RC-Monster Forums - View Single Post - Q. about gearing, and some more questions

Aero · 10:20 AM

e-revonut> thanks for clarifying :)

briang> thanks ditto :) i never use rollout, i know those calculator pages too, the way i see it, rollout is to maintain a rel.ship between torque and speed? i did some reading and some things look odd. like on this page:
http://www.rcuniverse.com/forum/m_3255405/tm.htm

where its written "Question 1: What size spur gear should I run? What about the pinion gear?
Well……. When selecting the spur gear and pinion gear size, you need to
understand that there is a direct ratio between the tire circumference (referred
to as roll-out) and the final drive ratio. That ratio, in most cases, should be
as should be as close to 1 to 1 as possible. 1 to 1? What? By a 1 to 1 ratio, I
am referring to one revolution of the tire to one revolution of the motor. In
doing so, we do our best to maintain the overall efficiency of the motor by
keeping it in the ‘Sweet Spot’. Here’s how..."

the bolded quoting sounds like zero gearing to me ? also, he mentions efficiency in percentages, as for rollout ratio, why is efficiency even in here, no matter the size of wheels and tires..the drivetrain is geared. i would assume that zero gearing would have the least in-efficiency. not that it matters, does it ? yes, a much-geared drivetrain would have some inefficiency, but that doesnt mean one should try to go with the least geared drivetrain does it ?

and a quote on the efficiency:

"We can check our overall efficiency by dividing the
roll-out by the final drive ratio. In this case, the 10.2101 roll-out, and the
10.44:1 final drive ratio means that we have less than a 3% total loss in
efficiency. In other words, the tire turns 0.977 times, for every 1 revolution
of the motor. Generally, it is best for your motor to gear your vehicle within a
+ or - 10% margin. ( In the case of this formula, +1 to -1 is an acceptable
margin.) "

..i dont see how that efficiency is logic. would it be 'top speed' instead of efficiency ? it may mean that 3 % of speed become 3% of torque or vice versa, as thats all a rollout is ?

where does the idea behind rollout 1:1 inherit from, i checked my esavvy for rollout and seems it IS pretty close to 1:1 (inch) rollout with the stock 20t pinion, all stock setup. so i figure rollout is good for defining a speed/torque.

but, speed/torque is 'defined' by the motor ? if one slaps a torqier motor on, gears less in drivetrain, the rollout is eventually changed. so using briang's calculator my rollout now is 1.8:1, i dont see how that can be 'inefficient'. on the post from rcu, i should take my final drive gearing (10.2) and deduct rollout (18.5") - now where on earth does that bring me..

i did check the rollout on stock stampede vxl too, rollout is pretty close to 1:1. Now, with 3s and spur/pinion changes, the rollout is then 2.2:1

i dont think there's such a think as inefficient rollout. ?

btw, i find it more useful to look at the 'axle torque' using briang's calculator. less axle torque= more top speed. and then eventually using a temp meter

thanks for replying guys i appreciate it. i will read up on the posts now ;)

	(#4)
Aero RC-Monster Stock Offline Posts: 25 Join Date: Jun 2009	01.02.2011, 10:17 AM e-revonut> thanks for clarifying :) briang> thanks ditto :) i never use rollout, i know those calculator pages too, the way i see it, rollout is to maintain a rel.ship between torque and speed? i did some reading and some things look odd. like on this page: http://www.rcuniverse.com/forum/m_3255405/tm.htm where its written "Question 1: What size spur gear should I run? What about the pinion gear? Well……. When selecting the spur gear and pinion gear size, you need to understand that there is a direct ratio between the tire circumference (referred to as roll-out) and the final drive ratio. That ratio, in most cases, should be as should be as close to 1 to 1 as possible. 1 to 1? What? By a 1 to 1 ratio, I am referring to one revolution of the tire to one revolution of the motor. In doing so, we do our best to maintain the overall efficiency of the motor by keeping it in the ‘Sweet Spot’. Here’s how..." the bolded quoting sounds like zero gearing to me ? also, he mentions efficiency in percentages, as for rollout ratio, why is efficiency even in here, no matter the size of wheels and tires..the drivetrain is geared. i would assume that zero gearing would have the least in-efficiency. not that it matters, does it ? yes, a much-geared drivetrain would have some inefficiency, but that doesnt mean one should try to go with the least geared drivetrain does it ? and a quote on the efficiency: "We can check our overall efficiency by dividing the roll-out by the final drive ratio. In this case, the 10.2101 roll-out, and the 10.44:1 final drive ratio means that we have less than a 3% total loss in efficiency. In other words, the tire turns 0.977 times, for every 1 revolution of the motor. Generally, it is best for your motor to gear your vehicle within a + or - 10% margin. ( In the case of this formula, +1 to -1 is an acceptable margin.) " ..i dont see how that efficiency is logic. would it be 'top speed' instead of efficiency ? it may mean that 3 % of speed become 3% of torque or vice versa, as thats all a rollout is ? where does the idea behind rollout 1:1 inherit from, i checked my esavvy for rollout and seems it IS pretty close to 1:1 (inch) rollout with the stock 20t pinion, all stock setup. so i figure rollout is good for defining a speed/torque. but, speed/torque is 'defined' by the motor ? if one slaps a torqier motor on, gears less in drivetrain, the rollout is eventually changed. so using briang's calculator my rollout now is 1.8:1, i dont see how that can be 'inefficient'. on the post from rcu, i should take my final drive gearing (10.2) and deduct rollout (18.5") - now where on earth does that bring me.. i did check the rollout on stock stampede vxl too, rollout is pretty close to 1:1. Now, with 3s and spur/pinion changes, the rollout is then 2.2:1 i dont think there's such a think as inefficient rollout. ? btw, i find it more useful to look at the 'axle torque' using briang's calculator. less axle torque= more top speed. and then eventually using a temp meter thanks for replying guys i appreciate it. i will read up on the posts now ;) Last edited by Aero; 01.02.2011 at 10:20 AM.