Servo replacement

WoodiE

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Can't wait to get my small 2s packs to power the servo. Should be a game changer on this truck.
A game changer? I'm guessing this thing will flip the Kraton over on it's back from a stand still! :D

Please do keep us posted on how you like it.
 

RCROD

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Wow, almost 700 oz/in. of torque. You better have the end points set up on that beast. Not too long ago, over 300 oz/in. of torque was something...
 

Motorider

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Is there a reason why you are adding a 2s battery to power the servo instead of running an external BEC?
Actually, yes. I have learned from a large scale aircraft builder that servos will deliver better performance and last longer when directly powered off of a battery. This guy powers his servos in 5k to 20k airplanes with 2s lipo power. The power from a BEC is very dirty. Basically all it is, is a few FETs that are switched on and off very rapidly to give the effect of lower voltage output. BECs tend to get very dirty during peak amp draw. Voltage can sag and the square wave can get ugly. That can cause problems for the electronics onboard of the servos. A decent battery will eliminate all of those problems and should yield a long life for my servos.

The weight is negligable on the heavy kraton. I'm using a 2s 950 turnigy pack. Testing will tell me how much runtime I will get out of the rx pack.
 

Motorider

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Quick video of first test of savox 2290 servo. It's not the fastest, but it has no problems throwing the big wheels around. Does your truck have this much toe out?
 

chevys10zr2003

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Actually, yes. I have learned from a large scale aircraft builder that servos will deliver better performance and last longer when directly powered off of a battery. This guy powers his servos in 5k to 20k airplanes with 2s lipo power. The power from a BEC is very dirty. Basically all it is, is a few FETs that are switched on and off very rapidly to give the effect of lower voltage output. BECs tend to get very dirty during peak amp draw. Voltage can sag and the square wave can get ugly. That can cause problems for the electronics onboard of the servos. A decent battery will eliminate all of those problems and should yield a long life for my servos.

The weight is negligable on the heavy kraton. I'm using a 2s 950 turnigy pack. Testing will tell me how much runtime I will get out of the rx pack.
I might have to try that in the future sometime. I just added a Castle 20 amp external BEC and was curious as to your reasoning. May be a dumb question but is there a wiring diagram for using an external battery like you are doing?
 

Motorider

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I might have to try that in the future sometime. I just added a Castle 20 amp external BEC and was curious as to your reasoning. May be a dumb question but is there a wiring diagram for using an external battery like you are doing?
The easy way is to run the battery straight to the battery port on your rx. The pull the red or center pin out of your cable from the esc. Leave the ground and signal wire in to bond the grounds together in the rx. Job done. Very very easy. I just made a power cable with a jst connector on one end to connect to the battery and a servo connector on the other. When done, just don't forget to unplug it when you unplug your main batteries. I'll post back with some images later.
 

Motorider

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So the battery shows 8.72v or about 60% charge. I only charge my packs to 4.15v per cell. It should be good for 2 full runs per rx pack. If not I got 4 of the turnigys for 36 shipped to my door. Anyways you can see my Rx pack wire running along the battery tray. Man oh man this setup works great. Turns when and where I tell it to, no BS.
 

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nulli

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Isn't that a 7.4V servo? I wouldn't dare to put 8 or more volts through a $160 servo..,
 

chevys10zr2003

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Isn't that a 7.4V servo? I wouldn't dare to put 8 or more volts through a $160 servo..,
Technically a 2s Lipo is a 7.4v battery. I am not 100% sure but I think that the batteries are rated nominally and not peak and I wonder if servos are rated the same way.
 

Motorider

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A 2s lipo is 7.4v nominal. It will run all day on 2s. A 2s lipo under load will be very close to 7.4v.
 
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