7XL Vs 8L on 12 cells..which is better?
 

Hey guys, sorry if this has been debated before, but I've just brought myself an Emaxx, and currently have an 8L motor from a previous project I'd like to use in it. My limit is 12 cells (due to my Mtroniks Truck controller). Mtroniks say 45-50mph is possible, realistically I've been told 40-45mph is more accurate with an 8L?

So my question is, would a 7XL be more powerful on 12 cells? And would it have a higher top speed (if I wanted it)? I only really want 40mph or so but I'd like very good acceleration, and I don't know which one would be better. I'd also like to be able to gear that bit higher when I take it to a big field. I'm also guessing the 8L would give me longer runtimes because it takes less energy to spin its rotor, but I'm just guessing? About half my driving is done at part throttle when I'm just going for runtime but I like to have a lot of power on tap. Cost isn't an issue, because i'm in a position to sell my 8L for almost enough to buy an XL motor if it will work out better.

Also, what drivetrain parts am I likely to wear or destroy on 12 cells with either of these motors? I plan on picking up some idler gears from Mike soon, but I don't know if anything else will need replacing.

Thanks for any advice you can offer me :)

well a 7xl would probably run cooler and have more torque
cvds are a must and you will probably want to upgrade the diffs

The diffs hold up fair on the 12 cells. cvds is a must and the idlers to. The 7xl to me is a better motor for the maxx. On 12 cells you can gear higher for more speed and have awesome torque. You would need some 5 mm pinions if you don't have none. A good slipper is nice as well. The strobe is excellent but not necessary.

What other slippers are there besides the strobe? I'd like to stay with 32p gears simply because my LHS stocks them, and they don't the ofna ones. I don't mind buying a couple of 5mm pinions if the motor will be more powerful. I am considering cvd's, are there any dogbone kits I could buy for the front and rear? CVD's look so damn expensive :( But then I guess everything about this car is.

You could go to robinson racing but you would need a special spur for that to. I like the strobe much better. Get a couple extra spurs when ordering. If you set the mesh right it won't fail. Mike has a few cvd and shafts in the store. You can go with mip for wheels and center but I like the ue ones much better.

its the exact opposite. the xl will use less power since it will draw less amps thus discharge the batteries slower. so a xl will give more runtime and torque. thats why most of us use them instead of a L.

So the 7XL will give more torque and runtime, but a lower top speed compared to an 8L, which will draw more amps to rev higher, which results in less torque but a higher eventual speed/power output on 12 cells?

Looks like i'll get a strobe sometime..whats the best gears to use, the regular or delrin ones? Mike keeps spare spur gears in stock?

you have the genesis pro or the truck esc?

as he said in his earlier post, its a truck version.

the 7xl will be a good choice for 12 cells. and yes, the 8L will draw more amps thus more heat, less runtime, ect. an xl is certainly the way to go.

7XL would be my choice.

The 7xl will turn fewer rpm but pull a taller gearing for more speed from the torque. Run stock gearing on the 7xl verse 14 or 15 tooth on the 8L.

Hold on a sec, because this is confusing me. The 7XL draws less amps, thus less heat, but it will produce more power overall, and with correct gearing will result in a higher top speed than the 8L? That doesn't add up, because on only 12 cells the only way to get a lot of speed is through pulling a lot of amps..correct? So presumably if I geared an 8L to hit 40mph, and geared a 7XL to hit the same speed (via steeper gearing), they would both need to draw the same power to get to that speed? Would the 7XL get there faster because its bigger rotor = more torque?

Yeah, what you said is right Rtsbasic. Only difference is the 7XL will run slightly more efficeintly and also cooler.

Cool, so if I got a 7XL, and geared it 22/66 on 12 cells (for ~35mph with stock tyres, correct?) I would have more runtime and less heat than if I put my 8L in and geared that 16/66 (for again approx 35mph with stock tyres)? The only way I can see the 7XL having more power while pulling less amps is if there's a large efficency difference between an L and an XL, is this the case?

Thanks for all the help so far, starting to get my head around these bigger brushless systems a bit.

The 7xl has a rotor about 45 mm long. the 8L has one about 30mm long. That is where the torque difference comes in. It runs cooler for the fact that it is longer and has more surface to air contact to disapate the heat better. I would say the run times are going to be about the same really. But the power is much beter on the 7xl.

can a 7xl take 14 cells? and how many amps would it pull with 12?

The 7XL will be fine on 14 cells. You'll need a 9920 controller to handle the current. The actual current figures they give for motors are not very accurate.

actually thats incorrect. the 7xl will NOT have to pull the same amount of amps to get to the same speed because of the higher gearing thus not having to work so hard. basically the torque allows you to gear higher for more speed while not pulling as many amps and having a higher efficiency.

also, i think that you should get BETTER runtime because of the motor pulling less amps.

So the general concensus is that a 7XL runs cooler, draws less amps so easier on controller, has more torque in general, and if geared appropiately will hit a higher top speed than an 8L in spite of revving a lot lower (29,000rpm on 12 cells vs 41,000rpm), while not really affecting runtimes? The bit that confuses me, is the 7XL generates more power, while pulling in less amps than an 8L, you can only put out what goes in, and the efficency difference can't be that big can it? Or is it possible for it to pull the same number of amps but because the bigger surface area and larger rotor its able to do it without heat problems?

Which brings me to my next question :) What sort of top speed is realistic to hit with a 7XL on 12 cells? Mtroniks say a stock weight emaxx will do 50mph with their 8L/Truck ESC combo on 12 good cells, but I find that a bit hard to believe. In summer I go to a local bash meeting every weekend thats held on a very big field, so lots of top end is important to me when I go to this (mostly because there's only about 3 of us that run electric..against 20-30 nitro buggies and trucks, lagging behind some dudes stock savage would suck).

The efficiency difference is actually pretty minimal between these two motors. I think that if they are geared for the same overall speed, runtime would be about the same with either motor. The 8L would accelerate a little quicker than the 7xl, but the 7xl would run a bit cooler. Both will work quite well with 12 cells. The 7xl will be a much better option for 14 cell use, and would allow more speed and runtime with the extra batteries. For 12 cells, the 8L is a pretty nice motor, but the 7xl would get my vote due to its ability to dissipate the heat better, which will allow back to back battery packs with less heat. Both motors will be pretty impressive on 12 cells with good batteries, though. And I would use a 5mm shaft regardless of the motor used. The 1/8" shaft will need care when mounting the pinion(keep it close to the motor) to prevent damage to the shaft.

The brushless has alot better zip to getting up to speed. If you ran truck that can out accelerate the others on the track. You can beat them with the acceleration not the over all speed. My savage is decent on top end. By the time it gets there I have reached top speed slowed turned and back up again with my brushless.

I use an RC10 T3 for track running, this is purely bashing. I am comfortable with 40mph or so top speed, if I cannot get this with an 8L or 7XL on 12 cells I may get a warrior in future if I can find a good deal on one, but I'm not prepared to sink $200 into something that takes 3 months for a service, maybe i'm just spoilt by being within driving distance of Mtroniks :)

My 8L is only a 1/8 shaft. If that causes a problem at least its under warranty and I could obtain a replacement within a few days. I will take your advice and keep it as close to the motor as possible. When my Emaxx arrives i'll give the 8L a go and see what its like. Eventually I will get a 7XL as it sounds a bit better in every way, but I'm not sure there's enough difference to justify spending more dosh on another motor. Maybe i'll get it when I sell the EVX and titans..what are they worth these days?

Thanks for all the input guys, its much appreciated. Can't wait to get brushless running in my E-Maxx :) Will runtime with brushless be much difference to the titans? On a friends E-Maxx I get about 10 mins running with the titans, normally pretty close to WOT.

I recently converted over to Revo drive shafts, stub axles and RPM Revo bearing carriers on my gasoline powered Maxx project - these seem to be really beefy, and are relatively inexpensive.
I haven't purchased any of the hi-power BL systems yet, so I can't speak to their torque versus my 23cc gas engine, but I know I pretzeled my stock maxx driveshafts almost immediately.
Using Revo shafts offered me an inexpensive alternative to CVDs. Time will tell if they hold up as well though.

I am not sure what nitro motor to rate the torque of a brushless to. It seems to out do my .28 savage. I have broke a few cvds to.