1512 2.5D vs 3D on 5S?
 

I have currently got a 1512 2.5D (2050KV) in my 8IGHT and running it on 5S 5000mah geared at 41mph and it gets pretty hot 180F+ The 2.5D on 5S makes 37925rpm and most people recommend motor rpm's to be between 30K - 35K. I once had the buggy geared at 44mph and it was great (apart from the temp of course) had plenty of speed. Was thinking of giving the 3D a go and see if temps would go down. 3D on 5S makes 31450rpm which is 6400rpm difference. Is the 3D going to be able to run at 44mph or becuase it is a slower motor than the 2.5D it won't be able to run that fast without overheating?

I ran both the 2.5d and 3d on 5s and there was no difference in heat for me even when both were geared for the same top end. You are definitely running hot though. I would double check your bearings and make sure your motor wires are secure and not fraying inside the can as this can cause heat.

yea i just ran a 2.5d on 5s 4000 geard for 39mph and it never got over 143 with my mm never breaking 95, and it was 70 outside. id do like edumakated suggested and check your bearings and connections and also set your timing on your controller to low or lowest, and set your start power to medium or low which ever works best. these will help lower the motor temp.

30 -35K is only for feigao motors. Neu motors can go much higher before efficiency starts to drop off.

The 3D has more resistance than the 2.5D, which means it will heat up more at a given amp rate because copper loss = resistance x amps^2 and the 3D has about 1.4 times the resistance as the 2.5D. The only time a higher wind motor will run cooler is if iron losses (energy lost in the magnet) are signficant, but this only happens at high rpms.

And btw, Y winds are slightly more efficient than D winds, so you may be better off going with the 1.5Y rather than the 3D. But before doing anything, try different pinion gears and record the temps each time. A GOOD motor should run the coolest with the smallest pinion gear, and gradually get hotter as the pinion gear goes up. If your motor still gets hot with a small pinion gear, there is something wrong with your motor or setup.

so your saying the 3d is gonna get hotter than a 2.5d on 5s ???????????????


id like to know before teckno ships me my teckno version of the 3d, i could call them first thing in the morning and change to a 2.5d ?????????????

edit*** the 3d is more efficent than the 2.5d, but the resistance is .012 compared to .006 of the 2.5 so isnt the resistance realted to the amount of wire used to make the KV lower in the 3d???? i always thought the lower kv motors had a little more resistance?

some one have a better explanation? ive confused my self reading on this subject....

That may be true, but the resistance you are speaking of is really small compared to the inductive reactance of the coils, so the heat increase will be marginal.

I got my timing set to low and start power set to low. Would changing the start power to medium help at all? Before I changed the diff fluids from 5/10/2 to 7/10/3 and updated the firmware on the MMM temps were usually around 165F. Thinking of maybe putting the front diff back to 5000. I think I amy of overfilled my center diff to so might take that apart and check. Nothing in the drive train seems to be wrong. I just got a 12T pinion in so might give that a try which will gear it at around 38mph but I think that may be a tad to slow for my track. The track isn't huge but the back straight and main straight is pretty long

thanks brian,

and wont the 3d pull less amps under the same voltage (5s) than the said 2.5d so it will be running cooler and more efficent, even though the resistance is very slightly higher, the lower amp draw over comes the other figures in the heat equation right?


and for drift, try your start power at medium and see if you notice any difference. but it could be a ton of things, including your drivetrain, and you wouldnt even know it, your gear mesh effects it, the gear mesh of your diffs is important also, take the pinion off and push your buggy on a hard floor, if it doesnt roll 4-5 feet "Silently" with a very light push then id be checking there first. did you check your motor bearings for any play?

my gear mesh was too tight on my front diff awhile back after i redid (too many shims on the wrong side, and my motor was running a good 20* hotter than normal after i fixed that my temps went back to normal.

another thing to look at is it really doesnt matter that the neu is up 170-180 they told me their motors would run fine all day long at these temps, so check your temps and sceduled stops through out your run and after it gets up to 170 see if it goes anyhigher as you continue to run and find out where it tops out, in our 30 minutes july 4th a main my 1515 was running 175 at 15 minutes and at the end of the race it was 173, they will top out like this, and nue told me as long as its below 190 its fine to run them at that temp as long as needed.

My 3d didn't run any hotter than my 2.5d. Also, since the 3d is pulls less amps, I get about a minute or two of extra run time as well. I ran FIVE full packs (20+ minutes each) this weekend on our indoor track and temps never broke 110 on the motor (it was about 45-50. Temps for my 3d usually run below 150 on a hot summer day after 10 to 15 minute main. I also had a 1515 and it always ran at 160-175, but never got any hotter similar to what Rootar is saying. Most of these motors just find a temp that they tend to run at and stay in that range. As long as you aren't getting above 180ish, I wouldn't worry about it but you are definitely running on the high side for that setup. I would break your car down completely (diffs and all) and rebuild it to see if there is any binding or something hidden you can't easily see.

If you are trying to go the same speed and don't change the voltage the avg. amp draw on the 3d will be higher or as high as the 2.5d. You are making each of these motors do the same things and just using different ways to get there. 18.5v is constant so you are gearing up the 3d making any gains a mute point vs the other, larger gearing = higher avg amp draw = additional heat. I'm going to say the 2.5d is the correct motor and something else is wrong iMO, bad connections in the bullets something.. else, do more trouble shooting! I would re-solder all connectors to the motor, look for binds through any shafts etc, bearing issues (diffs or axle) etc etc.. You could always go w/ the 3d and move to 6s lipo if you find nothing.

Im running a Medusa v2 60mm 2000kv on 4s geared for 40 and never get over 130 unless it's mid summer then its about 150 and this is after hours of use (15/48). I am using mechanical brakes though, not sure of your setup.

stum the 3d drawing as many or more amps on 18.5v compared to the 2.5d would only be true if you had extremely high gearing that REALLY REALLY loaded the motor, but only 40mph isnt anything for either of these, so the 3d will definetly draw les amps than the 2.5d on the same voltage. its only marketed as a 70amp motor while the 2.5d is a 78, this is at max voltage but you must take into account when running on the same voltage the 3d Will be more efficent on 5s and up, now getting down down below 5s i dunno how they react as much to the slower rpm because that would be a
large gear up to run the 3d at 40mph on 4s

EDITED **** (wrong thread)

i think most of all high ambient temps are to blame here. what would happen if you shipped it over to somone in the states and they were to test it? my guess it would be around 150F or less. this is whats happening to everyones motor at my track anyway. nitro motors seem to handle it fine but the electrics dont. but that said i got a cheap $30 HC motor of the same kv and length. had just as much torque but after 2-3 minutes of going up and down the street with an 80mm fan over it it was at 180F and climbing... whereas my neu in the same environment is around 100F...

the track seems to heat them up alot more than bashing around the yard, and i think ive figured out why. onmy track at least 99% of the time im on the throttle. thats what heats it up i think. it just doesnt get a chance to rest and cool down. in the yard though, you tear to one end, roll around then gun it again for a short amt of time. anyway thats what i recon is the cause of the temps and i think we just have to live with it!.

What it really comes down to is what motor best suits the application. If you are using ~15 volt packs, you don't want a low turn 4,000 kv motor just to go 30 mph and you don't want a high turn 1,000 kv motor in order to go 60 mph.

Keep in mind that just because a motor draws less amp geared to go a certain speed, doesn't mean it is more efficient. Efficiency directly relates to how well a motor can hold it's rpm. Otherwise, torque is basically proportional to current no matter what. You could have two 2,000 kv motors and even if one is 50% efficient and the other is 90% efficient, they both will have the same torque per amp. However, the 50% efficient motor will be spinning much slower than the 90% efficient motor. And btw, you can treat a 1,000kv motor with twice the pinion gear size as being equivalent to a 2,000 kv motor, and refer to the torque at the wheels instead.

Another example, if you gear a 1.5D for 40mph, it will create lots of wheelspin and will get up to speed very quickly. It will also draw a lot of current to do so, but not because it's inefficient. The excess amperage directly correlates to the explosive acceleration that the 1.5D will have in constrast to the 3D also geared for 40 mph. Such comparsion with the 2.5D and the 3D will be more subtle.

thats a better example thanks speedyBL

Well I checked over the drivetrain today and it all seems normal. I put a 12T pinion in and changed the start power to medium but won't have a chance to give it a proper run till tomorrow. I took it for a quick run in the street and it doesn't to long to get to top speed. Probably be under geared now for the track. I do notice how ever that when the motor is connected to the spur the buggy is alot harder to push and when driving it sort of feels like I am running drag brake but I have that dissabled

on our track the HIGHER i geared my buggy, the lower the motor temp was (it wasnt running at full throttle in alot of places but only 3/4, and had alot of letting off due to the extra speed, but in turn the esc would be hotter, and so would my batteries and my little proteks couldnt handle the really high gearing (46 mph) but my 5s 5000 FP could but now im geared for 41 and the proteks can keep up with that and the motor never runs full throttle except on about 200 feet of the track. which is much better than 600 or so feet it would run at full throttle when geared for 35, gearing down never helped my temps..... so if the 12 is a bust gear up.

That maybe your issue.. you are calculating your speed wrong.. use 43/13 (3.30:1) for the 8ight buggy. At 12t you are at 44mph that is the top you would ever want that motor at iMO. To be honest 11t is a better starting point here is the calc. Looking at it the 3d would be a lot better for you on 5s as it would allow more gearing options, I don't even know if you can do an 11t pinion, at least with the Tekno v3 conversion I'm limited to a 12t as the bottom and it bearly meshes up. The 3d on a 14t is 40mph, then you can tweak up or down some... but I wouldn't buy another motor myself I would make do with the 2.5d at 12t and be happy, gearing down from what you had should reduce temps worst case run a fan on it during high heat summer. Just my2c

Differential Ratio: 3.3076923076923075
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 48
Pinion Tooth Count: 11
Total Voltage: 18
Motor KV: 2050
Tire Diameter (inches): 4.5
Tire Ballooning (inches): .5
Motor Current Draw: 80
Motor coil Ω: 0
Spur/Pinion Ratio: 4.36 : 1
Total Ratio: 14.43357 : 1
Tire Circumference (inches): 17.28 inches (438.88 mm)
Total Motor Speed: 36900 RPM
Vehicle Speed: 41.83 mph (67.2 km/h)
Estimated Adjusted Speed: 40 mph (64 km/h) - 5% loss
Effective KV Value: 2050
KT constant: 0.66 oz-in/A
Motor Torque: 0.27 ft-lbs
Final Torque: 3.97 ft-lbs
Final Power: 1440 watts (1.9 HP)

• 12t-43mph
• 13t-46mph
• 14t-49mph

Im running a 46T Spur. I checked the manual for the Losi ESC/Motor and they recommend a 12T Pinion when running a 45T Spur on 5S with the 2100KV motor.
My ESC temp is 130F and battery is 120F

What were you geared before? A 12t on a 46t spur is about 46mph on the 8ight buggy with a 5s lipo.

13T/46T. Where did you get those calculations from? On easy-rc.com, rcgearchart.com and some other one it says 38.6mph on 37925rpm, 110mm tires, 3.3077 ratio?

http://i33.tinypic.com/a5jcjo.jpg

??????????????????????????????????????

You have to calculate top speed with a .5 balloon on your tires, expecially at 40mph range you will get at least that much balloon effect... then re-run your numbers :)

Ok, well due to me having tonsillitis i haven't managed to take it down to the track to test it out

Tried the 12T pinion today and medium settings and no good, temp went up to 180F again, then tried it with the 11T pinion and back to low timing, no good temp went to 190F. Has to be something in the drivetrain somewhere. Going to have to strip the whole thing down and check. Before I changed to the new firmware on the MMM and no longer run the ext bec and also changed the diff fluids (5/10/2 to 7/10/3) the motor was running 165F on 13T. I do remember though that I had to rebuild the center diff becuase it was leaking and when I opened the diff there was a washer/shim on the oring and seemed to be the reason why as the washer wore out the oring and I checked the Losi manual and they didn't mention nothing about a washer

Drift;

Double check the motor wires just inside the can where they connect to the windings. You may have to look real hard, but see if there is any fraying or if a few of the strands are broken. If you don't secure the motor wires very tightly so there is zero movement, the vibrations can cause a few of the strands to break at the base of the winding. only a couple of broken strands can cause the motor to overheat and eventually it will just smoke itself. it is not something that you can easily see with the naked eye, but I have had this happen on a cuople of my Neu motors until I figured out I wasn't securing the wires tight enough.

See how I have the motor wires basically ziptied solid to the chassis brace?

http://i240.photobucket.com/albums/f...to/photo-1.jpg

if its in good condition and you can verify it hasnt been over 200 ever i may be interested in buying it. depending on the price of course. how does it run on 4s? (cooler or not?)
thanks,
ryan

I think I found the problem, the sun gear in the centre diff hosing was rubbing which was where I removed the shim from (rebuilt the diff and it probably hasn't had more than 2 hours running and the diff fluid was black). Haven't been able to test it as I noticed that my front shock shaft is bent and I cracked the hinge bin brace cover. Wont be able to go back to the track till 5 - 6 days (already got news parts on way). Hottest I think I remember was 188F. No way it has been at 200F