Hi, I have a JR 7100 which I would like to use on the elevator through a MK bell-crank. Is this servo usable on a 2m F3A model?

Thanks in advance

3DMike,

How much power does that servo have? I think Piedmont Models are running 4131's on their airplanes (90 oz/in torque). I have a 4721 on my Hydeout (120 oz/in torque) and it works like a charm.

Any idea what the 7100's torque is?

I've been using single 8231's @88 oz-in on pattern (2m EMC, Hanson Elan) and 1/4 scale aerobats (H9 1/4 scale CAP232's ). They do the job fine - if a 7100 is close to that you should be ok.

In the specs its only 3.5 kg, but it has all metal gears and is a low profile super servo. If needed I can put a 7000 on the elevator. I was just wondering if anyone out there have used this servo in their planes.

srry double post...

The JR 7100 is one of the Super Servos....It was designed as a wing servo..Low profile and is better than an analog servo its a pre-digital digital servo....It has tremendous holding power and is a great servo for pattern model...The parts are hard to come by to service these servos as they are no longer produced....but 7005 gears will work.

Be careful these servos are digital type servos and eat lots of power....even more than the digitals....Go with big battery pack and keep on top of it.....If this servo was still in production I would still be using it. I have 4 of them left and they are superb servos.


Troy Newman
Team JR

Thanks for that Troy. I was wondering if it would be usable for an single elevator servo, were these servos prone to failure. Why only rated at 3.5 kg's for a 2m model. Looking at other web sites it seems the 7100 is still in production but the 7000 were stopped. I am using older 7000's in the wing which are 4.5 kgs. Yes the 7000 sucks power as they are at full power 100% of the time but the 7100 use way less.

3.5kg-cm is about 50-60oz-in...but these servos are like the 7000's in that they run at high power to maintain position.....They are better on the consumption than the 7000's and the 4000's...but they still are digital like.

50ozs is plenty. and thats 4.8V go to 6V pack and get even more power if you are concerned about it...

I used these things on 120 sized birds with 140's in them....Like the Dr. Jeckyll II, my Ariel and even a Typhoon 2+2....They are a great servo...as I said before the biggest downside is they use lots of juice. In fact the super servos use more than todays digitals....that was big improvement on the digitals they reduced power consumption.

I would not hesitate to use those servos. They are good I never had any failures with them....I ran mine on 7005 gears to reduce slop as the 7100's are metal gears and get sloppier quicker.


Good Luck

Troy Newman