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HelicopterRadio - Spektrum DSM › DX7 + swash mix EXP setting + Sub trim
06-03-2009 02:17 PM  8 years agoPost 1
LaurenceGough

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UK

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Hi guys,

I know the swash mix EXP setting adds some expo to the centre of the servos travel, so the feel is more linear.

Does it allow for sub trim? What I'm saying is that if you have 20 points of subtrim on one servo would it off-set the servo EXP 20 points of subtrim?

I keep hearing EXP is good all the time but then I read that RC heli mag tested it out and it doesn't work with sub trim.

Anyone know?

Thank you.

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06-03-2009 02:25 PM  8 years agoPost 2
cbflys

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Nesconset, NY - USA

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When you enable EXP on the swash mix, it does as you state - produce a more linear travel in the pushrod with respect to stick movement.

The sub-trim does offset the center, so you have nothing to worry about there. The problem with the DX7 when sub-trim and EXP are used is that there is a very small error introduced and as a result will produce an equally small amount of interaction. The higher the sub-trim value, the more the error. So if you keep your sub-trim value very low, the interaction is negligable.

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06-03-2009 02:33 PM  8 years agoPost 3
LaurenceGough

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UK

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Humm, thanks for the reply!

I think I'm going to have to try mine off, I have to use quite a bit of sub trim on my heli due to the way it is designed (front cyclic links can't be equal as servos are angled to the side). Not to mention the horns can't be 90 without sub trim.

I'm also going to take all the servos out and re-grease them with the hitec lithium grease. (Giving them a clean first)

Edit:

My subtrim currently is Aile L10, Elev U12, and PIT L20.

I guess this is too much?

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06-03-2009 02:59 PM  8 years agoPost 4
cbflys

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Nesconset, NY - USA

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That's not an overly large amount of sub-trim. You should be fine leaving EXP on. You can try setting the sub-trims to zero and rotating the servo arm on the spline until you have it as close to 90 degress as you can get it. Then you should only need a very small amount of sub-trim to get it at exactly 90 degrees.

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06-03-2009 03:01 PM  8 years agoPost 5
LaurenceGough

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UK

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Thanks, but would the EXP setting (built in coding) still be effected by the sub trim? I would imagine that if it doesn't compensate for the sub trim there would be loads of problems caused..

I can't lower the sub trim any more I'm afraid .

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06-03-2009 03:22 PM  8 years agoPost 6
cbflys

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Nesconset, NY - USA

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It's not very bad at all, in fact - you probably won't even notice it.

You can look at the interaction yourself by moving the cyclic and seeing how much the swash ball travels up and down on the main shaft. Try it with and without the EXP enabled and you should be able to see the difference.

You will probably have to re-level the swashplate when switching between EXP enabled and disabled.

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06-03-2009 09:57 PM  8 years agoPost 7
Micro-Maniac

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Pasco,Washington Formerly: Captain Chaos

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JKos tested the DX7 for this - Here's a post of his results

http://www.runryder.com/helicopter/p3156249/

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06-03-2009 10:14 PM  8 years agoPost 8
RAK402

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Alhambra, CA

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"Thanks, but would the EXP setting (built in coding) still be effected by the sub trim? I would imagine that if it doesn't compensate for the sub trim there would be loads of problems caused..

I can't lower the sub trim any more I'm afraid."

The interaction caused by the use of sub-trim with Swash Expo enabled exists, but has become spectacularly overblown.

The amount of CCPM interaction created by using sub-trim with swash expo is insignificant compared to the interactions created by not using it. You are converting a rotary motion to a linear motion by the servo moving a push rod. When the servo is near center (near 90 degrees to the push rod) a few degrees of rotary motion will translate into a specific amount of linear motion to the push rod. As the servo rotates to either extreme, less of its rotary motion is translated to moving the pushrod in a linear fashion. Depending on what maneuver you are doing the different amounts of push rod movement from the three cyclic/collective servos at different positions in their arc of movement can be quite significant.

Swash Expo, to some extent, compensates for this.

Try an experiment:

Without Swash expo activated, hold full aileron and raise and lower the collective while watching the swashplate. The swashplate will do a sort of a hula as it raises and lowers. Note the position of the servo wheels and how much they move the push rods.

Try the same experiment with Swash Expo activated-there will be much less deviation in the swashplate than without.

Bear in mind that activation Swash Expo will decrease your overall collective range, so check this and reset it accordingly after activating Swash Expo.

The helicopter will be slightly slower, but smoother in response. There will be far less deviation in maneuvers such as axial rolls.

Team KBDD/Compass Team Manger/Experience RC/Team JR Americas/WR Field Rep

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09-05-2009 10:02 PM  8 years agoPost 9
200lappen

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Lapland,Sweden

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Work-around for the swash mix EXP setting + Sub trim bug in Spektrum
I can confirm the bug exists as others have noticed.
I found one method to keep swash mix EXP setting wich is good for the linearity of the swash movement. Simply don't sub trim, because it doesn't work right. There IS a bug in the radio if You use swash mix EXP setting.

Just leave sub trim at zero and do the necessary trim with the main trim switches on the front of the radio. You might perhaps need to trim a lot so the display indicator vanishes-but do trim as much as You need.
This main trim is not a afflicted by this bug - only the sub trim is, according to my observations, anyone against?

I have learned to follow these simple two rules to successfully setup the eccpm on my DX7/AR7000 radio combo, but I guess they might help anyone using any JR or Spektrum DSM2 gear:

The Manni Rules

1. All three swash servos need to be set to equal travel adjust, both positive and negative. I.e. positive travel adjust=negative travel adjust and same values on all three servos. Find the least common denominator that works good enough for all three. Period.

2. Sub trim needs be set to zero irrespective of any mechanical offsets You might have in Your setup. Do the best You can mechanically but leave the adjustments to the main trim switches on the front. Period.

The setup might not be perfect for the purists but for those flyers keen on linear feel on the sticks will be rewarded.

Manni
Gaui 200
Spektrum DX7

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HelicopterRadio - Spektrum DSM › DX7 + swash mix EXP setting + Sub trim
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