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Discussion Starter · #1 ·
I have an engineering question concerning spur and pinion alignment. Is there an efficiency or torque difference between a spur and pinion where the center line of the two gears are directly parallel vs. a condition where the pinion gear is lower than the of the spur?

My question stems from the fact that when you change your axles ride height you change the “attack angle” for lack of a better way of saying it, of the way the spur and pinion hit each other but you can still draw a strait line between their two centers.

What is the engineering solution?
 

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Discussion Starter · #3 ·
I know what I’m thinking but I am not smart enough to put it into words LOL I think it would have something to do with pushing two circles together, no matter if one is lower than the other, they still meet the same way and in this case, the same amount of teeth still mesh.
 

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McLin said:
I know what I’m thinking but I am not smart enough to put it into words LOL I think it would have something to do with pushing two circles together, no matter if one is lower than the other, they still meet the same way and in this case, the same amount of teeth still mesh.
Exactly. The motor and the axle don't care where the chassis is in relation to their mesh.

As long as the mesh is set, it shouldn't matter where the motor is located, radially, relative to the ground.

Joe
 

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Hankster is right on, there is no noticable efficiency difference but there is leverage moment that occurs. It does make some difference but not a huge amount for these type of cars. Most, if not all manufactures get the motor as low as possible and with the tire size defining where the axle centering is we are pretty much stuck with what we have today. The mass of parts and where they are positioned in the car form the ground plane far out-weighs the advantage you would get from the possible leverage moment gain.

This is great, another great thread to get everybody thinking about there cars. This type of thread is exactly what our sport needs because it gets people to thinking and hopefully working more on there cars to figure things out and that is one thing that is becoming more and more evident every day. We need an entire section on Hobbytalk geared around these sort of tech type questions. Like I always tell people, if you want to learn what different things do to a car, ask some questions, read some books and then test those changes on your car at the track.

Love these threads guys, keep them coming.

Brent Redlin
Up Front Design
 

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Discussion Starter · #7 ·
When I first looked at this I thought it would change the leverage point as well but let’s take a radical approach. What if the motor was sitting on top of the spur gear rather than the side, the gears would still mesh in the same manner with the same amount of teeth and the same angle of push (again, I don’t know the right terminology).
 

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i've wondered if reverse rotation would ever come back, instead of the front of the car trying to lift, would'nt it give more front bite under power ??
 

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You'd have to have a 3rd gear (Idler) in between the Spur and the pinion to see if that would work, along with stiffer center spring or T-Plate...If you used a reverse rotation motor on the Left side of the pod, it would still give you the same result as the right side (rotationwise), but you would have the weight on the left of the pod for weight sake which is the obvious,(Which has absolutely nothing to do with this topic, lol), but I'd hope you get my point..... :dude:
 

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Discussion Starter · #10 ·
Sorry Brent we posted together. Then if there is a leverage moment of occurance, would slightly below center be the correct location or exactly even with each other be correct. As you said, we are splitting hairs here but it's still interesting.
 

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ive often wondered the same problem.i do realize the torque moment that does happen actually pushes the front end of the car down and you realize more front steering at the start of a race as opposed to having the motor in back of the rear axel would result in lifting pressure off the front end. if you dont think so take the motor out of your car without unhooking it from the speedcontrol and give it the gas some serious torque there huh.but i also believe that being under the center line of the rear axel you will get less torque as you go lower i think lol
 

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Bill, after thinking a second, i realized that rotation would be the same, i tried to delete my post right after i posted it, Brad.
 

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McLin I dont know about angle of attack changing car handling , but and mind you this is from the race car world, where the power transfers to the spur[or ring gear in a car] the closer to center the less the power loss. ex. 9 inch ford is less effiecent than a 12 bolt because the 12 bolts pinoin is closer to center. The 9 inch has to push gear up and over becuase its on the bottom. The 12 bolt pushs the gear down because the its closer to the center. Its easier to push weight down than up, as far as the angle of attack and handling goes on a big oval where you dont lift once you hit it on the start the t-plate will settle back down and it wont affect it again unless you lift and go full tilt again.
 

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Flying5
The effect on efficiency your refering to is due to the fact that both the 9" Ford rear and 12 bolt GM rear end use Helical cut gears. Our pan cars use square cut gears and do not show the same effect of "wedgeing" the helicoil cut gears do.
 

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Discussion Starter · #15 ·
Theory:

If you take a large circle (in this case the spur gear) and from the center of that circle you mount an arm. That arm extends to the edge of the large circle. At that point you mount a small circle (the pinion gear). If you rotate that arm around the 360 degrees of the large circle, the small circle will follow the edge of the larger one and no matter where you stop that arm the small circle will be applying the same force to the larger one (Assuming they are gears and are meshed.)

If you were to place a motor on the small circle (gear) and rotate it around that big gear the same way it seems to me that it would apply the same force, in the same direction, with the same amount of torque and efficiency no matter where you stopped the arm.

If there were a good or bad place to run the pinion, it appears to me that at some point in rotating that arm that you would find a place that it would “bind” but of course it wouldn’t.

What am I missing here?
 

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I undrerstand what you said but a dyno dont lie, the 9 inch does not make as much power, mind you I have personally seen this with in race cars , the only advantage is that the 9 inch is real tough. Think of a swing set if you hold the swing off the ground 2 foot and let go see how high it goes then hold it 5 foot off the ground and look there is a difference.
 

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It's not possible to screw up a pinion/spur mesh combo as long as the shafts are in the same plane....... You'll always be "on center". Pretty much what McLin's last post stated. And several posts before that......

Heck, the 1/24th slot cars are all screwed up. The motor is at an angle to the axle, and the two shafts aren't even in the same plane and those things run just fine. It bugged me real bad when I first started racing those things, but I got over it......
 

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Ok, Hank is right with his drawing the motor placement will not affect the pressure angles on the gear.

What should be concerned is getting the pinion and spur as close to the same size as possible to increase the effeciency of the pressure angles. I know that SPURS are big and Pinions are SMALL and this is needed to get the most of the motor setup. So the only other way to get the Pinons and Spur closer to the same size is reduce the tire size.

If all possible, get the pinion over 10T. Under 10T and the pinion begins to look like a throwing star not a smooth circle. Other than the more available options in gearing choice, this would be why 64p would be better in oval over 48P. You would need a screaming motor to need a very small pinion in 64P.

Other things to consider, is ROLLOUT!!! this is more important that the extra little bit of drive train effeciency. A motor in the wrong load/rpm range will cut speed faster than improper gear mesh and the ideal 1:1 gear setup for gear effeciency.
 

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the ride height adjustment does change alot in the chassie .. i drag race 6 cell rc cars with ferrite motors and we change the ride height in the cars to help with tuning....by changing we can get the car to leave soft and prevent flipping the car over on the launch .. and since we time the cars 6 ft ..the times show a difference also .. it might only be .03 but its noticable all with the change of the ride height adjusters... when people have a problem flipping the cars the change in ride height fixes it quick... albie
 

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Discussion Starter · #20 ·
OK, let’s shift gears. In NASCAR they are constantly talking about “opening the shocks” or “closing up” the shocks. I am guessing they are talking about the rebound rate. I know we can change oil and piston size and spring rate but there has to be a more “scientific” way to approach this other than “……this feels good”.

I think it would be good to start a conversation about how what NASCAR is doing can relate to what we do.
 
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