Ventus 4.5 meter retrac servo - RC Groups
Thread Tools
Jun 22, 2007, 08:27 PM
Registered User

Ventus 4.5 meter retrac servo

I am finished building my Ventus and need help in picking the right retrac servo the one I am using is a Hitech 225mg and it seems to not have enough torqe to hold the retrac open it has a hard time going threw the doors what servos are you using for your scale
Sign up now
to remove ads between posts
Jun 22, 2007, 10:15 PM
In a little camper
Billymac's Avatar

I've got an old Graupner 4m Ventus, and I am using a Hitec HS-75. Seems to have enough power to get through it all.
If not a JR 971 (i think that's the number) will no doubt power it through. It has a LOT of torque.

Hope this helps

Jun 22, 2007, 10:34 PM
Registered User
k2k's Avatar
I will second the HS-75. I have used them in a couple of planes that size and had no trouble. This is the installation in my Ventus.
Jun 23, 2007, 01:38 AM
In a little camper
Billymac's Avatar
I tried the HS-75 on my LET 1/3 scale DG-600, and it would work while on the bench, but when I installed it into the acft, it lacked the power to push open the doors. And then it would stall. I forget how many amps it was pulling, but it was definitely too small. And everyone one knows that a stalled servo can lead to disastrous results. Especially when it doesn't have it's own power supply.

That's when I put in the JR 971. With a 5cell battery it has well over 300 in/oz's of torque No problems since.. It costs twice as much, but I feel more comfortable knowing that the servo won't be stalling, when I retract it.

If the hs-75 won't push through the doors; you might try a 5cell battery pack; that will help . Also watch your geometry on the servo arm compared to the retract arm.

Hope this helps,

Jul 02, 2007, 05:07 AM
bie's Avatar

replaced the HS-75BB after three failures on the retract of my large L-213A by a JR 791 (isnít that the correct number instead of 971?).

No more hassles since...

Jul 02, 2007, 10:59 AM
Registered User

JR retract is the way to go

I agree with the consensus on the JR retract servo.
IF you have a perfectly functioning retract, the smaller torque
Hitec is okay, but in the real world of grit, grass, and whatnot,
the higher torque is the way to go. Ask me why I know.
Jul 02, 2007, 12:19 PM
In a little camper
Billymac's Avatar
Andy, Kevin,

If you have the servo in front of you and it says JR 791, then that is most likely what I was talking about. I threw away the box after install, and I couldn't see the servo as it is on the backside of the landing gear.
Memory isn't what it used to be,, First the eyes, now the memory...Getting old is really starting to suck...

I find the hs-75 works for the 4.5m ships on down. Never seemed to have a problem with them. But I did use one for my big 1/3 Pilatus B-4. I think it has a FEMA type retract that works smoothly.

I really think that the servo size depends on the type of retract that you are using! The FEMA type work well, but the LET monstrosity is too big and heavy and requires the extra power.

Jul 02, 2007, 02:49 PM
Registered User
It depends on the retract, LET require a 180 degree servo, FEMA retracts use a regular servo so there are many choices when using a FEMA.
And Bill, how is that Windex coming? I flew the pants off mine at the JR aerotow, pretty sure it will be seen in the new Paul Naton dvd coming as soon as Paul gets it edited and printed.
Jul 04, 2007, 12:35 AM
In a little camper
Billymac's Avatar
The Windex was finished a few months ago (I think) And is ready to fly.
I haven't had the time to fly anything since I work at night. This has really put the dampers on my flying. I should have range checked it with the motor running last Sunday but forgot about it. A couple of friends want to be there when I do finally put it in the air.

I flew my Silent Dream on Sunday, and I couldn't remember how to activate the timer function on my 9303. Finally figured it out after a few minutes, or maybe I stumbled across it... But I did manage to core a few thermals and bring everything home in one piece.

Have cleared the bench since the WIndex was finished and now I'm getting ready for some slope action this weekend at Greens Peak. As well as a few honey-dos....

Wish I could have been at the JR event. Looks like you guys were swamped out there. I will definitely get the dvd when Paul gets done with it.

Jul 04, 2007, 12:01 PM
glider guider
glider guider's Avatar
The 791 is a great servo but there are a couple of points. It is non proportional and all adjustments are mechanical. It is also not rated above 4.8 volts so a 5 cell battery pack is out. One friend was using a 5 cell and it would seem at full charge the servo would shut itself down and not operate at all. On my 4.5m model I have used the Hitec 5645, cousin of the 645, and this has 143/168 oz of torque.
Jul 04, 2007, 01:30 PM
In a little camper
Billymac's Avatar
You're right the 791 isn't rated above 4.8 volts and all adjustments are mechanical in nature. For my particular application the 5645 (I tried) wasn't enough to push the LET landing gear through the lightly banded doors.
My 791 works fine on 5 cells.. Never saw it shut itself down with numerous operations on the bench. But now that you've mentioned it, I'll go back and check! Pehaps your friend had an older version of the 791??

A thought just occurred that maybe the JOMAR battery backer ( That I use) is regulating the voltage to the reciever?? I'll check that as well and ppost back the results.

Thanks for the info.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Valenta/Soaring USA 4,5 meter Salto authomassen Scale Sailplanes 8 Feb 09, 2007 03:15 AM
For Sale 4.5 meter semi scale electric Sperber scalesoar Aircraft - Sailplanes (FS/W) 8 Oct 10, 2005 01:31 PM
Whoops! engine size needed on telemaster to tow 4-5 meter scale planes kevin kavaney Scale Sailplanes 11 Nov 14, 2004 12:52 PM
4 and 4.5 meter electric sailplanes Sale scalesoar Vendor Talk 0 Sep 15, 2002 05:05 PM