You dont need a BEC (if you run this setup)

[Illeagle]

Well I figured we might have a little discussion on here and see what kind of drama gets stirred up (not that I condone it) but it always seems to happen.
A "guru" buddy of mine asked me why a bec is necessary and its my opinion it is NOT for this particular mini setup:

Your running a 2s lipo and fully charged its 8.4v (2 cells @ 4.2v each)

Your also running a newer style high voltage servo rated to run straight off of a 2s lipo or technically 7.4v.

Lastly your running an esc such as a Tekin FXR or Castle Sidewinder Micro/Mamba Micro

So if your servo is rated to handle that kind of voltage WHY are you running a bec? In my mini I have a sidewinder micro powering a Futaba 614ff rx. I ran the signal wire from my Hitec servo to the rx but my power wires are hooked to the battery input side of the ESC (in essence directly connected to the 2s lipo). I have been running it this way for months and no issues. I do not see how a BEC "in this setup" would benefit in any way. There is no way the bec will be able to supply any more amperage than the lipo itself will so this way the servo will receive max voltage/amperage.

DO YOU CONCUR?

[Arct1k]

Concur... if you are using a HV servo.

[WAM]

Originally Posted by Illeagle

DO YOU CONCUR?

No BEC with 2S. That's what I got from the tech guy at Hitec. But we were only discussing the 79XX series at the time. Dunno about the others.

Something else interesting from that call. I asked him the max amperage my servo (7954SH) would ever draw and he said if stalled, it could hit 8 amps. Wow. My FRX bec only puts out 3.

[Charlie-III]

Originally Posted by Arct1k

Concur... if you are using a HV servo.

+1, no real reason for an external BEC while running a 2S LiPO and a servo that can handle the voltage.

Originally Posted by WAM

No BEC with 2S. That's what I got from the tech guy at Hitec. But we were only discussing the 79XX series at the time. Dunno about the others.

Something else interesting from that call. I asked him the max amperage my servo (7954SH) would ever draw and he said if stalled, it could hit 8 amps. Wow. My FRX bec only puts out 3.

Yes, the higher torque servos can draw quite a few amps when stalled. Good reason to make sure the steering EPA's are correctly set.

[bikerj08]

Yep, I'm into running the servo straight from the 2s batt. I run hitec hv servos in my mini and on my xr10 and have the same set up for both. I am very happy with how its been working.

[Manning]

I'm running a 7954 straight off the battery in my MRC pro. Fun to put the front wheels in a little bind and wiggle the rear end.

[asw27x]

on my mini running a 7955 up front i dont even run a bec and i still wiggle the rear end around
my xr-10 is a different story (the 7954 is just not enough at 7.4) i stall it a lot

[Illeagle]

Ok, now that we are all in agreement, what have you found is the best 2s lipo to mount on the front axle next to the servo?

[elsewhere]

Little 350mah zippys from hobbyking...
I get about 10 min out of em.

[dstrbd1]

Here are some good options

Zippy 350mah 40x20x15
Zippy Rhino 360mah 43x21x15
Thunder Power 325mah 44x24x13
Turnigy nanotech 370mah 63x32x9

[JeremyH]

Originally Posted by Illeagle

So if your servo is rated to handle that kind of voltage WHY are you running a bec?

I dont....and my servo is not an HV servo.

[WAM]

Originally Posted by Illeagle

Ok, now that we are all in agreement, what have you found is the best 2s lipo to mount on the front axle next to the servo?

I had to mount my TP325 lengthwise and it was too vulnerable. Knocked it off at Saturday's comp. How have you guys positioned your axle-mounted batteries? The Losi cube was a good fit, but the longish skinny ones don't seem to fit well.

[Illeagle]

Originally Posted by JeremyH

I dont....and my servo is not an HV servo.

Don't tell anyone but I'm running the hitec 7955 on mine (technically only rated to 6.0v)

Originally Posted by WAM

I had to mount my TP325 lengthwise and it was too vulnerable. Knocked it off at Saturday's comp. How have you guys positioned your axle-mounted batteries? The Losi cube was a good fit, but the longish skinny ones don't seem to fit well.

Same thing here Bill. I like the fit of the losi cube but I would like a few more than the 12amps it can put out. The 65c tp 325mah supply's 21 amps but like u I do not like how it sticks out in front of the axle.

[ittybitty]

A couple of us had this very same discussion yesterday. Simply put, I run one because it just might provide some protection between my battery and my $100 + servo...that makes it worth it to me

[JeremyH]

Originally Posted by Illeagle

Don't tell anyone but I'm running the hitec 7955 on mine (technically only rated to 6.0v)

Yep. I have run two servos in the same setup (wired straight to the 2S lipo)....the Futaba S9155 and the S9157. They get warm, but not bad.

[WAM]

Originally Posted by Illeagle

The 65c tp 325mah supply's 21 amps but like u I do not like how it sticks out in front of the axle.

It weighs less than an oz. I'm tempted to stick an electronics plate behind the servo for everything except the battery. Then run that on the rear axle plate. At least it would make for easy changes.

[Frankenwheely]

Hell I run a 2s with the stock esc and no bec. No problems yet.

[Tgreer]

I've been debating on running my 7955 on my mini with no bec. My 5645 just crapped on me at the last comp, so I think I will give it a try. For you guys running the 7955 with no bec, are you having any problems, is it staying cool and running smoothly? Would love some feedback on you guys that are running this setup.

When I run this setup should I run my steering EPA at 100 or something a little less.

[WAM]

Originally Posted by Tgreer

I've been debating on running my 7955 on my mini with no bec. My 5645 just crapped on me at the last comp, so I think I will give it a try. For you guys running the 7955 with no bec, are you having any problems, is it staying cool and running smoothly? Would love some feedback on you guys that are running this setup.

When I run this setup should I run my steering EPA at 100 or something a little less.

Looking at that servo description on ServoCity, the 7955 is not a high voltage servo. Max rating 6V. You may or may not get away with it. By comparison, my 7954 is 7.4V rated and "2S compatible" stated on the packaging.

EPA's should be set to match the available steering throw, not an arbitrary number. The intent is to keep the servo out of stall.

[Illeagle]

Originally Posted by Tgreer

I've been debating on running my 7955 on my mini with no bec. My 5645 just crapped on me at the last comp, so I think I will give it a try. For you guys running the 7955 with no bec, are you having any problems, is it staying cool and running smoothly? Would love some feedback on you guys that are running this setup.

When I run this setup should I run my steering EPA at 100 or something a little less.

Mine doesn't even get warm. And I have been running for a good amount of time now. This is only my personal opinion and in no way factual but I think that when they switched from the 5955 to the 7955 (same specs) that they used the new programmable circuitry also and therefore probably is also 2s capable. I suspect they did not announce it until more testing was proven. My brother in law ran the 7955 in his xr10 for 8-10 comps using a bec set to 7.2v and never had issues.

Your EPAs need to be set to just befor the cvd's start to bind. That may be 60% or it may be 110% depending on your radio setup. Obviously it's very important to NOT got past the point of binding to keep the servo from failing.