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Old 01-08-2002, 07:16 AM   #1
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Default Mission Pulley Size

I know there is loads about the layshaft pulleys in the Schumacher Corner but i was wondering if anyone has any theories behind what the different pulley sizes do? - WITH PROOF PLEASE!!!!

Please try and keep to the point as a lot of people want a definate answer to this question so lerts try to get one!!!!
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Old 01-08-2002, 07:23 AM   #2
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They change the transmission ratio!..., but that you probably knew already. Should it make a difference? Well at least if the same spur is kept, it affects the position of the motor and thus the overall weight distribution.
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Old 01-08-2002, 08:37 AM   #3
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Hehe - yer, I got that one! - also i appriciate it changes the rotating mass and allows you to run smaller pinions but people seem to think there is more that this - is there, what other advantages are there (you will be running the layshaft at different speeds - will this make a difference). I understand the basics of most parts of the car, and some of the more technical stuff but being only 17 I was wondering if anyone with a degree in Physics or Engineering or the like could shed any more light on the subject.

I tend to find that when you change things like this and you expect a change you will find one, weather it is there or not, this is why I dont really like listening to peoples theories, because they are normally biased one way or the other!
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Old 01-08-2002, 11:04 AM   #4
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I'm a technical layman, like yourself, but I've been scanning the schumacher corner, and I think people are imagining the pulley differences.

The reason i think they are there is to allow you to get finer tuning options when running stock and modified motors - with the 17 tooth pulley you'll get more options with low gearings, because you won't have to switch to tiny pinions (which make a big jump in ratio per tooth, compared to a big pinion).

The low rotating mass thing would count in all uses, in which case people should always use the 17 - I don't believe anyone saying the 20 has better top end, unless we now think that heavy transmissions are better for top speed, because of the momentum (if that's the case, I'd better get my 1987 Tamiya Super Sabre out of my parent's loft).

I haven't seen the car, so i don't want to insult schumacher, but I think the real reason there's a choice of pulley is because the mission design is limited in the size of spur and/or pinion it can take, and the variable pulley is used to make up for a lack of gearing options.
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Old 01-08-2002, 11:55 AM   #5
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sosidge, I f you were looking at the rotating mass theory then you would run a 20, because you would then be using a pinion aprox 4 teeth smaller to attain the same ratio. This is the main reason that i have been running the 20. That along with the fact that we all know that larger pullys are better because the belt doesn't need to wrap as tightly. I have now switched to a 17 but not run it yet.
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Old 01-08-2002, 01:35 PM   #6
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The only factual thing i have found so far really is that the belt should run more efficently with the 20T pulley due to the larger radius it is running around - Other than that the other thing I have found is that it is easier to change the pulley than the spur!!!!! (Less screws)
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Old 01-08-2002, 02:00 PM   #7
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The 20 pulley is best, since the belt is bend less. And the smaller pinion is an advantage too.
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Old 01-08-2002, 03:26 PM   #8
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This is the conclusion that I am coming to as well, therefore would a 23 tooth pulley be even better?! - obviously we cant do this but Schumacher can. there must be an advantage for the 17 tooth pulley or why would we need it?!!!
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Old 01-08-2002, 05:00 PM   #9
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Boy racer......I think there is a couple of reasons for the 17t and 20t pulleys. One is the it lets you move the motor further forward and backward with the same spur. Also on the Axis cars you could not run a very tall spur and some people felt that it lacked the puch that other cars have. With the two pulleys you can get a wider range of gear ratios and tune the drive ratio to the track you race on. With the 20t pulley the car will be more efficent b/c of the increased belt wrap and bigger radius it puts on the belt. With a 23t pulley the over all ratio will be so much lower that you would have to run such a bigger spur to get any punch out of the car that the extra weight of the supr would probably offset the advantage of the 23t pulley.

Sosidge....I would have to disagree with your statement that Schumacher came out with the 2 pulleys b/c of the limited spur and pinion size. With this car you can run from a 95t spur on down in 48pitch and this is a wider range then some of the other cars on the market like the TC3 or Yokomo who only have a few spurs to choose from. So this car has one of the more adjustable gear/drive ratios of many cars on the market.
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Old 01-08-2002, 10:47 PM   #10
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I agree with Kevin, and also with Adrian previous reply on the main thread. The 17t and 20t allow for a greater adjustment range than would otherwise be available with only one drive gear. The 17t seems to work for smaller tracks, and the 20t for the bigger tracks. I've been running the 17t and getting run down at the end of the straight. Am going to change to 20t and try that. The other benefit (opposite of what we all have been thinking) is that with the 20t you would use a smaller pinion, which a higher (numerical) ratio for better torque. The same spur / pinion ratio with a greater differance between spur and pinion, the more acceleration (torque). I have found this to be true in both R/C and slotcar racing through the years. I hope this helps, I'm just an average person like yourself and no expert, but have raced for a long time. Good luck to you, this is a GREAT car!!!PS, I ran 34/116 64p at So-Cal, and changing to 29/116 with the 20t drive.
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Old 01-09-2002, 02:46 AM   #11
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Kevin - did you not just dis-prove your point to me by answering sosidge.

Mopar - So you are keeping the same ratio (well, gearing up by about 0.1mm/rev (with 64mm dia tyres)) - Out of interest what tyres and motor do you use?
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Old 01-09-2002, 04:58 AM   #12
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I dont want to confuse things more but here goes:

From my testing on a fairly large tarck(pic attached) there are definite differences. I run 12x2 motor(12T limit) with about a 5.8 to 1 ratio on rubber tires. I use the 20T pulley and when I have tested the 17T pulley with same overall ratio (5.8) the car wheelspins out of corners(fairly low grip) and reaches a low top speed too quickly. It over revs a lot! This seems to indicate that the way power is put to the wheels from the motor is seperated into components. ie spur/pinion is one application of power and that power enters another ratio which is the cars internal ratio. So maybe with one pulley power is transferred from the pinion/spur really quickly to the layshaft but the differing pulley size alters the speed at which this power is transferred to the wheels. Vice versa.

On the other hand TC3s with internal of 2.5 are just as quick as a Corally or Mission(20T at 1.8) So im a bit confused!
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Old 01-09-2002, 05:23 AM   #13
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Hehe! - so we still dont have a definate answer!!!!

Last edited by Boy666racer; 01-09-2002 at 05:30 AM.
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Old 01-09-2002, 07:24 AM   #14
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MattW - on the rotating mass thing, I'm not denying your pinion thing, but also, if you go with the 17tooth pulley, you can fit a noticeably smaller spur to get the same ratio as with a 20tooth.

If you use lightweight pinions (I use kimbrough's carbon graphite one's - nice), I reckon there's more drivetrain weight to be lost with a smaller spur than with a smaller pinion, especially as larger rotaing objects have more inertia.

I think a real engineer with a calculator should say what's best - perhap's Cecil Schumacher?

Also, it occurs to me on this "transfer of torque" thing, where a large spur feels "punchier", wouldn't the punchiest option be to have a spur and pinion that are as close as possible in diameter, and relatively large, because then the mesh would be at it's most efficent? But that messes up rotating mass as well.

The general point about bigger pulley's transferring power to the belt better I accept though - perhaps, with the advent of 3000's, the manufacturers should be looking at sub 1.8:1 internal ratio's, if there's so much to (apparently) be gained between a 2.1:1 and a 1.8:1, or king-size diff-pulleys (the losi's are 44 aren't they - what's their pulley size?)

Anyway, your mission's 17 pulley is one tooth bigger than my pro3's, so If we ever meet in a race you won't need to worry about me down the straights.
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Old 01-09-2002, 07:43 AM   #15
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If the xxx-s has a 44teeth diff-pulley, then looking at the overall ratios the pulley would be 24teeth. That gives an internal ratio of 1.83. Pretty close to Mission's...
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