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Thread: Gear ratios

  1. #1
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    Gear ratios

    So im wondering if my math is right.. with a 2400kv motor running 3s will have a max rpm of 26,640 and say my gearing is 18t pinion and 54t spur the gear ratio would be 3.0 or 3 turns of the pinion = 1 turn of the spur.. that means that (26,640 ų 3 = 8880) so my spur gear would spin at 8880 rpm at full throttle? Im just wondering if my math is right cause im running the stock vxl 3s system on 3s with stock gearing (13t pinion 54t spur) currently and want to experiment with different motors i ran this setup with the 18t pinion once and the top speed was insane but i want a more torquey setup cause it ran HOT that day haha
    Slash 4x4

  2. #2
    RC Turnbuckle Jr. Greatscott's Avatar
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    No...

    Check out Pg 25 of the manual.
    Submarine Qualified, Chief Inducted, Navy Retired

  3. #3
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    Quote Originally Posted by Greatscott View Post
    No...

    Check out Pg 25 of the manual.
    Ok i will look thank you
    Slash 4x4

  4. #4
    RC Turnbuckle Jr. Squeegie's Avatar
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    Try this:

    http://www.radiocontrolinfo.com/info...ar-calculator/

    Edit:
    FYI: Slash 4x4 diff gears are 13 pinion and 37 spur
    Last edited by Squeegie; 01-31-2019 at 03:40 PM.
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  5. #5
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    He's looking at just the math between the pinion and spur. The manual references using the 2.85 (37/13) to get the final drive number.

    There are more factors than simply pinion and spur. It's the size/power of the motor, the differential gear ratio, drive line drag, air drag and size of tires. The larger motor can be geared higher because it can produce more power to pull those gears. You wouldn't put a Toyota Yaris engine in a 3/4 ton pickup? I mean you could, but to get it to move and stay at speed compared to the OEM pickup engine it would need to be geared lower to do so and work harder which generates heat.
    The Super Derecho

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    Quote Originally Posted by Double G View Post
    He's looking at just the math between the pinion and spur. The manual references using the 2.85 (37/13) to get the final drive number.

    There are more factors than simply pinion and spur. It's the size/power of the motor, the differential gear ratio, drive line drag, air drag and size of tires. The larger motor can be geared higher because it can produce more power to pull those gears. You wouldn't put a Toyota Yaris engine in a 3/4 ton pickup? I mean you could, but to get it to move and stay at speed compared to the OEM pickup engine it would need to be geared lower to do so and work harder which generates heat.
    Thank you for the info i was just trying to be simple because my setup is gonna stay the same for a while (trencher x sc tires all around, proline sillverado short course body) although i might try out a flo tek body to get some better aero dynamics cause im trying to make my truck as efficient as possible and i heard of people swapping in x01 diffs but i am not sure if those are the same ratio as the slash but my diffs are in good shape yet so i dont see a need to upgrade
    Slash 4x4

  7. #7
    RC Turnbuckle Jr. Squeegie's Avatar
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    Same gear ratios, but some added strength components.
    Creativity is intelligence having fun. -Einstein

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    Quote Originally Posted by Squeegie View Post
    Same gear ratios, but some added strength components.
    Ok thank you
    Slash 4x4

  9. #9
    RC Turnbuckle Jr. El Sob's Avatar
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    You will be happy with the 2400 motor! I have an Ultimate edition with the sensored 2400kv motor and the Mamba X esc! I love it ♡
    Member of the 10,000 + posts club! Here to help!

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    Quote Originally Posted by El Sob View Post
    You will be happy with the 2400 motor! I have an Ultimate edition with the sensored 2400kv motor and the Mamba X esc! I love it ♡
    Yeah im just waiting for my motor in it now to break haha i want the 2400kv
    Slash 4x4

  11. #11
    RC Turnbuckle Jr. El Sob's Avatar
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    Quote Originally Posted by NoahP View Post
    Yeah im just waiting for my motor in it now to break haha i want the 2400kv
    I understand! My newest Ultimate edition has the older two pole Velineon motor system in her. When it finally goes out, it will promptly be replaced with a Mamba X esc and sensored 5mm shaft 2400kv motor
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  12. #12
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    Quote Originally Posted by El Sob View Post
    I understand! My newest Ultimate edition has the older two pole Velineon motor system in her. When it finally goes out, it will promptly be replaced with a Mamba X esc and sensored 5mm shaft 2400kv motor
    Yeah im anxious to upgrade but i dont wanna replace a perfectly good motor haha
    Slash 4x4

  13. #13
    RC Turnbuckle Jr. Greatscott's Avatar
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    Quote Originally Posted by NoahP View Post
    Yeah im anxious to upgrade but i dont wanna replace a perfectly good motor haha
    Meh... this is common in RC. When I do this I either sell the system I pulled out and reinvest the money into my RCs, or I shelf the system for future projects, or is something fails on one of my truck.
    Submarine Qualified, Chief Inducted, Navy Retired

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    Quote Originally Posted by Greatscott View Post
    Meh... this is common in RC. When I do this I either sell the system I pulled out and reinvest the money into my RCs, or I shelf the system for future projects, or is something fails on one of my truck.
    +1 I do this a lot, same for esc’s.

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    RC Champion Dcuda69's Avatar
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    Quote Originally Posted by Greatscott View Post
    Meh... this is common in RC. When I do this I either sell the system I pulled out and reinvest the money into my RCs, or I shelf the system for future projects, or is something fails on one of my truck.
    Yep...plenty of options. When I upgraded the Velenion in my Slash 4x4(perfect condition) I looked at it as an excuse to buy another RC as a home for it. It lives a nice life in a XL-5 Rustler I grabbed off Craigslist for $100. That motor/esc works very well in the lighter 2wd models. It's a hoot in the Rustler on 3s!
    Slash 4x4 Ult 2150kv
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  16. #16
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    Quote Originally Posted by Dcuda69 View Post
    Yep...plenty of options. When I upgraded the Velenion in my Slash 4x4(perfect condition) I looked at it as an excuse to buy another RC as a home for it. It lives a nice life in a XL-5 Rustler I grabbed off Craigslist for $100. That motor/esc works very well in the lighter 2wd models. It's a hoot in the Rustler on 3s!
    I was actually thinking of getting a cheap bandit off ebay to put it in haha thats a good idea cause ive always felt the need to have a bandit xl5 in my life idk why probably cause my buddy has one and he thrashes the crap out of that thing and it just takes it
    Last edited by NoahP; 02-02-2019 at 10:08 PM.
    Slash 4x4

  17. #17
    RC Turnbuckle Jr. Greatscott's Avatar
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    Quote Originally Posted by NoahP View Post
    I was actually thinking of getting a cheap bandit off ebay to put it in haha thats a good idea cause ive always felt the need to have a bandit xl5 in my life idk why probably cause my buddy has one and he thrashes the crap out of that thing and it just takes it
    Friends don't let friends buy Bandits... Now a Rustler on the other hand...
    (sorry, just can't get passed that goofy-looking wing)

    Case in point here, I pulled the XL5-HV and Titan motor out of my TRX4 and replaced it with a Mamba-X and 1900kv motor. The XL-5 and Titan have found a new home in my latest TRX4 build.
    Submarine Qualified, Chief Inducted, Navy Retired

  18. #18
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    Gonna be honest even though the Sidewinder 8th and itís 2200kv motor is the best way to put crazy power into a slash for cheap, itís brutalness comes at the cost, and being an actual 8th scale 6s system the thing makes the slash very heavy compared to using a 10th scale mamba x, so you break many more times collision wise, and also itíll mess up the drivetrain pretty good as itís a 1515. But hey, itís still an option

  19. #19
    RC Qualifier Panther6834's Avatar
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    The following is NOT to be taken as being intended specifically for your vehicle, as these are the calculations for my vehicle (Rustler 4x4). They are intended to give you a general idea of RPM at the transmission, based on three different Kv motors, two different Spur gears, and five different Pinion gears. Additionally, these calculations are NOT based on 3S batteries, but are, instead, based on 2S batteries. Although 2S batteries are labeled "7.4V", the actual max capacity output is 8.4V, and, as such, that is what was used for these calculations.

    The first two are for the stock Vileneon system, using the stock Spur gear, and the included 11T (pre-installed) & 17T (optional, included) Pinion gears. The max RPMs are as follows:
    Motor Kv Spur Gear Pinion Gear Max RPM
    3500 (OEM) 54 11 5,988.88
    3500 (OEM) 54 17 9,255.55

    The following RPMs are based on two motors I am considering (w/ 3300Kv & 4000Kv output), the two Spur gears I am considering (50T & 54T), the above-mentioned Pinion gears, plus three additional Pinion gears:
    Motor Kv Pinion Gear w/ Max RPM Pinion Gear w/ Max RPM
    50T Spur Gear w/ 50T 54T Spur Gear w/54T
    3300 11T 6,098.4 11T 5,646.66
    3300 12T 6,652.8 12T 6,160
    3300 14T 7,761.6 14T 7,186.66
    3300 16T 8,870.4 16T 8,213.33
    3300 17T 9,424.8 17T 8,726.66
    4000 11T 7,392 11T 6,844.44
    4000 12T 8,064 12T 7,466.66
    4000 14T 9,408 14T 8,711.11
    4000 16T 10,752 16T 9,955.55
    4000 17T 11,424 17T 10,577.77

    The formula for calculating any motors maximum RPM is quite easy:

    (motor Kv x max battery Voltage) / (Spur gear / Pinion gear) = max RPM to the transmission

    Using this formula, anyone can calculate the maximum RPM of any 'motor-battery-Spur gear-Pinion gear' combination. Using the chart I created, I will be able to better determine whether to keep the 4000Kv motor I already received, or whether to swap it for the 3300Kv motor. Whatever you decide to do, good luck.
    ~ Love, laughter & kindness makes the world better

  20. #20
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    Quote Originally Posted by Panther6834 View Post
    The following is NOT to be taken as being intended specifically for your vehicle, as these are the calculations for my vehicle (Rustler 4x4). They are intended to give you a general idea of RPM at the transmission, based on three different Kv motors, two different Spur gears, and five different Pinion gears. Additionally, these calculations are NOT based on 3S batteries, but are, instead, based on 2S batteries. Although 2S batteries are labeled "7.4V", the actual max capacity output is 8.4V, and, as such, that is what was used for these calculations.

    The first two are for the stock Vileneon system, using the stock Spur gear, and the included 11T (pre-installed) & 17T (optional, included) Pinion gears. The max RPMs are as follows:
    Motor Kv Spur Gear Pinion Gear Max RPM
    3500 (OEM) 54 11 5,988.88
    3500 (OEM) 54 17 9,255.55

    The following RPMs are based on two motors I am considering (w/ 3300Kv & 4000Kv output), the two Spur gears I am considering (50T & 54T), the above-mentioned Pinion gears, plus three additional Pinion gears:
    Motor Kv Pinion Gear w/ Max RPM Pinion Gear w/ Max RPM
    50T Spur Gear w/ 50T 54T Spur Gear w/54T
    3300 11T 6,098.4 11T 5,646.66
    3300 12T 6,652.8 12T 6,160
    3300 14T 7,761.6 14T 7,186.66
    3300 16T 8,870.4 16T 8,213.33
    3300 17T 9,424.8 17T 8,726.66
    4000 11T 7,392 11T 6,844.44
    4000 12T 8,064 12T 7,466.66
    4000 14T 9,408 14T 8,711.11
    4000 16T 10,752 16T 9,955.55
    4000 17T 11,424 17T 10,577.77

    The formula for calculating any motors maximum RPM is quite easy:

    (motor Kv x max battery Voltage) / (Spur gear / Pinion gear) = max RPM to the transmission

    Using this formula, anyone can calculate the maximum RPM of any 'motor-battery-Spur gear-Pinion gear' combination. Using the chart I created, I will be able to better determine whether to keep the 4000Kv motor I already received, or whether to swap it for the 3300Kv motor. Whatever you decide to do, good luck.
    Thank you that is very helpful i will use this formula from now on for any of my RCs when choosing motors
    Slash 4x4

  21. #21
    RC Qualifier NOFTCHX's Avatar
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    Very helpful. Thank y'all.

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  22. #22
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    I got a rustler 4x4 vxl and wondering can i just switch the stock pinion to a 18 or 20t pinion just for a touch of more speed?
    Quote Originally Posted by noahp View Post
    so im wondering if my math is right.. With a 2400kv motor running 3s will have a max rpm of 26,640 and say my gearing is 18t pinion and 54t spur the gear ratio would be 3.0 or 3 turns of the pinion = 1 turn of the spur.. That means that (26,640 ų 3 = 8880) so my spur gear would spin at 8880 rpm at full throttle? Im just wondering if my math is right cause im running the stock vxl 3s system on 3s with stock gearing (13t pinion 54t spur) currently and want to experiment with different motors i ran this setup with the 18t pinion once and the top speed was insane but i want a more torquey setup cause it ran hot that day haha

  23. #23
    RC Racer
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    You can but check the mesh of the gears and also watch the temps of the ESC and motor. It doesn't take much on some setups to make a lot more heat and running the motor over 160į is not good.
    Scott
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