four servo eCCPM Intrepid ?

[jdewer]

Hello everyone,

Just some engineering questions :

- Would the upper airframe of the Intrepid EB be tough enough to handle the torque of a 4-servo (45°) eCCPM set-up ?
- Wouldn't that be a cool thing to try ?
- Is there a good reason to not do this ?
- Would trying that void my warranty (rethorical) ?

Have a nice day.

Jan Dewerchin.

[ShawnK]

Why in the world would you want to do that? The Intrepid series of helicopters has the most interaction-free control system of any machine on the market. Making it a CCPM helicopter (especially a 4-servo CCPM helicopter) would turn the control system into a imprecise, interaction-laden piece of junk!

[jdewer]

Buddykitchen,

I would like to try that because I believe that it's simpler, less subject to wear and tear, and, because of those properties, safer.
I don't think that a brand like JR would give their top 3D model (VIBE) an unreliable control system ( although that's a 3 servo system). Vario has both 3 and 4-servo systems, Henseleit Helicopters uses a 3 servo system, etc...

If you have detailed information on why a well-built eCCPM would be imprecise or interactionladen then please, share that information, don't just shout a phrase about how bad it is.

The Bergen control system is perfect as it is, it's just something I would like to try, for the fun of it.

Jan Dewerchin.

[PaulH]

Part of the reason for the interactions is because of the 120 degree connection points. Using 90 degree connections to the swash would (in my mind) reduce the problem considerably.

Now you have me curious: What would be the benefits of using 90 degree connections vs. 45 degree (swash turned 45* from where it normally sits). Obviously at 45* you would have all four servos working all the time for every input. That's a lot of torque! 90* would only have two servos acting for cyclic but all four for collective.

There are some 90* and 45* models out there. I'd love to see someone who has experience with these models chime in.

[jdewer]

PaulH,


Obviously at 45* you would have all four servos working all the time for every input. That's a lot of torque!

Hence two things : torque and safety. With a 3 servo-system, you can't afford to loose a servo, with a 4 servo-system, it won't be easy, but you have a chance to recover and land.
The biggest advantage for me would be : all servos working with every movement of the swash-plate, evenly spreading the load.

Jan.

[heliman53]

I have a Vario Panther which I am currently flying 4 servo ccpm but I originally flew it with three. The plus is greater servo power, and with four servo some redundency the down side is that at extremes of travel with cyclic you get interaction because some of the servo arms are closer to 90 degrees to the rods and the others are farther from 90 so you get differential in part of the system while not in the rest. At small movements (cyclic) it is less pronounced and with collective alone all servos move the same so no problem. I also have a Bergen Intrepid Turbine and would not wish to change the excellent control system it has.Craig B

[jdewer]

Craig,

How hard was it to get the servos that matched ? Is it true that you need a set of servos coming from the same production batch with serial numbers as close as you can ?

You mention a difference in rod positioning. Does that mean that not all the angles from which you go to the swash-plate are the same ? Can you describe the interaction between the flight-axis ? roll with nick or a more non-linear interaction.

When looking at the construction manual of a Henseleit MP-V91 ( available on the henseleit web-site ) it seems to me that even with a setup that is not exactly 90° all around , you can get a interaction-free system.

I'll try to make up a drawing of how I think it can be done, without interaction. Not sure when that will get posted, though :)

Kind regards,

Jan Dewerchin.

[heliman53]

jdewer, I have never had any problems with servos not matching although I have used only analog servos on my own helis. However at work on UAVs we have used both Futaba analog and Volz digital servos again with no problems. As far as differential goe's what I am refering to is if you have the rods going from the servo horn 90 degrees to the horn and the horn level at hover all are equal now suppose you add collective to max as an example now all the rods will be greater or less than 90 degrees depending on whether swashplate rises or drops for positive collective. But they will all still be equal to each other, now if you maintain a collective setting above hover and push forward cyclic the servo in the rear will raise further lessening the angle even more and the servo in front will drop bringing the angle closer to or at 90 degrees, the servos on either side will not move and so you see with different angles in the rods differential is introduced. Some of this effect can be tuned out electronically, but it has a small effect most of the time. Flying my Panther about the only time it really is noticable is in manuevers like a death spiral, it takes a little more stick fiddling to get a straight vertical decent than my Xcell helicopter for example. Most of the time I don't really mind it. For a helicopter like a UAV which flies smoothly and at minimal bank angles it is a non issue for the most part. Craig