50 mph emaxx?
 

I just my hands on an Emaxx roller and wondered......what brushless motor,controller and cell count would it take to reach 50 mph?

Fifty mph - are you trying to get up to that speed and thats it or are you trying to run that speed for any sustained periods of time? Are you running 3300 batteries or li-poly - there is really no cut and dry answer unless you give some more info - Im sure Mike will be able to answer this question for you - i mean you could run a 7xl with a 72 tooth spur with a 22 tooth pinion and get 49.78 mph running 5 cell lipo in second gear - for how long i would imagine would depend on the speed controller - that you would need to talk to mike about..... hope this helps you

This rolling chassis weighs 9.9 lbs with 16 GP 3300s and stock wheels and tires.I do have a set of Clodbuster wheels,tires and adapters which are 1 inch taller and not much more weight difference.I know that kind of speed pulls alot of juice but I'd like to make a few passes and still get some bashing in before dying out.I know the Warrior 9918 is good for up to 18 cells,but is this asking to much of it?

I would definately waiting for mike to respond - my knowledge is limited on the current you are going to be pulling - but my guess is that you are going to work that speed controller way past its max - especially if you want to get a couple of passes and then do some bashing - based on the 16 cells and running a 66 spur with a 19 pinion you are gonna be at about 31.5 in 1st and 50.75 in 2nd - i would look into the 18130 or the 18150 just to be sure - but like i said i would DEFINATELY talk to mike about the speed controller and current ?'s before i did anything. I made a couple of mistakes with my controllers before i met mike and now i havent had any problems at all.. I am going to be upgrading to the 18150 in the spring - just to make sure i have no problems.......

By the way - thats my Gmaxx in the air indoors at our local track - running 12 cells with a 9L. We were trying to break the lights on the ceiling - We were about 2 inches from hitting them. :D :D :D :D

Hot-n-cold was pretty accurate with his advise. The 9918 warrior should handle the current for a speed run, but I would recommend dropping the gearing for bashing (or use first for bashing and 2nd for speed runs as hot-n-cold suggested). The 7xl can pull some current, so the best bet would be to get a speed control, that is a little more in the safe range (18120 should work quite well). On 16 cells, the 7xl will be quite a powerhouse for sure and will easily push 50+ mph. I would make sure you have cvds and upgraded diffs at the least. Your truck could lose over a pound easily by switching your tire/wheel combo to something along the lines of bow-ties (very light). This will make a big impact on run time, heat and current draw as well, because it is pure rotating mass that you are saving. My aluminum race maxx weighs just over 8 pounds (aluminum suspension, diffs, chassis, bulkheads, shock towers, cvds, etc.).

Thanks a lot for your help guys,but the reason I mentioned the Clod wheels and tires was with them being 1 inch taller was that the height would be a plus on the topend side,is my thinking off on that? Hotncold I see you mentioned li-po cells,I've been trying to talk to heli guys in 2 local hobby shops about these for offroad use and they beat the idea down bigtime.I understand the dangers involved being that these can be very explosive,but is there a place to go for accurate up to date offroad info this type of setup?

li po cells
 

You wanna talk to Mike about them - he is using them more and more - there are some pro's and con's, but if your careful ( charging )the pros outweigh the cons. Im sure mike will be able to give you some more info on this when he gets back into the office....

Your thinking is on the right track (taller tires = faster top speed), but in reality, you are better off with a lighter tire and gearing up to get the speed. The clod tires are heavy and have poor traction. If you add a tooth to the pinion and run smaller, lighter tires, you will have a quicker, faster truck with more runtime and less stress on the drivetrain. For Lipo, I play with them quite a bit in my on-road car (tc3) and a little bit in my maxxes. The technology is great, but you have to be careful or it can get expensive in a hurry! RCZone has quite a few lipo/brushless users as well. If you have specific questions, I can answer them pretty accurately and help steer you towards the proper set up as well as tips for success.

Not sure if mine goes 50mph, but it sure feels like it. I have the 7xl running 18 gp3300. I have a 70 tooth spur and 19 tooth pin. I need to make sure to watch were I am going. A crash with this setup would break alot of parts.

depending on which gear your running you are close....about 30 in first and 47.5 in second. Are you running all stock gear train on your maxx.. I know when i had mine - i ran her hard and melted the driveshafts. A lot of power like that can be extremely hard on a drivetrain - nice maxx - good luck with it...:) :) :) :)

Clean,straight forward and no doubt fast.By the way what speed control are you using?

im running a schultze 1897kwf with a 8l on 14 cells. It gets out of its own way

I have the Warrior 9918. 1st gear is useless and second gear is still out of control fast. Front end will come up at almost any speed. Not sure how the gearing works but would probably be faster with the correct gearing. It has lots of torque. So top end speed could mabey be faster with correct gearing. Center cvd's is next on the list. Went threw 2 of them on same battery pack.

Yep - when you start making that much power - the drivetrain is almost definately a necessary upgrade. Very Kool though.....

Wth this much power,any mods to tranny at all?

Ryan,

You will want to pick up an idler gear for the transmission eventually. The stock one will last until you get the rest of the drivetrain beefed up (cvds, diffs etc.), but once everything else stops breaking, this is the next weak link. They aren't that expensive, either. There is a thread on this board with a link to the part you will need.

Hey Ryan


Idler - Here ya go

http://www.unlimitedengineering.com/...ore/13407.html


:) :)

Havent touched the tranny yet. Well I was flying down the road and spun out of control and slid into the curb. Now I need to get a new chassis, bulkhead, turnbuckel, and shock. I new it was just a matter of time.

Curbing....
 

Thats how most of us started our projects - bash HARDER, break FASTER, break MORE, then replace, replace, replace with stronger - then repeat..... LOL - But then thats the fun of it in my opinion, - comparing it to a stock emaxx and see how much you've done and how much faster and more durable it is. It is definately worth it for me and probably to most of us as well... It IS a sickness ya know :) :) :)

50 mph for emaxx ain't all that hard. Top speed has NOTHING to do with weight. Weight just means it'll take longer to get there. Top speed has everything to do with max power of batteries - NOT the motor you're running.

A puny little basic 4200 can push an emaxx beyond 45 mph on only 12 cells - I know, I've done it.

A monstrous lehner 2280 on 12 cells will only push it around 45 mph also. Why? Because 12 cells can only give out so much power continouosly.

14 cells could hit 50 mph, but only for a couple of speed runs. 16+ cells would be needed. IMO.

At 50 mph, you need to stiffen suspension, lower chassis, and get better high speed tires or duct tape the insides of the tires to prevent excessive ballooning. Stock tires actually spin truer for me than most ProLine tires that I've come across.

Lipos is an easy way to get to 50 mph w/o much mods. Lipos are much lighter and so easier on drivetrain. I'm going over 50 mph with my lipos and doing it over and over and over on the same charge. I'm getting huge run time, very little heat, and awesome response with my STOCK emaxx running lipos. BUT, you have to be VERY CAREFUL WITH LIPOS.

I agree with the previous post, but would like to add to it. While a high top speed can be reached with a small motor, the motor will eventually fail if it is driven this hard continuously (I have "failed a few motors"). For continued high speed, a larger motor can dissipate the heat better and will last longer. Higher voltage (like Lipos) will also help keep the heat/amp draw down, which may also lead to increased reliability (as long as the motor is not over revved). I will also say that weight may not be a big factor, but it is part of the equation. It takes more energy to move more mass.

Energy = 1/2 mass x velocity^2
So yes, weight will use more energy to go faster, but velocity itself is the larger factor. Now, with RC cars, you have to add rotaional energy to this equation - I forget the rotational energy equation though.

With regards to small motors failing, Mike is right. A motor can only run as hard as it is able to dissipate heat. A huge motor that is insulated will fail, a small motor with good heat sinks and good cooling might be better.

Every motor has its inefficiencies. Let's say motor A is 80 percent efficient and motor B is 90 percent efficient. Let's say a motor can dissipate about 100 watts of heat. Motor B can handle 2x the power input than motor A!

That's why it's so important to get efficient motors. Brushed motors are less efficient and will run much hotter with less power input so that's one of the reasons why BL can handle more power.

Now, a typical small wind motor will be less efficient than a high wind motor (case in point, a Lehner Basic 5300 vs. a Basic 3100). Both motors are the same size, but the Basic 3100 is much more efficient. So, instead of using 7.2 volts with the 5300, I'd much rather go 11.1 or 14.8 volts with the 3100. Equal power, but much more efficient so less heat build up, more CONTINUOUS power.... blah blah blah.

So, I'm just saying get good cooling, good heat sinks, get a really efficient motor (but slow) and use high voltage and low amperage. You'll really have gobs of power, speed, and run time. Why do you think the Heli guys are going 10S lipo? They've already figured it out for us.

If you look at Lehner's brushless motor dyno charts, you'll see that for the basic motors, slower than the 3100, efficiency doesn't really improve so you don't need to go slower and higher voltage than 22.2 volts. However for monster trucks where amp loads can be very high, going even lower KV and higher voltage pans not because of gain in efficiency due to motor, but gain in efficiency due to lower amp draw through controller and wiring. Now I'm talking too much...

Yeah, what he said! great tech info lipomaxx! I have some slow motors intended for just this type of thinking on the way (1200 rpm/volt, 1600 rpm/volt). My plan is to use them in a lipo e-maxx with 6 or 7 lipo cells. I haven't decided on which ones yet, but as you already mentioned, the polyquest line of batteries seem to be high quality.

here is a HV setup discussed. (tried and tested to)

Lipo will be the new breed. (holding the hand firmly of brushless)

And a higher voltage will also be suffering less from the internal ressistance.

for that reason electricity we have got in our houses is transported at several kvolts. (thru 'high resistance' aluminum wires.. )


In small words; At higher voltages it's easier to be more efficient.

Actually, aluminum wiring has less resistance than copper... if you go by weight! That's why high voltage cabling is aluminum. Copper will sag too much because it weighs so much, same with silver. Aluminum is like 3x lighter but 2x more resistance (those are gross approximations) so there is less sag of the wires when stretched out over long distances.

You're right in that. I smell a bit of a scientist here..

I have got the same discussions with my brother in law, he's a scientist to. (discussions in the most possitive way)


Aluminium has got a higher resistance then copper per square inch.

And a high voltage system will be eassier more efficient then a low voltage system

No, not a scientist - high school AP physics and experience.

isnt the 8L only suppose to be run on 12 cells?

HotnCold doesn't run full power on his radio. I have run the 8L on 14 cells a couple times without any trouble, but it isn't recommended.

throttle
 

60-65% to be exact -

I've ran 51.9 mph with my E-maxx using 12 cells and a Hacker 7XL. The truck is very light and was using 24/51 gearing on stock diffs.
A trucks weight will make a difference. The light truck can pull a much high gear and is faster.
Those small basic motors are fine for the E-maxx if ran as a dual system. But one BIG single is the way to go.

Thank you,
Promod

Hello Promod!

I know you from maxxtraxx, i am buikpijn on that forum.

Nice to hear it worked out this well. What was your runtime and what is the kv-rating on the 7xl?

The Feigao 7xl has a Kv of 2382.

Ah, 2254rpm/volt..

I am going to try the Feigao 7XL on 16 cells. how did your truck accelerate and what esc did you used?

@Mike; I ment the Hacker 7XL..

The truck accelerated great even with the 24/51 gearing. But for bashing I ran an 18/51. The speed control was a Schulze 12.97. The trucks weight RTR (body,cells, no GPS) is less than 8 pounds.

Serum, I would use an 8 or 9XL for 16 cells. Slower turn motors for the number of cells used is the way to go.

Thank you,
Promod

I don't know the Hacker specs, but they are pretty close in specs.

Promod, so you've gotten over 50 mph on 12 cells. Congrats! That's pretty darn fast on 12 cells. What tires are you using, and how'd you get your truck so light? Tires and different chassis? My truck is at 9.0 pounds with 22.2 volts and 9.5 pounds at 29.8 volts with stock tires RTR with stock body. I wish I could really let my emaxx run, but too much salt and water on the street for traction. I can't wait till I can let it loose.

The idea behind the truck was to keep it light for 12 cells. I just took out weight every where I could. It has stock chassis(soon G-maxx),stock drive train,G3 suspension,Ti hinge pins and turn buckles,Aluminium pivot balls,no bumpers,no two speed servo,cut skid plates,cut motor plate. That is about it.
The tires used for the speed runs were TRC park tires. The stock tires are very heavy. For speed runs "street" tires will be faster. Any tread tire like stock,mashers,trail dawgs,meat hooks, etc are about 1 plus mph slower than street tires. Pin type tires like the bowtie and paqman seem better but are still slower than street tires.

Thank you,
Promod

Now there is someone who know how to do speed runs. Nice job Promod. Didn't you break 70 mph in a rustler? Or was that you?

Weight definately effcets speed runs alot. I have gone faster on less cells in my bandit(don't laugh cmon) because it is less weight. Lipos may be next muahah. I do the same thing . Change everything back to stock parts,take off bumper and wheelie bar,use small lite tires. It definately helps alot.

I am sure, it can be pushed further, as long as the cells are able to deliver more power... It's all about the maxximum power that the cells can put out.

Is this statement true?;

In one motorserie, the 5 turns and the 8 turns can deliver the same ammount of torque.. (all the specifications of the different moters i went thru, show me, that one motor of 2000kV delivers the same torque as a motor from that serie that delivers 4000kV

The 4000kV draws a higher current, that's logical..

I think it has got to do with the maxximimum amount of electric-magnetism that can be produced by the wires and handled by the magnetic energy that is stored in the rotor.

If i use this statement (which i think is right) you could also reach this high topspeeds with a 3000kV instead of a 2000kV.. It all depends on the efficiency of the motor, the motor will have opimal efficiency in a certain kV range.

All about efficiency and the maxxmimum amount of power that batteries can throw out.