R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 04-05-2012, 02:00 AM   #16
Tech Elite
 
niznai's Avatar
 
Join Date: Feb 2009
Location: All over the place
Posts: 2,940
Default

Quote:
Originally Posted by Evoracer View Post
I agree that spur size makes no difference. It's all about FDR and car setup. Is the drivetrain free ? Is the diff set up with more slip ? Spool or diff up front ? Belt tension ? All these things will have an effect.
That said, If our spur gears had any real weight to them then the argument would be different. A larger,heavier spur would have less torque effect but greater inertia effect therfore it would be better for higher speed and worse for acceleration. A smaller, lighter spur would be the opposite.
So...because we spur gears that have very little mass (weight), the effects are extremely minimal. Look for other factors between the 2 cars.
You are right about mass considerations, but there is something else.

Given that the spurs we use are basically weightless (read massless), the real benefit comes from having a larger spur radius which gives a better torque on the drivetrain. That is why people say large spurs give bottom end. Because they do. For the same torque applied by the motor you have a multiplication effect given by the larger radius of the spur. Not sure if it would be noticeable though (or perhaps not at all radius ratios - spur/pinion because remember the more teeth your pinion has, the larger its radius too, so that has a detrimental effect on the torque at the motor shaft)

Now if that can explain what our friend has noticed about his car, I don't know. Perhaps to check that the effect is real you should have a drag race with your friend after you made sure everything else is equal (batteries, ESC, setups, drivetrains free - same belt tension, etc.) If he does indeed pull ahead of you from a standing start then perhaps you can try his spur/pinion combo and then see if he still pulls you.

I have used only 64 pitch gears in my carpet cars and am very happy with them, but the most noticeable effect was the car was perfectly silent.
__________________
Team Greasy Weasel

The best upgrade to any car is some driver skill.
niznai is offline   Reply With Quote
Old 04-05-2012, 02:23 AM   #17
Tech Addict
 
djnsayne's Avatar
 
Join Date: Nov 2008
Location: As you can see....My hands are full
Posts: 543
Trader Rating: 11 (100%+)
Send a message via Yahoo to djnsayne
Default

I'm sorry but that makes absolutly no sense. The laws of physics go completely against eveything that was stated...... the obvious reason for the OP's concerns is that either his ESC, battery or driving style is the reason why his car is slower than his friends car with the same motor and FDR. It could also be a binding situation in the drivetrain, but thats not as likely.
__________________
Yes.... That WAS my EVADER that just passed you!!!
Evader BX PRO/Xray T206/ 3Racing F109
DJ Nsayne/Hitt Breaka Dj's/Sexy B Racing
djnsayne is offline   Reply With Quote
Old 04-05-2012, 06:05 AM   #18
Tech Elite
 
Join Date: Nov 2002
Location: NY/FL
Posts: 3,376
Trader Rating: 24 (100%+)
Default

Which statement DJ ?? I'm no engineer so very willing to say I'm wrong. My statements came from racing real cars both drag and onroad.
If you know the physics...please let us know.
Evoracer is offline   Reply With Quote
Old 04-05-2012, 08:15 AM   #19
Regional Moderator
 
CarbonJoe's Avatar
 
Join Date: Jul 2006
Posts: 2,661
Default

Quote:
Originally Posted by lee View Post
A larger spur will gives you bottom end but the large pinion that would be needed to get to the same FDR will give you top end.

No, equal FDRs give equal power, and equal top speed. The motor shaft and layshaft will all turn at equal speeds regardless of which of the following combos you choose. These spur/pinion combos all give the same gear ratio, so the FDRs would be the same:

80/40, 90/45, 100/50, 120/60

If the gear weights are close, the effect of that on acceleration would be negligible, especially if the car is already rolling. The same goes for 48p vs. 64p. What could affect handling is the position of the motor in the chassis due to the diameters of the gears, since you are changing the f/r weight balance.

As I stated before, the OP should try switching motors and leaving everything else the same. Or, find a dyno and dyno the motors. I'd bet they aren't as close as you think, and may need to be geared differently.
__________________
*** The Gate - Celebrating 8 years at the same location ***
The difference between genius and stupidity is that genius has its limits. - Albert Einstein
Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car
CarbonJoe is offline   Reply With Quote
Old 04-05-2012, 06:19 PM   #20
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

Larger spur/pinion combos will have a better mesh. The teeth meet at a lower angle and therefor don't slide across each other as much improving efficiency. In actual practice, it makes no difference until you get to really small pinions like under 20 teeth which can be very inefficient.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is offline   Reply With Quote
Old 04-05-2012, 06:26 PM   #21
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

Quote:
Originally Posted by niznai View Post
You are right about mass considerations, but there is something else.

Given that the spurs we use are basically weightless (read massless), the real benefit comes from having a larger spur radius which gives a better torque on the drivetrain.
This is very true if you are changing ONLY the spur. But, if you go to a larger spur and change pinions to get the same FDR, you are going to a larger pinion as well, reducing how much torque it exerts on that spur gear. They cancel each other out.

If you have a motor with 1 lbs/ft of torque at the shaft and a 10/30 gear for a 3:1 ratio. you get 3 lbs/ft of torque at the axle. Change to a 60 spur, you now have a 6:1 ratio for 6 lbs/ft of torque at the axle. Change the pinion to a 20, you are now back to a 3:1 ratio and 3 lbs/ft of torque at the axle.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is offline   Reply With Quote
Old 04-05-2012, 06:26 PM   #22
Tech Addict
 
djnsayne's Avatar
 
Join Date: Nov 2008
Location: As you can see....My hands are full
Posts: 543
Trader Rating: 11 (100%+)
Send a message via Yahoo to djnsayne
Default

Quote:
Originally Posted by CarbonJoe View Post
No, equal FDRs give equal power, and equal top speed. The motor shaft and layshaft will all turn at equal speeds regardless of which of the following combos you choose. These spur/pinion combos all give the same gear ratio, so the FDRs would be the same:

80/40, 90/45, 100/50, 120/60

If the gear weights are close, the effect of that on acceleration would be negligible, especially if the car is already rolling. The same goes for 48p vs. 64p. What could affect handling is the position of the motor in the chassis due to the diameters of the gears, since you are changing the f/r weight balance.

As I stated before, the OP should try switching motors and leaving everything else the same. Or, find a dyno and dyno the motors. I'd bet they aren't as close as you think, and may need to be geared differently.


The OP stated that they have to use the same locked endbell motor. You are right though, maybe his motor is just worn,or he as improper gear mesh....... since he hasnt bothered to say if his batts or esc are the same as his competitor, I'm really more inclined to believe thats where the difference lies.
__________________
Yes.... That WAS my EVADER that just passed you!!!
Evader BX PRO/Xray T206/ 3Racing F109
DJ Nsayne/Hitt Breaka Dj's/Sexy B Racing
djnsayne is offline   Reply With Quote
Old 04-05-2012, 06:28 PM   #23
Tech Lord
 
wingracer's Avatar
 
Join Date: Nov 2007
Posts: 12,861
Trader Rating: 24 (100%+)
Default

Quote:
Originally Posted by CarbonJoe View Post
What could affect handling is the position of the motor in the chassis due to the diameters of the gears, since you are changing the f/r weight balance.
I think this is where this myth comes from as it is VERY noticeable in pan cars. The bigger spur/pinion combo you can fit in a pan car, the faster it is but this is due to handling.
__________________
Sean. Certified speed crazed mowron.
Team Shepherd USA
www.ashfordhobby.com
wingracer is offline   Reply With Quote
Old 04-08-2012, 08:21 AM   #24
Tech Elite
 
niznai's Avatar
 
Join Date: Feb 2009
Location: All over the place
Posts: 2,940
Default

Quote:
Originally Posted by wingracer View Post
This is very true if you are changing ONLY the spur. But, if you go to a larger spur and change pinions to get the same FDR, you are going to a larger pinion as well, reducing how much torque it exerts on that spur gear. They cancel each other out.

If you have a motor with 1 lbs/ft of torque at the shaft and a 10/30 gear for a 3:1 ratio. you get 3 lbs/ft of torque at the axle. Change to a 60 spur, you now have a 6:1 ratio for 6 lbs/ft of torque at the axle. Change the pinion to a 20, you are now back to a 3:1 ratio and 3 lbs/ft of torque at the axle.

You're absolutely right if pinion/spur diameters change identically (i.e. the diameter increase in spur is equal to diameter increase in pinion, but I am not sure that is the case). Teeth count does not matter as far a torque is concerned (but I do agree that it does change diameter, and it might be that you're right and the diameter change is the same, I admit I never measured).
__________________
Team Greasy Weasel

The best upgrade to any car is some driver skill.
niznai is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
CRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks John Stranahan Electric On-Road 1776 03-01-2016 01:18 PM
Lots of stuff for sale Squidward R/C Items: For Sale/Trade 58 06-27-2010 09:20 PM
TeamNovak Brushless Stock Motors NovakTwo Radio and Electronics 15 02-26-2009 10:15 AM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 04:46 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net