Pinion and gear relationship

[ronhbar]

Theoretical question:

83/16 = 5.188

88/17 = 5.176

93/18 = 5.167

Three different ways to get to the same ratio with different gear and pinion. Is there a benefit to running any of these combinations over the others?

Thanks,
Ron
Losi XXX-T

[xaM]

smaller the pinion will give you more torque, the smaller the spur the more speed.
larger the pinion the more speed, the larger the spur the more torque.

I think thats how it works, im not positive though.

[PeterV]

I think the effects of the motor moving farther from the spur gear will be more noticeable than any effect of the gears getting larger or smaller. The gears are very light, and I doubt you'll detect any increase or decrease in performance because of greater or lesser rotating mass. Certainly, there is a difference on some level (it's physics, everything counts!), but I think the effect is lost in the "big picture" of a 3-pound+ car, multi-gear transmission, etc.

[rocknbil]

I usually pick a spur that allows me to use the widest range of pinions/clutchbells and still fit, so it's more a decision of flexibility in pinion changes than how it affects ratio.

[JHawlz9989]

I have to agree with Peter. When you think about the weight your adding with the 1 tooth bigger pinion, it MIGHT amount to 1/100th of an ounce. Maybe even a gram? It's like putting a basketball in the trunk of your real car and wondering if you'll go faster without it.
-Josh

[2ndGeneration]

Theoretical question:

83/16 = 5.188

88/17 = 5.176

93/18 = 5.167

Three different ways to get to the same ratio with different gear and pinion. Is there a benefit to running any of these combinations over the others?

Thanks,
Ron
Losi XXX-T

I think the information you are seeking was covered in this (http://forums.radiocontrolzone.com/showthread.php?t=200011) thread.
Hope This Helps

[ronhbar]

Thanks for the point. I missed that when searching.

Ron

[2ndGeneration]

If you count the time spent researching these forums ( 3 very late nights ) as well as the length of time spent on the thread, took all of 10 days to gather this information.
Hope it'll stick around for a bit so others might get some good from it.

[TC3Racer]

changing the spur and/or pinion will do the same thing. The spur just doesn't make as big of a change as the pinion does, thats usually why people dont change spurs when they want to make a gear ratio change. It doesn't make as drastic enough difference to benefit performance wise.

If you get a smaller spur and have the same piston you will have more torque and less top end. Same as if you just got a smaller pinion.

[Grant Tokumi]

changing the spur and/or pinion will do the same thing. The spur just doesn't make as big of a change as the pinion does, thats usually why people dont change spurs when they want to make a gear ratio change. It doesn't make as drastic enough difference to benefit performance wise.

If you get a smaller spur and have the same piston you will have more torque and less top end. Same as if you just got a smaller pinion.
Correction:
If you get a BIGGER spur and have the same pinion you will have more torque and less top end. Same as if you just got a smaller pinion

[Grant Tokumi]

I think the information you are seeking was covered in this (http://forums.radiocontrolzone.com/showthread.php?t=200011) thread.
Hope This Helps
At the risk of sounding like information law enforcement :), your other thread is a little different than this one. In your thread, your questions were exploring about how "change in ratios" affect performance. More like this:

87/15 = 5.80
87/16 = 5.43
87/17 = 5.12

93/15 = 6.20
88/16 = 5.50
83/17 = 4.88

Where this thread is exploring how the "change in pinion/spur while maintaining the same ratio" affects performance.
83/16 = 5.19
88/17 = 5.18
93/18 = 5.17

This is assuming you understand the fact that the difference between 5.19 and 5.17 (0.02 difference) is insignificant so all 3 gear combinations he presented result in essentially the same gear ratio.

Just trying to clear things up and eliminate misinformation for those who are trying to understand the concepts. :)

[2ndGeneration]

At the risk of sounding like information law enforcement :), your other thread is a little different than this one. In your thread, your questions were exploring about how "change in ratios" affect performance. More like this:

87/15 = 5.80
87/16 = 5.43
87/17 = 5.12

93/15 = 6.20
88/16 = 5.50
83/17 = 4.88

Where this thread is exploring how the "change in pinion/spur while maintaining the same ratio" affects performance.
83/16 = 5.19
88/17 = 5.18
93/18 = 5.17

This is assuming you understand the fact that the difference between 5.19 and 5.17 (0.02 difference) is insignificant so all 3 gear combinations he presented result in essentially the same gear ratio.

Just trying to clear things up and eliminate misinformation for those who are trying to understand the concepts. :)

Well yeah, we definitly want to do away with mis-information but the question being asked was still covered in the other thread as well, you will end up at the same ratio but the difference is in how hard the motor, esc, battery works in the process.

Original question on this thread;

Three different ways to get to the same ratio with different gear and pinion. Is there a benefit to running any of these combinations over the others?



First Instance,

Originally Posted by 2ndGeneration
Assuming that I can achieve practically any FDR what are the advantages, or dis-advantages, of running an 87 tooth spur verses say an 84 tooth spur, or even an 81 tooth spur?[QUOTE/]


The smaller the spur gear (also known as "gearing up"), the higher the top speed, but you lose low end acceleration. Plus you run the risk of overheating your esc, batt, and motor, since it has to work so hard.

Its kind of like riding a mountain bike in a parking lot. If you leave it at the highest gear, you can get up to very high speeds, but it takes a lot of effort to get there.

Second Instance,

Quote:
Originally Posted by Grant Tokumi
The smaller the spur gear (also known as "gearing up"), the higher the top speed, but you lose low end acceleration. Plus you run the risk of overheating your esc, batt, and motor, since it has to work so hard.



Thanks for the help.

So let me see here if I get it. Gearing up, smaller spur/larger pinion = more top end speed. Gearing down, larger spur/smaller pinion = more low end torq. Larger tracks with long straight sections, gear up. Smaller tracks shorter straight sections gear down !?! All of this within the limitations of the motor, esc, and batteries of course.

Or did I miss something here? Again :o :confused:

[Grant Tokumi]

the question being asked was still covered in the other thread as well, you will end up at the same ratio but the difference is in how hard the motor, esc, battery works in the process.
That is the error. In your thread, its the change in ratios that affects the motor, esc, and battery's performance. Gearing up changes the ratio by increasing the pinion size and/or decreasing the spur size, and runs the risk of overheating your esc, batt, and motor, since it has to work so hard.

So let me see here if I get it. Gearing up, smaller spur/larger pinion = more top end speed. Gearing down, larger spur/smaller pinion = more low end torq. Larger tracks with long straight sections, gear up. Smaller tracks shorter straight sections gear down !?! All of this within the limitations of the motor, esc, and batteries of course.
That statement is right on the money. You get it.

The difference is in this thread, the discussion revolves around changing pinions and spur gears without change in ratios. Little tricky, but possible. To simplify for understanding, consider a more round ratio (no decimals) of say 80 tooth spur and 16 tooth pinion.

80/16 = 5.00 ratio

If you increase both pinion and spur (unlike gearing up or down, which involves increasing one gear while decreasing the other), you can change them in a way that you do so without changing the ratio at all.

80/16 = 5.00 ratio
85/17 = 5.00 ratio
90/18 = 5.00 ratio
95/19 = 5.00 ratio
950/190 = 5.00 ratio

Ratio stays EXACTLY the same, but yet you've increased both the spur and pinion gear. And the question becomes what are the advantages/disadvantages of making those types of changes.

Your thread: What type of effect does changing gears on a mountain bike have on the biker. What is the right "gearing" for ____ condition.

This thread: What type of effect does making the front and back sprockets a little heavier have on the biker. This one is not an exact biking analogy like for your thread, but similar in the sense that it involves changes in the gears without changing the ratio.

Does that make sense? :)

[Dava]

Stop fooling around.

Using above example options:

A. 80/16 = 5.00 ratio
B. 95/19 = 5.00 ratio

- Both will give you same final speed.
- A. has smaller gears and will be lighter than B (maybe this is negligible but can affect acceleration).
- A. has smaller distance between pinion and spur centers (something to consider in some cars where there is little room for moving motor).
- A. spur, and mostly the pinion will wear out faster than B (each teeth will have friction against other more often).

[Scott S]

The main reason I change gears that result in the same ratio would be to distribute the weight of the motor differently in the car.

Say Dava's ratio's were used in a B4:

Using these ratios,
A - would put more weight toward the FRONT of the car, closer to being over the rear axles.
B - would put more weight toward the REAR of the car, farther behind the rear axles then A.

This change would make the car handle differently and is used whenever you need to make the slightest weight adjustment in the car w/o adding/taking away weight.

[cmdj_chris]

Changing both the pinion and spur to maintain a consistent ratio will not affect your overall speed or runtime. Using a test setup with one test battery pack, I ran my car with 3 different gear combos , maintaining as close a ratio as possible. For each setup, I ran the battery until it died 3 times then came up with an average runtime and top speed. Guess what, the difference was less than a thousanth of a second. I do have some other thoughts though.
1. For my car (x-ray T1) a taller spur gets my motor lower in the chassis. Gives me better cornering and thus, quicker laps
2. This is a bit of a stretch and might be kinda hard to follow. 93/18 has larger gears and therefore more surface contact between the gears(in the mesh). Now your powerplant will put out (x) amount torque at a (x) RPM. That being a constant, having more surface contact between the gears will spread out your motor's applied torque across more of the teeth surface. Granted this is a very small diference, comparable to the rotational mass argument. I'm not sure if this is an accurate statement, but I think that appling the same amount of torque over a larger area would make for a more efficient use of torque.

[bholio]

I personally would use the largest pinion out of the choices within the same overall gear ratio, if I knew I would be keeping that gear ratio.

A larger pinion gear will wear out slower because more teeth are doing the work, and because more teeth are in contact with the spur at the same time.

Bigger gears will help spread the impact of jump landings across more teeth, especially important if your slipper is set very tight.

A downside might be less freedom to experiment with alternate gear ratios. The large spur might start to interfere with gear covers and maybe even interfere with axles and suspension arms at extreme suspension angles.

[soreloser]

In off-road, the mentioned gearing would affect the handling of the vehicle like Scott S stated. The larger gears would move the motor farther behind the rear axles and this would give better forward traction, but you will loose side bite from the pendulum affect of moving the weight farther away from the front. The smaller gears would give better side bite and less forward bite because the mtoor will be closer to the rear axles reducing the pendulum affect.

Pendulum effect explained

Pivot point = front inside tire
weight = motor

take a pole 6 feet long, place a weight on the pole next to where you are holding the pole(the pivot point) and with the pole horizontal begin to rotate it around and stop it. It is rather easy to stop the pole from rotating. Now move the weight out to the end of the pole away from where you are holding it. Begin rotating it now and try to stop it, becomes much harder to stop.

[Grant Tokumi]

Thats a good explanation on how this "side bite" stuff works. I never did really understand that. So why is the pivot point on the front INSIDE tire instead of the outside? I've seen cars/trucks taking turns where the front inside tire is not even on the ground during the turn. Using your analogy, I'd intuitively think the outer tire would be the pivot point. Well .... actually, I'd intuitively think the center of gravity of the car would be the pivot point, but I think I can understand why you say it might be the front.

[crazyjr]

I think soreloser is right. the distance between motor and spur will affect handling but the bigger the pinion and spur the more rotating mass. Also the larger pinion and spur run smoother than smaller pinion and spur

[soreloser]

Thats a good explanation on how this "side bite" stuff works. I never did really understand that. So why is the pivot point on the front INSIDE tire instead of the outside? I've seen cars/trucks taking turns where the front inside tire is not even on the ground during the turn. Using your analogy, I'd intuitively think the outer tire would be the pivot point. Well .... actually, I'd intuitively think the center of gravity of the car would be the pivot point, but I think I can understand why you say it might be the front.

The reason I state the inside tire as the pivot point is when you lock the rear brake, the inside front tire is where the pivot takes place when the rear comes around. Otherwise the inside front tire would go from rolling forward to rolling backwards while the rear is sliding sideways, and this does not happen.

[Scott S]

The reason I state the inside tire as the pivot point is when you lock the rear brake, the inside front tire is where the pivot takes place when the rear comes around. Otherwise the inside front tire would go from rolling forward to rolling backwards while the rear is sliding sideways, and this does not happen.

Agreed 100%, just like in a real car doing donuts, the front inside wheel does not roll backwards. The car simply pivits around that wheel.
Very well said soreloser, nice posts.

[Grant Tokumi]

The reason I state the inside tire as the pivot point is when you lock the rear brake, the inside front tire is where the pivot takes place when the rear comes around. Otherwise the inside front tire would go from rolling forward to rolling backwards while the rear is sliding sideways, and this does not happen.

If the outside was the pivot, I don't see the inside tire going backwards if the car is moving forward. I see it slowing down, but not going backwards. And using your same reasoning for the inside tire being the pivot, if the inside front tire was the pivot, then the front outside tires would be speeding up very quickly in the turn, and I don't see that happening either......

And what about when the inside front tire is not even on the ground in the turn?

In any case, your pendulum concept still holds, regardless of where the pivot point is.... I was just asking for some clarification.

[soreloser]

Grant, I understand what you are saying and if the inside tire is not making contact with the ground, the outside tire does become the pivot.

Here is a hands on example as long as all tires are making contact with the ground:

To be a pivot point, I understand that to be the point that becomes a point that does not move during the pivot. With that in mind, get a car, any car, hold the left front tire and pivot the car counterclockwise(it would be like making a left hand turn with the inside tire being the pivot point), the outside tire does accelerate to go around the pivot. Now hold the right front tire and rotate the car again in a counterclockwise direction(this simulates the outside tire being the pivot in a left hand turn), thus the inside tire will try to rotate in reverse, this also holds true anywhere along the front of the vehicle except when the inside tire is the pivot. Otherwise it would not be a pivoting turn, it would be a sideways slide.

[Grant Tokumi]

To be a pivot point, I understand that to be the point that becomes a point that does not move during the pivot. With that in mind, get a car, any car, hold the left front tire and pivot the car counterclockwise(it would be like making a left hand turn with the inside tire being the pivot point), the outside tire does accelerate to go around the pivot. Now hold the right front tire and rotate the car again in a counterclockwise direction(this simulates the outside tire being the pivot in a left hand turn), thus the inside tire will try to rotate in reverse, this also holds true anywhere along the front of the vehicle except when the inside tire is the pivot. Otherwise it would not be a pivoting turn, it would be a sideways slide.
I understand and can visualize your example. Your argument seems to revolve around the fact that the front inner tire will never be spinning backwards in a turn. Therefore, the front inner tire HAS to be the pivot, because that is the only place in which the front inner tire will not spin backwards. Is this what you are saying?

If that is what you are saying, then it is falsely assuming that a car is not moving in a forward motion during the turn. A pivot can absolutely be moving while things are rotating around the pivot point. When the car is moving and turning, the pivot can be anywhere in the front end and the front inner tire will be still spinning in a forward direction, albeit slower than the outer tire.

A real life analogy of this is when your hold your car in your hand (car is not moving) and work the diff, one tire spins forward and one spins backwards. This does not mean that when you are moving and taking a turn, working the diff, that one tire spins backwards. They both still spin forward, but one just spins slower than the other.

But we are starting to talk about 2 different topics here. The pendulum is one thing, however, if we are talking all 4 tires on the ground and having full traction (not sliding), then the the pivot point by definition is an imaginary point on the side of the car. Steer a car left, then if you imagine the front left axle and rear left axle extending out until the 2 intersect, that intersecting point is the pivot point. That is assuming perfect ackerman with the outer tires. If the pivot point is anywhere other than that spot, tires are sliding.....don't you agree? And I thought its the "sliding/rotating" that you are referring to in the pendulum effect. A longer dragster type car will be very resistant to turning and slide compared to a rally car....

[Mild MAXX]

That is the error. In your thread, its the change in ratios that affects the motor, esc, and battery's performance. Gearing up changes the ratio by increasing the pinion size and/or decreasing the spur size, and runs the risk of overheating your esc, batt, and motor, since it has to work so hard.


That statement is right on the money. You get it.

The difference is in this thread, the discussion revolves around changing pinions and spur gears without change in ratios. Little tricky, but possible. To simplify for understanding, consider a more round ratio (no decimals) of say 80 tooth spur and 16 tooth pinion.

80/16 = 5.00 ratio

If you increase both pinion and spur (unlike gearing up or down, which involves increasing one gear while decreasing the other), you can change them in a way that you do so without changing the ratio at all.

80/16 = 5.00 ratio
85/17 = 5.00 ratio
90/18 = 5.00 ratio
95/19 = 5.00 ratio
950/190 = 5.00 ratio

Ratio stays EXACTLY the same, but yet you've increased both the spur and pinion gear. And the question becomes what are the advantages/disadvantages of making those types of changes.

Your thread: What type of effect does changing gears on a mountain bike have on the biker. What is the right "gearing" for ____ condition.

This thread: What type of effect does making the front and back sprockets a little heavier have on the biker. This one is not an exact biking analogy like for your thread, but similar in the sense that it involves changes in the gears without changing the ratio.

Does that make sense? :)

The only time you want to use a large spur is to set the motor/engine ferther away or closer to center to change weight distrubtion/ handling if you are going to keep the same ratio or close to it anyway. A spur with 72 teeh vs. a 65 tooh spur there is only a 20 grains weight different theres 748 grains in 1 ounce that's not alot of weight. Moving the motor 1/16 inch to the rear on an rc10t = 1/4 once on the rear tires. more traction at lonch and braking.

[soreloser]

Grant, I understand your point and totally agree. My example is when the rear looses traction and comes around as if your going into a 180 turn, you jam the brakes and the rear comes around while holding the front tire right on the corner. I completely agree when you do not loose traction that your description is correct.

[Mild MAXX]

Grant, I understand your point and totally agree. My example is when the rear looses traction and comes around as if your going into a 180 turn, you jam the brakes and the rear comes around while holding the front tire right on the corner. I completely agree when you do not loose traction that your description is correct.

What your talking about is sudden weight transfur. This is what causes you to spin out of control it is when your front is to heavy and the rear is to light try adding weight to the rear of your car to help get a weight balance going
you could also use 4 food serving scales to weigh your car remember a 50/50 weight balance dosen't mean a perfict handling car.

[soreloser]

What your talking about is sudden weight transfur. This is what causes you to spin out of control it is when your front is to heavy and the rear is to light try adding weight to the rear of your car to help get a weight balance going
you could also use 4 food serving scales to weigh your car remember a 50/50 weight balance dosen't mean a perfict handling car.


Mild Maxx, actually you would increase the pendilum effect if you add more weight to the rear. I do not mean for this to come across wrong either, but you jumped in at the end of something me and grant are talking about, go back and add all the posts I made concerning the pedilum effect along with what Grant stated and then you will understand why I said that.

[Grant Tokumi]

Did you all know that there is a link to this thread on the RC Car Action homepage?
http://rccaraction.com

Yikes! :)

[myndseye]

I can feel the fact that a slight shift in motor position may be of some importance in fine tuning the handling of your rc, even more in the case of the X-Ray type vehicles where a larger spur ultimately seats the motor closer towards the chassis thereby lowering the center of gravity. There is also room to argue that the use of larger pinions and spurs can fine tune the application of power to the ground because of more rotating mass to get spooled up. Throw in the fact that there can be huge weight differences in spurs and pinions from diferent materials and a company's efforts to lighten thier products with strategically placed holes and voila!

Plus, lets not forget (even though this is not really about this topic, but maybe relevant) that different ways to achieve particular ratios are important for those who run cars where there is limited space for super large spurs, motor adjustment, etc....

[losifreak2004]

The pendulum effect that soreloser has been talking about is the polar moment of the car. The closer the car's weight is to being centered on the car's polar moment of inertia, the faster the car will change directions.

Also something else to keep in mind...two bigger gears will have less rolling resistance than two smaller gears will. This will have a much bigger effect on the speed of the car than the actual weight of the gears. The trick with the XX-4 to get it rolling quickly was to put the biggest spur gear on it that you could find!

Aaron Waldron
Team Losi Factory Driver

[Siege]

One tangible difference that you will see with different gear combos that result in the same ratio is a variation in strength. Typically, when you have a higher tooth count on a gear, the individual teeth are smaller and weaker. Sometimes the difference isn't even worth worring about, sometimes it can make or break you. But the flipside is that bigger teeth, especially on straight cut gears, don't mesh as smoothly. This can add a lot of drag across the entire RPM band.

When I used to race slots, the gear strength and mesh were probably THE critical thing to keep adjusted properly. It was always a constant balancing act between reducing drag while hoping to avoid stripping out the composite pinions and crowns gears we used. The crown gears were especially sensitive, sometimes you would totally ruin 2-3 a night just trying to get things dialed in properly.

-Hans

[BY basher]

Use the pinion that will allow the motor to operate within it's optimal RPM range. Consult motor specs.

[sim600]

One tangible difference that you will see with different gear combos that result in the same ratio is a variation in strength. Typically, when you have a higher tooth count on a gear, the individual teeth are smaller and weaker. Sometimes the difference isn't even worth worring about, sometimes it can make or break you. But the flipside is that bigger teeth, especially on straight cut gears, don't mesh as smoothly. This can add a lot of drag across the entire RPM band.

When I used to race slots, the gear strength and mesh were probably THE critical thing to keep adjusted properly. It was always a constant balancing act between reducing drag while hoping to avoid stripping out the composite pinions and crowns gears we used. The crown gears were especially sensitive, sometimes you would totally ruin 2-3 a night just trying to get things dialed in properly.

-Hans

I think that is a good point to consider. But I think it's not really that the individual teeth get smaller and weaker. They are still the same size, but just that they are moved further away from their gear centers, so they can apply more force on each other and break something.

[auto2]

Ok I dont have time to read all tis but to me the only difference is weight distrabution. A smaller pinion will move the motor forward. SO you can maintain the same gear ratio and change the motor placement.

[davec-nitro-rs4]

OK, I did take time to read this, and I was surprised no one mentioned the obvious.

With a larger pinion gear, it is harder for the motor to turn the gear against a load. The further out from the motor shaft you place the "load" the harder it is to do the work. This is why short servo arms exert more force than long arms.

For the same overall gear ratio, the setup with the smaller pinion will put less stress on the motor, and will accellerate faster. This may be why some of the posts refer to smaller pinions give more torque and cause spin outs. The larger pinion slows down the application of motor torque to the drivetrain, regardless of overall pinion-spur ratio.

This is why powertrain manufacturers recommend the smallest possible gear on the drive side of a powertrain. It puts the driveline under maximum stress for the least amount of time, during initial breakaway from a stopped condition.

Ok, now I'll wait for you guys to shoot holes in this. And I apologize if I have restated what someone else has written, but I don't think I have.