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Old 04-09-2020, 01:02 PM   #1 (permalink)
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Default Tail Gain Adjustments

Just to note this is a fairly long post and covers a few topics 99% of you will never run into. Please keep in mind the default gains are fairly good for all models and the tail gain on the fc6250hx is very forgiving, the tail holds really well even with low gains.

However most heli guys like to aim for the best settings so below are some hints and tips on adjusting the tail gains for the FC6250HX.

Recommended tx gains;
Normal = 75
Stunt 1 = 70
Stunt 2 = 65
Hold = 85

It is important to realize you may need to adjust these based on your desired head speed. My recommendation is to use those values to start and set the PID gains below per your highest head speed.

Tailrotor endpoints, adjust the servo ball position on the servo arm until you see throw to the limits near 100% left and right endpoints. 90-110 is good, under 90 or over 110 is not considered ideal but will still work.

Most helis on the market have differential built into the tail bellcrank to ensure the proper balance in tail thrust taking into consideration the amount of torque generated to drive the main blades. In some cases you may run into a model that does not have the proper amount of differential built in and this will show as a tail wag that cannot be fixed by adjusting the tail gains. In these rare cases either decreasing the endpoint (usually left with clockwise rotating main blades) by 10% should help to provide the proper bias to the tail algorithms. You can also adjust the push rod length to achieve the same thing but this usually results in having to decrease the same endpoint which negates the adjustment you are trying to make, adjusting the endpoints is the best option for this rare case.

The actual servo center position does not impact the algorithms and is not actually used in anyway. The servo should be centered within the throw available with the arm perpendicular to the servo leading to balanced endpoints. On models with the properly designed tail rotor pitch mechanism with balanced left/right thrust bias centered within the throw will provide the best performance. For less than ideal tail bias please see the paragraph above.

Generally the fc6250hx will not show a tail wag even at very higher settings, to high of gain is usually only indicated/aggrivated during piro stops or during heaving loading of the tail rotor in a maunever.

Once the tx gain is set and the mechanical setup is taken care of move onto setting the tailrotor PID gains within the FC6250HX. The tail PID gains are fairly forgiving and the defaults will present no major issues on a wide range of helis, we have thoroughly tested between 180 and 700 sized helis.

Start with the tail P gain, test hop at your highest head speed and look/listen for oscillations on pirouette stops. If no oscillations are noted raise the gain 5% at a time until you begin to see/hear an oscillation on piro stops. If oscillations are noted on piro stops decrease the gain by 5% and test again.

After that it is time to move onto the I gain. Unfortunately this requires a little more skill in flight so please be sure you are comfortable with the procedure before performing the procedure. In fast forward flight at your highest head speed perform one or two fast pirouettes, if you note the pirouette rate varies then increase the I gain by 5% and test again. Keep adjusting until the pirouette rate in fast forward flight is consistent. If you note the pirouette rates oscillates at a high rate then the I gain is too high.

Generally if you bring the I gain up in the way discussed above you will find consistent pirouettes far before the oscillations begin. It is not necessary to push the I gain as high as possible, simply aim for consistent pirouettes. The tail will still hold very well even at low I gains, the above step is simply the best way to achieve the ideal I gain for the tail.

Tail D gain, if you have a fast and precise tail servo this will not be needed. However if you note the stops are not as clean as you would like you can raise this 5% at a time and look for improvements. Raising the tail D gain to high will result in erratic high frequency oscillations.

Based on model size, servo performance, tail ratios, tail blade lengths and overall tail authority the gains can vary from model to model. The default gains are a good starting point and the tail gain is fairly forgiving so do not be afraid to raise the value up as described above.

Due to the large variance in models on the market today, servos performance and wide range of tail authority the normal range for tail P and I gains is between 25 and 225.

Do not focus on the actual gain value, higher is not necessarily better, focus on the desired performance when setting the gains. I have two models that are exactly the same except for the tail servos, one model runs twice the P and I gain as the other however the flight performance is exactly the same.

Once the P and I gains are set and if you (and your tail drive) are up to it the best final test is big fast sideways loops loading the tail up. If you hear some oscillation in this case lower the P gain 5% and try again. No need to adjust the I gain on this one. If you are running D gain this can show here as well, in general if your tail servo is good you should be under 10% D gain.

Start and stop, these are here to keep you from slipping the belt or stripping tail gears on torque tube driven models. Defaults of 25 are a good starting point and you can raise the value up if you feel the start or stops are not aggressive enough. With belt driven tails the value is fairly forgiving and it is hard to damage the tail drive train however in the case of torque tubes I recommend being a little more cautious as it is far easier to strip the gears.

Once the PID gains are set you can use the tx gain function to make small adjustments to compensate for some oscillation in certain maneuvers and certain flight modes.

If you adjust per the notes above you will find the tail performance at lower head speeds is very good. However if you want to chase after perfection you also have the option to assign a flight mode switch in the setup menu and this will allow you to adjust the cyclic and tail PID gains individually for each flight mode. If you do decide to go this route it is very important to keep in mind the tx gain function is also adjusting the gain as well. In general its best to run one or the other to avoid chasing settings in 3 different places.

If you have any questions please feel free to post them here.

Thanks and Best Regards,
Brian Bremer
Horizon Hobby, LLC
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Old 04-10-2020, 07:08 AM   #2 (permalink)
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Thank you Brian, great info.
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Trex 700N-FB, 600N-FB,500E-FB, 500XT & 500X -FBL, Rex 470 LM, Fusion 480, 360, (2) 270's, Nano S2.
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Old 04-10-2020, 12:00 PM   #3 (permalink)
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Nicely stated. This will help with my setup (once I can actually get out and fly again) of my F3C heli. Take care.

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Old 04-10-2020, 01:45 PM   #4 (permalink)
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wow great infos Brian, many thanks! Mine FC6250HX shipped today, can't wait to fly it.
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Old 04-21-2020, 09:49 AM   #5 (permalink)
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Default FC6250HX tail gain adjustments

Brian,

Thank you for posting this information...I have been searching everywhere to see if other's have been having the same issue I am. I know this is a relatively new flybarless controller and I am new to flybarless helis, so maybe you can help me on this. Not sure if these gains/values for the PID tail gains are different for nitro than electric. I have an X-Cell 700 Nitro Whiplash powered with YS .90 engine. Though I have this set up and hovering I cant seem to get rid of a tail twitch and wag. What I have done so far was to adjust P gain from default 85% (with constant severe twitch/wag) down to 50% (with random twitching with wag) my head speed at hover is 1640 rpm. While adjusting the P gain from 70% the random twitching and wag is the same and no change to 50%. I was afraid to adjust lower than 50% as I didn't want to adjust so low that I lost control. Initially, when I began the flying part of this programming adjustments my head speed was around 1900 rpm at hover with the P gain I adjusted down to 73% and it seemed to have a steady tail; however, I was told that my head speed at hover should be at 1600 rpm rather than 1900 rpm for nitro so when I adjusted that down I cant seem to get rid of the twitch/wag. Does this FBL controller prefer higher head speeds and what is the appropriate head speed for this size engine/heli?....Also one other question I have on this FBL controller programming at the beginning the transmitter set up indicated to change the trim set up values in the transmitter to "0" can we go back after transmitter is set up to change values back to 5 and use the trims for small flight adjustments? I appreciate any suggestions you have.
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Old 04-23-2020, 04:35 PM   #6 (permalink)
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The gains are similar between electric and nitro models, overall they are very forgiving throughout a wide range of head speed as well.

Don't be afraid to bring the tail P and I gains up from 50 and that is expected on 700 size helis. Set the tail D to 0 until you have the P and I fairly close.

I suspect your gains are low which can cause a low frequency oscillation, bring them up slowly and you will find they are very forgiving.

I run normal mode around 1300 rpm, stunt 1 around 1700 and stunt 2 around 1900 for my 700's. It is just preference though.

What tail servo are you using?

What tail rotor blade are you using?

What tail ratio?

I can give you a guesstimate on the gains but those three questions are vital to the guess. For the most part you should be up near 100 for P and I on a 700, maybe higher if the model is lacking tail authority.

I would recommend turning the motor over by hand and it should be silky smooth, if you notice it feels a little notchy there is a good chance the bearings have rusted or pitted and that can cause a lot of issues on fbl controllers.

Thanks and Best Regards,
Brian Bremer
Horizon Hobby, LLC
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Old 04-27-2020, 05:06 PM   #7 (permalink)
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Thank you Brian...I'll run with this for now.
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Old 05-17-2020, 03:06 PM   #8 (permalink)
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Default TX inputs vs FC6250HX inputs

Brian,

Quick question...with the FC6250HX I want to confirm that we cannot use expo from the transmitter functions...only from the forward programming menu correct?
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Old 06-03-2020, 10:44 AM   #9 (permalink)
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I have not seen anywhere in the Forward Programming section where there is the ability to choose expo rates. As far as I can tell, Dual Rate and Expo are still a transmitter function with this controller. Hope this helps.

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Old 06-04-2020, 03:38 PM   #10 (permalink)
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Expo is set in the transmitter.

Tx dual rates can be used for a low rate if desired. You should set the deg/s for the cyclic and the tail @ 100% rate in the fwdprg menus 1st to ensure the highest resolution and then set your tx low rate if desired.

I would prefer a more consistent interface and having everything in the fc6250hx however tx firmware is what it is.

Best Regards,
Brian Bremer
Horizon Hobby, LLC
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Old 06-13-2020, 06:14 PM   #11 (permalink)
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Default FC6250HX short in the rudder channel

Brian,

Earlier in the thread I inquired on adjusting the programming in the FC6250HX FBL controller; however, after many flights adjusting up to near 100 on P&I gains then past 100 then back down to 20 the tail continued to twitch and wag with no change. I changed the push rod & ends, the tail blades, removed checked and re-inserted the tail boom, added thicker then thinner mounting tape under the unit, and re-calibrated but still the same twitch and wag. Turns out that the tail servo channel terminal in the FBL unit itself appears to have a short. When wiggling the wires the tail servo twitches but very slightly; however, the servo arm also drifts very slowly towards the rear. I replaced the tail servo but same problem. At the flying club today I was ready to just shelf this heli as I could not for the past 5 months figure out why I had this issue. I am new to the FBL world but after following all the instructions on how to program this unit and knowing the mechanics of helis I was clueless until today. While at the field one of the old timers but very wise asked to test something. He tapped on the FC6250HX FBL controller slightly and my tail servo twitched badly. Each time he tapped on it the servo would twitch as if someone bumped the rudder stick on the transmitter. This unit hasn't been in a crash as it hasn't flown over 5 feet off the ground due to the tail problem. I assume this is an isolated problem with these units; though I wanted to know if anyone else has had this problem. Also, I know i've had this controller for 5 months now but it's not damaged in any way so I will call Horizon Hobby on Monday to see if I can send this one back and get a replacement.
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Old 06-13-2020, 08:26 PM   #12 (permalink)
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There is a 3-axis rate sensor in the 6250hx, tapping it or moving it even slightly will cause the tail and other servos to move.

To validate this is a bad connection between the tail servo and the fc6250hx power everything up, go into the forward programming menu, enter the setup->tailrotor->output setup->subtrim. This will disable the tail control loop and center the tail servo while in the function, once you exit subtrim the control loop / servo will operate normally.

Now you can lightly tap on the fc6250hx or move the connector around and look for an intermittent connection. I suspect you will find no issues in this case.

I see you mentioned ys 90 earlier on. I would recommend the stock tape with a velcro strap around the fc6250hx to put a little tension on the tape. 3 Layers of 3m 4011 clear would work also but the velcro strap would still be needed.

The tape used will have a big impact on performance and stiff tape can transfer airframe / engine vibrations directly to the gyro.


Trims should remain at 0, normal mode may show some slow drifting however stunt 1 and 2 should hold solid. If you feel a need to adjust trims then either the gains are low or vibration may be affecting the sensor.

I would recommend Normal = 1400, Stunt 1 = 1750 and Stunt 2 = 1950 on the ys 91 and a 700 heli.

If using a governor I would recommend disabling it to make sure the motor is tuned properly and thr curve are close to correct.

What tail servo are you using?

What tail rotor blade are you using?

What tail ratio?

What tail end points in the 6250hx?

I can give you a guesstimate on the gains but those three questions are vital to the guess. For the most part you should be up near 100 for P and I on a 700, maybe higher if the model is lacking tail authority.

I would recommend turning the motor over by hand and it should be silky smooth, if you notice it feels a little notchy there is a good chance the bearings have rusted or pitted and that can cause a lot of issues on fbl controllers.

Thanks and Best Regards,
Brian Bremer
Horizon Hobby, llc

Last edited by brianbremer; 06-13-2020 at 08:48 PM..
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Old 06-15-2020, 09:23 AM   #13 (permalink)
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Default FC6250HX short in the rudder channel

Thank you for the reply Brian,

To answer your questions, the tail servo is a Futaba BLS254 brushless digital server. The tail blades are SAB 105mm CF. I assume you are asking the what the end points are in the Forward Programming set up which is 120/120 with full range. I checked the specs on the servo speed and it appears to be 200+hz but I also tried bumping it up to 333hz like the others; however no change. As far as moving the heli with everything powered on yes the 3 axis works correctly and compensates for it's movement. Even when I'm hovering and between the random tail twitches and jerks I have good response to the tail input. When the heli is on the bench and holding the rotor head still and tapping lightly on the FC6250HX unit the only servo that moves is the tail servo...all other's stay still with no movement at all. In fact the tail servo looks like it has turret syndrome it jerks so bad and again no other servo does that. I changed tail servo with a different one and that one did it too. I originally (before finding the short) used both layers of mounting tape that came with the FC6250HX to secure it, but then went to a single layer of tape thinking two layers were allowing too much vibration..obviously no change. I dont have a governor and do not plan to use one. Early on when I re-affirmed all of my mechanical components were correct, I pulled the engine as you recommended earlier on in our thread...the engine is good no pitting very smooth and it's still fairly new. Basically, It's definitely a short in the FC6250HX as agreed by many other club members who were there to see the servo jerk erratically. Additionally, with my P gain at default 85 and I gain up at 100 and higher the tail servo consistently drifts towards the tail even if i'm not wiggling the servo wire at the unit. The higher the setting the faster the servo drifts back. When I adjust the "I" gain down...the lower I go the slower the servo drifts back...at about 20 or less the servo seems to stop drifting back. Not sure if that plays a role in my tail problems; however, the erratic tail jerk and twitch from the unit acts just like it does when hovering, which leads me to believe that the problem is rudder channel inside the FC6250HX...both tested tail servos are good, the mechanics & engine are good, my cyclic servos, programming, and flight control are good, all works well except that tail servo plugged into the rudder channel. Is there a number I can call to request a replacement? I'd be happy to buy a new one and send this one back...and once confirmed that there is no damage to this unit, could I be reimbursed? Again, thank you Brian for taking the time to help me on this...seems I cant get any help calling Horizon Hobby.
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Old 06-15-2020, 07:03 PM   #14 (permalink)
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Thank you for the information, very helpful.

Its been a few years since I have run a BLS254 but I am still using a few BLS251's. My best guess based on end points and tail authority a good starting point is P=150, I=150 and D=5. Just to note these gains only apply to the older futaba bls tail servo, they perform extremely well but require higher than normal gains.

If the tail servo drifts from center to stop in less than 30 seconds do the calibration step. If it takes longer than 30 seconds then you are okay.

The slow drift is a very small error building up at a very high frequency, I am working to address the slow creep and making sure it does not impact the tail performance. The slow creep will not affect the tail hold at all in flight, the error is infinitesimal.

Try connecting the bls254 tail servo to one of the swash ports on the fc6250hx, I suspect the servo on the new port will show the same issue. You could also plug any newer digital servo into the fc6250hx tail port and test as well.

I am thinking it might be a logic level issue, some older servos run 5v logic level and most newer ones run 3.3v.

I ran into a similar issue earlier this year on a older 50cc airplane when installing a gyro system, the s9156 servos on the aileron showed random twitching on small inputs and gyro corrections and the s9155 elevator servos showed no issues at all. Eliminating the extensions addressed the issues on the s9156's however I needed the extensions so I ended up replacing the s9156's with newer digital servos and no problems since.

I have not seen any issues on the older BLS251, BLS252 and BLS253 servos but it is possible the BLS254 might be the exception.

The fc6250hx could have a bad connection in it but it is easy enough to try the bls254 on other ports to try and validate this, nothing worse than installing a new fc6250hx to see the exact same problem occur.

Nitro .91 I would recommend 4 layers of 3m 4010 Clear stacked and a velcro strap to compress the tape a little bit. This combo provides the best vibration absorption for nitro engines. The 3M 6mm white tape provided does work on most models but I find the 3m 4010 clear works better on nitro models.

https://www.amazon.com/Scotch-Perman...2265320&sr=8-1

I believe most walmart's carry it as well.

Make sure it is the 4010 clear, the 4011 grey is just to stiff for our purposes.

Thanks and Best Regards,
Brian Bremer
Horizon Hobby, LLC
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Old 06-16-2020, 06:00 PM   #15 (permalink)
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Default FC6250HX short in the rudder channel

Thanks, Brian,

I already purchased a new one to try it one more time....if the second unit works ok with the added tape and strap I will send the first unit back to Horizon Hobby. I haven't heard of anyone else having this issue, which is why I think I just got a bad one by accident. I will get this new one in place as you described and see how it goes. I assume that since my transmitter forward programming already has the values set for trim, end point, direction etc. that all I need to do with the new FC6250HX is to plug everything in and bind to it correct??
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Old 06-16-2020, 08:00 PM   #16 (permalink)
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The parameters are stored in the fc6250hx, forward programming just provides a interface to adjust the settings so you will need to take note of your settings and transfer them over. Or just set the new one up per the manual steps.

I have heard of one similar case on older digital swash servos

Let me know if you run into the same issue on the new unit.

Thanks and Best Regards,
Brian Bremer
Horizon Hobby, LLC
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Old 06-23-2020, 04:01 PM   #17 (permalink)
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Default FC6250HX short in the rudder channel

Brian,

Turns out that the new FC6250HX FBL unit works perfect with no twitches. I programmed it to match the original one and no servo jumping or movement even while lightly tapping on it. The tail stayed relatively solid in 6-7mph winds on stock setting and minor adjustment to about 100 as you said seemed good. Put several flights up on Sunday and no tail issues. Now that the tail problem is solved with the new unit; is there someone I can call at H.H. to explain the issue with the original one and see if I can get refunded or at least have the original one fixed?
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Old 06-23-2020, 05:14 PM   #18 (permalink)
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Glad to hear you have resolved the issue, also glad it wasn't the servo pulse voltage.

The best option would be to contact product support and please let them know I want the unit for evaluation. You can mention my name and if they have any concerns with the defective unit they can contact me internally.

They should be able to arrange the return and credit once the unit arrives as well.

Best Regards,
Brian Bremer
Horizon Hobby, LLC
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Old 06-24-2020, 08:30 AM   #19 (permalink)
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Default FC6250HX short in the rudder channel

Thank you Brian,

I'll attempt that today and if you could, I'm interested in what you find out when you inspect this.
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Old 06-29-2020, 04:00 PM   #20 (permalink)
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Brian,

Quick update....Since the date of my last reply, I called customer support and waited as long as I could before hanging up. I emailed Horizon Hobby Product Support regarding the return of the defective FC6250HX FBL unit as we discussed and included my contact information; however, I have yet to get a return email or call. I requested information of who I needed to send the unit to and where along with your request for it to be forwarded to you for inspection. So far I still have this unit and no contact with Horizon Hobby Product Support. It seems that the customer support from Horizon Hobby after the sale has declined drastically; although you are the exception and by no means aimed at you. If you can send me an address where I can send this FC6250HX unit so that you get it for inspection please let me know and I'll send it right away.
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