[bobmic]

I recently bought a few HK HXT900 and HXT500 and installed the 900s in a mini FuntanaX. Although the plane flies OK when setting up I notice that the servos are not very smooth.
Was playing with some Gyros which effect the travel and the effect is definitely increased it is like they have a low resolution in the movement even though these should be analogue servos.
I compared them with some eflite s75 and I can see the difference as the eflite has a smooth movement at the same travel.
I use a corona 72Mhz synthesized Rx and compared it to a Futaba PCM as I though the receiver effects the signal but the results were the same.
I did read in other places about Hitec HS-65HB but I am not sure it makes sense to >$21 per servo for this plane. anyone has experience with other servos like Corona Bluebird etc. I do want to have at least the same power and speed as the HXT900s - ~1.6kg 0.12s, and would like them to be able to work with a Gyro.
thx.

[Cougar429]

HXT specifically warns against using their 900 with a gyro due to the rapid cycling. It quickly burns out either the motor or electronics, (and yes, I can confirm this from personal experience. The warning from HXT was not known at the time) .

The 500 can work with a gyro, but I found the servo a bit weak.

I flew several 380 class helis with the HXT900's and found them to be excellent performers. In fact, one heli had close to 170 flights before servo failure. My only problem is I recommended them to just about anyone and their popularity is such I suspect some quality control issues may be at play now. On that note their popularity has garnered some cheap copies that definitely do not have the tight geartrain or resolution. I once was sent a set of MYSTERY brand that were literally the most horid servo I ever tried, (even worse than ESKY!). Along with serious slop the servo was noisy and operated backwards compared to the Hitecs and HXT's. The direction would not be an issue, but I won't even use them for throttle apps and ended up tearing them apart just for the lead and plug.

Depending on the model and flight loads you should be able to use the 900's. I have some buried in my Polaris and am confident they should work flawlessly in that less demanding role. However, if you want bulletproof reliability and the cost of the craft warrants it, nothing much in that size servo beats the HS-65.

In the case of your receiver I doubt you could put the system through the paces hard enough to see any difference. Likely the servo performance would dominate.

With the earlier Futaba PCM receivers the 1024 resolution was more than adequate for most apps, (don't know what the Corona has for resolution). Where I found them lacking was in their very slow lock times. Lost a couple of models due to this, (the reasons for signal loss were my own fault, but if the system had come back online sooner they would have survived). I now prefer the Berg 7P Rx since I retain the benefit of failsafe and they lock back onto the signal MUCH faster.

[bobmic]

I assume when you talk about lock time is the time it takes them to lock after loosing signal. The Corona does have a fail safe programming which I did not really follow as it is based on a number push button presses and counting LED blinks which is not very straight forward.
What servos should I use if I connect them to Gyros?

[Cougar429]

With no experience with the Corona I will take your word. I too have run into equipment far more complicated than it has to be, especially if the instructions are in "Chinglish"!

I have a Sombra Labs 7 channel receiver that, along with different failsafe modes, requires no crystal, (can run on 72 and 75 bands) has the ability to also set any channel to any output and daisy-chain two receivers together to get 14 channels. Like the Bergs it also has auto shift recognition. However, unlike the Bergs, which can be set with a PC link system, the Sombra uses a secondary card to program all the functions. It's not too difficult to figure out after you have read the instructions a few times. Other than that it's actually a pretty good receiver and when compared to the legacy Futaba PCM receivers, incredibly small.

You're correct regarding the lock times. It takes quite a bit of time for the receiver to recognize and start using the transmitter data, in some cases up to 5 seconds. My planes and helis can move quite a distance, (it's the vertical that hurts!) in that time. I had an incident early last winter on a first flight of my Harvard II, where, with cold hands I switched off the Tx rather than hit the elevator trim. Immediately recognized the error and switched it back on. The Berg came back immediately, where with the Futaba it likely would have done a goat into the frozen ground before responding again.

I have run different servos tied to the gyros on my helis, probably one of the most demanding apps for that set up. In your case I would not expect them to be working quite as hard, but there could still be high cycle times and heat. You want good airflow over the gyro and servo to keep them cool.

As for the servo, what size aircraft and flight dynamics will make a difference as to selection. Since I have no idea as to the size craft and loads imposed I can only use the heli reference for now.

For the rather smaller 380 class helis I found the HS-65, Futaba micro digitals and even the Align DS420 to be adequate and reliable. In the 450 class my options were the Futaba 9257/9650. I usually picked the 9650 due to the specs showing it capable of 6V and then did the 9257 gear swap to increase speed at little sacrifice to output torque.

On my 600 I mounted a HS 5925MG. Extremely strong and quick, but I have not flown that setup yet.

You should note that with this type of application digital servos are preferred due to their much quicker response time, (250-300 frames per second compared to 50 for analog) and much better holding power.

However, that behavior comes at a radically increased current requirement, so your electrical system should be matched accordingly. For a larger, high demand system with lots of digitals under heavy load, (some digitals can pull over 1.5A when stalled) a stock radio system can be strained to the failure point. For example, most ESC's onboard BEC functions can only handle 2-3A. The same consideration can be said of a stand alone radio system since the stock ON/OFF switch is rated at only 4A.

[bobmic]

Do you have any experience with Blue Bird servos? I saw a few mixed reviews on HK and was not too sure. I will also consider the GWS Naro+FH or Hitec HS-65HB although somewhere I read that the Hitec needs more current then other servos.
Once again I am talking about the Mini Funtana X which is 480 size plane with 43" wings
http://www.e-fliterc.com/Products/De...ProdID=EFL2425

thx