Key learnings for those new to mods

[newblood]

I got into the hobby a few months ago and have been addicted ever since. This forum has provided a lot of great advice and inspiration so a big thanks to all of you for sharing your experiences- much appreciated. One thing I love about the Cub is its versatility; it's highly customizable at an affordable price (and if said customizations fall through, the replacement parts are just as affordable).

After getting a fair share of flights (and interesting experiences) under my belt, I decided to perform mods to the Cub with the following objective: enable flying (including aerobatics) in windy conditions. To do this, I compiled a list of mods (after reading through what most of you have done. The major themes were: reinforcement, brushless, and ailerons.

Since my Cub has been through several interesting situations (including being stranded at a wildlife park through thunderstorms for a few nights), the fuselage and wings have become 'off balance'. As such, I wanted to rebuild the plane with these mods to start fresh. The issue, however, is that I have limited experience with hobby / workshop work so I wasn't fully comfortable with jumping in and buying all the parts only to mess it up. As a result, I decided to buy the power/electronic components and upgrade the existing Cub for the sole purpose of working with the associated tools and exploring any obstacles for when I do the rebuild. As a result, I thought I would share my learnings from this process in the hopes that it provides a fraction of the insight that you all have provided me.

General learnings[/u]

• If you're new to mods, test them out first.
  
• Having the right tool for each mod makes them much easier to implement.
  
• A Dremel ($40 Home Depot for cordless 4.8V) and a Weller Soldering Gun ($40 Home Depot) are great tools to have as they offer multiple uses and work well with foam (in addition to other materials).
  
• Test electronics (incl. motor and servos) before installing them into the fuselage/wing.
  
• Patience is key
  
• Having the "fixing / building it is just as fun as flying it" motto will help as if/when your mods fall through, you won't be discouraged and won't give up.
  

Removing the ACT[/u]
The ACT has commonly been found to cause crashes rather than prevent them. I decided to remove the ACT completely by pulling the sensors out of the fuselage:


Tools used

• Exacto knife
  
• Pliers
  

Learnings

• Sensors seem to be glued in so some force will be needed to extract them.
  
• Was easier when the Exacto Knife was used to create a small clearing between the 'lips' of the sensors and the fuselage by inserting the blade just under the lip (parallel to the fuselage) and tracing around it
  
• 'Thin nose' pliers (don't know the official name) are a big help
  

Strengthening the battery box[/u]
The 'popsicle stick' method was used.


Tools used

• Exacto knife
  
• Pliers
  
• Foam safe glue
  
• Basic nails used for hanging paintings (probably not the best to use)
  
• Packing tape
  

Learnings

• I was uneasy about drilling the holes post glueing the sticks onto the fuselage so I decided to them before
  
• I also found that the sticks would crack when trying to make the holes so I tried wrapping them in packing tape before making the holes. This helped a little but cracking still occurred. For the rebuild I will likely use alum. sheets with a Dremel tool.
  
• Cutting the foam to get the sticks to be flush with the fuselage is a little tricky with a hobby knife. A soldering gun with a cutting bit (or custom wire cutter) makes it a lot easier.
  

Wing saddle[/u]
Again, the 'popsicle stick' method was used.


Tools used

• Exacto knife
  
• Pliers
  
• Foam safe glue
  
• Packing tape
  

Learnings

• As you can see from the picture, the foam crushing can be quite significant. Therefore, much wiser to do this mod before the first flight so only one stick is used.
  
• Was unable to get the stick to be perfect shape with the fuselage. Had I had my Dremel at the time, it would have probably been easier.
  
• The front saddle (just above the window on the fuselage) also takes a beating so a mod for this might be beneficial.
  
• Might explore using an alum. sheet to create a unibody saddle for the entire 'wing bay' (sort of like a tray).
  

Tape reinforcement[/u]
I have found wrapping the plane entirely in packing tape to be a big help: it provides a fair amount of reinforcement in addition to paint protection, both at a very low cost.


Tools used

• Clear packing tape (lots of it)
  
• Exacto knife
  
• Cloth tape (for extra protection on wings and cowl)
  

Learnings

• Found wrinkles to be commonly caused when trying to wrap the tape around a part. Helpful way around this was to wrap each side individually by taking extra long strips of tape and taping the part to the table. Once the entire side has been taped, cut around the edges with the exacto knife. Repeat for each side.
  
• Cloth tape has a very strong adhesive but wrinkles are easier to come by and, when trying to create curves, you may experience some 'flaps' of tape. Going forward, may be better to apply cloth tape first and then wrap clear packing tape over the cloth tape to ensure a tight and smooth finish.
  

Carbon fiber wing hold down rods[/u]
Decided to replace the stock wing hold down rods (where the rubber bands hook onto) with carbon fiber rods. I know it's overkill but I wanted to test out working with carbon fiber and figured the fact that I had carbon fiber in my plane would help with the ladies.


Tools used

• Dremel with standard cut off wheel
  
• Masking tape
  
• 3mm OD CF tube
  
• Gorilla glue
  

Learnings

• 3mm doesn't fit the 'caps' perfectly. I used Gorilla Glue to try and fill the gaps but the alignment was a little off.
  
• The CF tube can also be cut with a exacto knife but requires a bit of force.
  
• Wrapping the cut line with masking tape helps control the CF fibers from flying all over the place.
  

Carbon fiber for main wing [/u]
To remove the majority of the main wing's dihedral, I placed the wing upside down and put one large pot of hot water on the center and two smaller pots with hot water on the sides for a few hours. I then inserted a 1000mm 10mm OD CF rod near the COG (thickest part of the wing I believe).


Tools used

• Soldering gun with custom wire cutter (wire cutter = metal string I had for hanging paintings)
  
• Masking tape
  
• Gorilla glue
  
• Cloth tape
  
• Ruler
  

Learnings

• The 1000mm x 10mm CF rod works well for this mod as it's very strong (I found rods to be stronger than 'strips') and has a good amount of weight (which I wanted to add in order to help fly in windy conditions). The length is also nice as it covers the majority of the wing's span.
  
• The soldering gun is a huge help for this mod, the cutting is very easy and clean.
  
• Better to have a smaller cut the first time rather than too deep / wide (snug fit seems to be better anyways).
  

Carbon fiber for tail wing [/u]
For the tail wing (horizontal and vertical stabilizers), I used CF strips (don't remember the measurements but I would guess 3mm x 1mm). I also replaced the stock Super Cub horizontal stabilizer with a stock T-28 stabilizer (greater surface area apparently leads to greater response).




Tools used

• Soldering gun with custom wire cutter (wire cutter = metal string I had for hanging paintings)
  
• Masking tape
  
• Gorilla glue
  
• Ruler
  

Learnings

• For the vertical stabilizer, I cut too deep and ended up cutting out the entire strip rather than making a groove for the strip. To work around this, I added a strip to each side and covered with clear packing tape.
  
• Might be beneficial to add strips (probably smaller) to the actual elevator and rudder in addition to the stabilizers.
  

Carbon fiber for fuselage 'spine' [/u]
I inserted a CF rod (same size as what I used for the wing hold down rods) for the spine of the fuselage. Thinking here was that it would not only add some weight but also prevent the fuselage from bending out of shape (which it had already done from my prior crashes but wanted to test the mod).



Tools used

• Foam safe glue
  
• Dremel with standard cut off wheel
  
• 3mm OD CF rod
  

Learnings

• The mod was easy to implement by inserting the rod through where the tail's vertical stabilizer's front sets into the fuselage (groove area). The 3mm OD size was a perfect fit.
  
• While this was very easy to do and adds some nice strength, it leaves the actual tail untouched so I'm not sure if there's a better way to this to include reinforcement to the actual tail portion of the fuselage (mine has split off before).
  

Carbon fiber for fuselage front [/u]
I inserted a CF rod (same size as what I used for the wing hold down rods) into the front of the fuselage (one rod on each side). This was done by creating one end of the rod a little pointy and drilling in from the firewall area.



Tools used

• Foam safe glue
  
• Dremel with standard cut off wheel
  
• 3mm OD CF rod
  

Learnings

• This was a little harder than the spine as there was no built-in 'guide' for where the rod should go.
  
• Using a soldering gun to cut a groove from the outside rather than drilling might not be feasible since the fuselage 'curves inward'.
  
• Might make more sense to have a shorter rod which goes from the firewall to the first few inches of the electronics compartment.
  

Ailerons [/u]
I cut 12"x1.5" ailerons and started the cut from where the wing becomes flat (I want to add flaps in the future so I wanted to keep some space for where those would go).





Tools used

• Foam safe glue
  
• Exacto knife
  
• Masking tape
  
• Fine sand paper
  
• Velcro
  
• Cloth tape
  
• Soldering gun with custom wire cutter
  

Learnings

• I butchered my first aileron (the lines were not straight), even with using a fresh blade for the exacto knife. I have become very comfortable with the soldering gun so I may use this going forward. The gun also has a standard cutting bit which would create a nice gap between the aileron and wing (approx. 1mm). I also find that the gun 'packs' the foam into a nice smooth finish whereas with the knife you may end up with uneven tears which need to be sanded down.
  
• For the bevels, I taped a ruler on the side of the aileron and used my hobby knife to cut the bevel with the ruler as a guide. This worked decently but going forward having a second guide for the top of the aileron will help ensure a cleaner cut. May also use the soldering gun for this as well.
  
• Test the servo's beforehand! I created servo pockets so that they would be embedded into the wing and out of sight (which worked very well with the soldering gun) only to find out that the servo's were reversed (i.e. left causes left aileron to go down as opposed to up). I then had to re-orient the servos (as shown in the third picture) as I didn't want to take apart the servo's and mess around with the the wires. Going forward, probably good to invest in a Y-harness which has the reverser built in.
  
• To keep the servo's in place, I used zero glue (since I knew I wanted to use these servo's for my fresh build). Instead, I added velcro and then covered them with cloth tape. This worked well.
  

Brushless motor [/u]
In going Brushless, I used the following core components from Hobby King: Hobby King Donkey Outrunner (1100kv), Hobby King OrangeRX receiver, Hobby King ESC 50A with built in BEC.






Tools used

• Gorilla glue
  
• Dremel
  
• Soldering gun
  
• Velcro
  
• Balsa wood
  
• 5 min epoxy
  
• Stock gearbox
  

Learnings

• The soldering gun made soldering on the bullet connectors extremely easy. I initially bought a cordless soldering iron from Home Depot ($20) and returned it the next day as it was not nearly as powerful enough.
  
• I initially wanted to use plywood to create a custom motor mount to glue onto the stock gear box but opted for balsa as plywood was a lot more expensive than I anticipated. This was a decision I now greatly regret (as explained in the results section).
  
• I decided to 'solder gun' a compartment for the ESC on the bottom of the front fuselage area so that the motor wires would go through the stock hole and the battery / receiver wires would go into the electronics compartment (I created a hole using the, shock horror, soldering gun). This worked very well as it added weight to the nose (my Cub has been tail heavy), created space in the electronics bay, and added a decent amount of protection to the ESC.
  
• Important to test the electronics before hand as not only were my aileron servo's reversed, the elevator servo was also reversed (pushing down on the elevator control would cause the plane to dive as opposed to climb). In addition the motor was spinning the wrong way (the plane was being pushed backwards rather than pulled forwards). The motor was an easy fix as you just need to switch any two of the three wires to make it go the other way. I couldn't figure out how to fix the elevator servo.
  
• Also important to ensure your prop will fit the shaft of your 'prop adaptor', not the motor shaft.
  

RESULTS [/u]
Even though the elevator servo was reversed, I really wanted to test the mods out and fly. The result was that my "testing" phase prior to me rebuilding the plane only lasted about 5 minutes. First flight: plane nose dives because I screwed up the elevator controls and the ailerons were getting stuck. The motor ripped completely off. I then tried to 'ad-hoc' repair this by wrapping copious amounts of cloth tape around the motor to keep it in place and it actually turned out ok till the plane nose dived again. This time, the motor stayed in place but was a little loose. I firmed it up and took off for a third flight. The plane got in the air (the brushless motor is insanely powerful!) but was a little hard to control due to off-balance / reversed elevator / ailerons getting stuck / body being off center. Eventually, I saw the motor fly out of the plane and then the plane proceeded to gracefully glide / crash land on a major highway (thankfully there were no cars so no third party chaos was caused).

The end result is I have lost my motor and prop. The ailerons ripped off and the elevator also ripped. Everything else was in decent shape.




Believe this is where the whole "fixing / building = flying" motto comes into play otherwise one would just give up out of sheer frustration. I have ordered a new motor and an actual motor mount from Heads Up RC and will proceed to take the learnings above into account when I rebuild the plane from scratch. For now, then, I have gutted the Cub and have stored the parts and will continue to use her for testing mods:


Hope this has provided some help to those looking to do some modding of their own and thanks again to all of you for sharing your experiences / expertise.

-N

P.S Anyone know how I can reverse my elevator servo without having to take it apart and re-solder?

[ginginho]

Your Rx looks like a Spekky compatible. If so, you should be able to reverse any servo in the radio. What is your radio?

[newblood]

I'm using the stock Hobbyzone Champ transmitter (I bought a Champ after losing the Cub in the wilderness and having looked for it / posted flyers...someone called about the Cub 3 days after I bought the Champ).

I was actually just testing the servo's and noticed that I managed to get it to work. I have 4 servo's total: 2 HXT 900's and 2 ParkZone 9g's. Initially, I had the HXT's as Rudder/Elevator and the PKZ's as Ailerons. When I switch it up and use the PKZ for Rudder/Elevator and the HXT's as Ailerons, they seem to work completely fine (in fact, the HXT's work in my initial embedded configuration of aileron servo's).

I'll have to double check this tomorrow but is it normal for servo's to be designed for a specific channel?

[ginginho]

Ah right, it is Spekky, but very basic. If you are going to grow your fleet perhaps you should consider upgrading to a Dx5/Dx6i.

Servos are not generally for specific tasks, although there are particular instances where some types suit better than others, such as for retracts. I suspect all you've found is one make is set to move one way from the factory, and the other in the opposite direction.

[killioughtta]

Hey, TL;DR but I noticed that HK Donkey motor on your SC. How's it worked out for you? I've been tempted to buy one to test it out on a foamie but I'm not too sure.

[newblood]

Hah well I wasn't able to test it out very long so won't be able to offer any objective advice but $6 for a motor which is powerful enough to rip out of the cowl and take a flight of its own is an OK motor in my book. The only thing to be mindful when buying them is to ensure you have a compatible motor mount which is strong enough to keep the motor in place.

[flydiver]

May 31, 2011 9:32:30 GMT 1 newblood said:

I'm using the stock Hobbyzone Champ transmitter

I was actually just testing the servo's and noticed that I managed to get it to work. I have 4 servo's total: 2 HXT 900's and 2 ParkZone 9g's. Initially, I had the HXT's as Rudder/Elevator and the PKZ's as Ailerons. When I switch it up and use the PKZ for Rudder/Elevator and the HXT's as Ailerons, they seem to work completely fine (in fact, the HXT's work in my initial embedded configuration of aileron servo's).

I'll have to double check this tomorrow but is it normal for servo's to be designed for a specific channel?

If it's that little 'toy looking' TX it is SHORT RANGE. It's not good for more than a few hundred feet. Mine (for a little PZ heli) does not have servo reversing. Get a TX suitable for the task.

"Normal" (3-wire) servos are not generally task specific, BUT, different brands are directional. One brand my go right when energized, the other brand left. That is normal and can sometimes be useful. Ailerons (and other symmetrical applications) must be used in matched pairs but you can mix it up otherwise.

If you were using 4 servos on an old lipo with a motor having a LOT of power it's quite possible among other issues you subject yourself to Spektrum BROWN OUT-another thing to learn about.

supercubclub.proboards.com/index.cgi?board=rg&action=display&thread=1858

Learning - ANY problem with a plane on the ground WILL bite you if you put it in the air. Those are not equipment failures, they are pilot errors.

Super write up. You obviously put a lot of time and effort in to it.

[renard80]

newblood:

While I am not qualified to comment on your mods, I offer my congratulations on your perseverance and on all the effort you have made with this post.

I am sure many people will benefit from your shared experience.

[newblood]

Thanks guys, appreciate it.

I just bought the majority of the components required for the rebuild. Will take pictures as I progress the build and provide a similar guide of how I took the above learnings into account when building from scratch and pre-maiden flight.

-N