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Am I doing something wrong?

Old 04-08-2012, 07:46 AM
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EXT2Rob
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Default Am I doing something wrong?

Ihave a couple of Evaders that Iconverted to brushless. I've been in this hobby for about 18mo. The stock gearing is a 87T spur with a 20T pinion. My LHS guy said the way to gear the car is to balance the heat between the ESCand motor, i.e. if the motor is too hot and the ESC is just warm, gear it down so the motor isn't as hot, and vice-versa. Is that more or less correct?

Now that the Brushless Evader is out, it rasies another question .... they've used a (what is it?) a 3960kv motor and a 24T pinion?
Ionce had a Castle 5700kv in the car, and currently have a EZrun 4300kv 35A system. Ilike the setup (87T spur 19T pinion) with this motor as it seems to have plenty of torque (spinns wheels easily on dirt) but also has a satisfying top speed over 40mph. My buddy & I have "rally-cross" races on our large, wide-open course, much faster than a typical Short Course. But am I running too high a KV motor for off-road?
Old 04-08-2012, 08:46 AM
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t9dragon
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Default RE: Am I doing something wrong?

I am not sure what you mean by "am I doing something wrong?"

Are you having issues with the gearing? Are the motor, esc or battery running to hot?
Old 04-08-2012, 10:07 AM
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dragnse7en
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Default RE: Am I doing something wrong?

Yep. You're doing everthing wrong. Throw it all in the trash, and go join an- anti r/c cult.
Old 04-08-2012, 05:05 PM
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kahnen
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Default RE: Am I doing something wrong?

Here's two pics of some data for you. One is of stock(Or hope so, if the data you gave was correct, kv/gearing) the other is with the ezrun you got. As you can see, to get roughly the same speed as the stock brushless you'd need to gear up to 22/87 from what you got now 19/87. Now, weather the 380 sized ezrun can handle that you'd have to test.

If this is what you was trying to gauge if you were doing something wrong by?
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Old 04-08-2012, 08:03 PM
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TheyDontWantMusic
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Default RE: Am I doing something wrong?

4300kv should be fine.

5700kv wouldn't have been, but I get the impression you're not using that anymore?
Old 04-12-2012, 11:46 AM
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EXT2Rob
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Default RE: Am I doing something wrong?

Hi guys,
Thanks for the input!  Kahnen, where'd you get that calculator? Looks pretty cool.  I guess what I'm getting at is that I'm still a little unsure of what a "good" setup is for the kind of running I do.  TheyDontWantMusic, you're right, I am not running a Castle system anymore, cuz something fried.  My buddy was the first to get one of those EZrun systems, and since it seemed to work so well in his car, I got one for the wife's car. Then when my Sv2 fried, and I got no help from Castle, and when folks around here said that I'd pretty much used it up, I thought, hell, why pay $150 for a supposed top-of-the-line, reliable product, when I can get one for HALF that, and it runs just as well?  And so it seems to. For how long, who knows? Guess I'll find out. Apparently, no one around here runs their car as much as I do (I'm retired, so I run pretty much everyday as long as it ain't wet) and despite the implication that brushless motors should last a long long long time, my Castle lasted only six months.  That just doesn't seem right to me.

So that's how I got to thinking, "Maybe I'm doing something wrong?"  Somehow I am over-taxing the system?  Or maybe I'm running too high a KV motor for the kind of driving I'm doing, or not a beefy enough ESC.  (The EZrun is a 35A ESC)  But even that little EZrun seems to have plenty of power, since it certainly spins wheels on dirt and at half throttle if you grab a hold handful, it'll wheelie and even maybe loose control.  I like how the car runs with the 19/87 gearing, but when we had a real warm day recently, and after running the car pretty hard, I noticed the motor temp was pretty high, approaching 150F.

BTW, the one thing that is missing from that calculator above is the fact that I am not running stock wheels/tires. I'm running these wheels http://www3.towerhobbies.com/cgi-bin...?&I=LXMV42&P=7 and proline Gladiators  which are a little bigger, which is why I geared it down a couple teeth.  And with this setup, my throttle is usually no more than half during a race, 3/4-throttle on straights, but it's nice to have that "little extra" if I REALLY want some speed.

So, does that give you anything to pick apart?  Or does it sound reasonable?
Old 04-12-2012, 12:05 PM
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EXT2Rob
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Default RE: Am I doing something wrong?

I swiped this quote from another thread:
"I would agree, you don't want to go much over a 3500kv motor in a Slash 4x4.  Higher kv motors are more for onroad cars with small wheels, you won't get nearly the torque needed to push a Slash 4x4.  Also, higher kv motors usually can't handle as much battery power.   If you try to put a 6000kv motor in that thing it will fry  the motor and esc. 

I have a 4600kv in my Stampede and I don't think I'd go any higher.  I usually swap in the traxxas 3500kv motor if I plan to do any extreme bashing because it puts alot less strain on my esc. The sales rep talked me out of getting a 5700kv motor and I'm glad he did, it would have only been useful for a few speed runs and nothing more. "   (Added bold for emphasis)

Now, they were talking about a Slash 4x4, and I'm running an Evader 2WD.  But it makes me wonder if that is where I might be a little off my mark? 


Old 04-12-2012, 12:22 PM
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Eman77
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Default RE: Am I doing something wrong?

I think, in general, running a 4300 kV setup in a 2WD offroader is just fine. I run the castle 5700 setup in my 4WD buggy offroad, and it's ok as well. Granted, the 4WD buggy is lighter than a 4WD truck, but you get the idea. I'm guessing a 2WD Evader is light enough though, so a 4300 should be fine. Not 100% on the 5700 though, for your specific truck...I'd think it might be ok though.

Granted, I don't run mine as often as you do (I just don't get the opportunity), so parts will wear for you much faster than a lot of us, I'm sure- which you pointed out.

That said, 150F on the motor isn't too hateful either, from what I recall. If you start hitting 170F+, then maybe it's time to worry. I think Castle even said under 200 F is ok (which seems crazy hot to me).

We'll see what others have to say about your truck specifically, as I can't speak about it directly, not having one.
Old 04-12-2012, 01:29 PM
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kahnen
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Default RE: Am I doing something wrong?

Here's a link to the Calc. Its a cool little program and has loads of preset stuff.
http://www.calcrc.com/

Here's the thread for it here at RCU
http://www.rcuniverse.com/forum/m_10...m.htm#11019836

As for your Ezrun, it should be fine in your Evader. I had the same ezrun 9t combo in my XXX-t(distant cousin of the Evader) for the longest time and I ran that onroad, off road and even at a local track for a season. I even it had it in my 2wd short course truck for a time. Keep it geared conservatively(like you are already by the sounds) and the motor bearings clean and oiled and it should last a long time. With the 35a versions your focus should be about ease and dependability not power and speed. If you want those your gonna need a more powerful setup(higher amp esc/540sized motor). What eventually killed mine was the use of 3s. The 4300kv in an offroader driving offroad was a bit to much amps for the 35a esc and it smoked mine eventually. If you plan to run 3s get a motor in the 3000 kv range or a higher amp esc. Actually states this in the manual now, the original one I got like 3 yrs ago didn't.
Old 04-17-2012, 07:13 AM
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EXT2Rob
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Default RE: Am I doing something wrong?

VERY good info Kahnan, thank you!  Especially the caution note about running 3s on the EZrun.  (Yikes, I can't imagine what it'd be like on 3s!)  Hmmm...just thinking....is it possible your ESC burned out because the stock fan can't do 3s and the fan failed, THEN the ESC got too hot?  Jus' wonderin'....

So higher KV motors will draw more amps from the ESC than lower KV motors?  Yet the lower KV motors have more torque/power?  Is that why, for instance, DTX can gear the BL Evader 24/87, while I have to run a smaller pinion to keep the motor cooler?  (They use a 3680KV motor, if memory serves)
Old 04-17-2012, 08:15 AM
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Brainanator
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Default RE: Am I doing something wrong?


ORIGINAL: EXT2Rob
Hmmm...just thinking....is it possible your ESC burned out because the stock fan can't do 3s and the fan failed, THEN the ESC got too hot? Jus' wonderin'....
I don't think so. For one, the fan will probably be running off of the BEC, so it will have a constant ~5V (like the receiver/servo).
Also, if your ESC depends on a fan to prevent over heating you're flirting with danger. Fan can help cool and keep ESCs/motors temps down a little, but depending on them is bad practice. Temps should be controlled with gearing.
Fans go out all the time while running offroad. One little pebble sucked into the fan can get it stuck, and if you are depending on it for cooling, no goood.
Old 04-17-2012, 09:27 AM
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kahnen
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Default RE: Am I doing something wrong?

Brainanator: Ezruns come with the fan wired to the power leads and say in the instructions to change to a higher voltage fan if you plan to run 3s. Most don't bother changing the fan but just rewire to run off the BEC like it should be.

EXT2Rob: I rewired the fan to run from the BEC so the fan wasn't the issue. I actually took the fan off the smoked esc and now use it on my motors since it still works. The fins on the motors (380 sized ezruns) are perfect for screwing a corner of the fan down to them. I was just pulling to many amps from the little esc to handle. I was trying to get more speed(obvisously ) and was pushing the limits of gearing, voltage and driving. Ended up going to far. When I took it apart after it stopped working , one of the FETS was charred and black and the board around it was warped.

So higher KV motors will draw more amps from the ESC than lower KV motors? Yet the lower KV motors have more torque/power? Is that why, for instance, DTX can gear the BL Evader 24/87, while I have to run a smaller pinion to keep the motor cooler? (They use a 3680KV motor, if memory serves)
Yes and no. Higher KV motors will draw more amps than lower Kv motors in general. Its how power is produced.

Amps x Voltage= Watts(the power)

Higher kv motors use low voltage/higher amps to get watts while lower kv motors use high voltage/lower amps to get watts.
An example:
We have first a 5000kv motor which pulls about 48 amps. We use a 2s (8.4v)lipo for battery. 48amps x 8.4volts= 403 watts

We just bought some 3s (12.6v)lipos and since we like the speed of the other one, we find a 3300kv motor that pulls about 32 amps. We take 12.6 volts x 32 amps= 403 watts

Both produce the same amount of power just in different ways. Now of course, gearing and tires will come into play changing things but motor wise, the same power can be produced no matter if a low kv or high kv motor.

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