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  1. #1
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    Got my new (to me) Slash, have gearing question

    Ok, got my Slash yesterday and have a gearing question in relation to heat. Here's the setup... Castle Creations 5700kv 4 pole motor with Sidewinder Sv2 ESC. Running on 6cell and 7cell Nimh. Gearing installed by the previous owner is 19/86 Should I drop down on pinion size or should this be good? I dont want to burn up the motor. Castles website recommends 12/90, which seems a bit extreme to me. I was thinking about grabbing a 15t pinion and checking that out. I have to run to Hobbytown after work to get a servo horn adapter anyhow, so I figure while Im there.....

  2. #2
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    Without knowing how you're driving it, there is no way to say.

    I run mine with 76/32 gearing for five minutes at a time. But it is all top end, no starting and stopping. No heat issues.

    Going the other direction for all torque, you shouldn't have an issue, but you must invest in a temp gauge.

  3. #3
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    I tend to "bash" (but without the carnage) Lots of starting and stopping, donuts, power slides. Some grass, some loose dirt, some loose dirt over asphalt. It will be "tractionally challenged" to say the least.

    The PO also said he never had an issue with excessive heat, but didnt go into detail on how it was driven. Judging by the body, it's seen its fair share of pavement. Black road rash on the roof and gouges in the rear skid plate suggesting wheelies. It wasnt all smooth pavement though as the front skid plate has some gouges in it too. I wouldnt say the truck was beat, but it certainly wasnt a shalf queen either.

  4. #4
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    I run 83/25 in my car. The acceleration isn't the greatest but once it gets going the top speed is good. You can also put a 34/83 but you'll have to kick it in the *** to get it moving but the top end will be fast as ****. Do you want torque or speed?

  5. #5
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    Top speed is going to be "great" to me no matter what. My last truck was a Stampede with a Trinity 27T race motor. About 20mph tops. This is going to be warp speed compared to that. This is my first brushless system. Ive already programmed the esc with Low Punch Control and lowest possible timing.

  6. #6
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    I would go with 83/25 0r 21. The 83 compared to the 86 has more torque to get off the line and the 25 or 21 pinion gear will
    Keep they higher end speed and if you want to stick with the 86 I would use a 13 pinion which is good for speed

  7. #7
    RC Turnbuckle Jr. O.G.'s Avatar
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    Quote Originally Posted by devestator View Post
    Top speed is going to be "great" to me no matter what. My last truck was a Stampede with a Trinity 27T race motor. About 20mph tops. This is going to be warp speed compared to that. This is my first brushless system. Ive already programmed the esc with Low Punch Control and lowest possible timing.
    My first truck was a Pede with a trinity green monster 27t motor. Those were the days.
    My Black & Blue Rally is faster than your color...

  8. #8
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    Thatcrazyrcmanct.... what you said about an 83t spur having more torque than 86 makes no mathmatical sense at all. In fact what you said about 83 giving more torque is the exact opposite. I have been around Rcs long enough to know that a larger spur gear gives a lower overall ratio and provides more torque. Same with a smaller pinion gear. You are recommending a 3.32:1 or 3.95:1 ratio with your 83/25 or 83/21. Your other recommendation of 86/13 yields a 6.61:1 ratio where currently I have a 4.52:1 ratio with 19/86.

    See the closer to 1:1 the ratio is, the higher the top speed, but the more stress is put on the motor...therefore more heat will be produced. Your 2 83t combos will raise my top end and raise the amount of heat in the motor. A lower gear ratio (like 6:1) will produce more torque and less top speed. It makes the motors job easier and reduces stress, which reduces heat.

    The biggest reason I was asking this was to find out if there would be a heat issue with the 19/86 combo or would I have to gear down to 15 or 12 to increase torque to reduce stress on the motor and reduce heat.

    OG... I go back even further than that... 1992 RC10T was my first truck... still remember running a Futaba MC210CB esc as it was one of the first reversing escs on the market. Futaba Magnum Sport radio and an Astroflight peak auto-detect charger for my Reedy 6 cell NiCd batteries. Whole setup cost my parents like $500 or so.

  9. #9
    RC Turnbuckle Jr. O.G.'s Avatar
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    You have me beaten by about 10 yrs. I got my Pede complete with MAC in about 2002.
    My Black & Blue Rally is faster than your color...

  10. #10
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    the more teeth on the gears is more speed less torque. Less teeth is more torque. that was all i was saying.

  11. #11
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    Quote Originally Posted by Thatcrazyrcmanct View Post
    the more teeth on the gears is more speed less torque. Less teeth is more torque. that was all i was saying.
    But what your saying is only half right. Thats only true with pinions.... a larger spur gear will go slower than a smaller spur gear. The closer they are in size, the more speed you will have.

    An 75 tooth spur will have a higher top speed than an 86 tooth spur. A 25 tooth PINION will have more top speed than a 15 tooth pinion.

    Pinion (smaller gear on the motor) - Larger = speed, smaller = torque
    Spur (larger gear on the slipper clutch) - Smaller = speed, larger = torque

    If you have a combo of 19/86 and go to 22/99 your truck will go the EXACT same speed since the gear ratio is the exact same. They both have a ratio of 4.52:1 meaning the smaller pinion needs to spin 4.52 times to make the larger spur gear spin once. To get this number, divide the spur by the pinion. The lower this number, the higher your top speed is and the lower your torque is.

  12. #12
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    Oh and I ran the truck with the 19/86 combo today. After 20 minutes of donuts and just general hooning around, the esc got hot enough to burn my finger... didnt even bother trying to touch the motor... I know that would be super hot. Going to try the 15t pinion on my next run and see how that does to cool the temp down a bit. I think I may need to upgrade to a Mamba Max and get an aluminum trans case. Or swap the motor to a lower kv rated one.

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