Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
May 26, 2020, 07:12:21 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1] 2   Go Down
Print
Author Topic: carbon motorstick  (Read 2612 times)
0 Members and 1 Guest are viewing this topic.
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« on: December 05, 2016, 11:24:22 AM »

I've recently been in contact with Roel at CCT with the idea of trying my hand at a carbon stick. From the bit of searching I've done, it's clearly better to use some sort of two halves tube mould rather than the brass mandrel I've been using for my balsa sticks. Roel says that Kevin Lamers has had these machined. I wonder how to get a hold of one. I'm also trying to get a gauge on how much prepreg to order for about 5 sticks. Any tips appreciated.
best
Hans
Logged
USch
Platinum Member
******

Kudos: 33
Offline Offline

Italy Italy

Posts: 1,151




Ignore
« Reply #1 on: December 05, 2016, 12:09:12 PM »

Have a look at the topic "New F1N build" at
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21370.0

Kevin talks about the motor tube for his model and about how much material he is using.

Urs
Logged

Fast up-Slow down
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,576



Ignore
« Reply #2 on: December 05, 2016, 12:21:20 PM »

I've recently been in contact with Roel at CCT with the idea of trying my hand at a carbon stick. From the bit of searching I've done, it's clearly better to use some sort of two halves tube mould rather than the brass mandrel I've been using for my balsa sticks. Roel says that Kevin Lamers has had these machined. I wonder how to get a hold of one. I'm also trying to get a gauge on how much prepreg to order for about 5 sticks. Any tips appreciated.
best
Hans

I believe Kevin used a straight male form for his motorstick.
Logged
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #3 on: December 05, 2016, 01:15:37 PM »

Have a look at the topic "New F1N build" at
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21370.0

Kevin talks about the motor tube for his model and about how much material he is using.

Urs
[/quote

Wow Urs, very useful link, thanks. The picture Kevin posted is of a sizeable mould! Does all that go in a regular kitchen oven? Maybe there's some vacuuming involved. I'm going to have to get my head around how this all works. This is not a case of some pre preg tape around a brass mandrel!
Hans
Logged
Tmat
Titanium Member
*******

Kudos: 68
Offline Offline

Canada Canada

Posts: 2,944




Ignore
« Reply #4 on: December 05, 2016, 02:43:12 PM »

Bill,
It appears that Kevin is using a Female mold (CNC machined aluminum) with a Male silicone rod used to apply internal pressure. No vacuum is used Hans. When the mold is heated, the silicone has a much higher coefficient of thermal expansion than the aluminum and applies a large pressure internally to the prepreg. Stretching the silicone makes the diameter smaller and thus can be extracted. Most people don't have access to CNC equipment however. ;-)


Tmat
Attached files Thumbnail(s):
Re: carbon motorstick
Logged

F1B guy...
But don't hold that against me!
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #5 on: December 05, 2016, 03:04:30 PM »

Bill,
It appears that Kevin is using a Female mold (CNC machined aluminum) with a Male silicone rod used to apply internal pressure. No vacuum is used Hans. When the mold is heated, the silicone has a much higher coefficient of thermal expansion than the aluminum and applies a large pressure internally to the prepreg. Stretching the silicone makes the diameter smaller and thus can be extracted. Most people don't have access to CNC equipment however. ;-)


Tmat

Hi Tmat,
true, but he says he had this machined in China courtesy of Alibaba!, so 'anyone' can do it. So he wraps the prepreg around the silicone rod, one layer lengthwise with a 1mm overlap, and one length spiralled along the silicone rod, places it in a female mould half, then screws on the other half. Sticks the entire business in an oven and the silicone presses more firmly on the prepreg for the reasons you mention. When cured he disassembles the two halves and can pull the silicone tube out due to it stretching and therefore narrowing when pulled. From the photos I've seen the sticks seem quite a bit narrower than typical balsa, so you'll need to make a narrower balsa boom, which might make them a bit flimsy.
Hans
Logged
Tmat
Titanium Member
*******

Kudos: 68
Offline Offline

Canada Canada

Posts: 2,944




Ignore
« Reply #6 on: December 05, 2016, 03:07:58 PM »

Hans,
Naturally Kevin made a tapered carbon tailboom as well!
I've seen it posted elsewhere. Same method.

Tmat
Logged

F1B guy...
But don't hold that against me!
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,576



Ignore
« Reply #7 on: December 05, 2016, 03:11:51 PM »

Bill,
It appears that Kevin is using a Female mold (CNC machined aluminum) with a Male silicone rod used to apply internal pressure. No vacuum is used Hans. When the mold is heated, the silicone has a much higher coefficient of thermal expansion than the aluminum and applies a large pressure internally to the prepreg. Stretching the silicone makes the diameter smaller and thus can be extracted. Most people don't have access to CNC equipment however. ;-)


Tmat

Tony
I'm old but the brain still occasionally functions! See below:


http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=17528.0

(reply #8)
The tube in the first post was made by me. The material for it is the 19 gsm prepreg you can buy from CCT. Yesterday, I flew the tube (which has no bracing at all) for the first time and loading a fully wound F1D motor to it was peanuts. I haven't tested what a breaking motor does to it yet, but time will tell. I expect it might be able to even survive such a thing.
This tube was made with first an UD layer in length direction on an aluminium form followed by wrapping it with a 2 mm wide piece of the same material. After curing, this spiral layer was sanded down by 30% or so. For F1M simply using 2 lengthwise layer followed with a spiral layer that isn't sanded down, should suffice I would say.

Kevin

(reply #11)
Quote from: Tapio Linkosalo on March 16, 2015, 11:56:46 AM
Do you use a conical form, or how do you release the tube from the form?

Nope, it is not conical. Releasing is quite difficult, but with some persistence you will succeed. The expansion coefficient of the aluminium tube helps a bit ;-)

Kevin

(reply #13)
Cure at 140C, released at room temperature. It is still quite tight, but it is possible to release it.
The tube has a high gloss polished surface. Release agent is Marbocote 227CEE, in my opinion the best stuff for non porous surfaces.

Kevin

(reply #15)
I simply rest the aluminum form vertical on the table, grab the carbon tube (which is shorter than the form) with my hands and push down against the table. What also worked sometimes was tack glueing the carbon tube to the table on one end, and then pushing the aluminum form out with something.

Kevin
Logged
piecost
Gold Member
*****

Kudos: 8
Offline Offline

United Kingdom United Kingdom

Posts: 465



Ignore
« Reply #8 on: December 05, 2016, 03:36:55 PM »

I wonder if plumbers freezing spray could be squirted in the inside of the mandrel to aid removal. It might be prudent to try with a mandrel before investing in a mold.
Logged
jakepF1D
Gold Member
*****

Kudos: 8
Offline Offline

United States United States

Posts: 456


1996 World Champs



Ignore
« Reply #9 on: December 05, 2016, 04:10:13 PM »

Kevin sent me the 3D model of his mold, and I'm having it made in the machine shop where I work.  The first half was completed this morning, and the second half should be done by next week.  The mold will make 5 different size tubes.  4mm and 4.5mm OD for motor tubes, 1.25mm and 1.5mm for wing posts or prop spars, and a tapered tube for making tail booms. 

I also have some 19gsm carbon in transit from CCT, so I should be able to make my own carbon tubes by the beginning of 2017. 

Unfortunately I won't have time to test these tubes until after the US F1D team finals in June, so for now I'm sticking with my Aikman motor tubes and tail booms.
Logged
USch
Platinum Member
******

Kudos: 33
Offline Offline

Italy Italy

Posts: 1,151




Ignore
« Reply #10 on: December 05, 2016, 04:20:21 PM »

About reply #8
you dont need any spray to cool down the mandrel. As a matter of fact carbon composites have near to zero thermal expansion-retreat in a wide range of temperatures, up to 200°C and much below 0°C. So all you have to do is putting the mandrel and carbon tube in a freezer to help release. The slack you get depends on the difference of moulding temperature and demoulding temperature and the material for the mandrel, choose one with a high thermal expansion, f.e. aluminium.

Urs
Logged

Fast up-Slow down
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #11 on: December 05, 2016, 04:52:58 PM »

Kevin sent me the 3D model of his mold, and I'm having it made in the machine shop where I work.  The first half was completed this morning, and the second half should be done by next week.  The mold will make 5 different size tubes.  4mm and 4.5mm OD for motor tubes, 1.25mm and 1.5mm for wing posts or prop spars, and a tapered tube for making tail booms. 

I also have some 19gsm carbon in transit from CCT, so I should be able to make my own carbon tubes by the beginning of 2017. 

Unfortunately I won't have time to test these tubes until after the US F1D team finals in June, so for now I'm sticking with my Aikman motor tubes and tail booms.

That's interesting. A mould for all the components! Do you have any idea what kind of weights you can expect from the components? I guess a 1/4" (6.33mm) mandrel is just going to yield a heavy stick.
Hans
Logged
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,576



Ignore
« Reply #12 on: December 05, 2016, 05:40:17 PM »

Kevin sent me the 3D model of his mold, and I'm having it made in the machine shop where I work.  The first half was completed this morning, and the second half should be done by next week.  The mold will make 5 different size tubes.  4mm and 4.5mm OD for motor tubes, 1.25mm and 1.5mm for wing posts or prop spars, and a tapered tube for making tail booms.  

I also have some 19gsm carbon in transit from CCT, so I should be able to make my own carbon tubes by the beginning of 2017.  

Unfortunately I won't have time to test these tubes until after the US F1D team finals in June, so for now I'm sticking with my Aikman motor tubes and tail booms.

Those tube sizes are tiny. Do you have info to indicate they are strong enough?
Logged
jakepF1D
Gold Member
*****

Kudos: 8
Offline Offline

United States United States

Posts: 456


1996 World Champs



Ignore
« Reply #13 on: December 05, 2016, 06:00:12 PM »

Only the experience of Kevin.  Keep in mind that the hook to hook distance only needs to be about 6-7 inches for a new rules model, and the motors are quite small at 400mg.  The bigger challenge will be determining whether the tube will twist enough for proper wing wash at launch torque.
Logged
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,576



Ignore
« Reply #14 on: December 05, 2016, 06:19:23 PM »

Only the experience of Kevin.  Keep in mind that the hook to hook distance only needs to be about 6-7 inches for a new rules model, and the motors are quite small at 400mg.  The bigger challenge will be determining whether the tube will twist enough for proper wing wash at launch torque.

I'd be thrilled to have a stick that didn't twist at all. But that's just me and my contrarian views.
Logged
Tmat
Titanium Member
*******

Kudos: 68
Offline Offline

Canada Canada

Posts: 2,944




Ignore
« Reply #15 on: December 05, 2016, 06:39:58 PM »

I'd be thrilled to have a stick that didn't twist at all. But that's just me and my contrarian views.

Bill contrarian?
Never ....


Tmat ;-)
Logged

F1B guy...
But don't hold that against me!
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #16 on: December 05, 2016, 06:42:58 PM »

Only the experience of Kevin.  Keep in mind that the hook to hook distance only needs to be about 6-7 inches for a new rules model, and the motors are quite small at 400mg.  The bigger challenge will be determining whether the tube will twist enough for proper wing wash at launch torque.
It might be nice to request this 3d mould drawing from Kevin, but I'm curious what the cost of having this machined might be. Amazing to read that his wall thickness is 0.03mm. On the F1N thread he writes: "The UD material, once released from its backing foil has no stability at all. After 2 layers are stacked at 0/90 degrees and pressed together under vacuum". Sounds like you need to invest in a vacuum pump and some bagging too.
Hans
Logged
jakepF1D
Gold Member
*****

Kudos: 8
Offline Offline

United States United States

Posts: 456


1996 World Champs



Ignore
« Reply #17 on: December 05, 2016, 06:53:11 PM »

I'm not sure a stick that doesn't twist would result in an efficient model.  I want the wing to be flat during the cruise, and that would be difficult to achieve unless the stick twists.
Logged
jakepF1D
Gold Member
*****

Kudos: 8
Offline Offline

United States United States

Posts: 456


1996 World Champs



Ignore
« Reply #18 on: December 05, 2016, 07:02:04 PM »

It might be nice to request this 3d mould drawing from Kevin, but I'm curious what the cost of having this machined might be. Amazing to read that his wall thickness is 0.03mm. On the F1N thread he writes: "The UD material, once released from its backing foil has no stability at all. After 2 layers are stacked at 0/90 degrees and pressed together under vacuum". Sounds like you need to invest in a vacuum pump and some bagging too.
Hans

I had the mold quoted through a place on Alibaba for $200 plus shipping.  I will probably end up paying more to have it made in our shop, but it's much less risk.  Buying through an unknown Chinese CNC shop was a bit of a concern for me.  

All Kevin did was use the vacuum to apply pressure which helps bond the 2 layers before putting it in the mold.  My Foodsaver will work fine for this purpose.  I've already used it to make some smaller composite parts, and it worked great.
« Last Edit: December 05, 2016, 07:16:33 PM by jakepHLS » Logged
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #19 on: December 06, 2016, 03:22:19 AM »

It might be nice to request this 3d mould drawing from Kevin, but I'm curious what the cost of having this machined might be. Amazing to read that his wall thickness is 0.03mm. On the F1N thread he writes: "The UD material, once released from its backing foil has no stability at all. After 2 layers are stacked at 0/90 degrees and pressed together under vacuum". Sounds like you need to invest in a vacuum pump and some bagging too.
Hans

I had the mold quoted through a place on Alibaba for $200 plus shipping.  I will probably end up paying more to have it made in our shop, but it's much less risk.  Buying through an unknown Chinese CNC shop was a bit of a concern for me.  

All Kevin did was use the vacuum to apply pressure which helps bond the 2 layers before putting it in the mold.  My Foodsaver will work fine for this purpose.  I've already used it to make some smaller composite parts, and it worked great.

Interesting. Do you think there may be issues of keeping the layers flat in the Foodsaver vacuum bag?
Logged
USch
Platinum Member
******

Kudos: 33
Offline Offline

Italy Italy

Posts: 1,151




Ignore
« Reply #20 on: December 06, 2016, 04:59:09 AM »

Just a guess, but from experience I am sure it will work.

To "glue" the 2 layers together put them one on top of the other with the liner outside of course. Lay on a flat, clean surface and pass over it with a small iron as used for Monokote. Keep the temperature low at about 40-45°C. The low temperature will have to be tried to be sure the resin in the pre-preg will just get tacky to stick the 2 layers together.

BTW, vaccuum is not a big problem. Just get an old compressor from a useless fridge, thats about the best you can have at 0$. They do not move a huge air volume per minute, but they go up to -0,95bar depression. And to empty a small vaccuum bag you dont need big compressors. Another advantage is they are very silent.

Urs
Logged

Fast up-Slow down
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #21 on: December 06, 2016, 12:13:21 PM »

thanks Urs that makes sense. Plecost might have a point in trying an aluminium mandrel to begin with. In the F1N thread there's talk of spiralling a 2mm wide piece around the mandrel. I'm sort of envisioning laying the cloth on a table and ironing the edge of it onto a mandrel with release agent on it, rolling the material around the mandrel and again carefully ironing the overlap. Then a similar attachment method with the spiral piece. I imagine the cloth being prepreg it might not be so difficult to cut without bunching.
Logged
jakepF1D
Gold Member
*****

Kudos: 8
Offline Offline

United States United States

Posts: 456


1996 World Champs



Ignore
« Reply #22 on: December 06, 2016, 12:35:57 PM »

Interesting. Do you think there may be issues of keeping the layers flat in the Foodsaver vacuum bag?

I would put the carbon between layers of MDF or plywood and put the whole setup inside the bag.  That will keep the carbon flat and apply even pressure everywhere.  I would also do as USch mentioned and warm the prepreg to get the resin tacky.
Logged
USch
Platinum Member
******

Kudos: 33
Offline Offline

Italy Italy

Posts: 1,151




Ignore
« Reply #23 on: December 06, 2016, 01:42:01 PM »

If your good wife allows you can apply even pressure with her iron (set at low temperature)  Grin

Urs
Logged

Fast up-Slow down
brabazon
Bronze Member
***

Kudos: 0
Offline Offline

United Kingdom United Kingdom

Posts: 31

Topic starter


Ignore
« Reply #24 on: December 07, 2016, 01:01:11 PM »

I'm not sure a stick that doesn't twist would result in an efficient model.  I want the wing to be flat during the cruise, and that would be difficult to achieve unless the stick twists.
I think you raise an interesting point. My models seem to require a fair bit of stick bow. I would imagine you're going to get stick bow even with carbon. Probably not as much as with a balsa stick, but I hadn't considered that perhaps the wash in situation is even more important. I have seen the French team fly carbon sticks in the mine. They flew well, and look cool, but they didn't beat balsa on the two occasions I've been privileged to go.
Logged
Pages: [1] 2   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!