ofremmi

Boy's
This autumn I have made some tests to try to determine the amount of work the servo's in our planes are actually doing. The reason for this is to get some facts behind the servo-selection for upcoming projects. I have made some flight tests with the servo-current sensor of the EagleTree logger attached to one servo at the time. Then I have made a servo-test-rig at home to test them in a controlled environment, and finally the results from these to test have been compared. You can find it all at my WEB-pages (NB! new address, update your links) at : http://www.ofremmi.info/

Regards from Norway (Yes... it's dark and cold here now)

f3a05

Congratulations, on having the ability,enthusiasm, patience,and dedication,to do this research, and for publishing the results in so clear a way.
Just one query-how sure can you be, that the Eagle Tree logger is accurate, in its reading of peak currents?
I'm just asking, because, in my very limited, and non-technical, experience, the peak currents recorded(obviously much bigger) with regard to maximum currents used in static testing of several F3A outrunner motors,varied quite a lot,depending on the device used to measure the current.....
From memory, the Eagle Tree logger read something like 20%-30% less than a "Watt-meter ammeter" for the same static full-throttle test.

ofremmi

f3a05 : Very good comment. Thes afternoon I have made a static test to verify that the two systems measure compareble currents. The max sample rate of 10Hz (for servo current logging I would like to be able to sample faster) from the ET-logger is too slow to catch the highest (and shortest) peaks that I can detect with my test-rig where the sample rate is 10000Hz. Brief results and discussion can be found here : http://www.ofremmi.info/F3A/Technic/...rvo_flight.htm

patternflyer1

My Feedback: (11)

Very cool info Ola...

I also like your info on TBL.. Seems to me that is how the Nats here should be scored.. I wouldn't mind putting an article on TBL in the Kfactor..

Very good info on your website.. Thanks for taking time to share with us..

Chris

Gregg G

My Feedback: (7)

Do you have anymore Futaba servos you tested?
thanks
Greg

ofremmi

Hi agai
I do not have any modern Futaba servo's, but a friend of mine come over with a couple the other night. Apart from that I have also been able to test several others that I had lying around (inside models), some old stuff (pre-digital) and some quite new.
Ola

Jetdesign

My Feedback: (8)

So according to this data, please tell me if I am wrong, but the max torque needed by the rudder, on a 2M plane in the highest level of pattern flying, was ONLY 21oz-in?

Is there really no need for these super high torque servos?

ofremmi

Hi
No-no, it's not THAT easy. What I state is that this is a more realistic value for the load actually applied to the servo. Then you must find a servo that is able to move reasonably fast with this kind of load, has the required accuracy, are able to withstand vibration (for those running IC engines) etc. Let me give a couple an examples of how to use the data.
0 : It's a fact that all servos becomes slower with increasing load, compare the 8900G with the 8455, without load the 8900 is significantly faster than the 8455, but with 2 kgcm load they are more or less equal.
1 : What to select, a JR DS8401, or DS8455b (very strong against less strong but faster). From test results one can find that with the 2kg load the 8455 is way faster than the 8401, and thus plenty strong for the intended use.
2 : What to use, one std. size servo on elevator, or two smaller ones. Lets compare one 8401 with two 3421SA's From test results .. Speed : 3421 @1kgcm = 0.21s 8401 @2kgcm = 0.22s, Accuray : 3421 @1kgcm = 2.22° 8401 @2kgcm = 2.4°. So these two compare quite well, then the selection is down to other factors.
etc.ect

stek79

Wonderful work Ola!!!

Many thanks for sharing this, I'm looking forward to see more servos.

stek79

Ola,
do you plan to benchmark smaller servos too?

It would be good to see how do the various micro servos compare with respect to accuracy.

Thanks again.

ofremmi

Stek79
The test-rig I have made is not really sutable for the smallest servos. It seems to be Ok for mini's, like down to 20g size. For the smallest ones the mass of the moving things like axles, reference potmeter etc is so big that it will influence to much on the test results. I plan to test more servo's as soon as I can borrow some (i do not want to buy servos for testing).
Thanks, Ola

najary

Hi Ola,

I tried to understand your articles about:

Servo testing analysis
http://www.ofremmi.info/F3A/Technic/...rvo_flight.htm
Servo test results
http://www.ofremmi.info/F3A/Technic/...st_results.htm
Servo testing
http://www.ofremmi.info/F3A/Technic/...rvoTesting.htm

I found them too complicated for me, since I am not an engineer.

I think it is time to rephrase the thumb rules for Servo requirements for EP plane and for IC plane separately.

As for the minimum torque requirement, I suggest that it will be calculated and presented as the maximum torque that was needed in your flight tests, multiplied by safety factor.

How fast should the servo be ? Do we have to use the fastest servo that we can get ?

Do we still have to use nylon gear for EP plane, Or we can go for metal gear ?

To determine if a servo is accurate enough, what do we have to look for ? Double bearings ?

Due to the developments in our equipments that happened in the last years ( EP planes, brushless servo technology…), maybe we have here an opportunity to save some tens of grams ?

Here are some examples of new servos:

http://translate.google.co.uk/transl...N%26start%3D40

https://www.der-schweighofer.at/arti...ital_brushless

https://www.der-schweighofer.at/arti..._digital_speed

https://www.der-schweighofer.at/arti..._bb_mg_digital

In behalf of all the F3A community, I would like to thank you in advance if you will be so kind and rephrase the thumb rules for Servo requirements.

Very best regards,

Isaac Najary
Isarel