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21.5 Brushless Motor/Battery/Gearing combo needs help

21.5 Brushless Motor/Battery/Gearing combo needs help

Old 05-21-2014, 01:52 PM
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Default 21.5 Brushless Motor/Battery/Gearing combo needs help

Hi,

i am using the speed passion 3.0mm 21.5R motor, 4600/70c shorty lipo, hobbywing stock-spec esc, and have a 75 spur, 35 pinion with a FDR of 4.28. i replaced the factory bushings in the front & rear ball diffs but I'm not super impressed with the power performance at this point.

My chassis will only allow for shorty lipo's so I'm limited in battery options with more milliamps. i haven't experimented much with the esc or radio settings but it seems these two avenues wouldn't make a difference. I realize the 21.5 USGT series isnt as fast as 17.5 or 13.5 classes but im hoping i can squeeze a little more out of my setup.

Any ideas?

Thanks,
Garrett
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Old 05-21-2014, 02:00 PM
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Im running a thuner power 21.5 with HT rotor in a gt3 class. My fdr is 3.4 but im told it should be even lower like a 3.1. I am fine with the way the car is as I can keep up with everyone.
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Old 05-21-2014, 03:00 PM
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Maybe it's me but that FDR seems very low. I think most of the setups I've seen run around 3.5 or so for a 21.5.
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Old 05-21-2014, 03:06 PM
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What chassis are you running? I have yet to see on that strictly limits you to shorty packs? Agree with /\, you need to gear up as your FDR is too higher. Should be high 3's for USGT.
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Old 05-21-2014, 03:11 PM
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I bet they are using 48 pitch.
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Old 05-21-2014, 03:24 PM
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Originally Posted by thecaptain View Post
I bet they are using 48 pitch.
What does that matter?
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Old 05-21-2014, 03:29 PM
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I am using 48 P but it doesn't matter. Fdr is fdr whether 48 or 64P
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Old 05-21-2014, 04:35 PM
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Klaymon - I am going to plug in a 40 or 45 tooth pinion to achieve 3.3 or 3.7 FDR and see what the difference is.

Mkiiina - I am running a schumacher sst2000 which was setup for nicad stick packs. I had to move all of the electronics around to mount the lipo of the side of the car with TEKNO velcro straps.

TheCaptain - I am using 48p gears, haven't tried 64p yet.

I used to run 4000 or 5000 nicad packs with my 27 turn stock motors and that seemed much faster than the newer items in my first post. Guess it's all relative with the longer run times that lipo's offer.

Thanks,
Garrett
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Old 05-21-2014, 05:20 PM
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Ignore most of the "that FDR is too high/low" comments, unless they're from someone local to you. Smaller tracks tend to run a higher FDR, larger tracks will go a bit lower. Where is the timing set on the motor? I'm not familiar with that specific motor.. is the timing adjustable or do you need the timing board(s)? You should be safe in the 3.7 range at most places, just keep an eye on temperature. If your timing is still set to wherever it was when you got the motor, that can be a big reason you're down on power. If you mention where you're running or the track size/surface, you may get more accurate suggestions. Without trying to step on anyone's toes, anyone that suggests "way too high" or "way too low" FDR's (in the general 3.2-4.2 ballpark) without knowing what/where you're specifically doing this is guessing and will likely be wrong.

You should be fine with the shorty pack, most likely that's not a main reason you're down on power. If motor temps are okay and you noticeably slow down a few minutes into a run (after starting off well) then the battery may be a factor. The shorty pack will lose some voltage a bit quicker than a full size pack, I wouldn't think it would be much of a factor in USGT.. I'd sort the motor/gearing out first.
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Old 05-21-2014, 06:18 PM
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i have been running my 25.5 at 3.5 on a large track all winter (96x48) and car ran fine. now that we are outside i am running a 3.9 and its plenty fast and much faster than my 25.5. previous poster is correct in the gearing range. go by temp. too hot gear down (smaller pinion) no heat, gear up till you run under 140. i dont go over 140 temps.
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Old 05-21-2014, 07:35 PM
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Lasagnacat - I don't see any timing marks on the side of the can nor any screws telling me that I could rotate the timing. Also, I run my TC on a 96x40 well maintained indoor carpet track with very little temperature impact.

Dragonracing - any good recommendations for a temp gun to keep the running temp in check? I have an extra fan that I will be installing to keep the temps under 140 hopefully.

Thanks,
Garrett
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Old 05-21-2014, 08:02 PM
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The port where the sensor wire plugs in should slide a little bit in a slot in the endbell. It's not much timing adjustment, but that's how you change the timing on those SP motors. Make sure the port is as far to the right as it will go (counter clockwise) to get the maximum timing (20 degrees, I believe).
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Old 05-21-2014, 10:24 PM
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Originally Posted by Ghartman581 View Post
Lasagnacat - I don't see any timing marks on the side of the can nor any screws telling me that I could rotate the timing. Also, I run my TC on a 96x40 well maintained indoor carpet track with very little temperature impact.

Dragonracing - any good recommendations for a temp gun to keep the running temp in check? I have an extra fan that I will be installing to keep the temps under 140 hopefully.

Thanks,
Garrett
raytec, check welding shops for them. ive had mine for 15 years. works fantastic. i also run a wtf fan on my car. i dont run without a fan period.
http://www.raytek-direct.com/shop/it...9shU7MLevD_BwE
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Old 05-21-2014, 10:53 PM
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Why do you mention diff bushings and what are we supposed to do with this information if we don't know what chassis you run? Why does that have anything to do with motor/gearing/battery?
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Old 05-21-2014, 11:03 PM
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Originally Posted by Ghartman581 View Post
Hi,

i am using the speed passion 3.0mm 21.5R motor, 4600/70c shorty lipo, hobbywing stock-spec esc, and have a 75 spur, 35 pinion with a FDR of 4.28. i replaced the factory bushings in the front & rear ball diffs but I'm not super impressed with the power performance at this point.

My chassis will only allow for shorty lipo's so I'm limited in battery options with more milliamps. i haven't experimented much with the esc or radio settings but it seems these two avenues wouldn't make a difference. I realize the 21.5 USGT series isnt as fast as 17.5 or 13.5 classes but im hoping i can squeeze a little more out of my setup.

Any ideas?

Thanks,
Garrett
Not familiar with the SP motor but a FDR of 4.28 seems too big for a 21.5 motor unless its a very short tight track & particularly if 20 degrees is the max timing possible. The real issues in FDR are the size of the track, how much timing you have in the motor, and the stator/rotor combo being used. Less timing generally needs a smaller FDRs to get the same lap times. Set the timing to at least 30 degrees or higher if possible or the max if the SP is limited to 20 degrees and start playing with FDR until you can get lap times in the area you want. (BTW I'm running 55 degrees in my 21.5 motors and have a FDR of ~3.6 but it's a big flowing outdoor track, at 20 degrees timing on the same track I would need a much smaller FDR to get the same lap times). Be careful to monitor motor temps frequently ( every two or three laps) as you decrease the FDR and keep the motor under 160 degrees until you are comfortable you can make long runs without overheating the motor, then make final adjustments in FDR & timing to make sure you can make run time with your batteries. Without a dyno you are shooting in the dark as to where to set the timing of the motor to get the best efficiency and power. It's going to be all trial and error. For example In VTA car my 25.5 motor was awesome at 45 degrees of timing, but sucked too much battery and faded in the last two minutes of the 12 minutes mains we run (it was 160F at end of the main). After experimenting, I've now dropped the timing to 30 degrees as well as dropping the FDR (to compensate for fewer RPMS) and I'm running faster laps and the motor is less than 130F after a 5 minute run. Looking forward to the next "any 25.5 motor" VTA race. Have fun!!

PS end bell timing isn't always the only timing in a motor. My ORCA 21.5 motor has 30 degrees of timing built into the stator so when the end bell says 10 degrees, the total timing in the motor is really 40 degrees. Be sure to check with SP to see if there is timing build into the motor beside the end bell timing.

Last edited by John Wallace2; 05-21-2014 at 11:43 PM.
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