Trex F.A.Q. Updated 4-24-2007

[Cryofix]

Scoopy I would love to see that but I cant write that as I am not totally sure about it

anyone interested?

[oscillator]

Cryo,

thanks for doing this. Could you add the formulas for computing head speed based on motor KV, pinon, etc?

Thanks,
Mark

[jasonak]

the 401 still is a little confusing to me,the part about 0 gain is that for all servoes or just for digital? the wholl 401 thing has got me confused to be honest,lol i watched the video but mine still not jiving but i dont have a 7chp either.

[BobRob]

Q: What should I do if my Center of Gravity is not right? Trim it out or try to adjust the CG?

A: If you trim it out mechanically or electronically it will only help when the heli is upright. The problem will be compounded when inverted.

For example - if you're tail-heavy the nose will try to pitch up (toward the main rotor) - you add foward cyclic trim, so the heli is now always trying to push the nose toward the skids. Now flip the heli inverted - you're still tail heavy, so the nose will still try to pitch up, but now that is toward the skids, the same place that your trim always has the swash pushing. Now you have CG and trim both forcing the nose towards the skids.

Much better to move stuff around to adjust the CG instead of using electronic trim or mechanical trim adjustments.

Bob (not Finless)

[p00rboi]

I'm in need of some alternate methods of checking the gear mesh. I'm using the jgf 450th and the motor is noticably tighter (notchy) so the head won't spin freely.

Thanks

[rdlohr]

Please add the info from that link that Bob put in answers to all the different REX types. That gets asked regularly.

Also, add "SA" to the list of gyro mounts I make.


Thanks
Rick

[rdlohr]

Collection of stuff I posted on other forums. Put what you want in the FAQ if its not redundant:

Here are some general notes to ponder for some of the newbies:

1) To avoid glitches, high current noisy electronics (like the ESC, motor,and Battery) should be placed physically as far away as possible from the low current electronics (like the receiver, gyro, and servos). The ESC to motor wires should be as short as possible and away from everything else to the extent possible. These wires are like spark plugs and they generate lots of RF noise that can affect the receiver and the gyro. (be aware that some motor wires are NOT made to be cut though). Following this philosophy will keep you the most immune to glitching. The new Spectrum transmitters and receivers are great for suppressing glitches also, but you should still do proper component placement.

2) Consider shortening your servo and gyro wires. Every wire is like a mini antennae for noise so the shorter they are, they less chance of picking up noise. Always leave a little slop in the servo lines to accommodate rebuilding your servos gears if you have to (especially if you don't have metal gears). Shorten wires by cutting off the connector and an installing new connectors. If your are skilled with a soldering iron, you can possibly reuse the existing connectors. NEVER try resoldering the servo or gyro end. Its too risky to be heating active components when a connector is so easy to put on.

3) Move the gyro off the top boom where the flybar can hit it. I've said it before, but it will get trashed. Its the most expensive component and not worth risking.

4) If you haven't watched the Finless video over on helifreak, you owe it to yourself to watch them. They will reinforce the best setup philosophies and allow you to dial in your heli on the bench to the point where you will hardly have to tune it at all in the field. Finless has spent many hours filming the entire build process and capturing some of his 20+ years of knowledge for us for FREE! They are very well done.

5) Get a set of gorilla gear for your landing gear. You will break the stock versions.

6) Consider getting a set of gorilla flybars. They fly great and are equally tough.

7) If you are breaking lots of stabilizer fins, consider getting a set of my fins. They are much more durable.

8) If you are doing any type of 3D, flips, loops, etc, get your headspeed up to 2800 or above.

9) The Align Pro 325 blades are great for newbies. They are cheap and the absorb a lot of the impact when you crash. mp-tech has even cheaper wood blades that also fly well. Throw out those Align Fiber blades. Most people feel they are only good for stirring paint.

10) Stock up your stocking with parts. Keeping extra main shafts, main gears, flybars, feathering shafts, main/tail blades, servo parts, frame parts etc makes crashing much less painless and you will be back in the air quicker.

11) Buy a simulator. G3 and Reflex are probably the most main stream, but there are other good ones out there. Get proficient at any new skill on the sim before you do it for real.

12) Take advantage of the knowledge on the forums. There are many people out there that have already fixed almost any problem you run into multiple times. Considering joining many forums, it gives you access to more global knowledge. We new guys have so much advantage over guys that were into this a few years back.

13) Try to fly daily weather permitting. Stop on your way to work in the morning, or go out just before dark. These are the times when the wind is lightest so it makes it a bit easier for you to learn. Fly the sim on days you can't fly outside. Buy extra batteries to get more flight time. Realize that these machines are quite hard to fly and if you don't fly often it will be really hard to progress. Also, its a blast!

14) Consider buying a backup heli so you can fly when you main bird has crashed.

15) Remove and Re-loctite every screw on your heli that came preassembled.

Good luck and enjoy those beautiful birds you've been posting!

[Cryofix]

rick ill get to these soon, just need some more time

[rdlohr]

No rush. I was looking at a lot of newbie pictures on RCGroups, and thought I should tell them this stuff. Since I went through the effort, I thought may be our FAQ may need some of it.

[Jermo]

Can you post a thing about headspeed? I have the excel calculator but I have concerns about blowing up my battery, overspeeding my head, underspeeding the head...etc
My setup will be:
T-Rex 450XL HDE (from kit )
Align 3550 motor
Align 35 ESC

Jermo

[rdlohr]

Here is a well written snippete from another thread by redgiki that could maybe find a home in the FAQ...


There are different head speed camps:

1. Bob "Finless" White's NEED MORE HEADSPEED camp. Usually, anything above 2800RPM at 0 pitch will satisfy this outspoken crowd. Anything above 3100RPM has a good probability of exploding your wooden blades, so you need carbons to be able to drive that high safely.

Pros: more headspeed makes your heli dramatically more stable and wind resistant, while giving you tons of power for extreme 3D manuevers and even easier hovering for newbies.
Cons: Your tail sometimes explodes in midair like it got on the wrong side of Al Qaeda, and if you crash the bird running that kind of headspeed it results in quite a bit more damage (particularly stripped servos) than a lower speed. Flight times are often shorter than 7 minutes, and tales of destroyed LiPos are common.

2. The Aerial Photography "How low of a head speed can I get away with" camp. These folks are all about duration and inertia. 335 Pro Wood blades are popular with these people, and head speeds as low as 1600-1800RPM aren't unusual. Who needs 20C batteries when some nice 8C 3100mAh batteries will do the same job for this sedate crowd? Lots of Sunday Hoverers in this group, and they have a devoted following.

Pros: Long flight times, fewer destroyed LiPos, and relaxing fun.
Cons: Lots of tales of severe tail wobble (direct related to lower headspeed), uncontrollable tail spinouts if you punch the collective hard, higher pitch required, and some difficulty with wind.

3. The In-Betweeners. This is me. Living somewhere between 2200 and 2800RPM.

Pros: Decent performance, reasonable stability, 8-10 minute flight times.
Cons: Often the worst of both worlds from a stability, wobblies, duration, and LiPo durability standpoint.

[Jermo]

2800RPM, 12v battery, 150gear, looks like a 13t pinion. I'm looking at the hex 3s 2200mah 20c 12v packs, I just want to make sure that I'm not over taxing the batteries, over loading anything..etc..
I'm still very new to the lipo batteries and all.. just got my Gyro today.
Jermo


edit: changed 6s to 3s
edit2: ok .I'm confused, 2800RPM is at full throttle, if I configure to hover at around %75 of throttle that gives me an estimated RPM of 2100. If I set max RPM at around 3000RPM that gives me 2250RPM around hover. My radio only has 3 point throttle curves (JR XF-622). At 11.1v with a pinion of 14 RPM is estimated at 2942max which at 75% throttle is 2207RPM. 2207RPM is still low compared to 2800RPM.

Am I missing something here? My goal is a stable bird for learning. I'll worry with 3d..etc in a year or so when I can get this down.

I'll read more. Seems to be so much general info that the specifics are lost on me.
Jermo

[rdlohr]

Another nice snippette by BaracudaHockey

In order to control a collective pitch heli we need to mix two controls onto the left stick, that is throttle and collective pitch.

The PC and TC tell how much pitch and throttle for a given stick position. In a collective pitch heli (CP) we want to maintain a constant rotor rpm and vary height by changing the pitch of the main blades. As you increase the pitch of the main blades you increase the lift they create but you also increase the drag so the rotor system wants to slow down so you have to add throttle to maintain rpm. As you decrease the pitch to descend you unload the system and if you dont back off the throttle the rotor will overspeed so you want less throttle. Your pc and tc setup the relationship between pitch and throttle.

Flight modes allow us to have differerent pitch and throttle settings for various types of flying with each flight mode switch position being programmed separately.

Normal mode is where we do most of our training. Normal mode shuts the motor off at low stick (electric) or goes to idle (nitro) for the throttle and increases as the stick position increases, at the top of the stick movement we should have full throttle. Hover position should be about 5 degrees of pitch and 50 percent throttle around mid stick (more on this later). Usually the pitch is set up for between -2 and -4 degrees at bottom stick 5 or 6 at mid and 9 or 10 at top stick.

Idle up modes are used for aerobatic flying (stunt mode is the same thing), you can have several idle up modes with different head speeds, dual rates or whatever for different types of flying.
A typical idle up pitch curve would be -10 at bottom stick, 0 at mid stick and +10 at full stick with upright hovering at 3/4 stick, inverted hovering at 1/4 stick. Your throttle curve would be 100 percent at bottom, around 50 percent at mid stick going back to 100 percent at top stick so that at bottom stick you have full negative pitch and full throttle and at top stick you have full pitch and full throttle.

Once you get used to flying in idle up many people set up their normal mode to hover at 3/4 stick by manipulating the pitch and throttle points so that the helicopter doesnt jump when you flip the flight mode switch.

Other flight modes can be set up for different head speeds, competition often requires a different feel for hovering etc but many of us spool up in normal, flip to idle up and go fly, land at half stick, flip the idle up switch to normal and let the heli spool down. Different people do it different ways and this is just the basics so you understand whats going on.

[Jermo]

I'm still not clear on pinion selection /head speed.
When we refer to head speed XXXX is that at hover or full throttle?
Jermo

[Cryofix]

Jermo

This will have to do with your throttle curves, between 50% and 100% you should be in 80-85 range on your curve. Check head speed at 80, 85, 90, 95, and 100 if you are in the area of 2800 RPM at 80 to 90 then you are in good shape.

There are 2 ways to achieve this also, one way is in standard switch mode your curve should look something like this: 0,40,80,90,100 where the 80 = mid stick. You can tone this down however to bring the throttle up to 60% at mid stick then flip into Idle up or sports mode, then your sport curve should look like this: 100,90,80,90,100. Each of the above has to be adjusted according to what head speed you at at a specific point on your throttle stick.

[steve28]

throttle curve at mid stick in idle up should be over 90 . 80 is too low in my opinion , your heli will be more powerful with the mid stick point higher . In Idle up the goal is to try and keep your throttle as constant as possible this is why some run their speed controls in govoner mode , so with that in mind an ideal throttle cuve inidle up would be some number over 90 straight accross , mabey 95,95,95 or 98 or 100 . My curve on throttle in idle up is 100 , 95 , 100 .
you dont want your headspeed to drop whenever your stick pases through center

[bstokes]

Small hint on setting gear mesh from car guys.....

Use a plastic bag, like a parts bag. Put this between the pinion and main gear, then tighten your motor. Pull the plastic bag out and your gear mesh should be perfect!

[supertrex2]

Small hint on setting gear mesh from car guys.....

Use a plastic bag, like a parts bag. Put this between the pinion and main gear, then tighten your motor. Pull the plastic bag out and your gear mesh should be perfect!

wow thanks for the TIP!

[s9joe]

thanks alot for taking the time and effort to do this Cryofix

[KillerKanopies]

There's some pretty hand info in here!

I'd like to touch back on blade tracking. I've been turning up the head speed over the last few flights and have noticed that the tracking changes every time. Not just a little bit either. Maybe a blade thickness or two.

What do I need to look for?