MMM and Neu 1515 gearing ?'s

[dorji]

Hey guys, I am in the middle of a losi 8ight buggy conversion. I wanted to run a 1515 1y or a 2d. I think these motors are rated at 3 or 3.5 HP. Will this motor with a Mamba Monster Max and a 45t spur be able to handle a 20t or a 22t pinion? Will the amp draw from the motor with this gearing be to much for the MMM? Or will this gearing cause to much heat? I was also wondering if this higher gearing will help keep the front end down a little when you hit the throttle?
This is my first brush-less buggy conversion, and I'm still trying to figure out the right set up. Thanks for any help you guys can offer.

[The Dan]

The Neu 1515 1Y will draw 110 amps at the most, so the MMM would be fine. It's rated for 200 amps continuous. Just be sure to run it on batteries that can supply at least 110 amps continuously so the motor doesn't overdraw from them. That answers that, but I wouldn't recommend a 1515 motor for a buggy. That size motor can pull a truggy off it's front AND BACK tires, despite the center diff. Here, check out this guide to building up a brushless buggy:

http://www.impaktrc.com/product_info.php?cPath=298&products_id=3275

[dorji]

Thanks for the link. I greatly appreciate all the help. I noticed the set ups they use are pretty slow. I think they were all geared for about 35 mph.

I want to run a 4s at the track with speeds in the 40-50 mph range. Then switch to a 5s to run at the dirt bike track or general bashing in the 60-70 mph range. Then switch to a 6s to do some occasional crazy high speed runs75-80 + mph.

The only motors I found that could possibly achieve this would be a 2200 kv or the 2050 kv. My only concern is they have to be geared high. 45/18 or 45/20 gearing would have to be used. With a 35c 5000 MaH battery, will this gearing run to hot?

Also I need the motor to have enough torque to clear a couple of 20-25 ft. doubles and one 40 ft triple at the MX track. Would the 1509 have the HP (about 2hp) and torque to accomplish this?

Thanks again for the help.

[dorji]

Also would a 2550 kv motor handle a 6s lipo?

Thanks again for everything

[The Dan]

They suggest those 35 MPH motor/battery/gearing combos because anything faster or more powerful gets uncontrolable on the track. You'll be shredding tires and losing traction every time you hit the gas, which makes driving far too difficult and cuts your lap times way down.

I would recommend using their 4S so you could just up the batteries to get the bashing speeds you want. Don't go with the low-kv setups because they would be limited to 6S to get ~35 MPH.

I wouldn't worry too much about motor temps. You may be surprised at how hot these exact motor systems we're talking about get in true racing conditions. I went to Indy RC World recently where they had a 10-car field of brushless 1/8 buggies who used Neu 1512s, Medusas and Losi Xcelorins all on 4S without heat sinks or fans, and their motor temps averaged 190-200dF after each 5-minute heat. That really surprised me, but modified brushless touring car racers at my local carpet track, East Texas RC, get the exact same motor temps after their 5-minute races without heat sinks or fans, too. Racers don't have a problem with those temps, but I'm more of a basher, and would like my motor to run cooler.

I'm reconsidering suggesting a 1515 under the premise that the bigger motor would power the buggy easier and therefore run cooler. I know BrianG here is running a 1515 2D in his buggy I think, and he says it runs wonderfully cool. That's all I have to go by, but he's a mod, so I would ask him specifically about it.

[BrianG]

Yeah, 35mph is typically good for the smaller tracks. It's rare to get to top speed in such a short span - and even if you can, you are limited by wheel spin.

Any motor can draw well over its rating, but in very short bursts. I like to break down the amp figures into 3 categories for electric motors:

1) Instantaneous current, which is what happens at the initial take-off from 0rpm. This figure can very well be in the hundreds of amps, but only for a couple microseconds.

2) Burst current, which is what happens on heavy acceleration. Since the motor is already moving, this current will be somewhat lower than the instant current.

3) Running, or average, current, which is what you are drawing over the course of the pack. Simply determined by a calculation of runtime and capacity. If you run 20 minutes on a 5Ah pack, this will be 15A.

110A constant current is unrealistic in cars. If you drew 110A constant with even an 8Ah pack, the runtime would only be around 4 minutes! Realistically, figure ~15A average with 100-120A bursts for a typical 35-40mph buggy setup. If geared really high, expect 20A+ average with 160-180A bursts. But then, you are really pushing those cells!

If you gear too high, you may experience higher-than-normal current draws when you take-off. Because the motor is effectively being stalled trying to pull such a tall gearing, there is no back-EMF to help limit the current. And with no back-EMF, current is theoretically limited by motor's DC coil resistance which is really low. Example; a Neu 1512/2d coil resistance is 0.006 ohms. At 4s, that's a stalled current of over 2,400A! Of course, the battery, wires, ESC, etc will limit that, but you get the idea.

Also, if you gear too high, the motor will be spinning less revs per mph and the ESC may not be getting enough back-EMF pulses to effectively get rotor position and cogging may result.

Neu motors are good up to 60krpm. If you are doing speed runs, I would choose a motor that will hit close to that at full tilt and then gear appropriately for the speed you want. The higher rpms at lower speeds will be easier on the ESC and batteries, yet you'll get the top end you want. So, let's say you want to run 6s. You could run a Neu 1512/2d for around 58k rpm. Then, if you want 70mph, you'd probably be using a 15T pinion. Since you are running high gearing, I'd select the 1515/1.5d series instead for the added torque and power rating.

No matter what, speed runs are gonna be hard on the batteries, ESC, and motor. People routinely blow motors doing this. If you really insist on getting that crazy, I would consider voltages 8s-10s to get the current back down to manageable levels. But, fitting that many batteries under a buggy body and finding a car ESC that will handle the votlage can be expensive. Speed isn't cheap!

And yes, my buggy runs great with the 1512/2d on 4s. But I am geared for ~40mph.

[dorji]

Thanks for all the great info guys. A lot to think about.

I am more of a basher than a racer, so having the ability to clear big jumps and run on the cooler side is more important to me. The occasional high speed run would be fun but not as necessary. I'll probably run 5s 90% of the time but would like the ability to add the extra cell.

I have the Losi conversion kit, that came with a 45t spur and two pinions, a 15t and a 16t. So to start I will try the 45/16t combo. Will this be a low enough gearing to keep things pretty cool.

I am looking at the 1512 2d, but a fully charged 6s(4.2v per cell = 25.2v), the rpms come out to 64260. I am guessing the motor will not handle this? What about the 1509 1.5y (2400 kv)? I noticed that they have the same ratings as the medusa motors, 750 watts. I think that is about 2 hp? Will this be enough to clear big jumps with the 45/16 gearing. Or should I just go with a 1515 1y?

sorry for all the questions guys and thanks again for the help



Thanks again for the help guys.

[The Dan]

http://www.scriptasylum.com/rc_speed/_top_speed.html

That is a speed calculator for RC cars. Pretty accurate IMO.

The 1509 series would heat up much more because they're smaller and would have to be run at maximum current. Remember that the 1512s reached 200dF on 4S after mere 5-minute races. And no, 750 watts is a little over 1 HP.

I would still suggest the 1515 1Y or 2D. The 1Y is a very popular, versatile motor that can power anything you want from monster trucks to truggies. It is the kv that's going to be included in the new E-Revo brushless edition for good reason. Speaking of which, you could also wait for the full-blown Mamba Monster 2200 motor/battery combo to come out; that would save you a ton of money. It's priced at ~$300!

[dorji]

Thanks for the help guys. I think I will go with the 1515 1y.

[Bondonutz]

That's a great choice ! It's the same mill I have in my E-revo and I'm super happy with it. With the buggy being much lighter it should be a bullet, especially with 5s+ !!