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Feb 23, 2020, 09:42 PM
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Basically Im done building the airframe.

I still have to build the cowl but believe it or not Im held up by an $8, 2.25 spinner. I have to order it. It should be here later in the week. I cant build the cowl until I get it.


So I spent hours and hours looking at my plans with CF rods and different servo arms figuring out how I can install pull pull system for the rudder. It was quite difficult. I had clearance considerations, I had to make sure the elevator had clearance past the rudder. I also had to make sure I did not block the flap servo. I did finally work out a servo placement and built a tray.

Its just stuck in place while I work out the rigging.
Feb 24, 2020, 12:03 AM
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Hi there enjoying your build.
Couple things to consider
Flys really really well at the rearmost of the allowable c.g. range like it makes it feel perfect. You will need tail weight to balance regardless of where in the allowable range when a four stroke is up front . Ive used os 91 and enya 80 both worked well the os 91 was better.
Consider installing flight pack battery in compartment
Behind servos or hatch at rear under tail to hide weight. This plane will fly fast and hard to slow when nose heavy. Keep power on to the ground to land. It will stall abruptly nose down if too slow. Good luck with your chippy. Looking forward to reading more
Thanks for the thread.
Feb 24, 2020, 10:00 AM
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Quote:
Originally Posted by bustedbalsa
Hi there enjoying your build.
Couple things to consider
Flys really really well at the rearmost of the allowable c.g. range like it makes it feel perfect. You will need tail weight to balance regardless of where in the allowable range when a four stroke is up front . Ive used os 91 and enya 80 both worked well the os 91 was better.
Consider installing flight pack battery in compartment
Behind servos or hatch at rear under tail to hide weight. This plane will fly fast and hard to slow when nose heavy. Keep power on to the ground to land. It will stall abruptly nose down if too slow. Good luck with your chippy. Looking forward to reading more
Thanks for the thread.
Thank you !
Good to know on the balance points. I am hoping I wont have to add much in the way of weight. I was planning on making a spot for a hatch at the tail to add weight if needed. I may just leave a section of covering unattached so I can balance then seal it. Final balance being done when flying of course.
Feb 24, 2020, 09:39 PM
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Ok Im officially out of things I can do.


Ok I am officially out if things I can do without parts. I always knew I was going to need an order . I still need a few servos (digital metal gear for rudder). I also need a spinner (the only hobby shop within 39 min is dumping anything not foamy related).

now I need control horns. The kit I bought will only go down to 30mm either side of center. I need one 19mm after that I would have some clearance issues. I could make one out of ply if I get desperate, it would require me to reinforce the area where the tail wheel control rod is. I prefer a set of left and right 3/4 horns. I am hoping they are perfect. One consideration I need to think about is with such a small control rod the cable will see more tension and so will the servo under load.


Oh well. Perhaps it will be decent weather and I can maiden my biplane.

Anyway I did validate I have clearance with the flap servo and my elevator servo.
Last edited by Taxus812; Feb 25, 2020 at 07:36 AM.
Feb 25, 2020, 06:36 PM
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Ok busy work. I decided to play with the cockpit layout.

The idea of the pilot bust just sitting on top of the models seat is bothering me. It puts the pilot at the right height but seems odd.

I toyed with the idea of just leaving the flop pan out.

What do you think.
If I was going pilotless I would certainly use it. The one in the cover of the box has a pilot but no cockpit.
Last edited by Taxus812; Feb 25, 2020 at 07:04 PM.
Feb 28, 2020, 09:57 PM
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Looks great like the pilot do u have a paint scheme in mind for the plane?
Feb 28, 2020, 10:11 PM
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Quote:
Originally Posted by bustedbalsa
Looks great like the pilot do u have a paint scheme in mind for the plane?

Thanks
Since this is a nostalgic build for me I will be going with the original red stripes with white and blue. Just like my first one (that I never flew).

What do you think about the pilot mounting? I have been toying with the idea of not using the floor pan.
Feb 28, 2020, 11:05 PM
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So I got the pull pull installed/mocked up. It started out great even too easy. I should have known lol

I drilled out the exit holes for the cable with a sharp brass tube. I marked the path with carbon fiber rod tapped to the side.

The issue I had is I planned for a solid rod control horn. I didnt measure the minimum with. I need 38-40mm . The one I bought only went down to 60mm. So i had to get new ones. I liked the ones by Sullivan 3/4 they were perfect. However because I had to steady the tail wheel tiller arm the actual arm was higher than I planned. I tried to move the holes up using a file. It was a feeble attempt and I ended just cutting a section of the fairing , installing the wires and nylon tubing to protect from chafing. Then blocked in new balsa around it. Even though doing that made me sick to my stomach, the end result was fantastic.
Last edited by Taxus812; Feb 28, 2020 at 11:22 PM.
Feb 29, 2020, 07:49 PM
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Rudder pull pull complete. It only took me 4 days and two try’s to get something that probably should have taken a few hours to do.

Fantastic learning experience. My design was sound. I used a 19mm servo horn, 3/4” Sullivan pull pull control horns at the rudder. I added super thin plywood shims to make them the same width as the servo horns. The cables are parallel to the servo control horn.

The surprise was how much the wire moves around In the fuselage . I had to slot the deck with some pretty big slots and cut a bit of a former to make sure the wires cleared. Tomorrow I will ad gussets where needed (non really) and neaten things up. . If I was to design this another way I would use a pulley system. The servo would use pull with a single wire that was secured at the top . The rudder would have portions of the pull aft of the servo horn. This would keep the cables perfectly still. What I have is not bad the fairline keeps everything super smooth. The cables just move in all three axis and I needed to account for that.

Anyway here is a video with a really noisy digital servo.

There is no tension on the cables except what is needed to take up the slack. it is insanely smooth to move by hand. It actually surprised me quite a bit. The really cool thing is I get a full 45Deg of rudder.

Please note there is a ticking on the second video. That is because of a cable end hitting the fuselage. I trimmed it and it is gone.

(0 min 3 sec)


(0 min 6 sec)
Last edited by Taxus812; Mar 04, 2020 at 10:53 AM.
Feb 29, 2020, 09:42 PM
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Quote:
Originally Posted by Taxus812
Thanks
Since this is a nostalgic build for me I will be going with the original red stripes with white and blue. Just like my first one (that I never flew).

What do you think about the pilot mounting? I have been toying with the idea of not using the floor pan.
Thats how I did one of mine pilot dash and seat back
Mar 02, 2020, 02:31 PM
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Time for Math !


So I am looking at all the rudder deflection I gained by using Pull-Pull. I get a full 45 Deg of rudder (1:1 mechanical ratio). It also puts it at the lowest resolution of .42 deg per 1% of travel (when set to 1:1 mechanical).

I'm a glutton for punishment with to much time on my hands apparently and wanted to learn a few things. The manual only calls for 20 deg of deflection. (I more than doubled it). That has me thinking, should I try and increase the resolution by adjusting things mechanically or just adjust how sensitive the rudder is to stick input, using dual rates or even better expo. Not sure what a chipmunk could do with 45Deg of rudder. It could be fun ! I think the ideal may be somewhere in-between.

I got to researching how mechanical ratios affect actual resolution. I found a fantastic post the explained it where I think fully understood it. I added that post here (hopefully it cross references ok.) so I do not loose it. If I reduce the servo arm size I can increase the resolution . I wondered on a pull-pull setup if I could do that. So I did the math (yup I got a protractor and compass and drew pretty arcs and measured things). The slack produced on the non pulling side is less than .5mm at 45 deg , If I moved the ball links all the way in to 10mm (.5 : 1 mechanical ratio) For reference if move them out it is just the opposite but in the pulling side, I was curious). So decreasing the size of the servo arm, I would still get 30 deg of deflection and a significantly increased resolution with little loss in tension.

Longs story short it is feasible to add resolution mechanically using this pull-pull configuration without adding a bunch of slack negating my increase in resolution at full throw. This is not a pattern ship and I'm not that good a pilot, Slack probably would not be an issue. I may play around. Good thing is I can adjust it after I have flown it.


Here is the reference that spoke about.


Quote:
Originally Posted by wfield0455
Actually, you haven't thrown out 1/3 of the resolution, you've thrown out 1/3 of the travel, which is a completely different thing.

A servo with a resolution of 2048 for 120 degrees of travel, if it were truly capable of that resolution, would be able to position it's output shaft within ~.06 degrees per step. In reality, the end points have a max value of +/- 150 or 2048/300 = approximately 7, .06 degree steps for each point of end point value change. That means you can use the endpoints to change the servo travel by about .42 degrees for each point of change in end point value.

Assuming the above servo, if you have a 1" servo arm and your control horn pick up point is 1" from the hinge line, you will have a 1:1 ratio. With end point values of +/-100, that will provide approximately +/-45 degrees of servo rotation and also +/-45 degrees of control surface deflection, with a control surface precision of approximately .42 degrees which is the same as the servo. (yes, 100*.42 is 42 degrees but we're dealing with approximate values)..

Now lets change only the end point to a value of +/-150. Our servo will now rotate approximately +/- 60 degrees and without changing the servo arm or control horn the control surface travel will now also increase to +/- 60 degrees also but the precision of the control surface remains unchanged at approximately .42 degrees per percent of travel ). Only the travel changed.

Now lets change the servo arm from 1" to .75" and leave the control horn point and end point values the same. We now have a mechanical ratio of .75:1. As a result of the mechanical change, while the servo resolution has remained unchanged, the control surface travel will be reduced to +/45 degrees and the control surface precision will have been improved from approximately .42 degrees to approximately .3 degrees. In other words your control surface is now able to be positioned approximately 25% more precisely. This improvement was achieved by mechanically changing the ratio of servo rotation to control surface movement, not by increasing the resolution of the servo.

Wayne.
the whole thread is here. https://www.rcgroups.com/forums/show...rvo-resolution
Last edited by Taxus812; Mar 03, 2020 at 07:04 AM.
Mar 04, 2020, 10:30 AM
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Still waiting on parts.


Just an update.

Im still waiting on parts. I ordered a plastic spinner but for whatever reason it is taking weeks to get to me via FedEx. Honestly next week I can order the metal one I wanted. I decided to sell the Hitec HS-6965HB - Karbonite Digital Ultra Speed Servos. Someone got a deal since these are super fast and I sold them for $25 each (shipped). What I don't like is 1) They are carbonite and I have a large nitro. Hitec says that is not a the best. 2) at 6.6V they are not smooth. They telegraph each step. 4.8 they are great. sooooo I ordered 4 Hitec HS-5625MG Standard Digital High Speed Metal Gear Servo for the Aileron, elevator and rudder.

I also ordered a AR6610T DSMX 6-Channel Telemetry Receiver I will be adding a Temperature sensor and RPM sensor. I also ordered one of those smart batteries and charger.

The thing about this hobby is the Airframe cost you a couple hundred bucks but it then cost you another 5-6 hundred to finish it.


Speaking about finishing. I was dreading the fact that I need to paint the cowl and wheel pants. I can never figure out fuel proof paints. If I use X on top of Y will if peal and wrinkle? People tell me but it seems to leak out of my brain. I also don't have a spray booth. I will have to make room in my shed to paint. Color matching was a whole different (and expensive) thing. I was posting for help and Imodel sent me a recommendation to check out Wings West. I watched some of their videos and I am going to give them a try. I am not a painter and typically avoid it at all costs. However this is a small amount of paint since it is just the cowl & wheel pants and their setup seems like its is something I could actually do. I will do a mini product review from a novice when I get to that part. They use a base coat that is better mixed for paining airplanes (as opposed to cars). A few of the thing I like are 1) They mix their paint for painting models as opposed to a car 2) it is color matched to the Ultracote Red and white I will be using.

The clear is just 2K automotive clear which will be fuel proof. the cost they sent is about what I could get it for on amazon. That signals to me that they are not drastically inflating their prices.
Last edited by Taxus812; Mar 04, 2020 at 01:00 PM.
Mar 09, 2020, 08:56 PM
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Did some more work on the flight controls this weekend. I decided to use the included pushrod for the elevator. The carbon I picked had too much flex. I tried the included pushrod and it worked really really well.


I also cleaned up the pull pull cables guides tubes . I made some glue strips to hold the ends of the guides. They were intentionally left long. This way as the cables move they are never on a hard edge if they rub.
Last edited by Taxus812; Mar 10, 2020 at 09:53 AM.


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