Battery drainage

[R1Buggy]

Hey guys I'm new here, also I'm new to electric rc crawlers. I have search for a couple hours now and can't find my problem.
Was out crawling today with my lnc and my friend with his mk42 moa
We both run 4600mah battery. His lasted a good hour and I went through two 4600mah battery in 40 minutes. I can't see how a moa crawler doesn't use more battery over a single motor crawler.
I think it's my servo. I run a savox 277oz servo.
I read a bit about a Bec. As far as I see i don't need a Bec because my servo gets plenty of voltage. The servo drains to much battery, which my motor ends up with no power. Is the way to equal the voltage to the motor and servo, instead of the servo taking all the voltage?

Cheers

[indiana mudcat]

First on the runtime, your worm drive axles eat power, still that sounds a little short. Are your batteries NiMh or Lipo? Is your ESC set to Lipo?

You do need a BEC. It's a amperage thing, not voltage. The one in your ESC only puts out like 1 amp at five volts, your servo needs more. Without a BEC the ESC will drop power under hard steering.

The stock motor is a weak throw away unit that isn't helping either problem. I think they stall out every time the tires get traction.

[Trubble]

Originally Posted by R1Buggy

The servo drains to much battery, which my motor ends up with no power. Is the way to equal the voltage to the motor and servo, instead of the servo taking all the voltage?

No, not unless you're quite adept at building your own speed controller. Your ESC's internal BEC is designed and programmed for how much voltage and amperage it puts out. I've never seen an ESC yet that allows you to adjust that.
I find it exceedingly difficult to believe that a servo can draw enough amperage through 18-22 gauge wire, that it chokes off your main motor, even though it likely has 10-14 gauge wire. If this was even close to becoming a possibility, you'd first experience control issues such as glitching from your receiver not getting any amperage, and your ESC would be constantly shutting down as the BEC portion overloaded and went into some kind of thermal overload.

Originally Posted by R1Buggy

His lasted a good hour and I went through two 4600mah battery in 40 minutes. I can't see how a moa crawler doesn't use more battery over a single motor crawler.

There's a number of reasons why your and his runtimes are so unequal. My first guess is gearing type and gear drag. Every MOA I've ever seen has straight cut gears, almost all the force in those gears is lateral, or pushing each tooth sideways to push another tooth sideways. The only sliding there is would be when the tip of, say, a pinion comes in contact with the tip of a spur's tooth. As a matter of course, said tip is going to slide just about all the way down into the valley between the teeth it meshes with, and then back out again. But look at your typical R/C straight cut gear (as is in your buddy's rig), the teeth are maybe, what, 2-4mm max? That's all the further those teeth are going to generate any 'sliding' friction. Now look at your Losi's worm gear axle setup. While it is true that there is a lateral load on the teeth just like in any gear setup, there is also a huge amount of sliding going on between the worm gear and (for lack of a better term) the ring gear. In addition to the simple in-then-out sliding as the ring gear's tooth come into mesh, now, since the ring and worm gear stay in constant mesh, the worm gear's spiral tooth actually slides 'across' the tooth on the ring gear as well as pushes it along at the same time.
For this reason, keeping your axles' internals VERY well lubed is extremely critical, and even on the best of days, you're still going to experience some power loss with that setup.
As if that didn't confuse you enough, as you twist the worm gear, one of two reactions will take place. Either the ring gear will turn, as will the axle shafts and tires, or if the ring gear puts up resistance, the worm gear is free to move on the ring gear if it so desires. Every time you want to go forward you worm gear tries to slither towards the back of the truck, same but opposite is true going the other direction. The only thing holding the worm gear and not letting it move back and forth is the cutout in the axle housing. In addition to roller bearings to make the twisting nice and smooth, there should also be thrust bearings at the fore and aft ends of the worm gear. In a low power application like this, it wouldn't surprise me to find that they have used bushings or shims instead of a proper roller or ball type thrust washer. If your worm gear is trying to work it's way out the back of the axle, and the only thing holding it forward are a couple of shims sliding rotationally against one another, you just upped the ante for your need for an extreme pressure lubricant.

Bottom line; get them axle innards 'operating room clean' and lubed generously with the best lube money can buy for longer run times.

Even then, you're not out of the woods yet. Any electric motor will draw X amps at zero load. As you put a load on that motor, the amp draw will go up. In your single motor, all 8 pounds of truck has to be moved by one motor. (We'll just use 8 pounds as a 'control number', matters very little what your actual weight is) In an MOA, you would think since it has two motors, it would draw twice the electricity, but in reality each motor only has to carry a 4 pound load, thus you're back to reduced amp draw due to reduced load on each motor. And with twice the overall power being generated, your buddy doesn't have to get nearly as far into the throttle as you do to get/keep moving at a given pace. Less throttle needed, more runtime.


There's a mountain of other stuff to look for, but those'd be my first two guesses as to why the runtimes are off.


P.S.; Kudos to Mudcat, I forgot to even consider the LVC.

[R1Buggy]

Thanks for all the info guys will take it on board.
Only reason why I may think the servo is using to much power is because driving along flat ground when I use the servo the car slows down, then when I release the the servo so the wheels return to center the motor picks aback up again
But you said under hard steering the esc will drop power. So I need to get a Bec?

I am using a NiMh battery and have the esc set on NiMh

[ik632]

I had a similar problem in an old Stampede I had. I added a glitch buster (basically a capacitor connected to an old servo lead). The other thing is your batter may have a low C rating. Lastly, you may need a BEC with that beefy servo you have.

[SMR 510RR]

Are your end points set properly? Sounds like there may be some binding in your universals when you steer hard. Disconnect the front drive shaft, turn the crawler on and steer hard to the side, spin the drive shaft by hand and see if that feels different than spinning it with the wheels pointed straight ahead.

Setting EPA's is crucial in have a rig that works well and also will prevent you from burning out your servo.

[R1Buggy]

Originally Posted by SMR 510RR

Are your end points set properly? Sounds like there may be some binding in your universals when you steer hard. Disconnect the front drive shaft, turn the crawler on and steer hard to the side, spin the drive shaft by hand and see if that feels different than spinning it with the wheels pointed straight ahead.

Setting EPA's is crucial in have a rig that works well and also will prevent you from burning out your servo.

nOt sure ill have to check. Some times I don't have to turn hard for it to slow down. Some times a slight turn it cuts the power down to the motor.
Going to throw away the motor. Has no torque and I'll buy a Bec.
I'll check my end points later.

[flat6extreme]

There are so many variables in battery drainage that it's hard to pinpoint... Sometimes the batts themselves even being the same brand, age, and size perform completely different.

[alexchen86]

Thanks for that write up Trubble very informative. I never owned a worm drive rig except Losi's micro rock crawler I used to mess around with.

Well if the OP said the ESC was set to NimH then either his batteries are no longer fresh anymore compared to the batteries his friend was running on the MOA. When you save up some cash invest in lipos now that they are so affordable lipo chargers have dropped in price as well.

Check out cheapbatterpacks.com or hobbypartz.com both USA based.

And yes MOA rigs consume less power which is why you see most guys only running 600-800mah 4s packs and they switch off per two courses.

I run a 1100 3s 40C on my sportsman shafty and I can crawl at least 2 hours one a single pack....

[AX10wannabe]

what esc are you running?? i went through this about a week ago.

i bought an ax10 rtc and run 2s lipo 800mah batts.. it has the new 2.4ghz crap in it, everything worked fine stock figured i'd toss in my 645mg servo everything worked just fine still then i upgraded to the hitec 7955TG servo and the last time i ran the rig the AE-2 esc could not keep the power up so it would shut itself off and i'd lose all control, rig wouldnt do anything no steering or throttle so i'd turn off rig, let sit a couple seconds turn it back on and it was fine for a couple minutes. it would only happen under hard work of the servo, going straight or slightly turning it was fine. i brought it home tossed in my novak crawler esc and it works fine, took it for a drive in the house today.. i have a friend that runs the same servo and esc with no problems.. its very frustrating when you have to restart the rig every few feet. im not running a BEC until i absolutely have to but since i know how my setup works by watching my friends rigs i know i wont need one.

it sounds like the internal BEC in your esc cant handle the power so you have 2 options, get a better esc or add an external BEC.

unfortunately RC is the same as every other hobby, if you upgrade one thing then you'll break something else.. same with lawnmowers racing, transaxles are meant to cut your grass at 6mph not race at 35mph so we're constantly rebuilding them.

[R1Buggy]

Battery are brand new so was my friends battery
Both are same brand and 4600mah
Mine was on it's second charge and his was his first charge.
I'm still running the stock lnc esc.
Going to buy some lipos when my charger arrives.