tomato18

Queston:

what are the advantages/disadvantages of using a smaller pinion gear paired with a bigger spur gear as opposed to using a bigger pinion gear paired with a smaller spur gear to achieve the same final drive ratio... say 4.5:1?

Foxxrocket

Big pinion/ Small spur= less torque, more top speed.
Small pinoin/ Big spur= More torque, less top speed.

drperry

iTrader: (3)

To achieve the the same ratio... I don't think there's a difference...

I think it mostly gives you more options for a fine tuning your ratio.

Also, some vehicles can only fit certain sizes of pinions or spurs.

Theslowguy

iTrader: (9)

Like said above. You can fine tine and get it to fit. Another thing is to move the weight of the motor in the car. Other then that. Id the FDR is the same. There is no difference.

05forfun

iTrader: (81)

If both gear ratios are paired with the same pitch (either 64 or 48), your question is physically wrong because if you want to achieve the same ratio the bigger spur must pair with bigger pinion. I may misunderstand your question. Anyway if both ratios are the same, I don't think there is any obvious disadvantage or advantage. You may recall your physics class, the bigger radius the higher inertial force, which may affect the response of the motor a bit, but I doubt that many people can notice that.

skypilot

iTrader: (14)

THERE is a difference, i understand the question, it is possible sometimes to obtain the same gear ratios using different pinion/spur combos. it is my opinion that if you getting a 4.5 gear ratio with a 96 spur and you can obtain the same 4.5 gear ratio with a 106 spur, the the 106 spur combo will yield better over all performance.

OvalDude99

iTrader: (3)

I will agree, in carpet oval we used to run the biggest gears we could. It seamed to help the car pull harder off the corners.AKA accelerate better.

Just my two cents.

Theslowguy

iTrader: (9)

Well. If your rolled out the same. Your rolled out the same. If anything all you are doing is adding weight... I can't see the size of the gears affecting anything.

a_main_attendee

iTrader: (2)

Besides mesh, of course. The larger diameter the spur gear is combined with the smallest possible pitch will yeild to the lowest friction.

Dunno if one could actually "feel" that though.

Theslowguy

iTrader: (9)

Well that's the pitch... Not what we are talking about.

25-100 will provide the same results as say 21-84.

a_main_attendee

iTrader: (2)

Maybe i am confused?

A spur gear (hypothetically) that has 100 teeth coupled with a pinion with 50 teeth (both the same pitch) should, in theory, be more efficient than a spur of 50 and a pinion of 25 of the same pitch, though the gear ratio (2:1) is left unchanged.

Theslowguy

iTrader: (9)

Really? How? Maybe someone can shed some light for us?

a_main_attendee

iTrader: (2)

I base this off of the fact that as the diameter of the gear gets larger (with a constant pitch) the angle between each tooth is less agressive, a less aggresive tooth angle means better mesh and lower friction.

Think about it, a 3 tooth 64 pitch pinion gear will not mesh with ANYTHING, and if it does, the mesh will be terrible and there will be a lot of friction between the two gears as they rotate. I'm applying this logic into a whole "bigger is better" logic considering the fact that impossibly small toothed gears wouldn't mesh very well with their same pitch counterparts.

I may be way off though. Just a thought. It is the ONLY reason i can think of larger gears being more efficient (or just different gears, for that matter) than others even when the provided ratio is the same.

JR007

I think any effect of the friction due to the spur diameter would be negligible. The loss in power from the frictio of that one component interaction would pale in comparison to the power loss in the bearings, drive shaft etc.

In off-road RC10 style 2wd buggy it DOES make a difference, mainly because it moves the position of the motor and affects vehicle balance, as mentioned before.

a_main_attendee

iTrader: (2)

I figured as much, but then that brings me to how people could say that different gears with the same ratio could have more pull? Maybe its all psychological, lol.


And that indeed makes sense.