Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

MPCNC 2826/2822 Brushless RC Motor Foam Cutter

by dkj4linux Dec 19, 2015
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Hello !

I'm trying to adapt this cutter for the new MPCNC tool system (525).
It would be a great help if you could share the originals files of your design.
Of course as soon as the new design is be fonctionnal, i will share it here.



What size ball bearing did you use?

If you are an RC and/or scratchbuilder kind of guy, you more than likely have suitable bearings all around you. I usually rob mine from trashed/junked RC motors... but you can also get inexpensive replacement bearings from HobbyKing, etc. Get one that is 8-10mm OD with a 3mm ID (bore)... 8mm x 4mm x 3mm are pretty common in motors with 3mm motor shaft. The holes in the flywheel are sized such that 3mm machine screws self-thread into the plastic and fit the bearing bore perfectly... remember to include a small washer to space the bearing slightly clear of the flywheel face.

Thank you! Can't wait to get this going. :) Been reading on FT, RC groups and openbuilds forums. Nice work!

I love this just brilliant

Thanks. If you are interested in the most current information, you should check out my thread on the Flitetest forum, where this basic design is very actively being discussed... there have been many improvements/updates/variants since this "thing" was introduced.


My feeble attempt at designing a crosshead bearing design for this needle cutter
Reciprocating motion is now limited to a loop in the needle twisted above the bearing, the bearing has a 3mm hole for a small 3m screw to bind the needle into the bearing, all lateral movement for the most part should be eliminated and now motion should be limited to an inline reciprocating motion...similar to the design of really old and large diesel/steam ship engines

Not sure how well plastic will hold up with mega high rpm's but I hope you see where I'm going with this


If you see the design flaw in regular piston type the side load due to the connector rod being tied directly to the piston (this is why over a long time the piston itself wallows out the cylinder wall, with the crosshead bearing, all the side load forces are removed

I really hope you guys see where I am going with this


If this is of interest and you have ideas for a working model, come on over, say "hi", and join in the discussion. The last 25 pages or so concerns improvements/modifications to this needle cutter, some I think similar to what you are proposing...


what do you use for software to input your airplane plans? like how to i use this once its built?

Since you asked about "airplane plans", you'll usually start with the PDF files available from the various RC sites... RCPowers, FliteTest, etc. Download and convert them to DXF format... I use "pstoedit" or Inkscape most often. Then I use SketchUp/SketchUCAM or Estlcam to do most of the toolpath generation. I import the DXFs, scale/edit/arrange all the various parts into "sheets" to match the sheet foam dimensions I'll be using, set in the material thickness, feed rate, tool diameter, etc... and then use the CAM tools to create all the toolpaths. Once satisfied I generate/output the gcode to a file. The gcode file is then put on a SD card or opened up in RepetierHost, UGS, etc. and sent to the CNC machine to move the needle cutter appropriately. The Z-axis, i.e.needle tip, is zeroed on the top surface of the material. All of the score cuts are 50% of the material thickness... elevons, ailerons, scores, etc. Then all the thru-cuts -- inside/outside cuts. I also use 1/32" (0.8mm) for the bit diameter... it all seems to work pretty well. Other CAD/CAM software can be used of course... dxf2gcode, Inkscape, etc... anything that can output gcode, properly formatted for your CNC machine.

thanks, I think I can figure this out now. I have been running a few test runs with estlcam. and will see what I can do. I'll have to figure out the needle length and set the depth correctly for 50% score cuts, could be tricky with warped foam board. you mentioned using a 8mm bit, is that for a router but you use to cut the outer edges instead of the needle? and FYI,I'm using the mpcnc 525.

Jimmy, the needle is brought down to just "tickle" the surface of the foam to set Z-axis zero... I actually do it with the needle cutter running and listen for the sound and the small dot. Foam can be held down (weights, T-pins, etc) around the edges pretty well if you place it "crown-down" on the spoilboard so that the center of the foamboard stays firmly against the spoilboard. The kerf of a 0.025" needle is about 1/32" (0.8mm) so if you are doing inside and outside cuts, the CAM progam knows how much offset to apply... otherwise, you can probably get by in foam with just doing a centerline trace on all lines.

If you haven't already, check out my FliteTest thread... there's tons of content there including several cheap vacuum hold-down concepts. Some using, of all things, foamboard... needle cut grooves/slots and holes appropriately in 2-3 sheets of DTFB and laminate them together in a simple frame to form a vacuum system prefectly sized for DTFB. Check them out...

CartCurt's vacuum hold-down...

GremlinRC's mechanical hold-down...

Did you mean for the 2826 version to not have the guide mounting holes?

This was the very first version of the brushless foam cutter, using a 2200kv 2826, and the inflation needle guide was simply threaded directly into the plastic. Since then, because of higher cutter speeds and friction heating of the needle guide, more heat-tolerant guide mounting systems have been developed... hence the guide mounting holes in the later 2822 (1200kv) version. The most common method is now to use a wooden sub-platform to thread the guide into and then the whole guide assembly aligned and bolted to the bottom using the guide holes.

Please recognize that the brushless foam cutter has been designed/developed "out in the open" and most of the earliest and intermediate versions have been obsoleted and superceded by later foam cutter developments. Please check out my response to Rickmcolorado below for links to these later developments. -- David

Oh ok, I didn't realize that the 2826 version wasn't actively changed. I was looking to use that version due to having an extra 2826 motor lying around! Thanks, I'll make it work. Maybe I can just epoxy the wood piece to the bottom, seeing as most printed parts don't take too kindly to bring drilled... Thanks for the reply!

Drilling small holes through printed parts isn't a big deal (I do it all the time...) as long as you keep the speeds down and don't dwell in the hole too long. Just drill through both pieces at the same time or drill one and then "match-drill" the other as shown here... http://forum.flitetest.com/showthread.php?24251-Cutting-foam-sheets-with-a-needle!&p=282568&viewfull=1#post282568

The 2826 I had on hand was a 2200kv motor and I initially thought the speed would be an advantage. It isn't... and the lower kv motors -- somewhere around 1000kv -- better utilize the range of the servo tester's potentiometer. The useful speed range for this foam cutter design is about 4000 to 10000 rpm. Any higher than 10k rpm and things get way too "exciting" and stressful... for both you and the mechanism ;)

Also, if you haven't discovered it yet... set up an free account and use TinkerCad (https://www.tinkercad.com/) to import the STL and add the holes... group, save, and print. It's really simple to use and quite powerful. -- David

What size wire and what type of wire are you using? How far does the wire go into the foam board or how deep can you cut?


Thanks for your interest.

0.025" music-wire is what I normally use... Mig-wire can be used in a pinch The total length of stroke is 12mm using the 6mm hole position for the bearing (as shown) and determines the max material thickness or depth of cut... this is suitable for sheet foams up to 9mm or so thickness. Moving the bearing out to the 11mm hole position would yield a stroke of 22mm but is not recommended as it will greatly increase the required needle flex and shorten the needle life... unless you re-position the motor higher, relative to the top of the needle guide, to decrease the amount of required needle flex.

There is a "no flywheel" version of the foam cutter that uses a mousetrap/clothespin spring for the crank-pin that doesn't require the dynamic balancing the printed version requires. If you are interested and "handy"... start here:


There are also lengthy threads out on the RCPowers, Openbuilds, RCGroups and FliteTest forums that document in great detail the development of this foam cutter, its many versions/variations, and numerous really nice user builds/mods if you are interested. The most active are these (go to the latest posts for the most current information):





I am having trouble figuring out what parts I need to be able to build this after printing it. I am not sure what bearing to use, what tip is being used / recommend, and I am not 100% all the screws and bolts that are needed. A parts list would be very helpful.

Helpful but not at all necessary. This DIY foam cutter assumes you to be reasonably handy with tools and can be made to work with a wide variety of salvaged or purchased parts... and built in a variety of configurations, i.e. 3dprinted or conventional, flywheel or non-flywheel versions, inflation needle or welding tip guide, etc. Follow all the links on the ThingDetails page and, additionally, the lengthy foam cutter development threads on the RCPowers, RCGroups, and FliteTest forums. There is a wealth of information on this MPCNC-specific and other builds... and numerous user builds. Go to the more recent posts for the latest versions (https://www.youtube.com/watch?v=7yA7XSl-wnU) and ideas on what it takes to build a very simple but very effective and economical CNC foam cutter... the cutting method and basic operation remains the same, regardless. Join in and ask questions... these forums are full of very knowledgeable folks, eager to help.




-- David

Great tool. Just wanted to see if you had planed to update to the new tool mount with the new Z section.

No plan yet. I've not built a new middle assembly for any of my machines. I'm sure someone will do it pretty soon... it's a pretty easy mashup in Tinkercad. =8^)

Great thing David. Thanks for sharing.

You're very welcome.