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Old 10-02-2003, 10:31 PM   #541
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Hey, I fully admit im a newbie, so calling me such has no effect, but thanks for the quick answers and being good sports about my bad attitude today (sorry bad day). Its just that there have been other times that I've asked questions on the Mugen thread and gotten absolutley no response, and if I did, it was ussually like a sentence.
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Old 10-02-2003, 10:52 PM   #542
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Quote:
Originally posted by Walt
So, all of the first gear pinions, regardless of number of teeth, are the same diameter? Same goes for the second gear pinions (all same as each other, not the same as the first gear pinions)?

I'll have to see this to understand how they did that... I thought all the gears were the same pitch, therefore, more teeth means larger pitch diameter. Plus, the 'ratio' is not only the number of pinion teeth/number of spur teeth, but also the pinion circumference/the spur circumference. Therefore, how can the 18 tooth first gear pinion have the same diameter as the 15 tooth first gear pinion AND still have the same pitch, which would be required since they have to both mesh with the same spur gears???

Can anyone back up Fastharry on this? Basically, he says that any combination can be used, and the engine stays in the exact same position for any combination.

This seems to be breaking the laws of mechanics.

This concept has been used for years.

My old school MTX-2 uses the same type of gears but it's been used way before that in 1/8 on-road .
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Old 10-02-2003, 11:45 PM   #543
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Quote:
Originally posted by BossPlaya
Hey, I fully admit im a newbie, so calling me such has no effect, but thanks for the quick answers and being good sports about my bad attitude today (sorry bad day). Its just that there have been other times that I've asked questions on the Mugen thread and gotten absolutley no response, and if I did, it was ussually like a sentence.
No problems!! Glad I can help!!
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Old 10-03-2003, 01:17 AM   #544
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Quote:
Originally posted by Walt
So, all of the first gear pinions, regardless of number of teeth, are the same diameter? Same goes for the second gear pinions (all same as each other, not the same as the first gear pinions)?

Can anyone back up Fastharry on this? Basically, he says that any combination can be used, and the engine stays in the exact same position for any combination.

This seems to be breaking the laws of mechanics.
Walt, your thinking is correct. If the pinion were the same effective diameter regardless of number of teeth... you wouldn't be changing gear ratios at all!!! The gear teeth are all made to one module/pitch and will change the pitch diameter of the gear when teeth number changes.

If you drop or add a teeth on the pinion you can get away and not change the engine location..... only because the large gear pitch as a higher mesh tolerance.

To make your 1st pinion/spur combo mesh along with your 2nd pinion/spur combo..... the 1st gear pinion teeth+spur should equal 2nd gear pinion + spur teeth. If they're off by a tooth or two it's still close enough to work in most cases.
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Old 10-03-2003, 02:37 AM   #545
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finally fixed my motor woes. had an air-leak on the backplate.



first casualty at the track today. took the the sweeper turn after the straight too wide. I wasnt going that fast. but I managed to pop off both pivot balls on the front-left and the universal snapped. the upright seems okay. I'm just wondering how the pivot balls popped out. and I lost the two plastic cone washers.




anybody know a website that has replacement or hop-up universals???



also what weight diff grease/oil are you guys running?
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Old 10-03-2003, 05:08 AM   #546
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Quote:
Originally posted by boom
Walt, your thinking is correct. If the pinion were the same effective diameter regardless of number of teeth... you wouldn't be changing gear ratios at all!!! The gear teeth are all made to one module/pitch and will change the pitch diameter of the gear when teeth number changes.

If you drop or add a teeth on the pinion you can get away and not change the engine location..... only because the large gear pitch as a higher mesh tolerance.

To make your 1st pinion/spur combo mesh along with your 2nd pinion/spur combo..... the 1st gear pinion teeth+spur should equal 2nd gear pinion + spur teeth. If they're off by a tooth or two it's still close enough to work in most cases.


Thats not the case.......

I have all siz pinions in front of me...all the first gear pinions are the same OD...as well as all the second gear pinions and the groups of spurs.....

as far as pitch changing power delivery..I'm still not following that theory.....

I do run electric...changing from 48 pitch to 64pitch allows more gear ratio combinations.....and it allows you to change the the position of the motor for handling,and may be smoother and quitier for less noise,but a 5.81 ratio is a 5.81 ratio no matter what gears you use..

if i'm wrong,please explain..


I'm running the six tooth split on my car...it pulls fine......





I changed gear ratios by ONLY changing the pinions....








See the gear teeth?......See the pionions...both groups have the same OD..but with diffrent teeth combos......see the difference in the tooth shapes?...



ON My Serpent,you have to run both sets of gears so they add up to the same #...

you don't have to do this with the r40..
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Old 10-03-2003, 05:46 AM   #547
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Thanks for posting the picture... I see now what they are doing... it's the 'pitch diameter' that determines the gear ratio, but the overall diameter that deterines the mesh. They made some interesting compromises in the shapes of the teeth to achieve equal diameters with varying pitch diameters... very neat idea.

As for the different pitch question, I agree that ratio is ratio, and regardless of pitch, that won't matter. However, I think the arguement that is being made (and I don't necessarily agree) is that the finer pitch gears are so much more efficient that you can pull a lower gear with a given engine. Again, I'm not saying I agree with this statement, but I think that's their theory.

Thanks again for the explaination about the gear design (and the picture... picture worth 1000 words comes to mind...)
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Old 10-03-2003, 06:00 AM   #548
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I guess smoothness matters(which is why 64 is better in electric).....but ratio is the only limiting factor in gear spread..

Maybe they're saying that using finer teeth ALLOWS more gear combos so you CAN have a six tooth split..
but it's the 2 ratio combos that willl determine if the motor can pull the gear...

BTW,teh funny part is ,when you hold those gears next to each other,the spaces in between the hears are the same,only the tooth shape changes...

sort of like getting 10lbs of boloney in a 5 lb sack..
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Old 10-03-2003, 06:05 AM   #549
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thanks for the headz up on the gearing.

so if I understand correctly, that means I can run the purple 16T pinion (1st gear), and the green 21T pinion (2nd gear) and not have to worry about it meshing properly using the stock spur gears?
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Old 10-03-2003, 06:05 AM   #550
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Quote:
Originally posted by fastharry
I guess smoothness matters(which is why 64 is better in electric).....but ratio is the only limiting factor in gear spread..

Maybe they're saying that using finer teeth ALLOWS more gear combos so you CAN have a six tooth split..
but it's the 2 ratio combos that willl determine if the motor can pull the gear...

Right, unless they are saying that using 32 pitch gears is like running your car with the brakes dragging and running 64 pitch gears is like having a frictionless drive train... then it would matter what pitch you have, not just the ratio, but I don't think the difference in drag from the gears themselves is noticable, or even measurable.
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Old 10-03-2003, 06:09 AM   #551
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Quote:
Originally posted by BossPlaya
Hey, I fully admit im a newbie, so calling me such has no effect, but thanks for the quick answers and being good sports about my bad attitude today (sorry bad day). Its just that there have been other times that I've asked questions on the Mugen thread and gotten absolutley no response, and if I did, it was ussually like a sentence.

Boss,baby..I didn't see the original thread......Sorry bud..


The HPI R40 has spacers in different widths..they go right on the pivot ball and when you tighten the pivot ball,they stop the ball from screwing in(theres a rib on the pivot ball they rest against)..

Front track width and front camber can be set with this..rear toe also..

but the car is so easy to set up,I'm not using them...

The rear has a camber link on top..so thats easy also...


the good part of using them is that if you wreck,you can fix the car quick..using the spacers theres no need to re set up the car..
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Old 10-03-2003, 07:20 AM   #552
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Let's see if we can clear this up: Finer pitched gears transfer power more efficiently than coarse pitched gears, much like a fine threaded 1/4" bolt torques more smoothly than a coarse threaded 1/4" bolt.

There are friction losses in all mechanical gearing; the finer the pitched gears the less frictional loss there is, so:

given a 1.3 HP engine, and fine pitch gears with 95% efficiency and coarse pitched gears with 90% efficiency, the fine pitch gears will transfer 1.3 x .95 = 1.235 HP, and the coarse pitch gears will transfer 1.3 x .90 = 1.17 HP.

Can you realistically see the difference? Probably not while racing, but in a side-to-side shootout you may be able to. If you couldn't realize a difference then why do people lay out big bucks for replacement bearings, CVD's, low friction belts, etc...... it's because it's all about reducing friction all around the car. 5% from the gearing doesn't seem like a lot, but if you then get 3-5% from the bearings, 3% from the CVD's, 3% from the belts, all of a sudden you've got 14-16%!! You do the math.....and see if you think that amount will make a difference.
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Old 10-03-2003, 07:33 AM   #553
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As far as those same-diameter pinion gears, the only way they can accomplish that is to rely on the spur gear being able to accomodate different pressure points on it's gear teeth based on which pinion gear is being used. Essentially when you change pinion gears, the actual pitch diameter of the spur changes as well because the contact point on the spur gear will move either in (as with the higher count pinion teeth) or out (as with the lower count pinion teeth). When this happens you are effectively changing the gear pitch, but because you are not changing the spur gear itself HPI has given you a Variable Pitch Spur Gear, and it is varied through the use of the different pitched pinion gears. Pretty ingenious application on a R/C car as it keeps you from having to move the engine when you change gears.

To tie this into the above conversation about gear efficiency, when you put the lower tooth number pinion on the car you end up with a more coarse pitch than if you have a higher tooth pinion on the car. So let's say you have a 16/50 combination. (I don't know if 50 is a valid spur, but work with me). If you could replace them BOTH with a fine pitched 16/50 combination you'd be better off. As always, "in theory".
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Old 10-03-2003, 08:35 AM   #554
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Quote:
Originally posted by KMac
Let's see if we can clear this up: Finer pitched gears transfer power more efficiently than coarse pitched gears, much like a fine threaded 1/4" bolt torques more smoothly than a coarse threaded 1/4" bolt.

There are friction losses in all mechanical gearing; the finer the pitched gears the less frictional loss there is, so:

given a 1.3 HP engine, and fine pitch gears with 95% efficiency and coarse pitched gears with 90% efficiency, the fine pitch gears will transfer 1.3 x .95 = 1.235 HP, and the coarse pitch gears will transfer 1.3 x .90 = 1.17 HP.

Can you realistically see the difference? Probably not while racing, but in a side-to-side shootout you may be able to. If you couldn't realize a difference then why do people lay out big bucks for replacement bearings, CVD's, low friction belts, etc...... it's because it's all about reducing friction all around the car. 5% from the gearing doesn't seem like a lot, but if you then get 3-5% from the bearings, 3% from the CVD's, 3% from the belts, all of a sudden you've got 14-16%!! You do the math.....and see if you think that amount will make a difference.
Doing the math is the easy part, it's getting the actual numbers that is difficult. If instead of 90% for course and 95% for fine you substitute in 99.8% for course and 99.85% for fine, it doesn't make a difference. I am currious what the actual efficiency of the gear train is (anyone have these numbers?)

90% seems awfully inefficient to me, and therefore an unrealistic example. Let's take your example of a 1.3HP engine. If the gears were only 90% efficient, that would mean that 10% of that 1.3HP would be dissipated in the gears. That's .13 HP or nearly 100 watts. Now, we all know how much heat comes off of a 100 watt light bulb... no where near that amount of heat is coming off of the gears in our cars, in fact, they are not even warm to the touch after a 30 minute race, so the efficiency of the gear train must be significantly higher that 90%, for either type of gear.

Even if you assume that the engine is only putting out, on average, half of it's maximum HP, you'd have to dissipate 50 watts in those gears, and I think they'd melt.

However, the change is still incrementally better, so as long as the finer pitch gears are strong and reliable enough, and truely are more efficient, no matter how small the gain is, it is still a gain, so you might as well use them.

BTW, this, in my opinion, is a technical forum at it's best. No yelling, no accusations, just talking about the facts behind a good question...
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Old 10-03-2003, 11:21 AM   #555
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Quote:
Originally posted by fastharry
Thats not the case.......

I have all siz pinions in front of me...all the first gear pinions are the same OD...as well as all the second gear pinions and the groups of spurs.....

I changed gear ratios by ONLY changing the pinions....

See the gear teeth?......See the pionions...both groups have the same OD..but with diffrent teeth combos......see the difference in the tooth shapes?...
Thanks for the picture fastharry,

I'm still baffled by this MC Escher gear design. I'm just wondering how pinions with different kinds of tooth pitch can mesh with a spur gear of one particular pitch. Since you said all you have done is gone down in pinion teeth count... that means larger teeth profile to maintain the same pitch diameter. (KMAC speaks of a variable pitch spur on the R40 that meshes to any pitch pinion. please read below)

Also..... if HPI thinks they can emulate a gear ratio change by going to coarser or finer teeth (the powerloss stuff spoken of earlier) Why are their 1st/2nd pinion+spurs all different sizes....They could make both pinions 15mm... both spurs 50mm..... and just make the 1st gear really really fine teeth... and the 2nd gear really really coarse teeth.... Why make them have different pitch diameters? (KMAC... the first and second spur gear should be the same size then)

Before anyone picks up an otherwise absent negative tone from reading my post, I just want to be able stop scratching my head for the rest of the day..... I'm not questioning anyones stated facts here.

I might have to buy a R40 just to find out what the heck is going on.

Last edited by boom; 10-03-2003 at 11:27 AM.
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