KST DS725MG power requirements in a 700?

[Atomic Skull]

I bought a set of the Turnigy branded version (same servo as the KST with a different label) for the 700 I'm building. I have heard that these draw a lot of power, will a 2S lipo with two leads feeding the FBL controller be enough?

[greekpilot]

i see you got no reply unfortunately, but i will be using the same ones on my 700 (goblin or max v2, havent decided yet, and the ds525 for tail).
have you flown your bird yet? what are your thoughts on these servos? performance wise and consumption wise?
Thanks

[P.I.Engineer]

i've got about 10 flights on mine, running off a western robotics hercules bec at 6v, seem to be running great.

i changed my motor too, so i don't know if the servos are any better

[Atomic Skull]

Originally Posted by greekpilot

i see you got no reply unfortunately, but i will be using the same ones on my 700 (goblin or max v2, havent decided yet, and the ds525 for tail).
have you flown your bird yet? what are your thoughts on these servos? performance wise and consumption wise?
Thanks

I did a teardown thread here:

https://www.helifreak.com/showthread.php?t=702830

I can't fault the internal built quality. So far they seem like very good servos.

2S lipo seems to be enough but I don;t fly hard smack either.

Here's what it looks like now:

[greekpilot]

Yes i have already read your teardown thread, it actually played a big part in my decision to go for them Skull. what capacity is this rx pack and how many flights is it good for?
As i can see you have replaced the esc and motor. Man, apart from the tail servo we have identical setups. Are these the 690mm blades? what flight times are you getting and at what rpm?

[Atomic Skull]

Originally Posted by greekpilot

Yes i have already read your teardown thread, it actually played a big part in my decision to go for them Skull. what capacity is this rx pack and how many flights is it good for?
As i can see you have replaced the esc and motor. Man, apart from the tail servo we have identical setups. Are these the 690mm blades? what flight times are you getting and at what rpm?

I'm actually going to replace the tail servo with a TGY-525MG (KST DS525MG) and use the current tail servo in my 550. Note that the 525MG is 333hz maximum so if you are using an FBL that can't drop down to that on 760us servos get the brushless version instead (which can do 500hz). Also with the brushless KST servos you might as well get the branded version because the Turnigy version isn't much less and you can get some pretty good combo deals online.

Vbar is 333hz maximum even with 760us servos btw.

Those are 690mm blades, I'm getting around 8 minutes at 1800rpm but the packs come down with 3.9v per cell so I can probably get another minute or two out of them.

RX pack is 1500mah, after four 8 minute flights it's around 7.9v down from a full charge.

[greekpilot]

Wow, these are impressive numbers, I hope I will reach the same flight times with same rpm on the goblin also. I will use the spirit, it can do 333 and 760, so I am fine with that. Thanks Skull

[Atomic Skull]

Originally Posted by greekpilot

Wow, these are impressive numbers, I hope I will reach the same flight times with same rpm on the goblin also. I will use the spirit, it can do 333 and 760, so I am fine with that. Thanks Skull

760us is the pulse width not frequency. There appears to be some 760us servos that can only go to 333hz (such as the 525mg) while most can do 500hz. some FBL units will run a 760us rudder servo at 500hz with no option for 333hz.

If you are using a Vbar this is not a problem as it runs 760us servos at 333hz always. (interesting fact, it also runs the cyclics at 143hz in digital mode)

I ran into problems with the motor "chirping" with an accompanying tail twitch when using the vbar governor with the YEP/Rotorstar ESC set to auto timing on the Gartt motor no matter how low I set the governor gain. Setting it to 18 degrees timing and 8khz fixed this. I later found that YGE recommends starting at 18 degrees and 10khz on 8-14 pole motors so I'm going to try raising the PWM a bit more. Also MrMel recommends using plane/middle on 700-800 helis with the vbar governor because it's easier on the ESC.

[greekpilot]

Yes I know what you mean about the servos. The spirit can do 720s with up to 560Hz, no problem. If your motor run good with 18 and 8 and your happy with the power, I would leave it there, higher pwm will increase the temp on the esc as well. .Not saying you are going to burn it by goin to 10, but just keep it it mind. Your flight times are great so obviously sth is working well there .
I am not sure how many poles this motor is though... It says ten, and the suggested timing and pwm are 18 and 8, just like you have it set. Are you happy with the rjx blades? I got the fbl ones, not sure how much of a difference they have with the energy, but quality wise do they seem nice? I read a couple of posts, when I had already ordered and received them, about them breaking at the root during flight and I am worried now

[Atomic Skull]

Well I found out it wasn't the timing, it was the PWM. It doesn't like to run higher than 8khz or the motor will start acting up after about the middle of the pack. So for now I'm running 8khz and auto timing.

RJX blades are easily as good as Align and Ive never had a problem with them. Read about any product and you'll always find a few people that had problems. For one thing, what headspeed were they running with them? Some people's idea of "normal" headspeed is "just below exploding".

I just installed the KST rudder servo (turnigy branded version), and it's night and day difference. Perfect stops with 100 gain and stock settings except for stop gain A:40 and B:-40. (using a negative stop value lets you run higher gains without an overly hard CCW stop)

The 525MG will not fit into the hole for the rudder servo because the fit is very tight and the strain relief will get in the way due to how high it is on the servo case so I had to mount it inside the frame like this:



I used an old Trex 500 full size rudder servo mount and some 25mm M3 aluminum spacers I had laying around. A Trex 600/700 elevator/rudder servo mount (H60183M) would also work as would an Assault 700 rudder servo mount (costs about $4 for the Assault version). The way I did it requires hard mounting but you could use the grommets and eyelets with the rudder servo mount.

A good trick for keeping the servo centered on the screws when hard mounting is to cut some gaskets out of 10 AWG silicone wire insulation and put them on the screws. It'll fill up the hole and keep the screw centered.

[greekpilot]

That is one great mod brother, congrats..

[Atomic Skull]

I like the Trex 700 rudder mount better. With the grommets and eyelets the servo ball lines up perfectly in the center.