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Old 07-30-2003, 10:36 AM   #1
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Default Gearing Technique - Better Acceleration

taken from http://www.schumacher.clara.net/setupguidegearing.htm


Quote:
2.4 Spur/Pinion Combinations

It is advantageous to use the smallest combination of spur and pinion as possible. As a rough and crude example:

Gear Ratio 1 is 50 / 25 = 2
Gear Ratio 2 is 80 / 40 = 2

Gear ratio 1 will allow the car to accelerate faster despite it being the same as gear ratio 2. The reason is down to moments of inertia. An object which is smaller and lighter requires less energy to get it moving. So this extra energy is transferred to the wheels of the car and gives more acceleration.
so in a REAL WORLD example.. using an MR4TC Custom - internal drive ratio 2.2

66T spur / 22T pinion x 2.2 internal drive ratio = 6.6
78T spur / 26T pinion x 2.2 internal drive ratio = 6.6

thus the 66T spur & 22T pinion combination would be faster than the other one, right?

i asked around.. and MO, a respectable member here told me that...

Quote:
If you are looking for the most acceleration, you would not want to go with a small spur anyway. For more acceleration, you want a higher final drive ratio, which means you want a small pinion and large spur.

It has more to do with leverage. Imagine trying to turn a steering wheel on a real car. The bigger the steering wheel is, the easier it will be to turn.
so i dont quite understand what MO is saying (im not so bright) and it seems to me that both the statements are contradicting...

so is it better to have a small spur & small pinion combo, or a large spur & larger pinion combo ? for the same final drive like my example above...cause if you use a larger spur.. over the smaller spur to achieve the SAME final drive ratio.. the larger spur will always has a larger pinion as compared to the smaller spur...like the example above

by the way, whats the smallest spur that would fit in a MR4TC Custom/Special ? I was thinking to get the RRP Super Spur 48P 60T.. will that be too small to fit? the shopkeeper told me that its very small and that the pinion might not be able to make contact even.. any experienced MR4TC driver can clarify that? or tell me whats the smallest spur the MR4TC can accomodate

thanks in advance...
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Old 07-30-2003, 11:09 AM   #2
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Default Gearing Technique - Better Acceleration

Example (1):

Larger diameter, heavier Pinion. MORE mass to accelerate, especially if it is a Steel Pinion. Small Spur to Larger Pinion has MORE contact area and MORE possible friction.

Example (2):

Smaller Pinion diameter, less mass to accelerate. Larger Spur weighs slightly more, but should be insignificant because of the minor weight difference and the lower rpms that a Spur turn at.

Anyone else have some thoughts?
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Old 07-30-2003, 11:27 AM   #3
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I'm not familiar with the MR4TC, but if changing the spur size, affect the motor position up/down, I wold definately go for the largest spur, since this lowers the motor, which again means a lower center of gravity. Which you want....

Talking about the real world.... If you got the best motor, the best matched batteries, you have taken the grese out of the ball bearings, in short if you have done anything possible to make your car faster, then the small weight reduction of the pinon might make a difference. Just my opinion.
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Old 07-30-2003, 11:29 AM   #4
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I'm so confused...
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Old 07-30-2003, 11:46 AM   #5
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Hey all,

I don't think you understand what I am trying to say

I know that using a higher gear ratio will give me better acceleration, that's not a problem. The variable I am trying to compare is the difference in efficiency between using a pair of large gears and a pair of small gears, for the same ratio. As far as I know, using smaller gears will be beneficial, because there is a lot less mass and size, thus a lot less inertia to overcome when accelerating (like installing a lighter flywheel in a fullsize car).

The only two things that are confusing me now is whether there would be any detriment to torque by using a small pair of gears (with the gear ratio being the same, MO's example only applies to a single wheel, I am talking about two wheels, and as far as i know there should not be a difference), and also if, physically, what is the smallest spur and pinion combination that would fit in a MR4TC-custom (standard motor mount). Currently the smaller spur I have found is a 48P 60T which I intend to use, what i need to know is the smallest size pinion I could use with that.
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Old 07-30-2003, 11:55 AM   #6
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Quote:
Originally posted by Cole Trickle
I'm not familiar with the MR4TC, but if changing the spur size, affect the motor position up/down, I wold definately go for the largest spur, since this lowers the motor, which again means a lower center of gravity. Which you want....
motor moves horizontally on the mr4tc, so that won't really apply.. well, it would shift the CG front and back, but that won't make such a huuuge difference.

Quote:
Talking about the real world.... If you got the best motor, the best matched batteries, you have taken the grese out of the ball bearings, in short if you have done anything possible to make your car faster, then the small weight reduction of the pinon might make a difference. Just my opinion.
Hmmm in terms of standing mass lighter, smaller pinions and spurs will make a tiny difference, but once you get things spinning inertia comes into play. Seeing the rather high speed at which the pinion spins, this is where lighter mass would make a difference. A lighter, smaller spinning object requires less force (and thus less time) to spin up to a certain rotational speed. But yes, perhaps you would need the skill level of Masami to really take advantage of that difference, but a difference is a difference, and that's why people will spend the extra cash for that extra 0.05V from fancy matched batteries.
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Old 07-30-2003, 12:52 PM   #7
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Not to throw another variable into the mix, but 64P gears are supposed to be more efficient, so you probably want to look at them as well. The whole sallest gears possible in a respective ratio makes logical sense to me, although I haven't done any testing and I am not nearly a good enough driver to be able to tell the difference on the track (yet).
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Old 07-30-2003, 01:54 PM   #8
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Actually the gears with the more mass are better if you're a good driver. This may be hard to realize but the key is heavier gears are also harder to de-accerarate which means if you're a good, smooth driver you'll be able to carry more corner speed and make smoother transitions. In fact I've known drivers to fill up the pinions with lead for that extra mass. If you're an on off throttle driver you'll never see it.

In truth I will always use the largest combination possible to put the motor as low as possible in the chassis. Other than the batteries the motor is by far the heaviest component on your car. Overall the lower you can place you motor will have a far greater effect on your car then the gear mass of your pinion and spur.

Last edited by calvin; 07-30-2003 at 02:45 PM.
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Old 07-30-2003, 08:42 PM   #9
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Quote:
Originally posted by calvin
Actually the gears with the more mass are better if you're a good driver. This may be hard to realize but the key is heavier gears are also harder to de-accerarate which means if you're a good, smooth driver you'll be able to carry more corner speed and make smoother transitions. In fact I've known drivers to fill up the pinions with lead for that extra mass. If you're an on off throttle driver you'll never see it.

In truth I will always use the largest combination possible to put the motor as low as possible in the chassis. Other than the batteries the motor is by far the heaviest component on your car. Overall the lower you can place you motor will have a far greater effect on your car then the gear mass of your pinion and spur.
That is something that I thought about when I saw Masami's 1/12 that won the worlds. He used a steel (yes, steel) pinion on the car.

I don't drive electric, so I won't say more and make a fool of myself, but I feel any difference you find will be negligible and your time could be better spent elsewhere... but then again, we all want the fastest car possible, even if we go to strange extremes to reach it.
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Old 07-30-2003, 09:42 PM   #10
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With 48P I've been told by some factory drivers that you shouldn't go any lower than a 18T pinion, if you need to gear down go with larger spur. They didn't say why but I think it might be b/c with smaller diameter pinion there are less teeth that are interlocking with the spur at any given time, so more load is placed on them while they slide in and out which will hurt effeciency more than power. Where with bigger diameter gears with same ratio some of the load is taken off of the teeth letting them work more effeciently. You'd think the friction load should be the same no matter what, but maybe it isn't. Just my opinion.
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Old 07-30-2003, 09:50 PM   #11
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Small spur & pinion makes sense only from an Inertia point of view; be it advantageous or not is up to the driver.

Very small pinions however (anyone remember <10t 32dp pinions??!)... can have teeth that "rub" the spur's teeth more than normal... so this would be less efficient. Smaller teeth reduce this effect.


Bear in mind too:
1) you're limited by the space between motor & layshaft as to how big/small your spurs and pinions can be...
2) spurs don't come in that wide a range of sizes...

Its all much of a muchness anyway... any "advantage" would be about ~0.002% at the most. Clip a corner during your race and ALL advantage (if any) would be straight down the drain.


If one's worried about such minutae, how about:
-how much paint weighs, and different colours weigh differently
-peaking your battery right at the startline (portable 12V battery!)
-leave your tyrewarmers on up until the starting buzzer ( " )
-rebuild with new set of unlubed ceramic bearings for every race
...
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Old 07-30-2003, 09:58 PM   #12
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Masami probabely just did it for weight restrictions. If you have a heavier pinion it creates more rotating mass. Now yes, your motor will want to keep going instead of slowing once it's up to speed but when you are excellerating it will take longer to reach top speed due to more mass. If you a smooth driver you don't need a heavier pinion to keep you going you can just pull the trigger harder to keep your speed up.
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Old 07-30-2003, 11:33 PM   #13
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The minimum number of teeth in a pinion has to do with practical physical limitations. There is a maximum number of teeth for a given pitch size that you can put in a circle and still keep within engineering tolerances. I'm pretty sure you've never seen a 2 or 3 tooth 64p gear.
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Old 07-31-2003, 01:23 AM   #14
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Quote:
Originally posted by fatdoggy
Masami probabely just did it for weight restrictions. If you have a heavier pinion it creates more rotating mass. Now yes, your motor will want to keep going instead of slowing once it's up to speed but when you are excellerating it will take longer to reach top speed due to more mass. If you a smooth driver you don't need a heavier pinion to keep you going you can just pull the trigger harder to keep your speed up.
Personally, I think that would be a dumb way to add weight. He already had tabs on the rear end just past the side plate thingee (okay, I can't explain it properly... sorry), but if he needed to put even more weight on his car, he'd put it here (which he did) because it is almost as far rearward, and much lower on the chassis.

Again, I don't race electric, but a heavier pinion that would slightly increase driveline inertia would a llow a person to get more off the throttle and coast more around a turn allowing the capacitor to more effectively store energy and allowing the car's runtime to be slightly longer... a great concern for 1/12 onroad mod with 8 minute races. A theory, but, when you get a pro's setup and see something bizarre like this, you don't always get the comment from the racer that rationalizes such strange equipment choice.

And I totally agree with WC's last comment.
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Old 07-31-2003, 03:18 AM   #15
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Quote:
Originally posted by fatdoggy
Now yes, your motor will want to keep going instead of slowing once it's up to speed but when you are excellerating it will take longer to reach top speed due to more mass.
more or less what im trying to say.
an advantage is an advantage..

like i said. you give me a matched racing batt. pack.. and a normal one..makes no difference to some..

i'm just trying to find out, or rather, confirm the best gearing technique available..

as for finding spurs, RRP has 48P 60T, the smallest available.
whether it can fit in the car, i think it depends since every car is different

and again, the motor mount on my MR4TC moves sideways, not up & down.. so it'll just move the CG back and forth..

so..i still dont know whether what i said, above, is correct or not

Last edited by versa; 07-31-2003 at 03:24 AM.
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