1515/1y vs. 1515/2.5d

[jnev]

Well, as many of you know, I am trying to sell a lot of my unneeded rc car stuff to fund for a Neu motor to go into my Revo. I was originally planning on running the 1515/1y on 4s lipo, but I knew that I would want to run a higher voltage in the future and wouldn't be able to use it. The 1515/2.5d on the other hand, will run 5s great, but, not too sure on 4s. My set up is a Revo with stock diffs (soon to be 1/8 buggy diffs after these fail), Revo tranny locked into 2nd gear with wide ratio gear set, and 5.6 inch 40 series tires.

According to BrianG's calculator:
With the Neu 1515/2.5d - 20t pinion - 4s lipo - it will go 38.76MPH, but the RPMs will only be 25,160. I am afraid that it would heat up too much from having it over rev, and not having enough load on the motor. But the good news is that in the future, I will be able to run more voltage on it.

With the Neu 1515/1y - 16t pinion - 4s lipo - it will go 40.12MPH, and the RPMs would be 32,560 which is perfect for efficient running. But if I ever want to run a higher voltage, I will need a new motor as far as I know.

Let me know what you all think of this right now. I am leaning toward the 1515/2.5d and having Mike make me a custom pinion that is 22t or similar, so that it won't be underloaded. And then when I run 5s or 6s, I will just gear the pinion way lower.

[What's_nitro?]

Actually, if you're looking for 30-35K rpm, the 2.5d would be "under-revved" and should actually run cooler. I would think if you have plans for a higher V setup then the 2.5d would be the way to go. At 5s it would only be 31K rpm, 6s would be 37K which I suppose is little high but top speed would be incredible.

[BrianG]

Motors don't necessarily heat up from low-revvs, it's underloading that heats them up. Actually, if you want ~40mph speed, a low revving motor could be overloaded due to the gearing needed to compensate for the low rpm.

From experience, the Neus have no problems running at or near 40krpm.

[suicideneil]

All other things being equal, which motor would pull more amps? Im guessing the smaller 1512 2.5d since it has less torque than the 1515 1y, but then again it has a lower kv rating = higher resistance so lower amp draw.... confusing.

[jnev]

suicide - I actually said the 1515/2.5d. This stuff gets very confusing, but I must say very interesting as well.

I am still not sure which would suite me better though. I would like to be right around 40mph, but any higher would be fine with me.

Has anyone ran a 1515/2.5 geared very high? Did it still run efficiently and run cool?

BrianG - So what you are saying, is that it would be better to gear down on a high KV motor rather than gear up on a low KV motor? Would it run cooler this way?

[BrianG]

Originally Posted by jnev

BrianG - So what you are saying, is that it would be better to gear down on a high KV motor rather than gear up on a low KV motor? Would it run cooler this way?

Well, neither really. An appropriately chosen motor for the battery voltage you have, geared for the speed you want (within reason) is the best bet.

If you wayy underrev and overgear (to compensate) a BL motor, you have more chance for cogging since there are less back EMF pulses for the ESC to read. Not to mention your burst current will be higher because of the higher load.

If you spin a motor too fast, you start getting heat for no reason even though it isn't loaded as much with short gearing.

[Patrick]

Originally Posted by jnev

Has anyone ran a 1515/2.5 geared very high? Did it still run efficiently and run cool?

I have run mine geared 12.5:1 a bit in my not so light maxx, on 5s2p 8000mah truerc packs (a 3s and a 2s). You probably have seen this before, but this is what it does http://www.youtube.com/watch?v=ZMZeTJFA2f4 I should make another shorter vid with a better camera, but I don't have one.
Anyway I use a nitro temp gauge looped around the motor, and running it like that (with a bit more stopping and slower driving though) for at least 20 minutes, probably more, (the last 5300mah of the pack) the motor was a bit less than 50 c (122f). The hottest that motor has ever gotten is 50.2c when we did an endruro race at the end of one of the inter-club meets. It was an all in (probably over 30 cars), last man standing thing just for fun. This was mostly against 1/10th buggys and trucks running nimh and brushed motors (mainly, because of rules for there class), so after 22 minutes when most of then were finished and packing up to go home they stopped it, because they got bored (only me and another maxx still going). My car was only geared 15.9:1 though for racing and it was about 80f that day, but I think 122f is a good temp. When I charged those packs 2 weeks later they took 3300mah

When I first got that motor and I was waiting for the lipo's to arrive I tried it out on 12 and 14 cells nimh at racing just to see how it would go. It was geared 12.5:1 again and it had some decent power and speed, nothing amazing, but not slow. I don't think it quite reached 40c (104f) in a 5 minute race.I don't know how it'd go geared for 40mph on 4s though, might do it ok, but depends how light your car is.
People do run the 1y's on 5s sometimes, and 2200kv at 18.5v is a max speed of 40700 rpm and a bit less once you include volt drop and motor loading, so it's not like it's out of the question all together. I guess it depends on how long it will be before you change batteries. At least with the 2.5d there's a lot of room to make it faster later.

[lincpimp]

Not sure if this will help, but I tried a 10l feigao on both 3s and 4s, geared to produce the same top speed. I will say that the 4s sytem was superior to the 3s system, both in heat, power and runtime. On 3s the motr was turning about 27k and just did not feel that powerful, plus I was spinning a 20tooth pinion. On 4s it was spinning around 36k and I am using a 14 tooth pinion now. To be honest it feels like a completely different setup. It is generally said tyhat around 35k is a good speed to run thse motors and it seems to be true. If the neu motors will handle around 40k rpm I would suggest to run it at that speed. You will use lower gearing and most likey have a more effecient system. Just my opinion, and it is based on a feigao motor which is crap compared to the neu. But cheap, and they can be made to work properly. What we really need is a xxl feigao, maybe that will run cool! I just received some kb 45mm xl motors and they should be able to cope with heavier loads. Good luck with the decision.

[suicideneil]

Confusing & interesting, yes! I would have thought gearing down a high kv motor would be better, but then again some motors are said to run better if overgeared....

I like the idea of using the smaller 1512 motor since it would be more than powerful enough for my ideas- for you though the 1515 2.5 sounds like a nice motor.

[suicideneil]

I kinda guess going by that info, its a case of matching the motor kv to the voltage resulting in an rpm range of 30-35,000 rpm- with sensible sounding gearing that gives you your desired speed of 40mph or so, whilst also considering amp load on the batteries & esc.... like I said, confusing!

[BrianG]

lol. Not really confusing, just a lot to think about. I always start by deciding what battery I want to use and then go from there.

[jnev]

Well, I will start off with the battery I already have which is the TrueRC 4s2p 8000mAH pack. So far, the performance of it in my buggy has been incredible!!

[jnev]

Thanks for all the help guys. This is just getting harder and harder to decide.

However now, I am leaning more towards the Neu 1515/1y. I will run this motor geared 16/36 with the wide ratio gear set. I will just continue saving up for when I decide to go higher in voltage. Hopefully this motor will run as cool as I am hoping it to... and without a fan.

[SpEEdyBL]

Go with the 1y. The 2.5D is a less powerful motor, meaning it will struggle more the reach the same speed. The 1y will only overheat more if it is underloaded. In such case, it would be better to go down to a 1512, instead of requiring the biggest pinion gear you can find to get your desired speed, so in my mind a 1515 2.5D isn't much of an option.

[jnev]

I will wait for a few more replies... but I am almost certain that I will go with the 1515/1y.