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Help! ES9251II servos vs. ES9051

mayan

Well-known member
#1
Hey everybody,
I am super bumped out after waiting for a month and a half for my servos to arrive with a few problems in the middle. I had finally received the servos. Although I have received the wrong servos and received ES9251II servos instead of the ES99051 servos I wanted.
This is a link to the servos I have recieved: https://www.banggood.com/EMAX-ES925...r-RC-Airplane-p-1362121.html?cur_warehouse=CN
Do you think that these servos can work with the FT mini plane series? Or do I have to find something else to do with them?
 
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Arcfyre

Well-known member
#3
I don't see why they wouldn't work. They look a little small, so probably good for one of your SpiTTT builds. It also appears that they are digital servos, which means that you may see a higher current draw compared to analog servos.

In a 2-4 servo application this shouldn't be too much of an issue, but if you were to add in flaps and retracts you would start running the risk of your RX browning out.
 

Keno

Active member
#5
The difference between these the9051 and 9251II it 4.3 Grams vs 3.6 Gram servo, meaning they are a smaller. In most mini probably OK. One thing you do not want to do, when you put the servo arm screw in place don't have them energize or you can strip their gears.
 

mayan

Well-known member
#6
Yeah their size is what worries me the are so small I am afraid to touch them. Currently running my minis with 9g servos cause that’s all of what I had to date after breaking all my 5g servos.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#8
What do you mean by brown out the RX and why?
Firstly I use 3.7 gram plastic servos in my minis through to 9 gram plastics, (It just depends upon what is available at the time), without any issues at all.

A brown out is where the Rx and servo voltages drops below 5 volts for whatever reason. The most common reason is that either the BEC on the ESC overheats and shuts down the Rx volts to protect itself or that the total current being drawn from the BEC is in excess of the BECs ability in which case again the BEC will shutdown the Rx voltage to protect the BEC.

So the caution raised was that you need to be sure that the BEC in the ESC can supply more than enough current to operate all the Servos and the Rx at the same time. If not you risk a brown out where the Rx stops working, the servos could either freeze or even drive to travel maximum and of course a crash normally ensues!

Hope that clarifies things a little for you!

Have fun!
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#11
It sure does how do I know if it an esc has enough voltage?
Firstly plug all the electronics together and then turn on the Tx and slam the sticks from max to min rapidly and continuously, (so that all servos are driving and then reversing continuously), to see if the Rx stops receiving. If it does stop receiving the BEC current rating is too low.

Next secure the motor and fit the prop to it and do the same test with the motor running at full throttle until the battery is flat, (cover the ESC with something to stop the air helping the cooling). If it fails then the ESC cannot handle the heat generated and could cause problems without adequate cooling.

Mind you, once you have done the test once and verified it all works together you do not need to repeat the exercise every time you use the same setup!

Have fun!
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#15
View attachment 121651
Here it is don’t know what it means. @Hai-Lee any thoughts?
OOPs only 2A BEC and it is a serial BEC at that! CAUTION do not add too many servos!

As a safety margin I would recommend that you use no more than 4 Servos and that is on 3S. Only 4 if the ESC runs cool or is very well ventilated! If the ESC runs hot limit it to 3 servos or even to 2 if the ESC runs very hot!

If running 4S I would recommend that you consider fitting an external UBEC for safety if using 3 or more servos!

Do not use with large high current servos EVER!

Just my recommendations of course and I would encourage your experimenting and testing to verify if you lose Rx volts at anytime before putting it into the air.

Have fun!
 

Arcfyre

Well-known member
#17
You run the risk of pulling more than 2A through your built in BEC. When that happens the RX usually shuts off to protect itself. When that happens it can be harmful to a flying model.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#18
I’ll do the tests and find out if it holds any chance that this can damage any electronics?
No risk of damage as it is the current handling of the BEC you are checking and it is actually self protective. To the Rx and servos it will be like the battery going flat at worst!

have fun!
 

Keno

Active member
#20
I think the best way and safe way is to buy a large enough BEC to run all your stuff if you find the need to do so. I have parallel to ESC's BEC outputs and it added the extra pwr that I needed. In saying that, there are circuit designs that can and can not be paralleled. You would have to do research to find compatible circuitry. It is the same as paralleling two batteries. I have been reading the post above on this and I have not experienced any problem with running 4 small servo on a 2 amp BEC. Digital servos require more pwr but I doubt that even four 9 gram servos would be an issue. It is better to know for sure and some test stated above would be in order. Remember that when you place a servo or motor under stress that they will demand more pwr. As I have implied I have not really seen this as a problem to be stressed out on with FT size planes, unless you need a lot of servo to do goofy things. Ah well, for what it worth it is only one persons opinion I am sure there is round filing can close to your workbench.