RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

JR 791 retract servo with LiFe pack.

Reply

Old 08-31-2012, 11:08 AM
  #1  
radfordc
Thread Starter
My Feedback: (14)
 
radfordc's Avatar
 
Join Date: Apr 2005
Location: Lansing, KS
Posts: 1,580
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default JR 791 retract servo with LiFe pack.

I'm using a JR 791 retract servo in my TF P-47 ARF and I'm also using a 2 cell A123 LiFe pack. When I first connected the servo I was surprised to see that it didn't work, but I quickly found out that these servos will only work with 4.8 volts. In order to make the servo work correctly I needed to drop the voltage. The way I did this was to add 2 diodes in series in the servo extension lead and this seems to be working so far.

Anyone see any problem with this approach, or have a better solution?
radfordc is offline  
Reply With Quote
Old 08-31-2012, 12:12 PM
  #2  
pilotpete2
 
pilotpete2's Avatar
 
Join Date: Oct 2002
Location: Lyndonville, VT
Posts: 3,298
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.

As long as the diodes are of adequate size to handle the current and aren't getting too hot when the gear cycles you should be fine. Heck, whats the worst that can happen, a gear up landing if a diode fails[&:]
Pete
pilotpete2 is offline  
Reply With Quote
Old 08-31-2012, 12:20 PM
  #3  
radfordc
Thread Starter
My Feedback: (14)
 
radfordc's Avatar
 
Join Date: Apr 2005
Location: Lansing, KS
Posts: 1,580
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.

I think the "worst" would be a half way gear up landing!
radfordc is offline  
Reply With Quote
Old 08-31-2012, 02:21 PM
  #4  
aghost
My Feedback: (13)
 
aghost's Avatar
 
Join Date: May 2002
Location: Amarillo, TX
Posts: 1,228
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.

I use LiFe batteries and need 4-cell voltage in a couple of planes for specific items. JR has a 2 Channel Voltage regulator I use. At $30, the diode's are probably cheaper.

This solution is not necessarily better, but here is a link to the item.


Brian
aghost is offline  
Reply With Quote
Old 08-31-2012, 03:10 PM
  #5  
pilotpete2
 
pilotpete2's Avatar
 
Join Date: Oct 2002
Location: Lyndonville, VT
Posts: 3,298
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.


ORIGINAL: radfordc

I think the ''worst'' would be a half way gear up landing!
I think you be right
Pete
pilotpete2 is offline  
Reply With Quote
Old 08-31-2012, 05:25 PM
  #6  
Truckracer
My Feedback: (19)
 
Join Date: Apr 2004
Location: Des Moines, IA
Posts: 4,915
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.


ORIGINAL: pilotpete2

As long as the diodes are of adequate size to handle the current and aren't getting too hot when the gear cycles you should be fine. Heck, whats the worst that can happen, a gear up landing if a diode fails[&:]
Pete
+1

The diodes should be fine. I would use ones rated at 3 Amps rather than the 400X series that are so common and rated at 1.0 A! These should be available for pennies each.
Truckracer is online now  
Reply With Quote
Old 09-01-2012, 04:59 AM
  #7  
BuschBarber
Senior Member
My Feedback: (2)
 
Join Date: Jan 2002
Location: Rochester, NY
Posts: 4,756
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.


ORIGINAL: Truckracer


ORIGINAL: pilotpete2

As long as the diodes are of adequate size to handle the current and aren't getting too hot when the gear cycles you should be fine. Heck, whats the worst that can happen, a gear up landing if a diode fails[&:]
Pete
+1

The diodes should be fine. I would use ones rated at 3 Amps rather than the 400X series that are so common and rated at 1.0 A! These should be available for pennies each.
I have an H9 P47-150, with a 791 Retract servo on each Main gear.. I use a Castle Creations BEC Pro and a 2500 LiFe pack with JR921 Rx. Never a problem.
BuschBarber is offline  
Reply With Quote
Old 09-01-2012, 03:49 PM
  #8  
radfordc
Thread Starter
My Feedback: (14)
 
radfordc's Avatar
 
Join Date: Apr 2005
Location: Lansing, KS
Posts: 1,580
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.

I think that a voltage regulator is a better solution. The plane has a redundant battery system...two 1300 LiFe batteries and two switches. I'm going to add two Turnigy VRs ( http://www.hobbyking.com/hobbyking/s...idProduct=4319 ) and this will reduce the system voltage to 5v and provide up to 6 amps of current. Less than $10, too.
radfordc is offline  
Reply With Quote
Old 09-02-2012, 06:54 AM
  #9  
dirtybird
My Feedback: (5)
 
Join Date: Jan 2002
Location: San Tan Valley, AZ
Posts: 5,768
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.


ORIGINAL: radfordc

I think that a voltage regulator is a better solution. The plane has a redundant battery system...two 1300 LiFe batteries and two switches. I'm going to add two Turnigy VRs ( http://www.hobbyking.com/hobbyking/s...idProduct=4319 ) and this will reduce the system voltage to 5v and provide up to 6 amps of current. Less than $10, too.
I have to disagree with you. Two diodes are a simple solution that will be bullet proof it the diodes have the rated current. A regulator has many parts to fail and getting one one from Hobbyking is questionable in itself
dirtybird is offline  
Reply With Quote
Old 09-02-2012, 11:11 AM
  #10  
radfordc
Thread Starter
My Feedback: (14)
 
radfordc's Avatar
 
Join Date: Apr 2005
Location: Lansing, KS
Posts: 1,580
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.

Your right about the diodes being more reliable than a VR. But, the servos that I'm using are Hitec and are not rated for 6 volts so I'm taking a risk by running them on a LiFe pack. I've already had to replace a couple of jittery servos and the high voltage may be the problem.

Using 1 cheap VR would indeed be a high risk, but by using 2 in parallel the risk is greatly reduced. Part of the preflight check is to be sure that each battery, switch, and VR is functioning properly independent of the other. If one VR fails in flight the other one will continue to provide power. Both VRs would have to fail for a total failure.

I am using several different types of electronics (receivers, voltage regulators, servos, etc) from HobbyKing and am totally satisfied so far.
radfordc is offline  
Reply With Quote
Old 09-02-2012, 12:49 PM
  #11  
dirtybird
My Feedback: (5)
 
Join Date: Jan 2002
Location: San Tan Valley, AZ
Posts: 5,768
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: JR 791 retract servo with LiFe pack.

Two diodes in series will reduce the voltage to 5.1V.
dirtybird is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service