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  1. #1
    RC Racer
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    How to choose a motor?

    I'm considering upgrading the motor in my Slash 4x4 to get some more acceleration with possibly a bit more top speed (but more acceleration is more desirable than more top speed). I've done lots of searching and reading about attributes of motors (# of turns, kV rating, etc) and understand all the general concepts, but I cannot find any solid information on how to crunch the numbers to pick the motor that is right for your goals. Can anyone point me to such information?

    For example, I think I want to get a Novak HV Pro motor, which comes in a variety of number of turns (and therefore, kV ratings). I have confirmed with Novak that within this line of motors, the kV rating and the torque of the motor are inversely and proportionally related. The HV Pro 5.5T (3700 kV) spins 23% faster than the HV Pro 7.5T (3000 kV), but also has 23% less torque. If I geared both motors for the same wheel RPM/Volt, the result would be the same acceleration and same top speed from both motors, but different sized pinion and/or spur gears. So how do I choose between the different motors?

    There is obviously some physical limit to gear sizes that will fit, so I know that is part of the equation. From what I've read, it seems much easier to gear a Slash 4x4 higher than stock without trimming parts than it is to gear it lower than stock.

    Is the answer simply to get the lowest kV rating on a motor such that I can physically gear it up to my desired top speed? Or is there some reason that it would be preferable to go with a higher kV rating and lower gearing?

    Again, I'm not looking for generalizations like, "if you gear a motor up, it'll give you more speed, but the motor will run hotter." I understand those concepts. I'm looking for information about how to start with some goals and calculate which motor is best to meet those goals.

  2. #2
    RC Champion
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    http://www.scriptasylum.com/rc_speed/_top_speed.html

    That link will help you a lot but you will need to find some info on ur own to see what ur speed will be. But what i would reccomend is staying away from the novak motors and try a CC or LRP motor. If you want to have the ability to gear high or low I would do the 2650Kv MMM motor and a 3s lipo but you will need to get the MMM ESC too so just depends on what you want to do.
    BLEmaxx-3905
    Fam. last words-Hey yall watch this!

  3. #3
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    Thanks for that link. It'll definitely be helpful for estimating top speed with various configurations, but it still doesn't help me in the situation where I have a range of Kv ratings that could get me the top speed I'm looking for. If I've narrowed my search down to a specific line of motors, and there are 2 motors in that line that can be geared to give me the speed I want, is it better to pick a lower Kv rating and gear it higher, or to pick a higher Kv rating and gear it lower to obtain the same speed?

    BTW (in case it is helpful) - What I want to do specifically is stick with 2s lipo and get more acceleration without losing any top speed (gaining speed is welcomed but not necessary). Of course, I'd like to do this without overheating a motor. I don't care about the ability to go 55+ mph. I just want to be able to get up to about 35-40mph with maximum possible acceleration. If there's a setup that keeps the motor temps down, but gives me more speed and/or acceleration than I'm looking for, that's fine too. I can always adjust the throttle range on my transmitter and/or adjust to using the power wisely.

  4. #4
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    If money is no option then try this motor: http://www.castlecreations.com/produ...1509-1_5d.html.

    That motor will allow you to gear up and down pretty well and give you good speed and amazing torque and if money is an option you could try and find a motor roughly same size and kv.
    BLEmaxx-3905
    Fam. last words-Hey yall watch this!

  5. #5
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    I have been running the Novak HV 6.5t with the Castle Mamba Max Pro. About a week now... I love it.. loads of bottom end grunt, just a bit lacking in top end speed on 2s... 3s, speeds are good, and it'll run for litterally hours without heat issues, i am currently geared 18/52, using the center diff. Last night, I ordered the 5.5HV motor to give that a whirl... I was going to get the 4.5HV, but that is only 2s rated, and I do like to gear up, and throw some voltage in my trucks now and then...
    Slash 2wd w/ Novak
    Rusty w/ Castle

  6. #6
    RC Turnbuckle Jr. asheck's Avatar
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    For the HV motors, this is how they stack up.

    If your main driving is going to be on 2s, you want the 4.5, for sure.

    If most of your driving is 3s, then either the 4.5 or 6.5 can be used.

    If most of your driving will be 4s, then go with the 6.5.

    This seems to fit into both the gearing range, and the motors efficiency range the best.

    I was going to get the 4.5HV, but that is only 2s rated,
    It's funny how now all of a sudden your not supposed to run 4s, but for years it was fine, and sold as a motor to run up to 14cells. I have been using mine for years on 4s, with no problems. Admittedly it is the 1/8 in rotor, but can't see where that would make a huge difference. It's their speed controller that can't handle the motor on 4s.
    Last edited by asheck; 03-01-2010 at 03:51 PM.
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  7. #7
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    I thought the same as you Doc...but have found that IN THEORY I can gear up my HV4.5 Pro motor up enough to do over 50 fairly easily (with 15/54 gearing...so I don't even have to change the spur) and THAT is plenty fast enough for me!

    What's more...I can gear 12/54 (again not having to change the spur from the stock set-up) and get 40+ out of my truck just by swapping the motor for the stock Velineon 540. The stock setup on 2S does 30mph on 13/54 (the stock gearing). So just swapping out the stock Velineon 540 for the Novak HV4.5 Pro motor gains you another 10mph, which is MORE than enough for SC indoor racing. Swap out the 12t pinion for a 15t and your at 50+...which should be MORE than enough for most outside tracks I'd say!

    Now I say this is in THEORY because I'm just using the link that J Dub posted up above, and I haven't yet gotten the motor. I simply adjusted the script and made sure that it was correct for the current Velineon 540 motor, then switched to the Novak motor and this is the info I got back.

    Once I actually GET the motor I'll be able to post more accurate info (assuming I can ever get a speed run done that is) and more than just THEORIES!

    If you want an HV4.5 Pro there is only one place online that I have found that has it. It was recommended to me in another thread...I have forgotten who it was that posted it orginally...but the link is

    www.nitrohouse.com
    Paul Valenti

    Slash 4X4 #25 (Mark Jenkins)

  8. #8
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    Quote Originally Posted by asheck
    ...
    It's funny how now all of a sudden your not supposed to run 4s, but for years it was fine, and sold as a motor to run up to 14cells. I have been using mine for years on 4s, with no problems. Admittedly it is the 1/8 in rotor, but can't see where that would make a huge difference. It's their speed controller that can't handle the motor on 4s.
    The HV4.5SC Pro is a NEW motor, designed to work specifically on 2S. You MAY be thinking of a different product? In any case...they make OTHER models that have a 4.5 motor...could be that you mean one of those?

    No biggie either way. If you try to buy the motor from them you are taken to shoptron.com and the description of the HV4.5SC motor says that it is designed specifically for 2S lipo and the tech specs say specifically that it is for 2S lipo only.
    Paul Valenti

    Slash 4X4 #25 (Mark Jenkins)

  9. #9
    RC Racer
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    Quote Originally Posted by asheck
    If most of your driving is 3s, then either the 4.5 or 6.5 can be used.
    Here's what Novak tech support told me via email:
    The 4.5 is no longer recommended for use with any battery larger than a 2 cell Lipo, so if you are wanting to use a 3 cell Lipo pack at times, the 5.5 motor may be your best choice.
    I already have 2s batteries and would prefer not to purchase 3s batteries.

    A Novak HV 4.5 on 2s lipo with stock gearing should give me about 40mph. That's plenty fast for me. The question now shifts to motor heat. Would this setup be prone to overheating when bashing in less-than-ideal conditions (grass, sand, snow, etc)? If so, then I would probably be better off with a HV 5.5 that would be less stressed on stock gearing for the rougher bashing while still topping out around 30mph, or I could gear it up to ~40mph with a 17t pinion when I'm on smoother tracks and asphalt.

  10. #10
    RC Turnbuckle Jr. asheck's Avatar
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    The 4.5 is no longer recommended for use with any battery larger than a 2 cell Lipo,
    This is what I mean.
    The HV4.5SC Pro is a NEW motor, designed to work specifically on 2S.
    It's not really a new motor. They just are no longer recommending it to be run on 4s. Here's the old combo , listed as up yo 14 cells. http://www3.towerhobbies.com/cgi-bin...?&I=LXUYD7&P=7 Even on their motor page, they list the 4.5 on 14.4 volts http://www.teamnovak.com/products/br...spec_chart.htm All the specs listed for the new 4.5, is the same as the old 4.5. The 5.5 which they still sell as a 4s motor, is pushing the same rpm's on 4s, as the 4.5 on 3s.

    As I said this 2s only thing is something new they've started to push. IMO it stems from them not offering a good ESC to run with it. The only ones they have that do a really good job, are limited to 2s.

    BTW I'm a big Novak fan, and was recommending this motor to be used in this vehicle, long before the vehicle was released. But Novak Tech support knowledge is horrendous. On another sight they offer tech support, and some of the answers given are really laughable.


    So as always, do what you feel safest with. But from my experience, and judging by all the old specs on this motor, 3s would be just fine.

    Here's where the Novak tech explains, all of what I said.
    When we discontinued the 4.5 HV Pro motors, we took back a lot of them from distributors---we are goods guys.

    So, we had all of these 4.5s in our motor mfg department collecting dust. Then Jay Halsey and Bob started looking for some system for the Ofna SC and decided on the Havoc Pro/ HV 4.5 Pro motor. They seem to be doing well with this combo.

    This is why we are combo-ing this up for sale. We OEM these 2S Combos to NitroHouse. Many of the other SC vehicles do not seem to have room for this longer 550 motor, so this may be a limited market, but this set-up seems to be winning races.
    Last edited by asheck; 03-01-2010 at 05:13 PM.
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  11. #11
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    Cool...thanks for the explanation/info!

    I see you are in Kansas City...do you go to Fastlane Raceway in Blue Springs?

    I bought the HV4.5Pro motor but I bought a CC Mamba Max Pro ESC to go with it. So I know that I COULD run 3S with my motor if I wanted to. I just don't think I want to take the chance that Novak might not warranty it IF I have problems, and I don't think I could bring myself to LIE about it.

    Although I will say...I'll bet the truck would be PLENTY fast with a 3S and probably run cooler to boot!
    Paul Valenti

    Slash 4X4 #25 (Mark Jenkins)

  12. #12
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    i got the 5.5, i run 3s its awesome, super smooth, you won't regret it

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