Ok guys I'm a believer now!

[sjcrss]

I think you should ask newe...since he is the ubec glitch king....he might have some answers...lol

hey you guys! So is the mamba esc and 9xl going to outrun the hv-maxx? and what gearing do guys recommend? My trucks an emaxx carbon fiber chassis with custom alluminum arms and rpm knuckles with bow tie tires running on 14.4 nimh

[crazyjr]

On 12 cells, the mamba/ 9XL is a great combo. it will need an external power source so need a battery pack or ubec and remove the middle wire in plug to reciever. I'm running 17/66 32 pitch gearing and think i got room to gear up, but will not know till i know the problem with the signal.

so ur having problems with the combo? or with your reciever? what do u mean ill need a battery pack or ubec? I'm sorry u'll have to excuse me cause i really dont know anything about brushless systems.

[crazyjr]

I think the BEC is overloading, it will lose signal every once in a while. The way i was told if it overloads it will cut-off and restart, so i think thats whats happening. I'm running a bigger than recomended motor and running the bec at its limit, so i expected it to happen. I will get back to you tomorrow or tuesday at the latest and tell you if the reciever pack helps.

No problem with inexperience, I was there a few months ago, did a lot of reading before i took the plunge, but till you get you're feet wet you don't know as much as you think

[BrianG]

Originally Posted by carlog80

so ur having problems with the combo? or with your reciever? what do u mean ill need a battery pack or ubec? I'm sorry u'll have to excuse me cause i really dont know anything about brushless systems.

The BEC in just about every ESC I can think of is just a linear voltage regulator. This means there can be a lot of heat dissipated on the regulator, and gets worse the more cells you use and the more servos you use. If you are running anything more than 2s (or 6-8 cells) I would use a BEC. Some people use the ESC BEC up to 12 cells, but I am a bit anal about such things. The excess heat from the regulator will heat up the heatsink for no reason.

A UBEC is a digital device, meaning it uses pulse-width modulation to regulate the main battery voltage down to 5v or 6v for the servos. These are MUCH more efficient and hardly heat up at all.

If you are REALLY interested, here 's an example:

Linear BEC (found in ESCs):
dissipated_power = ( main_batt_voltage - 6v ) * servo_current

Let's say you are running 12 cells and are running a servo that draws an average of 1A at 6v. The heat the ESC heatsink has to dissipate is; ((12cells * 1.2v) - 6v ) * 1A = 8.4 watts. That is quite a bit believe it or not. This equates to about 41% efficiency (output wattage / input wattage). Also, 1A will be drawn from the main batteries just for the servo (even though it is only using 6v), which reduces runtime. At 16 cells with this same 1A servo, efficiency would be down to 31% and heat up more (13.2 watts).

A digital UBEC (and they almost always are) runs between 80%-90% efficiency. So, if the servo draws 1A at 6v, the UBEC only dissipates about 1W or less of power (at 85% efficiency) and draws only ~.4A from the main batteries. And with more cells, the UBEC will draw less current from the batteries yet still be just as efficient or more.

This example is a little off because a servo won't draw 1A all the time, but you get the point.

[crazyjr]

Thanks BrianG, that helps me a lot

[BrianG]

No problem. I actually thought I overdid it at first.

[crazyjr]

Na, it explains a lot about why it would cut-off. I tryed it because Castle said it would, but i'm running a bigger motor and it may have an impact

[glassdoctor]

As Shawn described it to me, what happens when the mamba's bec is overloaded is that it will shut off the bec to let it cool and then turn right back on, and it will do this 20x per second if neccesary.

So what you see is a radio glitch as you are getting, because the rx is losing power for a fraction of a second.

This would be very obvious if you run a Spektrum because they take about two seconds to power up if power is lost.

[Finnster]

I had some glitching with (both) my becs, used a Rx pack and it was smooth as silk. Had a hard time finding a good place to put the BEC. My try it again later.

I actually had way more glitching w/ my FM than AM. ???

[BrianG]

Originally Posted by Finnster

I had some glitching with (both) my becs, used a Rx pack and it was smooth as silk. Had a hard time finding a good place to put the BEC. My try it again later.

I actually had way more glitching w/ my FM than AM. ???

FM frequencies might be closer to the UBEC switching frequency to cause interferece. AM frequency is generally lower and further away from the UBEC frequency so the band filters on the AM radio are more effective. Just a theory.

hey thanks so much for the explanation BrianG. Kinda hard to swallow all that. So ur saying with my setup of the mm and 9XL ill be needing a UBEC to be safe? But I think all ill be using will be a 7.2v 2s 4000mah batt's Anyway wats the diff with the Feigao 540C 9XL Brushless Motors & a Feigao/Nemesis/Wanderer "9XL" Brushless Motor? And i should get a gearing of 17/66 32 pitch ?

[coolhandcountry]

Originally Posted by Finnster

I had some glitching with (both) my becs, used a Rx pack and it was smooth as silk. Had a hard time finding a good place to put the BEC. My try it again later.

I actually had way more glitching w/ my FM than AM. ???

Was that with the 27 fm or 75 fm?

[Finnster]

Originally Posted by coolhandcountry

Was that with the 27 fm or 75 fm?

The Am was 27, and the Fm was 75.

The Am was pretty good, I would just get an occational glitch at long range, but it was the "slam on the brake" variety, so I switched it out.

The Fm is a XR3i, I wanted it so I can adjust servo trims and to turn down the brake some (the MM/XL would front flip easy) but it was undrivable. It had a range of ~30ft, and even ran away on me a time or two. :031: Put in the Rx pack and all is fine.