L66H37 V0.2 LiPo Crash Protector Carbon Fiber Cage for drone frame

Intro

Name: Sugalime3D FPV L66H37 V0.2 LiPo Crash Protector Carbon Fiber Cage for drone frame

It can be used on the Mirro35 drone frame or almost any other 3-4" drone frame, though the arches (bows) might not be able to be spread quite as wide. The more rectangular the top plate is, the better, and the more securely and stable the cage sits on.

PURPOSE OF IT:

Reducing the risk of a LiPo damage and LiPo fire because of a drone crash.

It's actually questionable that so many people take the risk of their LiPo batteries being subjected to impacts from crashes. They're basically playing with the fire. Damaged LiPo batteries can catch fire later while charging or even spontaneously in storage. They endanger their own lives and the lives of others in the house building. The property is also at risk and therefore also financial risk as a result.

A burning LiPo battery can destroy your drone. Tell me, how do you safely remove a sparking LiPo from the drone ? And then, do you just leave the burning LiPo there because you can't put it in your backpack or car ? Leaving it behind is illegal and—depending on where it’s left—could start a forest fire... It is therefore better to avoid LiPo damage by all means !

Timeline

Check regularly for updates. More parts will likely be added if the tests are successful (TPU parts, carbon fiber parts, ...) !

* July 13, 2026: Publication date: Starting with Bow 0tilt OPCO turned45XZ.

Selected posts from social media of this project (new to old)

https://www.tiktok.com/@sugalime3d_fpv/photo/7651990681170251030

https://www.tiktok.com/@sugalime3d_fpv/photo/7649392975356742934

https://www.tiktok.com/@sugalime3d_fpv/photo/7649114760083967254

https://www.tiktok.com/@sugalime3d_fpv/video/7643972052671646998

https://www.tiktok.com/@sugalime3d_fpv/video/7643669904998026518

https://www.tiktok.com/@sugalime3d_fpv/video/7624712236430298390

Specs

Compatible LiPo sizes:

LiPo battery with it's straps and the Lipo pad max dimensions is: 66 mm in length, 37 mm in height.

However, you also need to consider or select the right size so that the cables come out properly through the cable opening...

Compatible examples Year 2026 (No guarantee !):

* LiPo 4S 850 mAh for example in 58-62 x 32 x height 32 mm

* LiPo 4S 750 mAh for example in 58-62 x 31 x height 27 mm

* LiPo 4S 650 mAh for example in 58-62 x 31 x height 22 mm

Not compatible examples Year 2026 (No guarantee !):

* ...

CARBON FIBER THICKNESS:

The bows are 2,0 mm

The side plates are 1,5 mm

Used Screws: M2 regular

Used Standoffs: M2 D4 (or M2 D3,5)

Available editions so far

Labels:

"OPCO" = Outer Perimeter Chamfered Only

"turned45XY" = Turned 45° on XY axis. Arms parallel to carbon fiber pattern.

"NC" = No chamfers

"NCS" = No countersinks

" " (No label) = Designer's edition "Director's cut" (Like the designer wishes it to be cutted/milled :D)

See descitption CNC service Chamfer editions for the detailed description of the labels

* Bow OPCO turned45XZ

More parts are comming soon (no guarantee !)

After the allready uploaded 0tilt edition top plate has been successfully tested, I will add more (no guarantee):

* Bow 0tilt NC turned45XZ

* Bow 45tilt OPCO turned45XZ

* Bow 45tilt NC turned45XZ

* Side plate non cable side

* Side plate cable side SLOW

* Side plate cable side FAST

* Side plate non cable side OPCO

* Side plate cable side SLOW OPCO

* Side plate cable side FAST OPCO

* Side plate non cable side NC

* Side plate cable side SLOW NC

* Side plate cable side FAST NC

...

Bows configurations: standoffs and screws

You could also leave off the side plates. However, keep in mind that something (like a tree branch or a thin post) could still strike the LiPo from the side; since the LiPo only has reinforced plates on the top and bottom, it is vulnerable on the sides, front and rear.

STANDOFFS:

For M2 Standoffs D4 (or D3,5)

Length: It depends on your existing top plate of your drone. You need to find out yourself...

Here for Mirro35 drone frame:

4 BOW CONFIG without side plates:

If you have a 45° tilt, there are 2x "bow cam tilt" in the middle.

Screws: M2 12,0 mm

Central Standoff: 8,0 mm

Outer Standoffs: 7,0 mm or 6,0 mm with 1,0 mm Spacer. Or 6,0 mm (Than it will be a bit less wide, no problem...)

...

3 BOW CONFIG with side plates:

If you have a 45° tilt, there are 1x "bow cam tilt" in the middle.

Middle part: 11,5 mm (or smaller) in length.

Outer part: 2,5 mm (or larger) in length,

2 BOW CONFIG

Theoretically, it works with just two bows (arches), but If the LiPo straps come loose, there is a higher risk of the cage tilting downwards from the top plate. Therefore I recommend at least 3 bows.

Weight calculation (theoretically)

Bow (without chamfers) = cm^2

* 2,0 thick T-700 carbon fiber = g / bow.

4 bows = g

• Weight of M2 titanium screws
• Weight of M2 aluminium standoffs

If the drone is at XX g without cage and 450mAh Lipo. With the LiPo Crash Protector it is approx XX % heavier.

But keep in mind that many pilots, especially Bando pilots, mount a TPU horn at the front to protect the LiPo battery. TPU is very heavy. Presumably this kind of TPU protector is just as heavy, but doesn't protect the LiPo as well as this LiPo Protector Cage. So overall this cage is the better solution in my opinion.

Designed to international standards

Based on DIN EN ISO 7721 and ISO 10642. And close fit (not normal fit) with screws MX regular (not MX fine).

M3 screws ISO regular M3x0.5:

Screw Clearance M3 Holes: 3.20 mm (clearance close 3.2 not medium 3.4 mm)

M3 90° Countersink: 6.50 mm diameter (not the theoretical max of 6.94 mm)

(with FreeCAD PartDesign_Hole, ISO regular, clearance setting close/fine, results in 3.2 mm hole)

M2 screws ISO regular M2x0.4:

Screw Clearance M2 Holes: 2.20 mm (clearance close 2.2 not medium 2.4 mm)

M2 90° Countersink: 4.40 mm diameter

(with FreeCAD PartDesign_Hole, ISO regular, clearance setting close/fine, results in 2.2 mm hole)

M1.6 screws ISO regular M1.6x0.35:

Screw Clearance Holes: 1.70 mm (clearance close 1.7 not medium 1.8 mm)

M1.4 screws, ISO regular M1.4x0.3:

Screw Clearance Holes: 1.50 mm (clearance close 1.5 not medium 1.6 mm)

CNC SERVICE

You can give the CNC service the STEP files; it contains all the information, including details about the plate thickness and chamfers.

Design for Manufacturing

The project was designed with the practical CNC process in mind to ensure the CNC service faces no difficulties and can cut the part quickly and cheap—for example, through a design that is as simple as possible (balancing functionality and simplicity), large fillets, minimal chamfering, ...

List of services

(No guarantee of legitimacy, these are all the ones I found, not the ones I tested.)

You can buy my frames Made in ROC (Taiwan) at the Sugalime3D FPV Frames With Zero Design Fee Shop:

https://www.armattanproductions.com/pages/shop_product_grid/10788

The frame is currently not listed on any other of the stores, so you will need to request a quote.

* Made in Canada: CNCdrones dot com; CNCMadness dot com; ...

* Made in France: FPVCNCdrone dot com; ...

* Made in Germany: Ahltec dot de (Inh. Angelika Leonhardt); carbonforce dot de (CarbonForce® GmbH), carbon-composite dot com (Carbon Composite AG); carbon-express dot com (CARBON-EXPRESS GmbH), carbon-posten dot de (Inh. Sandra Schmidt); cg-tec dot de (CG TEC Carbon und Glasfasertechnik GmbH); ...

* Made in People's Republic of China: CK-Carbon Fiber Store (Aliexpress store ID 1104334140 or search for 1005012382499688 (item)); FPVdroneframe dot com; pcbway dot com; ...

* Made in Republic of China (Taiwan): armattanproductions dot com (Armattan Productions Co., Ltd); ...

Carbon fiber material international standards

Choose what you consider the best sweat spot for your purpose or choose T-800S if money is not a factor to be considered.

Tensile strength is the factor when it comes to arm breaking. Tensile modulus (stiffness) is the factor for vibrations and resonances that can be transmitted to the gyro.

* T-300: Tensile strength: ~ 3530 MPa. Tensile modulus (stiffness): ~ 230 GPa. The affordable and most used standard.

* T-700S: Tensile strength: ~ 4900 MPa. Tensile modulus (stiffness): ~ 235 GPa. Used on expensive high-quality premium frames.

* T-800S: Tensile strength: ~ 5685 MPa. Tensile modulus (stiffness): ~ 294 GPa. Consumer ready in the future. This aerospace and commercial aviation standard is becoming affordable for the consumer hobby market. By now, some very expensive premium drone frames actually use it.

Plate rotation for carbon fiber rectangle pattern matching arms

Should be good. It doesn't really matter that they're mostly right angles. The CNC manufacturer should normally position them correctly using this STEP files for side plates and the Bow turned45XZ.

ADVICE FOR MYSELF THE DESIGNER (so i never foget in future project exports): In FreeCAD the STEP export has to be saved with "Export single object placement" otherwise it won't be rotated by 45° if the FreeCAD transform feature (with Right click in the tree on the body) was used later !

Fillets

The fillets are always chosen to be as large as possible (better for durability) and never have a radius below 0.50 mm (standard milling heads have a minimum limit).

The smallest fillet radius used in this project:

Outer fillet: mm

Inner fillet: 1.95 mm

So it can be milled with a D3.9 mm CNC theoretically (not recommanded), D3.5 mm CNC practically (should work well).

Why fillets always need to be slightly larger than the drill diameter you want to use:

If the milling cutter matches the inner corner radius exactly, the tool tends to "wrap around" the corner (increased wrap angle). This can lead to vibrations or tool deflection. If tolerances allow, it is often advantageous in CNC milling to specify a slightly larger inner radius in the CAD model; this allows the cutter to navigate the corner smoothly rather than having to change direction abruptly...

The minimum inner corner fillet is selected as follows :

* R 1.2 mm D 2.4 mm (2.0 mm cutter with 0.2 mm clearance every side)

* R 1.45 mm D 2.9 mm (2.5 mm cutter with 0.2 mm clearance every side)

* R 1.7 mm D 3.4 mm (3.0 mm cutter with 0.2 mm clearance every side)

* R 1.95 mm D 3.9 mm (3.5 mm cutter with 0.2 mm clearance every side)

* R 2.2 mm D 4.4 mm (4.0 mm cutter with 0.2 mm clearance every side)

...

This makes it possible to always use the largest possible milling cutter. This speeds up the CNC job, thereby making it more cost-effective...

Chamfer editions & Edition labels

The chamfers are important to prevent the electric cables, the LiPo straps or your fingers skin from being cut.

4 labels

* NC NCS: Edition is without chamfers and without countersinks. This edition is only available if a Designer's Edition with countersink exists for the part. Advantage: Requires the least milling work. The cheapest option.

* NC: Edition is without chamfers (NC = No chamfers) Advantage: The (second) cheapest option.

* OPCO: Edition is with "Outer Perimeter Chamfered Only". Requires often only a bit more milling work using a buck side chamfer mill.

* NORMAL (Non labeled): It is the designer's version "Director's cut" . Like the designer wishes it to be. Version includes maximum of meaningful chamfers. Disadvantage: A part with a lot of chamfers on both sides can be very expensive especially when holes or radii are small, depending on the capabilities of the CNC manufacturer. The effort and time involved in the milling process can increase significantly. Consequently price can be 2-3x higher than that of the NC NCS version. Sometimes the OPCO edition already is the designer's edition.

Buck side chamfer CNC process

The CNC service typically creates the double sided chamfer using a special drill head (buck side chamfering) that first makes the chamfer on top then on the bottom, or they use a high accuracy plate turning process if the holes are too small for the special drill.

Public example of buck side chamfering

https://www.youtube.com/shorts/9M66unswJ7c

Creating round edges without chamfer milling

The sharp corners can also be rounded off without milling chamfers: They place the part in a in a tumbling drum and they use a sharpening stones tumble vibratory deburring method, or they use other methods to remove the corners sharpness. However, the corners aren't rounded off as much with this method—especially if the manufacturer does not give it a lot of time to it. The edges remain relatively sharp and it doesn't match the quality and smoothness of chamfer milling. COSTS: Sometimes rounding the corners like this is cheaper, sometimes milling the chamfers is cheaper—it depends.

THE FRAME IN THE PICTURES AND ASSEMBLY FILES

If you like it.

Mirro35 V0.5 drone frame:

https://www.thingiverse.com/thing:7379639

DEVELOPMENT FUTURE (Planned changes for the next version)

*No

DEVELOPMENT HISTORY

PREVIEWS VERSIONS:

L66H37 V0.1 LiPo Crash Protector Carbon Fiber Cage for drone frame

https://www.thingiverse.com/thing:7377442

GUARANTEE

Use at your own risk ! It is in version 0.2 and not 1.0 !

This version is the first version i will order at a CNC service. I guess it should work. However, it has not been tested yet. Big and/or small errors are possible. The design is still in the prototype phase. I have not ordered and tested the part through a CNC service yet. Therefore, the part may still be revised and then appear as V0.5 on a new page. Maybe tests will be successful and this will be the final version of the Mirro35 drone frame.

Used 3D CAD software

FreeCAD 1.0.2 was used for this project.

COPYRIGHT & CREDITS

PRIVATE USE:

You are allowed to download and copy and modify the frame for private use and upload and publish a CAD mod/remix with credits (My name and the link to this one); please note the license terms specified below. For non-commercial purposes, i.e., hobby videos or picture in the internet, me or the name of the frame I don't expect to be mentioned in videos or pictures or description. However, I appreciate it if you mention the name of the frame and the designer in the vid/pic itself or description.

COMMERCIAL USE:

I permit to download and use and copy and modify for commercial sales. However, I expect the designer name and product name to be mentioned in the title or description of the product with the product name: "L066H037 LiPo Crash Protector" and the designer name :"Sugalime3D FPV" or "Sugalime3D FPV design" or "designed by Sugalime3D FPV".

Examples:

[Your Brand] Sugalime3D FPV L66H37 LiPo Crash Protector Carbon Fiber Cage

[Your Brand] L66H37 LiPo Crash Protector Carbon Fiber Cage Sugalime3D FPV design