
allows us to remove:
mainshaft- 5th and 6th gears, dogs on 3/4
countershaft- teeth on 5th and 6th

we also remove the 5/6 shift fork.

if you only want to remove 6th, then

[Bill Kunst]

Okay, maybe stupid question. As in it could be obvious, and you don't want to tell.

How much weight is this?
How much power (dyno) is this worth?

If you dont want to answer the second, just let me know if it is "noticeable".

Just curious,
Bill

[Duff]

not sure on weight
say 500g of rotating mass, and 100g of fork.
havent weighed it myself.

as for power, we have never done a back to back comparison, and the last thing i want to do at the moment is split the case of our dyno engine to see what the difference is.

i dont drive, so i dont know if its noticeable http://fsae.com/groupee_common/emoticons/icon_confused.gif

its easily a 500g saving, and concidering you can do it with an angle grinder, why wouldnt you? (unless your gearing doesnt allow it)

[Jersey Tom]

I'll save every ounce of weight and rotating inertia I can. By itself not noticeable but if you do it no every part it sums to a big difference.

[Boston]

If you translate the rotational inertia of the gears to translational mass, you will find it is negligable. That said, its definatly worth it to remove those gears as they are pretty heavy.

[Bill Kunst]

Just was curious, thats all. It would be cool to have back to back dyno tests, though.

[VFR750R]

Remember that after the primary reduction ratio these parts have even less inertial effect as the transmission shafts are turning much slower then the crank. Say you remove 4 lbs total, other then removing 'unused' weight, and waste of probably a couple dozen man hours, what will it get you?
Anyone here should be able to assume a steel disk approximately the size of the gears in question and assuming a reasonable acceleration rate for the shafts they are on come up with a powerloss for the gears. Not knowing what most of you have for dyno facilities(although I can assume they aren't state of the art repeatable to .1hp which you would need to measure the difference), you're better off doing the math.

So here it is.
Primary reduction 1.82(for F4I)
Crankshaft accel rate (guess, 2000rpm/s)
Primary trans shaft accel rate 1099rpm/s
4 steel disks average 10cm diameter, 1cm thick
Inertia of single disk .5*M*R^2
Density of tool steel = 7.715g/cc

Disk volume = 39.27cc
Disk weight = 303g
Inertia = 3787.5g/cm^2 = 3.7875kg/cm^2 = 3.7875*10^-4 kg/m^2
1099rpm/s = 115rad/s^2
T = .04355Nm per disk
T = .174225Nm total or .129 ftlbs or .22hp at 9000rpm

This assumes worst case senario on gears because they obviously are not solid and not all four are going to be 100mm in diameter. I'm sure my guess for accel rate is off but on the correct order of magnitude for the first traction limited gear.

You'd be better off trying to underbalance the crank or reducing your clutch size (way more inertia there).

[Mike Claffey]

This is the sort of work that can be done while you are wokring in the area - ie changing the shift pattern from 1-n-2 to n-1-2.

[Charlie]

You're right I wouldn't tear the engine apart just for this. But it's hardly a 'waste of man hours' if you're already in the engine. It's a pretty simple thing to do.

I was able to take over 3 lb of rotating mass out of an F4i without doing any machine work at all, and it was just a matter of a slightly different assembly technique. Of course there was the 'wasted' hours while I weighed things and planned it out. http://fsae.com/groupee_common/emoticons/icon_razz.gif

Now the 3 lbs of inertia might not have been significant for power, but it couldn't have hurt, and 3 lb out of your overall engine (and car) isn't bad either.

How many man hours have teams worked to shave 3 lb off of thier frame?

[Duff]

fork = 85g
5th and 6th gears on the mainshaft = 400g
teeth and dogs on other gears = 100g (guessing)


Originally posted by VFR750R:
Say you remove 4 lbs total, other then removing 'unused' weight, and waste of probably a couple dozen man hours, what will it get you?

ive spent the last 8 months saving 3kg from our dry sump. almost 600g in a couple of hours sounds like a good bargain to me. the fact its rotating is just a bonus.

even if you havent already got the engine in pieces, you can split the case and put it back together in a couple of hours


Originally posted by Charlie:
I was able to take over 3 lb of rotating mass out of an F4i without doing any machine work at all, and it was just a matter of a slightly different assembly technique.

did you forget to put in the cam shafts? http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
3lb is about 1400g. would love to know how you managed that.

leave off the alternator?
or run a 2 gear car?

cheers

[Jersey Tom]

Say you remove 4 lbs total, other then removing 'unused' weight, and waste of probably a couple dozen man hours, what will it get you?

Holy crap are you kidding? I'd be ecstatic to drop 4 lbs off the car! I'm excited pulling out .1 - .15 lb out of bellcranks.

You should see the Champ Car guys.. excited about the weight reduction by changing their 1/4" tophat bolts to Ti from steel. Weight savings of what.. 20gram per wheel?

.5% makes the difference between podium or not. In vehicle weight thats what.. 650lb car and driver.. 3-4lb? Yea. I'll spend some hours to drop that weight. Or in F1 where pole and second in the grid are .003% apart.

[Parker]

while the gearbox is brought up, quick question. How would one go about finding information on changing the shift pattern from 1-n-2 to n-1-2?

Parker

[Charlie]

Originally posted by Duff:

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Charlie:
I was able to take over 3 lb of rotating mass out of an F4i without doing any machine work at all, and it was just a matter of a slightly different assembly technique.

did you forget to put in the cam shafts? http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
3lb is about 1400g. would love to know how you managed that.

leave off the alternator?
or run a 2 gear car?

cheers </div></BLOCKQUOTE>

No 1st gear, besides that lets just say that Honda made some changes from the F4 and F4i that make some parts swapping desirable.

We had a lightened crank as well that brought to total savings over 5 lbs. Unfortunately, this engine never raced, I don't think. Though it served some dyno time and may have raced after I left, not sure.

[Duff]

Originally posted by Charlie:
No 1st gear, besides that lets just say that Honda made some changes from the F4 and F4i that make some parts swapping desirable.

clutch and crankshaft?

if the F4 clutch can still get the power to the ground it would deffinantly be worthwhile.

[Mike Claffey]

Originally posted by Parker:
while the gearbox is brought up, quick question. How would one go about finding information on changing the shift pattern from 1-n-2 to n-1-2?

Parker

Parker one of the simpliest ways would be to look at the shift barrel. Open up your engine and do a few shifts to see how it operates. You will notice the selector forks move down tracks. Depending on the position of the selector forks different gears can be engaged. Change the geometry of these tracks to suit your required shift pattern. You can also modifiy the shift characteristics to suit how your driver/designers want it.

Regards,

Mike

[Jersey Tom]

Yup. Best way is redesign of shift drum. Good challenge.

[VFR750R]

Ok 4lbs is alot for a single area of the car, but by itself isn't going to make a measurable gain in performance. As long as you are making the commitment to light is right in other areas it makes sense, but I've never seen anyone calculate weight loss to points in the competition and I feel it would be fairly flat between 400 and 550lbs.

Here's why I feel this way.
i've seen 40+lbs of lead added to the car and not effect skidpad.
i've seen 20lbs added to the back of the car and it go faster on an autocross type course
I've seen our tallest driver be the best at skidpad
I've seen a 225lb kid be one of the fastest drivers we've ever had.
if you reduce car weight, driver becomes more significant portion of total weight...which is variable and starts having larger effect on spring and shock settings(may or may not be significant, you decide)
if you reduce car weight, sprung to unsprung weight becomes less favorable if you keep 13inch wheels
10inch wheels require large commitment to keep car even lighter to limit shorter uprights loads to keep car stiff and limit deflection at tire contact patch.

I know a lighter car will accel faster for the same power, but a car with more rear weight or higher cg will too.

Has anyone with a feather weight car added some tungsten or lead on the bottom of thier frame or close to their current CG height and see what happened to their performance?

Of course this has been discussed a LOT before, here was one I found by search

http://fsae.com/eve/forums/a/tpc/f/125607348/m/46710996...10457521#43910457521 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/46710996521?r=43910457521#43910457521)

[Jersey Tom]

Well I tell ya what.. a light car is sure a lot easier to carry around.

Drivers are the biggest variable at this level. But I do everything I can to give the maximum accelerative potential to him/her at all times. Easiest way is cut weight and simplify.

[KU_Racing]

Im kinda betwwn VFR and the 'minimum at all costs' weight philosophy. VFR's points are all correct, but at the same time:

Average F1 Race: 60 Laps
Average Lap Time: 75 seconds
Total Time: 4500 Seconds

F1 car weight: 500 Kilos
.5% of 500 kilos: 2.5 kilos

.5% weight savings has potential of saving .5% of lap time during all full-throttle acceleration

Average time at full throttle for an F1 lap: 70%
(3150 seconds at full throttle)

Possible time saved from .5% weight savings in F1 race = .5% of 3150 seconds = 157 seconds.

Before everyone flames me, I know.. not perfect calculations yadayadayada. The point is, there is something to be said for small weight savings.

[Duff]

Originally posted by Bill Kunst:
How much weight is this?



handed the gears in to the workshop last night, and got them back this morning.

711g is the total saving (2 gears, a fork, dogs off 2 gears, and teeth off 2 gears)

call it 700g saving by the time we put some ally spacers in.

cheers

[the fat LION]

an ounce here and there really does add up after a while..its definately worth it as long as u arent sacrificing durabilty (not that thats really a problem by taking out a few gears)

[Bill Kunst]

that is considerable, Duff.