| Table of Contents | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Context
This page was created by Daniel Puratich to standardize how custom hardware is designed with respect to mounting hole dimensions and mounting patterns during the 2023 competition cycle and is being improved over time.
This document is valid for at least 2023 System Architecture & 2024 System Architecture . This document , and directly refers to Connector Standards as well for implementation. This standard was initially discussed as a part of 2023-02-11 - EE Hardware Mounting Hole Specification in the RFC Forum as a collaboration between WARG’s electrical and mechanical subteams.sub-teams.
This document is being revised over time. When creating new board designs, check the recommended specifications below before beginning. Both mounting hole size and spacing are standardized and must be followed for WARG hardware.
Common Mounting Holes Sizes
For Going forward, general custom EE flight PCBAs going forward we will follow this the mechanical mounting hole and pattern specification listed below. These mounting holes can be found in our Altium library.
...
Larger is welcome if it is (1) designed with collaboration with the mechanical team and (2) generally intended for a specific application. You can do anything as long as it is well backed up with engineering information. For example, https:
“Large” Boards:
...
Preferred dimensions for PCBAs
...
M3
//uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2694545459/LED+Board+Rev+3?search_id=824a823d-a091-44cd-a839-e67436297d92&additional_analytics=queryHash---e0fa16d9bc21f8c98c92d9fbd02b64297e9353182612e9bd2a87080f9ae2fbc1 uses M4 mounting holes and is intended to share bolts with a mechanical system.
Sizes
These mounting holes can be found in our Altium library.
M3
3.40 mm hole diameter
0.10 mm hole diameter tolerance
6.00 mm annular ring diameter
“Medium” Boards:
M2
Used Advised on any PCBA with area exceeding 750mm^2 and less than 2500mm^2exceeding a board area of 900 mm^2
a vast majority of WARG boards fall in this category, if you aren’t sure, use these M3 holes.
M2.5
Not recommended
M2
2.40 mm hole diameter
0.10 mm hole diameter tolerance
4.20 mm annular ring diameter
“Small” Boards:
No Mounting Holes
- This is because Running
Do this for any smaller boards because running holes smaller than M2 is not really practical as per past conversation .
Used on any PCBA with area less than 750mm^2No mounting holes will be present on board of this size.
Mounting will be done with double sided sticky tape or Velcro and the board should be designed to facilitate this.
- This is because Running
Mounting Hole Parameters
All Mounting Holes follow the following parameters:
Size
Electrically/Galvanically not connected to the PCBA GND Plane
This is because we want our potentially conductive drone frame to be at floating potential in accordance with General System Level Electrical Placement & Routing Guidelines
Can be connected to an CGND/ESDGND for ESD purposes though if proper analysis is done.
Eight vias should be placed evenly in the annular ring around the drill hole
Via’s should be plated drills in whichever drill size is used on the board
This is done for mechanical stiffness.
Altium doesn’t like this, it thinks the vias are shorted to to mounting holes (their net is "No Net") and it keeps complaining about it in DRC. I have to go into design rules → unrouted nets and then set the custom query to “InAnyNet” . Because “No Net” is not actually a net in Altium, use “InAnyNet” to return objects that are actually assigned to a proper net.
via dimensions should be reasonable, up to designer, preferably use the same via size as you use elsewhere on the board.
Proper clearance from components
Electrical component soldering pads should be at least 1mm away from the annular ring
This is done to avoid damaging the components when mechanically securing the board.
Board may flex under mechanical load and we do not want to crack components (especially ceramics like big capacitors).
Mounting Hole
...
Mounting Hole pattern will be: 30.5x30.5mm
...
Pattern
The mounting hole pattern will be 30.5x30.5mm for most PCBAs. When measuring the centre-to-centre distance of your mounting holes, you should get 30.5mm for both the X and Y axes. Boards of this size will use M3 holes specified above.
This means that if you are building a board, try to fit it in this pattern. If it cannot fit, then expand the board size while keeping the holes within a grid that falls within 30.5x30.5mm pattern. For example, a larger board could have a pattern of 30.5x61mm.
This is the general recommendation for stand alone PCBAs. For hats or boards intended for specific mechanical requirements you are encouraged to make educated engineering decisions about how you want to do hole patterns. An example is https://uwarg-docs.atlassian.net/wiki/spaces/EL/pages/2594996231/RPI+Interface+Rev+B?search_id=8ec06e56-4f5a-45d7-8608-c7b5fcaa8475&additional_analytics=queryHash---7d2c48e78a27d21f150b620681696259928cd14daa6e640c84eaf507c582ec26 which uses its own mounting pattern to fit the Raspberry Pi.
Mounting Hole Pattern Philosophy
This 30.5x30.5mm pattern is commonly used in COTS world for 5” propeller quadcopters so we’re picking that up on WARG as well. Larger quads basically have no patterns because it’s assumed a fully custom application specific airframe.
There are other standards for quads that are smaller than 5” props including (but not limited to) 25.5x25.5mm is also standard for smaller drones, but at our class of airframe we’ve never built any aircraft small enough to warrant this pattern. Most our aircraft are quite large. Generally 5” quads are designed around 30.5x30.5mm pattern with M3 clearance holes while smaller drones with say 3” props are built around smaller patterns with M2 and M2.5 holes.
In the past we made a mistake and actually used 30x30mm. See conversation around mounting hole mistake discussion (it’s 30.5mm bc that’s 1.2” so yea …). In theory 30x30mm will work its just really tight.
Historical WARG Hardware Patterns
Project Pegasus uses a 30x30mm mounting pattern in it’s frame.
This holds for Pegasus 1 and Pegasus 2
Servo module 12S first rev uses 30x30 mounting pattern.
ZP3 uses something that’s not 30x30mm (someone plz add in here).
...
32.5x32.5
TODO: add more
COTS Common Patterns
Pixhawk is not 30.5x30.5mm
TODO: add more COTS items for reference, some that meet the specs, some that dont, links appreciated
Mounting Hole Standard Specifications Exceptions
Exceptions can be made to this in some cases. This is meant to be the general rule. If a WARG board is violating these rules please ensure proper engineering justification is given!
Common Dimensions
Try to fit board dimensions into these common configurations
Standard 30.5x30.5mm M3
TODO give dimms & link examples
Standard 30.5x61mm M3
TODO give dimms & link examples
Standard 61x61mm M3
TODO give dimms & link examples