Plastic frame questions & opinions

[EKron]

I believe the time has come to replace the main and tail drive gear bearings in my plastic framed 425 but have some questions and decisions to make and am soliciting opinions.

First of all, I have a totally brand new frame & lower battery mount complete with all brand spanking new bearings, front & rear main gears, tail drive gear and OWB and shaft.



My questions are as follows:

• Would you rather split your existing frame and sneak in the new bearings or use the new frame and move everything over?

• The previous owner of my Hurri appears to have used some kind of goop as a bearing retainer at least on the mains that I can see. Is this recommended and if so, what should I use?

• On my existing frame, I carefully Dremelled out some material around the top and bottom OWB shaft bearings so I could get them out without splitting the frame. I'm not so sure this was a good idea. Would you do this on a new frame?

• Finally, and this is probably way out there but it looks too tempting to not try, has anyone ever tried machining out the plastic frame and installing the metal bearing blocks from the CF frame?

This looks like if would work perfectly except for maybe the bottom OWB bearing mount which doesn't have a lot of support?

Thanks in advance for your thoughts.

--Elisabeth

[Jerrymac]

Well, lets see. It's your helicopter, and your repair project so..... the frame is for you to decide, but.......


1. I would split the frame slightly and replace the bearings if there is nothing wrong with the old frame. Might need that new one in the event of a frame breaking crash.

2. Yes, a tiny bit of Shoe Goop.....

3. I did this same thing on all of my plastic frames since those OW shaft bearings don't seem to last too long......Easier to replace that way.

4. I tinkered with this idea a few years ago, but, instead, I have just been upgrading all of mine to HeadHunter frames. They have 2mm CF frame sides, bearing blocks at OW shaft are machined bigger to use the same bearings as the main shaft, direct to swash servos, and a sliding motor mount to make setting gear mesh a breeze.

One thing I did on my plastic frames years ago when I built them was to add a frame stiffener to the motor mount to keep the frame from twisting in this area. I used a piece of 1/4 inch aluminum, drilled and tapped the bearing end of the motor mount, bolted the new plate on and then drilled and tapped holes in the sides of the plate to bolt through the frame.

If I can find the old pics I will post them, sorry for poor quality, old camera.....

[EKron]

Thanks, Jerrymac.

I think I'll go with you suggested to just flat rate some new bearings into my existing frame. Since the Headhunter frames are no longer available as I understand, that's not much of an option. I did see a guys Hurricane a few weeks back with a white translucent G10 frame that looked awesome that apparently he machined himself but I don't know who's it was or how to find out if he is making and selling them but it was really cool.

I do have a bit of a top frame strengthener of sorts made out of 1/4" Lexan and several in the lower frame as well but will be remaking them out of aluminum. Probably go with a upper version like yours bolted to the motor mount.



In the meantime, I think I'm going to experiment with my plastic frame and try adding the metal bearing blocks? All e RC has the plastic frames in stock for $25 bucks and the bearing blocks for $30 bucks so if I screw it up, it's not like I'm out a major fortune. If it does work, it should add some rigidity and improve bearing serviceability.

I'm so busy for the next week + it is not going to happen overnight but I'm kind of jazzed by the idea. I love fabricating and modifying stuff. For example, my homemade tail servo mount and "industrialized" 450.

-- Elisabeth





note: I broke my Futaba 9257 and am now using an Align DS525M tail servo on my 450. Fixed the 9257 but the Align servo is faster and made for bigger helis so it is mucho powerful too. My homemade mount contraption is rock solid for what it's worth and I really dislike boom mounted servos.

[EKron]

OK, I'm doin' it!

Parts I ordered from All e RC yesterday got here today and even though I'm up to my eyeballs with work, I simply had to take a break and scope out my idea of putting metal bearing blocks in my plastic-less-than-fantastic frame.

First, I simply laid the bearings in my new frame to check the width. Perfect fit.



Then I fiddly farted around checking hole alignment and it was good so I couldn't resist wasting more time checking vertical alignment. Perfect fit!



Next, I have to find some time to grab the Dremel and remove the plastic bearing mounts. I'm going to start out all aggressive with what ever cuts best because I love getting hot melted plastic in my hair and making a huge mess (not). Then I'll build up a little jig to secure each side level and use my drill pres as a ghetto mill for the finish work. I'm sure I can do this well without wrecking it but I'll have to be careful to get a nice factory look.

The bottom OWB bearing mount is pretty sketchy at this point and I'll just have to decide if there's enough meat left to support it when I get that far? I'm excited! This is going to be fun to try. At worst, I've wasted thirty bucks for the bearing blocks and twenty-five bucks for the frame and the bearings can always be used by themselves.

Chop chop time! The delineation between the plastic bearing blocks and the frame is so obvious it's like daring me to whack them off. (Ok, so no whacking off but you know what I mean)



Bacon and bananas! W00t!

-- Elisabeth

[Jerrymac]

Yep, the main problem is the lower OW shaft bearing mount. Once you chop it, there will be nothing left to attach the aluminum mount to. You could probably fabricate some small plates and attach them to the outside of the frame, then attach the bearing block to it. OR, you could just leave that one single bearing mount in the frame and not use the single lower aluminum block.

Lastly, ( IMO the best way ) you could also shave a few mm off of each side of the lower aluminum block, then you could shave less material off of the plastic frame. That way you would still have something to attach to. The frame is 20mm wide at the lower bearing. The bearing is 12mm OD. That gives you a total of 8mm to play with. You could shave the aluminum block down to, say, 16mm wide. That would give you 2mm left on both sides of the bearing, and 2mm of frame left for attachment.

Double the fun.......You can whack off the frame, and bearing block too.

[Bearclaw]

Just be aware that this will be a weaker setup and will allow more flex into the system. Think about how the bearing blocks are formed with the frames utilizing the screws to simply hold them together, with all that plastic re-enforcing the screws. With the aluminum blocks, you only have the heads of the screws pinching the plastic frames to the block, and the plastic being softer (not weaker, just softer) will allow the head of the screw to flex and therefore the whole frames flex.

In other words you are reducing the surface area and support area by using the aluminum bearing blocks.

Do you get what I'm saying or am I just being confusing?

Either way, fun fabrication, and experience!

[EKron]

Gah! Haven't had a second to work on this. Been tracking down a vibe on my 425 and just replaced all the bearings in the frame which was fun. Not as bad as I thought as I was able to remove all the frame screws and rear motor mount and pry things apart and get all the bearings in. Some of the bearings were really hammered and I'm surprised the heli even flew well but after all my work, I still had a vibe that I finally tracked down to my flybar. Stupid noob! It measured out okay and I counted number of turns putting the paddles on but it must have been off just enough to be a problem? Anyway, the tail fin is no longer a high speed blur.

Agreed, when I go with these bearing blocks, the lower OWB mount is going to take some thought but the idea of taking some material off the metal block to leave more of the plastic support is something I'll look at closely.

Bearclaw, I see what you're saying but really think any induced flex from the screw heads molded in the plastic would be negligible compared to screws going through a flat piece of CF. The holes in the metal bearing blocks are threaded and all but of a few of them allow the fastener to go in one side and out the other. I'd say that during manufacturing, one side was drilled and tapped then the piece flipped over and the other side done. Otherwise, the threads would line up.

Assuming a long screw would go the threads from one side to the other, assembling everything and using a nylock would be pretty tricky to get properly tensioned. Haven't given it that much thought yet because I haven't gotten into it. I may have to drill out all the threads which I agree may reduce rigidity but I might also be able to just drill out the threads on one side or something like that?

Time will tell, if I ever get any. At any rate, thanks all for the feedback and advice. When I make some progress, I'll post an update.

-- Elisabeth