BobCat Elevators
 

I am finishing my BobCat and I have two questions/problems:
1) The elevator servos do not travel perfectly in synch. I am using JR 3301's with a 10X transmitter programmed for dual elevator servos. I can get the center and endpoints matched up but they seem to travel at different rates, with one servo lagging in the middle then catching up. The linkage geometry is as good as I can get it. Does the Matchbox solve this? Or is this even a problem? I have used dual elevator systems before without any problems. I guess I just never noticed the difference since the elevators were farther apart.
2) I have never used a gyro, but I have heard lots of rumors lately. Which one should I buy?
Thanks for any help.

BobCat Elevators
 

Spence,

What you are describing is normal. Once verything is set up I would go to screen 24 (servo speed) and dial down the speed of the faster servo until they travel very close to the same speed. I want to say I have one servo set at normal speed and one set at around 271 degrees for the two servos to travel at the same speed.

John Redman
Team BVM, Jet Cat USA, Shutlze Chargers

gyro
 

Roger

Check with Kevin W. about a gyro. Kevin is having good luck with the one he is using. I going to use the same one.

BobCat Elevators
 

One of my elevator halves travels farther than the other. No noticeable issues with this. Thought I'd see a change when pulling up hard, like in a loop. No problems. Also, I flew mine 5 times before installing gyro. Not really sure it's needed. If you want to test fly over here in Dallas, let me know. We have a new field east of Denton.

Good luck with it.

Mike Jensen

Re: gyro
 

Bob,
What gyro is kevin using?? Almost lost my BC last outing when the JR460T locked the rudders at full deflection :stupid: Somehow...I managed to get it home safely.....

Todd

BobCat Elevators
 

kevin is using the gya 350

http://www.futaba-rc.com/radioaccys/futm0807.html

i'll let him elaborate on the way he has it set up. an automatic "heading hold" kicks in that you want to avoid.

Re: Re: gyro
 

Hey Todd - what rudder servos are you using, how many cells in your battery, and are you using a regulator (if so, what voltage).

David Reid, Vernon, and myself all had this full-deflection problem happen with 3421 servos and an unregulated 5-cell pack. Installing a regulator seemed to cure the problem, and then shortly after that BVM started recommending a different rudder servo - perhaps partly because of the above issues, and partly because BVM rep Harley Condra managed to melt his servos.

BTW, I have the 450, not the 460 - not sure what DavidR et al had.

You might also want to look at what gain you are using. Following our full-deflection issues (discussed here at great length on at least two different threads), a lot of people were recommending backing away from the very high percentage gains that were common at the time.

Gordon

BobCat Elevators
 

FWIW, I am using JR 8417 servos on my rudders in the Bobcat and the old JR 450 gyro. Settings are 5% rate for gear up and 60% rate for gear down.

Also running 2 1700 mah 4 cell batteries wth regulators.

John Redman
Team BVM, Jet Cat USA, Shultze Chargers

BobCat Elevators
 

Gordon,
I hear ya and remember that thread well! This was not a servo lockup but a gyro lockup. Here is what I have installed:

JR460T Gyro
JR8411's on rudders
5 cell 1800mah receiver pack
MH 5.2volt regulator

I am running about 40% gain gear down and 0% gear up. The gyro went full left deflection with the gear in the UP position?? I did have some concerns about this gyro since I would have to sub-trim the rudders every day I went out, depending on the temperature the rudders were always out of trim either to the left or right. Once trimmed for the day all was fine. I was performing some low speed vertical snaps just before the gyro went south, once the rudders went full deflection the plane snapped on me several times in level flight. I fought the snaps trying to get myself lined up to land. I then dropped the gear and the rudders centered and allowed me to land. With the gear up the gyro deflects full left, gear down it is fine. Last time I will be using a JR Gyro :-(....
Todd

BobCat Elevators
 

I have two 5 cells with regulators. 460 gyro, 0 gain at wheels up and 35% wheels down. using the original BV recommended servos. 35 flights so far and no problems.

Mike Jensen

BobCat Elevators
 

Hey Todd;

I do not want to insult you, but when you turn on your plane you must NOT move the plane for a few seconds. That time allows the gyro to find center. If you turn the plane on and move the plane or bump it in any minute way, your trim will be changed every time. This MAY be part of your trim problem. (Some Peizo gyros drift due to temp and loose mounting too)

My Bobct has a dutch roll on take off. Right after the gear is up, it flys great. On windy days, I need almost 100% gyro gain to stabalise landings.

Also, I had the same problem on my elevators servos NOT tracking well, it showed up in loops and pull ups. I ended up with gluing a half an inch tab to the bottom of the faster elevator (one elevator side only) at the trailing edge. That allowed true tracking when moving up.

BobCat Elevators
 

I never can remember that number for some reason. :D

This gyro uses the ATV on the controlling channel to adjust the gain (from -100% to +100%), the AVCS (futabas goofy heading hold function) kicks in when the ATV on the contrilling channel goes anywhere above +60%. You want to make absolutely sure that the AVCS is not able to come on!!!!!!

I have mine set to go to as much gain as possible without AVCS coming on (probably about +60%) when the gear is down, and 0% gain when the gear is up. The gear channel is Y'ed to the gyro to control gain, this creates problems since it is neccessary to adjust the gain of the gear channel to properly control the gyro, but then the gear servo will be out of adjustment for proper throws to move the retract valve. I had to experiment with servo arm length and linkages between the retract servo and the retract valve to get it to operate correctly without binding. This would not be a problem if you were to use a seperate channel to control the gyro gain. If you have a radio that allows you to disable switches you could mix the gain control to the gear channel and not even have to worry about any other switch positions, my radio (PCM10SX) does not have this function so I chose to use a Y and avoid complicating my preflight and landing checklist.

BTW, for what it is worth I am using 9011 servos on my rudders and a single 4-cell (2400 mah) battery pack.

BobCat Elevators
 

Ehab,

No insult here :-). Yes, I am aware that you have to pause during power-up for the gyro to find center. Problem is, center was never the same from day to day and I always had to sub-trim the rudders for first flight of the day. The gyro is securely mounted as well. This is definitely a defective gyro.....

Todd

BobCat Elevators
 

Todd,

Other than the PITA setup of the GYA 350 and the gain which is limited by the useless AVCS on the upper end of the scale I have been very happy with it's performance. It centers perfectly ever time, even with the huge variations in temperature that Texas weather requires us :D to fly in. I have around 60 flights on my Bobcat with no (knock on wood) gyro problems.

BobCat Elevators
 

Thanks for the info Kevin, I ordered the 350 on moday so I should have it soon... Hope this eliminates all my gyro issues :-)

Regards,
Todd

Bobcat
 

I had the JR gyro for the first 5 flights in my Bobcat, I had problems with it centering(I had to keep trimming the rudders before each flight), I tried different gain settings with my radio but it did not seem to correct it, I switch to the Futaba gyro and use the same settings that Kevin is using and have had ZERO problems with the rudders.
I did have an experience this past weekend that concerned me. I did a level high speed pass over the runway, when I got to the end of the runway I went to pull up and I had to pull the stick all the way back to get the plane to respond. I have read in other posts that a few Bobcats have been lost to elevator failure, I also talked with Kevin, he has the same experience pulling out of a dive. Has anyone else experienced this?
I am going to switch to JR9411 servos on my elevators, These are higher in torque(82oz vs. 56 oz with the JR3301)and they also have metal gears. I just don't want to lose my Bobcat to servo failure, I enjoy flying it to much.
Roger you will love the way the Bobcat flies. Post some pics of your Bobcat when you finish it so we can see it.
David

BobCat Elevators
 

Getting full gain without heading hold from the GYA350, or any other Futaba gyro is quite easy.

If the gain control channel is set to -100% you get 100% gain in normal mode. Set the control channel to +100% and you get 100% HH gain. Set the control channel to 0% (the center position) and you have zero gyro gain.

If you want 50% normal gain, set the gain control channel to -50%.

If your radio displays the channel output as 0% to 100% instead of -100% to +100%, then the gain would work like this:

Radio
Settingʰʰʰ Gain
===============
0% ʰʰʰ 100% normal
25% ʰʰʰ 50% normal
50% ʰʰʰ 0%
75% ʰʰʰ 50% HH
100%ʰʰʰ 100% HH

BobCat Elevators
 

:thumbup:


Thanks for the tip Phil!!

Todd

BobCat Elevators
 

The problem I had/have is that I am using the retract channel to control gain (two position switch) and without reversing the servo (or changing the mounting and linkage) the gain would only go the the side with AVCS (HH) with the gear in the down position.

I have no problems with the way my airplane is set up and flying now so I don't really want to mess with it, but I do realize now that there are some other options for setting this gyro that might be a little easier.

BobCat Elevators
 

Thanks for all the help guys. I'll let you know how it works out.

BobCat Elevators
 

For others out there, Horst Lenerz's electronic retract valve is handy is this application, use the gear channel to set the gyro gain, and then you program the retract valve, both direction and pulse width, independantly.

df
 

Todd
I remember Tony F. saying that when the rudders deflect full left in flight it's like the Gyro was shorted out or turned off and on again. Similiar to power up before flight. I'm just about done with Bobcat #2, when I went to get servos and another 460t, the price seemed low. The hobby store clerk told me they were being discontinued and didn't know what the replacement would be. I hope someone comes up with a remedy.
Scott

JR Gyros
 

The 460T problem that you all are encountering is nothing new. I bought a 460T when they first came out and almost lost my bobcat to the problem. I put the problem out on here and had everyone swearing up and down that it was ME with the problem and not the gyro, I even had one of the JR Reps that prowl the board saying that it was a superior gyro and that it was probably my fault. Since then I sold both of my 460T's and was lucky enough to buy a JR 450 gyro which works flawlessly.

As far as futaba gyros everyone that I know who has used them has fallen in love with them.

As far as JR products I think they are having some serious problems with quality control. After losing my bobcat to a faulty elevator servo I have gone to hitec. I am not trying to start a flame war but for the company that is supposed to make the best servos and gyros they have been quite marginal lately.

Just my .000000025 worth.

patrick.

Servo
 

Patrick,
What servos were you using and what hitec servo are you going to use?
David

servos
 

David,
I was using what was recommended by BV. Now I am going with the hitec 5945(?) 180oz all the way around. I am also going with flaps on this bobcat so I won't need the gyro.

Patrick.