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Thread: Added DIG servo, time for a BEC?

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Old 05-13-2009, 05:32 PM   #1
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Default Added DIG servo, time for a BEC?

I'm running a Rooster Crawler with a Spektrum DX3.0 and up until just now never had any problems except an occasional annoying throttle glitch.
Now with the DIG servo the truck will completely lose power for a moment and lurch into reverse (which is what it does when I first turn it on 'till it finds the transmitter). I also at the same time upgraded my steering servo to a HiTec 7955TG. I'm thinkin the extra bit of load from both the new servos is draining too much from the ESC?
Lookin at the Novak #5465 5 amp BEC.
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Old 05-13-2009, 08:38 PM   #2
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An external BEC is always a smart thing to have on your ESC. I can't tell you if this is the cause of your problems, but I'd look into one anyway. It will keep your ESC from working too hard and heating up as much. I personally like the Castle Creations BEC because you can change the output of it... not sure about the Novak one you mentioned though.
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Old 05-13-2009, 09:00 PM   #3
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Quote:
Originally Posted by jnev View Post
An external BEC is always a smart thing to have on your ESC. I can't tell you if this is the cause of your problems, but I'd look into one anyway. It will keep your ESC from working too hard and heating up as much. I personally like the Castle Creations BEC because you can change the output of it... not sure about the Novak one you mentioned though.
X2

That 7995tg can draw some amps. You will realize it's true power with an external bec. I can't say enough for how the cc bec improved the performance of my super running 2 tg servos.
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Old 05-14-2009, 12:41 AM   #4
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X2

it is always time for a BEC you paid for that servo so you might as well get every oz of torque out of it!
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Old 05-14-2009, 05:10 AM   #5
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X2 on a castle bec. the novak bec is rated at 5 amps? (I don't own one so I don't know) but the castle bec is rated at 10 amps and as mentioned above with adjustable voltage, if you don't have the castle link, just order it from HH and ask him to set it for you!!!
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Old 05-14-2009, 07:21 AM   #6
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I got mine from Holms and had him set it to 7 volts.

I run the power directly to the steering servo and even though I haven't had it on the rocks yet, it is a BIG improvement.

My Mamba is rated at 5 volts and had to power the steering and dig servos and the steering was weak.

If you plan to power both servos, I'd make sure you know how many volts each can handle...I didn't check my dig servo so I'm just powering the steering servo because it's rated to 7.2.
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Old 05-14-2009, 09:19 AM   #7
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Thanks fellas!
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Old 05-18-2009, 10:07 PM   #8
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Just an update on this, I picked up a Castle BEC and link. Set the voltage at 7 volts and had at it. I wired everything just like the diagram on the package. It was better initially but after 5 minutes the reciver started acting up again, like it was momentarily losing power. My Dig servo was getting real hot too, but it's a cheap Toward Pro so...anyway it wound up burning up and made the RX shut down. Came home and put a HS 645MG in as the dig servo. Made sure my EPA's are dead on and went at it on my pile in the back yard. Eventually same thing, dig servo getting warm and the RX is acting up again. So tonight I rewired it all. Now my servos are getting power straight from the BEC, the RX is getting power from the ESC.
Played around in the lving room for a few minutes and man the dig servo is scorching. Wondering now if maybe I need to back down the voltage (7 volts) off the BEC?
Thoughts?
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Old 05-19-2009, 04:51 AM   #9
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your 645 is only rated for 6 volts as are 90% of the servos out there
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Old 05-19-2009, 07:15 AM   #10
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I posted somewhere else, but, I fried my CYS servo because of the 7 volts...had the BEC wired directly to it which saved my dig servo.

I threw a 645 on for steering because of the comp this weekend and had the Prez set the BEC for 6 volts.

It is now hooked up like the Castle diagram and working fine.

Stick to the 6 volts...even if the seller lies about the servo rating.
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Old 05-19-2009, 07:20 AM   #11
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Quote:
Originally Posted by allgm1 View Post
your 645 is only rated for 6 volts as are 90% of the servos out there
I run my 7995's and 5955's at 6.5V and no problems so far....
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Old 05-19-2009, 10:17 AM   #12
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Actually I had a brain fart, I have the BEC set at 6v, not 7.
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Old 05-19-2009, 10:19 AM   #13
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If your dig servo is getting hot, then you dont have your endpoints set properly.
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Old 05-19-2009, 10:21 AM   #14
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Quote:
Originally Posted by JeremyH View Post
If your dig servo is getting hot, then you dont have your endpoints set properly.

Yep.
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Old 05-19-2009, 10:54 AM   #15
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If I back off the endpoint anymore it won't stay engaged in 4wd. I adjusted the throw until it just barely engages enough to stay locked in.
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Old 05-19-2009, 09:33 PM   #16
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hey kev, i was looking at your dig servo mount...it looks like the servo horn is mounted directly to the shift rod on the dig...if thats true...i bet the servo is binding a little in order to keep it engaged...the servo horn needs to move in an arc...when its mounted directly to the rod like that it cant...might look into adding a short linkage in between there...but then again i might be looking at it wrong...

the BEC should really only be hooked up to the steering servo...dont worry about the wiring diagram that came with the BEC...hook the power wires from it to the deans at the battery or to the wires coming from the battery at the ESC...then cut/splice the wires coming from the BEC so that the red and black wires go to the red and black on the steering servo...and the yellow wire from the servo goes to the Rx...i ended up using some pieces of servo extensions to hook it all up so that i could still hook the BEC to the castle link easily...i can show you some pics if you want...
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Old 05-20-2009, 02:31 PM   #17
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If your dig servo is required to maintain pressure on the dig to keep it engaged, then the servo is going to heat up to some degree. Fast digital servos don't require much position error to ramp up the output force. The dig servo shouldn't really require much power from the BEC if things are setup correctly. However, it may draw a current surge when engaging/disengaging the dig which could glitch the BEC output voltage enough to cause receiver problems. Linear BECs have better trasnient response than switching BECs and can handle these current surges better. The switching BECs rely on their output capacitor to provide the current surge, but they are almost always too small IMHO.

~petev
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