jackalope54

My Feedback: (2)

Hi all. I'm pretty much a newbie to flying (advanced beginner) and am very interested in Pattern flying - VERY impressed with the control demonstrated by Pattern pilots and the quality of their aircraft.

I bought a Venus II and installed standups on all control surfaces - my first plane so equipped. I could not get the aileron clevises over the hinge lines and 1 control rod is 2mm longer than the other (meaning there is a 2mm difference in the distance from the servo output shaft to the standup between the left and right ailerons). This obviously introduced a lot of differential. No problem on HIGH rate - just adjusted the End Points as needed. The problem showed itself when I tried to set the LOW rate - excessive differential. Being new, I attempted everything mechanical and electrical I could - offset the servo arms, changed the control arms, drank too much beer thinking about it, etc. - all to no avail. Asked in Futaba radio support forum but was unable to follow their solution (re Linkage-induced differential - oldest thread). My servos are on separate channels so I am using AILE-DIFF as the wing type.

After speaking with a number of friends about it (looking for a transmitter programming solution but finding none), reading and rereading my manual (I have a 10C), I read the Futaba 14MZ online manual to see if that radio has a feature to program out differential. I found no procedure but noticed a statement about RATE that is used to correct linkage problems - no examples were given, however, for its use. I remembered seeing the word "RATE" in my manual in the AILE-DIFF section so thought I would explore this further - couldn't hurt at this point, right?

I discovered what more-experienced Futaba users probably all know - that changing the RATEs in AILE-DIFF (or in FLAPERONS) can correct mechanical differential issues. I've never before paid attention to this screen as I've always been able to get control horns on the hinge lines.

This adjustment has given me a new setup regimen that I would appreciate some comments about.

1. Start by setting Dual Rate switch to High Rate
2. Set subtrims to zero and end points to maximum in both directions
3. Center the servos achieving minimum Subtrim
4. Adjust RATE in AILE-DIFF or FLAPERONS screen (whichever you are using) to achieve required HIGH rate control surface deflection in both directions
5. Now set Low Rates - there should no longer be any differential

This worked on my plane. I'm wondering now how RATE affects the servo, ie. do higher RATE values give better resolution or more torque or longer servo life, etc? Or none of the above? Any other comments concerning this regimen? And finally, what precisely does RATE do - how does it differ from End Point and are Dual Rates a percentage of the End Point values meaning that the left AND right aileron servos MUST have the same values to prevent differential?

Thanks in advance for your help!!

cmoulder

Not sure what you mean by standups(?) Control horns??

Always it is best to do whatever it takes to get the control linkages as closely matched mechanically as possible and servo arms at the same angle (reversed left and right, of course), before beginning any radio programming.

Forget differential at the initial trimming stages. You never know how much you will need until flying the model and observing its flight characteristics.

Use a [link=http://www.hppilots.com/main/page_product_gallery_3d_pro_info.html]surface deflection gauge[/link] to set up control surfaces. It is virtually impossible to get control surfaces to match mechanically, so only by measuring with some sort of gauge will you know the surface travels match. Any time you see a radio programming screen with all the up and down values matching, you can be almost 100% sure that the travel amounts are NOT identical.

jackalope54

My Feedback: (2)

Sorry for the nomenclature confusion - was told the control horn that is just a long bolt that goes through the control surface was called a standup.

I did use a deflection gauge to make sure I have equal movement in both directions on both HIGH and LOW rates and yes, the END POINTS are the same on both surfaces - by adjusting the RATE in the AILE-DIFF screen to the high rate deflection needed, I didn't have to change the end point values for either aileron. The RATE values ARE different for both ailerons.

Trying to figure out what RATE actually does compared to End Point. In this application, seems like End Points are just a baseline for the Low Rates IF the low rates are just a percentage of the end point values.

I know - I'm probably making this as clear as mud.

Thanks

bjr_93tz

A really ugly way to fix your problem if you simply CANNOT do it mechanically first is to run a single aileron setup for the left wing and mix the right hand wing servo in with a point curve.

Personally I'd never do this but it would work and you could use this to get your differential as well if your plane needs it. It's a really clumsy method but if your linkages are way out and can't be corrected it may be your only choice.

Flaperons would require clumsy mixes as well...

cmoulder

End points merely "tell" the servo what the absolute maximum travel range is. This is a nice safety catch to make sure you don't exceed the mechanical range available and stall the servo, possibly burning it out.

To get best possible resolution, the highest rate you use will of course be somewhat less than the end point. If end point is 140%, high rate may be about 125%. You want to leave a little "wiggle room" to match surface deflections at max. Position the servo linkages on the servo arms and surface control horns to use as much of the available travel range as possible on high rates.

Back to your original post, with the threaded rod type of control horns, if the distance from the surface of the little plastic fittings is different, simply screw in the one that is farther out until its distance matches the shorter one.

jackalope54

My Feedback: (2)

Wow - I really am being clear as mud!

Bjr - this whole exercise in frustration began because I was trying to get RID of mechanical differential. I didn't get the control horn clevises on the hinge lines. To fix it mechanically, I would have to remove the control horns, drill larger holes through the ailerons to allow angling the control horns enough to get the clevises on the hinge lines and either fill in around the control horn bolts with epoxy or glue in CF tubes of a size the bolts would fit through at the proper angle.

Bob - I did make sure the distance from the aileron up the bolt to the clevis is the same on both ailerons.

The 10C radio only allows high/low rates to be set on channels 1-4 - therefore the aileron on channel 1 "controls" the low rate setting - if there is ANY linkage geometry difference between the aileron on channel 1 and the aileron on the other channel it CANNOT be adjusted merely by setting different Low Rate values for the aileron NOT on channel 1. You just can't get there from here. :-)

Bob - what APPEARS to be happening is RATE sets the maximum arc/travel of the servo. End points then seem to work within that RATE-limited arc. In other words, RATE seems to override End Point. As the Low Rate seems to be just a percentage of the End Point value on channel 1, the End Point values MUST be the same on both sides. Adjusting RATE values to give the maximum deflection needed allows me to set the End Points to the SAME values on both ailerons and remove the linkage-induced differential.

The downside is I'm not using the full travel of the servo since I only need 18 degrees of deflection on High Rate. I have the control rod attached to the innermost hole on the servo horn - next step is getting taller/longer control horns. I'm assuming that the highest RATE values will give me the best resolution and the maximum torque.

Anyway, thanks for your help!!

OhD

END POINTS allow you to set the servo end points for each channel just like SUBTRIM allows you to set the neutrals for each channel. For example you can set the end points on the right aileron without affecting the left aileron. On functions like ailerons and elevators where you have a servo on each surface you want to set subtrims and endpoints first so that the elevators, etc., track from one end to the other. Once that is done, never touch the end points again, unless you change servos.

RATES or AFR on Futaba are used to set the travel of a FUNCTION. When you set the aileron AFR/DUAL RATE you will set the travel of both ailerons just as adjusting the normal TRIM adjusts both ailerons.

Normally one sets the endpoints to some value that is more than one expects to need and then sets AFR for high rate and dual rate for low rate.

Hope this helps.

Jim O