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Oct 25, 2020, 12:56 PM
It's all about scale models!
MrSmoothie's Avatar
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Main Gear Wheel Improvements

I made two other modifications to the main gear wheels before flying today.

I used Robart Scale Wheels on this model. One thing I don't like is that the supplied bearing choices are US and not metric, although a few line up close enough. For 5mm axles, though, you're out of luck. I don't know why Robart doesn't "get with it" as far as where the hobby has headed. Even if they had to manufacture (just) the bearings in China to avoid expense... But not my business.

You can use aluminum tubing (and none of the supplied bearings) to use on 5mm axles, but the fit will be a little loose with some wobble, which means the tire might intermittently rub against the strut.

A flying buddy just got the Eflite 1500mm P-51D and alerted me to this post -- "Celestine" had done a 3D file to replace the bearing half of the Robart wheel (same 3.5" diameter I use on the D.250) which utilizes ball bearings.

This was designed to use the ball bearings which came on the Eflite's stock wheels. I happened to have some 8x5x2.5mm bearings on hand which I'd purchased on a whim. I took this modeler's file into Tinkercad and modified the hub for my slightly smaller dia. bearings, and also made the axle portion of the hub narrower to fit my already trimmed gear axles. Later, I got some 10x5x4 bearings and again modified the file; that's what I have on the Dornier.

These work fantastic -- not only does the wheel spin with ease, but more importantly, has zero wobble and no chance to rub against the strut.

I decided to do the same on the smaller 3" wheels on my Yak "SteadFast" and other models I have, and created a design for the 3" wheel's smaller hub from scratch in Tinkercad.

The other problem with Robart Scale Wheels is that I've probably exceeded the tire weight capability with the Dornier. I noticed that if the model sat too long in one place, it started to look like the tires had gone flat. The tired are hollow rubber, so I wondered if anybody had tried filling the tires with something to increase firmness. In the course of researching that, I discovered that Robart actually sells tube-shaped foam specifically designed to be cut and stuffed into the tires -- four different sizes, in fact, for the various diameter tires. I guess the reason I'd never heard of this is because none of the dealers where I buy Robart wheels actually carry the foam filler products!

I was about to order some from Robart, when I wondered if I might be able to do the job with something on hand. I save lots of various packing materials for just this reason. I found white packing foam -- I'm not sure what the material is, it's not foam rubber, and it's not styrofoam, but more like a plastic foam, white in color, fairly firm and easy to cut. I'm sure you've all seen it. The sheet I had was 10mm thick, but actually two 5mm sheets glued together. After a bit of experimenting, I found I could cut two strips about 7/8" wide, and trim to fit exactly inside the tire, obviously the outermost strip longer in length, with no gap between the ends after trimming. I did this at the same time I was replacing the hub (with bearings) half of the wheel. Once reassembled, the tire still had give, but much better for the weigth of the model than before. This proved to be true on my flight tests today -- no "flat tires."
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Oct 25, 2020, 01:07 PM
It's all about scale models!
MrSmoothie's Avatar
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For once, I remembered to take some new shots on the runway *before* the first flight, with the new added details. You know, just in case...

I'm envious of the guys who seem to always have a photography aficionado at the field, proficient in telephoto in-flight shots. This is one model I'd love to have some nice aerial pics of.
Oct 25, 2020, 04:42 PM
Failure is not an option
casor's Avatar
Nick - bubble in the canopy adds a lot, I really like it. Amazing was a small detail can do.

Re the wheels, I have the same problem. I have tried resting them on firm foam which helps a little. Otherwise, there's no getting around that you still have rubber between a heavy model and the hard floor. I have made stands similar to what they use in a museum that the support the LG strut, not the tire.
Oct 25, 2020, 05:27 PM
It's all about scale models!
MrSmoothie's Avatar
Thread OP
As it happens, I have to transport and hangar this model unassembled, gear retracted. So the issue was only visible while taxiing, and obviously the tire would compress against the hub on each landing. I think the white plastic packing foam really did the trick today.

Thanks on the canopy! As I've said, I'm not trying to add every possible detail -- I add the ones that seem interesting to me or have a story, or might be fun figuring out how to execute. I harp on canopies a lot. When I look at really well done (often larger) models, they always seem to have the canopy framing correctly sized. Even on a model as large as this Do335, the factory's twice-too-wide canopy framing makes the entire model look toy-like.
Oct 29, 2020, 09:33 AM
It's all about scale models!
MrSmoothie's Avatar
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More Accurate Weight Numbers

I have a decent digital postal scale and thought I might get a more accurate set of figures than I achieved holding the model while standing on a bathroom scale.

Fuselage: 10 lb, 4 oz. Note that this includes approx. 7 oz. of nose weight. It also includes scale details such as the wing cannon blisters, and cockpit/pilot.
Wing Panels: 5 lb, 3 oz.
Roaring Top 6s-6250-35c: 2 lb.

Total Flight Weight: 17 lb, 4 oz. I've been saying "17 and a half pounds" for months, so I wasn't far off.

The new lipo of choice, the Liperion 6s-6000mAh-65c weighs 195gm (nearly 7 oz) more than the Roaring Top. I'll be able to remove almost all of the added nose weight. Since the lipo's weight is not as far forward as the added weight (back of firewall), I think I still need to leave 1 - 2 oz. (the lipo can only slide so far forward due to hatch clearance). I'm sure an engineer could calculate this exactly. I'm no engineer...
Oct 29, 2020, 04:00 PM
Sleepy Hollow, IL

I just got the nose strut and wheel assembly for the Freewing 80MM A-10 today. It measured 3/4 inch shorter in length from bottom of wheel to top of strut. What did you do to compensate for this difference in length?

I do like the compression rate of the struct compared to the one supplied with the plane. T reduce the compression rate in the main wheel struts, I took out the split pin holding the inner strut to the outer strut and cut 4 coils off of the spring. This got the compression rate to just the right amount.
Oct 29, 2020, 04:52 PM
It's all about scale models!
MrSmoothie's Avatar
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Hi Amp,

I remember making some changes to the nose strut, but don't remember what I did -- the plane is at my office, so I'll have to take a look tomorrow and see if I can figure out what I did. The nose strut change has worked out great, and if you look at my most recent video, you can see it compressing while taxiing -- in a way that the mains do not.

I, on the other hand, am very interested in how you went about getting the main struts apart -- that spring is so strong as supplied that by the time you compressed it, the retract would bust through the top of the the wing! I looked at the struts a long time trying to figure out how to get them apart!

Is the split pin the one that travels in the slot? And isn't the slot only on one side? If so, how did you remove the split pin? I'm looking forward to your answer on this -- I've spent a lot of time looking for replacement struts, but if I can get the spring compression right, there'd be no need.

I've done the same thing (removing coils) on other gears recently, such as the nose gear on the Freewing T-33. On that strut, the spring is compressed at least a half inch before you can put the "slot screw" in. Way too stiff, and leads to "pogo" antics if you make an impact on landing.
Oct 29, 2020, 05:00 PM
It's all about scale models!
MrSmoothie's Avatar
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Amp, I'm going to take a guess at how you got the pin out.

Since the pin (and travel slot) are only on one side, first you inserted a small bit into the pin, and drilled through the strut on the opposite side, to provide a location.

Then you drilled a larger hole, just through the strut, from the opposite side.

Then you used a hardened punch of appropriate diameter through this newly drilled hold to knock the pin out.

Or did you have an easier way?
Oct 29, 2020, 05:31 PM
It's all about scale models!
MrSmoothie's Avatar
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Freewing 80mm A-10 nose strut

I had to go and see what I did. This is what happens when you have too many projects (or get too old).

OK, it's clear to me what I did.

I made an extender segment that's 18mm in length. I have a mini-lathe so I probably started with an aluminum bushing from the hardware store.

The OD was turned down to slightly larger than the strut diameter. This was drilled out with a 5.5mm bit. Cut to 18mm in length. Three holes drilled and tapped for two grub screws and spring screw (with hex head).

If you've been reading this log since the start, you'll recall I used a couple of steel washers as spacers between the steering yoke and trunnion. I cut a 3mm segment at the same time as the 18mm extender.

I doubt the 5mm connector pin that came with the strut was anywhere near this long, so I'm pretty sure I cut some 5mm K&S music wire to length and ground all the needed flat spots for the various grub screws.

Where, you may ask, did I find 5mm dia. K&S wire? Directly from the company. They insisted there's "no demand" for metric wire in the US and could not provide me with the name of a single dealer who carries and sells their metric sizes online. I tried to convince them that if nobody carries the product, it's impossible to gauge demand -- and that 95% of the R/C hobby comes from China/Vietnam and is entirely metric. I don't think I made any headway. Kind of reminds me about Robart and their seeming unwillingness to embrace metric. Oh, also Dubro with SAE-only hex head bolts. But don't get me started.
Oct 29, 2020, 09:42 PM
Sleepy Hollow, IL
Mr Smoothie,

To remove the split pins from the shafts I made special puller based on the design that Ford Motors came up with to pull pins from steering columns. I used a 3 inch long bolt which I tapped for a 3mm screw and screwed in a 25mm long 3mm screw into it. Then I fashioned a 3/4 inch dia. aluminum tube to go over it. This tube is hollowed out to just slide over the bolt and cut back to rest on the curvature of the strut. By holding the bolt still and tightening the nut it backs the pin out. The split pin is first tapped for a 3mm thread matching the thread on the puller 3mm screw. See the pictures below and this will all make sense. I removed 4 coils from the spring. May have to remove one more to more closely match the A-10 spring compression.

I also attached a picture of the type of 5mm shaft pieces that I found. I tracked them down by searching for hardened tool steel rod.

Just finished making a spacer as you had done and tomorrow I am making the 5mm shaft piece with the flats as needed.
Last edited by ampmaker; Oct 29, 2020 at 10:26 PM.
Oct 30, 2020, 07:55 AM
It's all about scale models!
MrSmoothie's Avatar
Thread OP
That's an amazing solution. I've seen the general idea for extraction before. But I would never have guessed that the split pin could be tapped -- struck me like it'd be hardened metal and snap the tap.

Did you reuse the same split pins? Seems like there'd be no reason not to.

I'm REALLY intrigued by the 5mm stainless stell shafts! These could be the solution for several problem retracts I have that are constantly bending back just enough for the wheel to not clear the well. If I can't find them, I'll be back in touch. Thanks for the great information!
Oct 30, 2020, 08:04 AM
It's all about scale models!
MrSmoothie's Avatar
Thread OP
I found the pins on Amazon:

Interestingly, the photo shows them marked HSS -- one reviewer says:
Good precise lengths of metal, but these appear to be HSS (High Speed Steel) as printed on one bar. They are highly attracted to magnet and thus unlikely to be stainless. Fortunately I didn't need stainless so these should work fine for me. The steel is *quite* hard.

Have you put a magnet on yours?

I also found these on amazon -- they claim to be "304 stainless steel" -- I think I'll give them a try.

Of course, then I'll be complaining about cutting stainless steel and grinding the flat spots. Suggestions appreciated!

EDIT: the worst review of the second link says they can't be 304 stainless as they are magnetic.

I'm wondering if HSS would be too brittle -- likely to simply snap under load, like how a drill bit breaks?
Last edited by MrSmoothie; Oct 30, 2020 at 07:20 PM.
Oct 30, 2020, 07:24 PM
Sleepy Hollow, IL
The RilexAwhile rods are magnetic. I don't know what grade they are as mine are not marked like in the picture. Also, I know that there are grades of stainless steel that are magnetic.

I cut the rods with a metal chop saw and then ground them to exact length with a 9 inch disk sander. To grind the flat spots I used my mill with a 1/4 inch four flute end cut mill bit.

I did reuse the split pins. I use a small tack hammer to pound them back in.
Oct 31, 2020, 03:00 PM
It's all about scale models!
MrSmoothie's Avatar
Thread OP
I've wanted a mini milling machine for a while, but never thought I'd use it enough to justify the cost. Putting flats on connector pins would have made it worthwhile by now!

I had to look up what a metal chop saw is, but I see now. They use metal cutoff wheels. Another tool I don't have currently.

I'm going to get some of those RilexAwhile 5m shafts in any case and see what I can do with them using what I have.
Oct 31, 2020, 03:07 PM
eat, sleep, FLY FLY FLY
Mr.frankenjet's Avatar
Dremel works well for most small stuff

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