Need help with buggy conversion

[pinolelst]

Buy both.It'll give you a reason to build another car with the motor you don't settle on this time.:027:

pinolelst

I really hate being so ignorant about something that interests me so much.

I just don't understand. If the 12L would thermal the escs that you mentioned, how is it that a larger motor (ie, 7XL) that draws more current and has fewer winds going to run cooler? Is it just because the 7XL is so much more efficient that it produces less heat?

OK, well let me ask this. With a proper load, can I say as a general rule that an XL motor will always run cooler than an L motor with a similar kv rating?

Do you think that the MM can handle the 7XL without stretching it? Should I just go with the 8XL? I want my whole system to be comfortable.

LOL, yeah, I was just looking at the gorilla stuff and I already have the urge to get on ebay and find me a Revo roller.

Anyway, I just used the calculator and it appears that around 8 pounds of load is the max for an L can motor. I think I'm going to play it safe and go with the XL. Runtime or no, I can't have the thing over heating on me. Besides, the 7XL appears to be able to get me to 40 with relatively mild gearing.

[sleebus.jones]

Originally Posted by AAngel

There's one thing that I don't understand about these brushless motors. That is their ability to generate torque. Does the torque go up as you reduce the number of winds, or is the ability to generate torque a constant among a line of motors? I mean, do all L can motors generate the same amount of torque with the number of winds affecting only the number of rpms/v?

The torque is pretty much consistent across the can size. That's because the max torque is determined by the amount of magnet engaging with the coils. IF you can feed the max current that motor wants, then you'll have the same torque. It's not the same as brushed motors at all.

I think i've said this before, but I'm running a 10L in my 1/8 buggy. I'm about to shoot some video of it today, I'll be running it on 6 cells, 7 cells, 3S LiPo and 12 cells, all so anyone watching can see the difference. With the 11/46 gearing now, I can tell it could use a bit taller gearing. I've got a 13T pinion on the way, which should be about perfect. According to my calcs, a 13/46 + 4S should have plenty of torque and hit 40 mph easy.

Sleeb

[glassdoctor]

Originally Posted by AAngel

I really hate being so ignorant about something that interests me so much.

I just don't understand. If the 12L would thermal the escs that you mentioned, how is it that a larger motor (ie, 7XL) that draws more current and has fewer winds going to run cooler? Is it just because the 7XL is so much more efficient that it produces less heat?

OK, well let me ask this. With a proper load, can I say as a general rule that an XL motor will always run cooler than an L motor with a similar kv rating?

Do you think that the MM can handle the 7XL without stretching it? Should I just go with the 8XL? I want my whole system to be comfortable.

Yes... in general an XL should run cooler with the same load. I think in reality the XLs run cooler because they can pull a higher gear at a lower rpm (wihta lower kv) in other words, guys have switched out an L for an XL.... but normally the XL has lower kv.

As for my 12L Hacker/Feigao... I'm not the only one who had the MM work where several others had failed. RotaryRocket had the same experience with his buggy, using a Pletty Maximum motor. And remember, my motor may be pulling higher amps than a normal 12L. I clocked it with my gps at 55 mph on an old 4s lipo. And this was geared 13/44... it did 40+ at 10/44. So I think this motor runs faster than a 12L is supposed to. If I geared that thing 18/46 with better lipos I wonder what it would do? 65+? :)

The 7XL does have fewer winds, but it's not a "hotter" motor. It does have more ability to pull high amps but it also has inherently more torque so it won't work as hard to do the same job as an L size motor. Check out the charts that show the resistance and idle current of some different motors... the numbers don't change much for a given kv... XL,L or S.
http://www.hackerbrushless.com/motors_b50constants.shtm

Again, thanks alot guys. I do have the 7XL on the way. As I said, I made my motor mount, so I know what needs to be done. I ordered some 7075 aluminum sheets cut to 2.5X3". All I'll need to do is drill and tap some holes. Do you guys think it would be better to have the motor off to one side, but mounted toward the front of the buggy, or center mounted with the gear engagement being above the center diff? My intention is to be able to mount two 2S packs. One on each side.

Or...do you think it would be better to just mount the motor in a conventional way (off to one side toward the back) and have all of the "equipment" on one side of the buggy and the battery (single 4S2P pack) on the other? I'd love to be able to use a single pack, but the buggy has to have a good weight distribution for racing purposes.

I just don't know what battery chemistry to go with. I have lipos, but they worry me. They are fine for bashing, but I don't know about racing 1/8 scale buggy. I can recall some crashes that I've had running nitro, and I seriously doubt that a lipo cell would have survived them in tact. Of course, my concern is with the fire that will result from a pack being punctured. I'd hate to think that I could looose my whole buggy (not to mention other buggies and corner marshalls) because a battery was damaged in a crash.

I believe that I have three other altenatives. The first is the A123s. Considering the ability of these cells to deliver current, I might be completely happy running a pair of 2S2P packs. Assuming a 10A charge rate, I figure that a pack will charge in 30-40 minutes. Of course, it would be expensive considering that I'd need to buy two pack and two chargers; or, more ideally, four packs and two chargers. How do you guys think the 7XL will run on the A123s? Will I be giving up much by going with 4S A123 rather than 4S Lipo?

My second consideration is lithium manganese. These also have the ability to charge at a 2C rate, but I don't think that they deliver as much current as the A123s, although they do have the voltage of the Lipos. At $75 a pack, it would only run me $300 for two sets of 2S2P packs. Of course, I understand that there have been problems with the 3.8Ah packs. I can find them, but don't know if I'll get the bad ones. I could move up to the 5.8Ah packs, but the price doubles and so does the weight (just about).

My last alternative is good ole nimh. I can get IB4200 cells for under $6 each and just load them up into the solderless tubes. For the price of the other chemistries, I could get a butt load of nimh cells and just run two 6 cell packs.

Again...comments please.

Thanks,
Tony

[squeeforever]

I would go with LiPo's to be honest. If your that worried about them, I would do some preventative measures that will ensure there safety. I have seen some companies put CF on the top and bottom. That should prevent alot of things that could happen. Another option is make some kind of box for them. There is a Revo around here somewhere that has a little box for LiPo's. It was made of 2 pieces of L profile aluminum and a small hinge (piano I believe he said) and lined with foam.

[sleebus.jones]

Originally Posted by AAngel

I could get a butt load of nimh cells and just run two 6 cell packs.

butt load of NiMh (12 cells :) ) = 1.8 pounds
4S 4000mAh LiPo = 0.8 pounds

You make da call! :dft003:

Sleebus

[BrianG]

Originally Posted by squeeforever

I would go with LiPo's to be honest. If your that worried about them, I would do some preventative measures that will ensure there safety. I have seen some companies put CF on the top and bottom. That should prevent alot of things that could happen. Another option is make some kind of box for them. There is a Revo around here somewhere that has a little box for LiPo's. It was made of 2 pieces of L profile aluminum and a small hinge (piano I believe he said) and lined with foam.

Some Lexan would be a good choice too. That way you could see if there was a cell starting to puff, or if the heatshrink gets melted like I saw from another user here (can't recall who ATM). But, won't encasing the packs reduce cooling efficiency because of no airflow?

Weight is definitely an issue and going with the nimh would be counter productive on that issue. I did order some 6061 aluminum channel. The channel is 47mm wide, while the battery is 34mm wide. I'm considering using the 2100HV cells to make my packs. Although they are a bit thicker than what maxamps usually uses to make car packs, they are also considerably shorter and narrower. This would allow me to protect the packs with some sort of dense foam on three sides. I don't think that I'll want to completely encase the packs. I want to be able to visually inspect them.

Where can I get lexan and/or carbon fiber. I've heard that carbon fiber is really easy to work with and tha CA bonds it like concrete.

[BrianG]

You can get sheets of Lexan at many home improvement centers like Lowe's, Home Depot, Menards, etc. I've heard good things about GraphiteElegance to get the CF you need. However, it's not as "pretty" as stock pieces as there is some surface pitting between the weaves.

If you're not concerned with cosmetics as much, you could also use fiberglass. It is easy to work with and available locally. Just pick up the resin/hardener at most department store automotive departments. You can use either real fiberglass cloth or fleece (available in the craft section). I always look at the remnant section as it's cheaper. Color of the fabric isn't important IMO as you'll probably be painting it. The fleece is easier to work with IMO. Just stretch it over a frame (cover with wax paper first) and then saturate with resin/hardener. Do the otherside as well and you'll have a nice sturdy case. A little sanding and it can look really nice.

[glassdoctor]

If you want some "safeer" lipos that are also perhaps the best performing cells you can buy, talk to Larry at Kokam America. Just ask for the cells that Shawn at Castle was using.

They are the ones you can put a nail through and they won't flame.

Or you can just buy a couple of the Orion hardcase packs.... I'm told those have the same Kokam cells inside, and they cost about the same as loose cells or shrink wrapped packs from Kokam.

[pinolelst]

Just FYI.I drove a 16d nail through a puffed cell a couple years ago and nothing happened except I could now see through the center of the cell..Your Mileage May vary...


pinolelst

Hey guys,

I just wanted to thank all of those that took the time to give advise and share their experiences with me on this project. For better or worse, I've settled on a setup to start off with. Luckily, it turns out that there are optional aluminum center diff mounts for my buggy, so I'm just going to mount the motor mount to the center diff at four points. This should be sufficient and I won't have to worry about chassis flex.

My setup is going to be:

Sportwerks Turmoil 1/8 scale buggy
Feigao 7XL motor
Mamba Max controller
Maxamps 4S2P 6Ah battery packs

This setup should pretty much duplicate my buggy's weight distribution before the conversion. I hope to have this up and running within a week of receiving the aluminum that I ordered.

Thanks again.