Go Back  R/C Tech Forums > General Forums > Electric Off-Road
Help me understand gearing please > Help me understand gearing please

Help me understand gearing please

Reply

Old 06-14-2005, 04:49 AM
  #1  
Tech Apprentice
Thread Starter
 
Join Date: Sep 2003
Location: Bronx,NY
Posts: 56
Default Help me understand gearing please

When it comes to the spur gear and pinion gear. What configuration will boost top speed? What configuration will increase acceleration?
rcburner is offline  
Reply With Quote
Old 06-14-2005, 05:08 AM
  #2  
Tech Elite
iTrader: (28)
 
Join Date: Oct 2004
Location: Michigan
Posts: 3,329
Trader Rating: 28 (100%+)
Default

Bigger pinion = more top speed.
Smaller spur gear= more top speed.

Smaller pinion = more low end punch.
Bigger spur gear = more low end punch.

I believe changing one tooth on the pinion is equal to changing four teeth on the spur. Meaning if you change the pinion it's a more dramatic effect than the spur. At least that's how it is on my GT. Not sure what pitch gears you are working with.
jbrow1 is offline  
Reply With Quote
Old 06-14-2005, 10:43 AM
  #3  
Tech Addict
iTrader: (4)
 
DrOlds's Avatar
 
Join Date: Oct 2003
Location: Kansas City
Posts: 644
Trader Rating: 4 (100%+)
Default

Originally Posted by jbrow1
I believe changing one tooth on the pinion is equal to changing four teeth on the spur. Meaning if you change the pinion it's a more dramatic effect than the spur. At least that's how it is on my GT. Not sure what pitch gears you are working with.
Actually it's the other way around-4 teeth on the spur is about the same as 1 tooth on the pinion.On electrics we are usually using spur gears around 80-90 teeth and pinions some where around 20.

Here's the basic formulas to calculate gearing-

spur / pinion = external ratio example-88/22=4 or 4:1 ratio
external ratio X transmission(or internal)ratio=overall ratio
example- 4 x 2.4(B3 transmission)=9.6 or 9.6:1

tire diameter x pi(3.14)=circumference of tire 3"x3.14=9.42" of travel per tire revolution

tire circumference / overall ratio = rollout(distance traveled per motor revolution)

Example- 9.42"/9.6 ratio=.98125" rollout
or 235mm/9.6 ratio=24.5mm rollout

It is more common for rollout to be given in mm. but the formula is the same.
DrOlds is offline  
Reply With Quote
Old 06-14-2005, 01:02 PM
  #4  
Tech Elite
iTrader: (28)
 
Join Date: Oct 2004
Location: Michigan
Posts: 3,329
Trader Rating: 28 (100%+)
Default

Originally Posted by DrOlds
Actually it's the other way around-4 teeth on the spur is about the same as 1 tooth on the pinion.On electrics we are usually using spur gears around 80-90 teeth and pinions some where around 20.
And that's just what I said, one tooth on the pinion is like changing 4 teeth on the spur.
jbrow1 is offline  
Reply With Quote
Old 06-14-2005, 01:20 PM
  #5  
Tech Addict
iTrader: (4)
 
DrOlds's Avatar
 
Join Date: Oct 2003
Location: Kansas City
Posts: 644
Trader Rating: 4 (100%+)
Default

Yes it is! Sorry
DrOlds is offline  
Reply With Quote
Old 06-14-2005, 02:53 PM
  #6  
Tech Elite
iTrader: (28)
 
Join Date: Oct 2004
Location: Michigan
Posts: 3,329
Trader Rating: 28 (100%+)
Default

RC Burner, the forumula he posted above is used in onroad racing with foam tires. Our tires (offroad) are basically all the same size and don't vary that much. So just the pinion size and spur size is what offroaders worry about.

I just got into carpet racing last winter, so it was informative for me. Thanks!

Last edited by jbrow1; 06-14-2005 at 06:38 PM.
jbrow1 is offline  
Reply With Quote
Old 06-14-2005, 05:20 PM
  #7  
Tech Apprentice
Thread Starter
 
Join Date: Sep 2003
Location: Bronx,NY
Posts: 56
Default

thanks guys! good info!
rcburner is offline  
Reply With Quote
Old 06-27-2005, 03:03 AM
  #8  
Tech Adept
iTrader: (6)
 
howerc's Avatar
 
Join Date: Feb 2005
Location: Sunnyside, Washington
Posts: 147
Trader Rating: 6 (100%+)
Default

do you increase/decrease the spur to improve run time?
howerc is offline  
Reply With Quote
Old 06-27-2005, 05:19 AM
  #9  
Tech Master
 
Team Duratrax's Avatar
 
Join Date: Aug 2004
Location: NSW, Albury/Wodonga
Posts: 1,674
Default

Bigger spur gear and a smaller pinion gear will increase runtime slightly.

Sean
Team Duratrax is offline  
Reply With Quote
Old 06-29-2005, 01:15 AM
  #10  
Tech Adept
iTrader: (6)
 
howerc's Avatar
 
Join Date: Feb 2005
Location: Sunnyside, Washington
Posts: 147
Trader Rating: 6 (100%+)
Default

thanks for the help
howerc is offline  
Reply With Quote
Old 07-24-2005, 05:21 PM
  #11  
Tech Master
 
Platinum_Racing's Avatar
 
Join Date: Jun 2005
Location: Rowley MA
Posts: 1,844
Default

What ever you do be carefull not to overgear or undergear your motor. This could lead to severe motor damage, including killing it forever, Its not just your gear ratios that matter, its the size of your tires, they play a major role in how you should gear your car.
Platinum_Racing is offline  
Reply With Quote
Old 07-24-2005, 05:30 PM
  #12  
Tech Apprentice
Thread Starter
 
Join Date: Sep 2003
Location: Bronx,NY
Posts: 56
Default

Originally Posted by Platinum_Racing
What ever you do be carefull not to overgear or undergear your motor. This could lead to severe motor damage, including killing it forever, Its not just your gear ratios that matter, its the size of your tires, they play a major role in how you should gear your car.
Could you elaborate more on the issue of the tire size?
rcburner is offline  
Reply With Quote
Old 07-24-2005, 06:57 PM
  #13  
Tech Master
 
Platinum_Racing's Avatar
 
Join Date: Jun 2005
Location: Rowley MA
Posts: 1,844
Default

Your tires also determine how you should gear your car. a tire that is 2.2 inches in diameter will travel further in one rotation than a tire that is 1.8 inches in diameter. There is a sweet spot for every track, every car, basically every situation. If you run wide open all the time, you can get away with faster gear ratios, but if your constantly accelerating, you should gear it lower, this will lower the motor temp, make your batteries last longer, and make your car perform better. If you swap tires to ones that are slightly larger, drop between 1 - 3 teeth on your pinion to compensate.
Platinum_Racing is offline  
Reply With Quote
Old 07-25-2005, 06:10 PM
  #14  
Tech Apprentice
Thread Starter
 
Join Date: Sep 2003
Location: Bronx,NY
Posts: 56
Default

Originally Posted by Platinum_Racing
Your tires also determine how you should gear your car. a tire that is 2.2 inches in diameter will travel further in one rotation than a tire that is 1.8 inches in diameter. There is a sweet spot for every track, every car, basically every situation. If you run wide open all the time, you can get away with faster gear ratios, but if your constantly accelerating, you should gear it lower, this will lower the motor temp, make your batteries last longer, and make your car perform better. If you swap tires to ones that are slightly larger, drop between 1 - 3 teeth on your pinion to compensate.
When you say faster gear ratio, do you mean increasing the pinion to get more top speed or decreasing it to gain more accelaration?
rcburner is offline  
Reply With Quote
Old 07-25-2005, 07:05 PM
  #15  
Tech Master
 
Platinum_Racing's Avatar
 
Join Date: Jun 2005
Location: Rowley MA
Posts: 1,844
Default

I'm sorry, I meant to say higher gear ratios. Yes, install a larger pinion or a smaller spur.
Platinum_Racing is offline  
Reply With Quote

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


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Terms of Service