New Airtronics RDS8000 FHSS System - Exp and D/R ??

[Rc_HeliPilot]

I just bought a new RDS8000 2.4Ghz system. I'm generally happy with it so far, but I was disappointed to learn that, for helis, the EXP and D/R switch has no affect. The switch only applies to fixed wings.

Global Hobbies says that you set EXP and D/R for the flight mode (i.e., normal, idle-up 1, idle-up 2) and that's it. You can't just switch it off or switch between two settings.

I was able to do this with my Futaba EX6.

Is this as much of a short-coming as it seems to be? Do you think this is a bad design?

[tz250w]

I'm using both the RD8000 (FM) and RDS8000. The selections are pretty much the same as far as I can tell so far. I guess I'm not quite sure what you're getting at. I only use flight modes, not D/R. Do you mean you want to set different EXP for all flight modes and all D/R modes individually?

If so, my next question is... why? But I can see that if you had that ability in another radio, you might think it's a "shortcoming". Futaba often has zillions of settings that most people don't use (or need). Cool for those that like all the bells and whistles but I get along fine with mine.

Besides, more than two toggle switches to poke and I'm starting to get nervous...

[Farrell]

Hey guys,

Just so you know, the c-mixes can be used for some cool stuff. Mix elevator to elevator ... and you can get elevator dual-rate that can be toggled with the c-mix switch. The same is true for aileron to aileron.

As a side note, c-mixes come in handy if you want to remove CCPM interactions too. Mix pitch to aileron, and/or pitch to elevator.

-Farrell

[Rc_HeliPilot]

Hi Farrell,

Can you elaborate on eliminating interaction with c-mixes? I've read that the Futaba 7C has this feature. How do you approach it with c-mixes on the RDS8000?

[Farrell]

I'll start out with a short into. CCPM interactions occur when one or more of your swash plate servos travel just a little bit more or less than the other servos. Due to the nature of the beast, every servo is slightly different. For example, one servo might rotate up to 60 degrees, while another identical servo might rotate up to 61 degrees, perhaps your third servo rotates up to 59.5 degrees...

What this results in is interaction. When you give full collective (left stick up) you will get full collective pitch, and maybe a slight tilting of the swash plate. So you might get a small elevator or aileron input, despite the fact that you did not intend to have that effect. The same is true for negative collective (left stick down), you may get some elevator or aileron effects. The effects are usually small, only a few degrees of tilting, or less.

My current CCPM heli, a Dragonus II N-Plus with Airtronics 94091Z servos, does not have any noticeable CCPM interactions, but I'll fake it for the sake of this example. See the photos below. Imagine that your swash is perfectly level at mid stick (zero degrees collective), but that it tilts forward at low stick, and tilts backward at high stick. Essentially, when you ask for negative collective pitch, you get a slight forward elevator input. When you ask for positive collective pitch, you get a significant backward elevator input. To keep this relatively simple, we are going to assume we have no aileron interactions.

http://rcheliguy.com/images/rds8000_cmix/before.jpg

So now we know what we are trying to eliminate. Lets make a simple plan, with some educated guesses:

- When I am at low stick, I need to mix in a little back elevator
- When I am at high stick, I need to mix in a lot of forward elevator

So we navigate to the ETC menu, and down to the first C-Mix screens. For each c-mix you have three screens to play with as you navigate down through the ETC menu.

The first screen will say "MAS c-mix, 1: xx" This means you are on your first c-mix, and selecting the master channel. Since our interaction is the result of collective pitch commands, you want to set "MAS" to "PI".

Next we navigate to the next screen down in the ETC menu, and it will say "SLV c-mix, 1: xx" This means you are setting the slave channel for your first c-mix. Since we want to cancel out an unwanted elevator input, set it to "EL".

http://rcheliguy.com/images/rds8000_cmix/rds_cmix1.jpg

OK, so now your RDS8000 knows what channels it will mix, now it needs to know how much mixing it should do. Go down one more screen in the ETC menu. Now it will say "P->E c-mix, 1:xxx%" and there will also be a small arrow pointing up or down, located above the percentage. Move your left stick up and down. The arrow will point up when the stick is at the top half, and the arrow will point down when the stick is at the bottom half.

http://rcheliguy.com/images/rds8000_cmix/rds_cmix2.jpg

Looking back at our educated guesses, we want to mix in a little back elevator when we are at low stick (negative degrees of pitch). Move your stick to the low position, and use the INC/+ button to raise the percentage value from 0% to some value. I ended up with 30%, but keep in mind I over exaggerated my interactions to make it obvious in the photos. You may use less than 5-10%...

Do it again with the stick at the high position, and in my exaggerated example I had to use 100% mixing to counteract the massive backward tilt when giving full collective. You can use negative percentages if the tilting was in the opposite direction...

Keep in mind that the C-Mix switch on the front of your transmitter needs to be in the up position to have an effect. The up position turns on both C-Mix's, and the down position turns off both C-Mix's.

The final result should be a level swash plate at low, mid, and high stick.

http://rcheliguy.com/images/rds8000_cmix/after.jpg

This long winded post might make it appear really difficult, but it's not. It's trivial... Just play with it for a minute, and you will quickly see how it works.

-Farrell

[Rc_HeliPilot]

Thanks a lot, Farrell. It doesn't look difficult at all. I really appreciate all the trouble you went to to explain the technique.

I've used Bob White's videos for eliminating interaction using interaction using sub-trims with my former radio system. Would I just focus on achieving a level swash using my RDS system and not worry about using a bubble level in the process?

Thanks again,

Chris

[Farrell]

You can use a bubble level on the paddles to get that extra bit of precision, but I have not found it necessary. Bob mentions optionally using P-mixes to remove all of the interaction, including the interaction you get between low and mid stick, or mid and high stick. I believe that would entail mixing abilities such as curves for elevator and aileron. The RDS8000 does not have the ability to setup a curve for mixing, only two end-points.

At the end of the day, a level swash at low / mid / high are about as perfect as the majority of flyers will notice anyway, and it seems Bob agrees (based on him comments in the video.) Fell free to chime in, Bob, if I'm wrong.

-Farrell

[Tyler]

I use a little bit of expo, but I don't use dual rates. I learned long ago that setting up helis with the most simple programming is very beneficial: straight line pitch curves, linear throttle curves, one stunt flight mode, one regular mode, and throttle hold. I also fly with one headspeed all the time. Therefore and RDS 8000 is advanced enough for "MY" needs.

Tyler

[Rc_HeliPilot]

Thanks again. I appreciate both additional tips.

Chris

[b terry]

and i played with the swash settings and did not need to mix elevator, had the wrong swash setting. going by the manual. if your two front servos do not go down when you apply foreward evevator, you have the wrong setting.

[Rc_HeliPilot]

What swash setting were you using? I have a 120 degree CCPM configuration with the elevator servo on the tail side of the main rotor.

Thanks

[b terry]

also have the trex 500. there is only 2 settings you can use, the other 2 will not move the cyclic servos up or down with elevator.that is your problem as i did the same thing. then start reversing channels 1, 2 and 6. you will get the aerlion and pitch servos to move up and down with elevator.

[Rc_HeliPilot]

Right. I'm okay on my swash control movements. Thank you.

I notice that the servo arm travel on my swash servos appears to be a bit limited. May need EPA. I'll have to flight test to make a good judgement.

Thanks again.