Configurable Remix Duncans Boxes

Overview

This is a remix and expansion of Duncan's battery boxes.

I've had the worst luck when it comes to batteries leaking. Invariably, once one battery starts to leak, the corrosion triggers others to leak. Thus, my primary requirement for battery storage is that no battery should touch any other battery. His design achieves this while also being somewhat compact.

This remix aims to consolidate as much as possible into a single parametric design while adding the ability to use cylindrical cuts and the standard half-disc coin battery cuts as well as magnetically latched lids. Open the "Configuration Table" and activate the desired battery type. Parameters not in the configuration table are available via the "Modify, Change Parameters" command.

One goal is that the design should be able to reproduce exactly the shapes that Duncan's design created. A perfect match probably isn't straightforward due to the fact that the slack included in Duncan's design varies by battery type. However, all other design aspects should be identical, when using the supplied parameters (except I think I use a larger divider thickness of 1.2 instead of 0.8). The extrusions and face offsets are copied directly from his design for the tabs, pips and such.

Selecting the configuration options of cut type as rectangle, outer buffer as no, and latching as tab will produce a Duncan style box. Update: The grip configuration should be "no" unless the latching type is magnetic. It's the extra body volume that accommodates the magnets that is used for the grip recess. Otherwise, the cut may not leave enough material to prevent the print from coming apart.

The included battery types are:

• AAA
• AA
• C
• D
• N
• A23 (or 23A)
• PP3 (9-volt rectangular batteries)
• CR123A
• L18650 (L for Lithium-ion simply because some CAD programs have issues with configurations not starting with a letter)
• CR2016
• CR2025
• CR2032

Design

I followed the techniques that Duncan used on his original design along with extracting any non-parametric values into configuration and user parameters. I consolidated all battery types as configurations within a single Fusion360 design file.

Another difference is that for the battery storage cells, I sketched and created a single cut, then created a 2d linear pattern for the cut feature as opposed to using the linear pattern within the sketch tool.

I also ended up with Fusion360 misbehaving by flipping the direction of dimensions when the driving parameters changed. This is due to the fact that Fusion360 does not store the direction of the dimension, only the value. Thus, if a sketch line is set to be a particular distance from another line, that sketch line can suddenly get moved to the other side of the reference line. There are reports of this happening to many users under a variety of conditions. I experienced it most often when a configuration option could be set to a zero value for a particular variant. Then when the value was changed back to a non-zero value, the direction wasn't preserved.

The solution is to use line offsets rather than linear dimensions. Use the "Modify, Offset" command on the reference line. This command actually stores the direction chosen into the timeline. (The state of the "Flip" button in the command dialog.) A new line will be created at the specified offset and direction. You can then use the "coincident" and "colinear" constraints to specify the position of your sketch items. Remember to set the new offset line to be construction geometry so that it doesn't influence later operations like extrusions, etc.

Configuration Options

The specifics for the different options are:

• Cut type (all sketches defined on the top of the box surface)
  • Rectangle - Rectangles of battery_width and battery_depth are padded with the slack_rect amount and extruded as cuts for a distance of half the sum of the battery_height and slack_height
  • Cylinder - Circles of diameter battery_width + slack_dia are likewise extruded as cuts for half of the total of battery_height and slack_height. The value of battery_depth is ignored.
  • Coin - A rectangle with the width of half the battery_width and a depth of the battery_height plus slack_coin_height is fully revolved as a cut using the right edge of the rectangle as the axis.
• Outer buffer
  • No - The design matches Duncan's.
  • Yes - The extra wall thickness around the battery compartment volume means that the battery storage cells that are in the top and bottom row along with the left and right column won't lie immediately next to the raised lip/overlap. This can make getting to coin cells easier.
• Latching
  • Tab - The latching mechanism is copied directly from Duncan's design. A tab is created in the overlap along with a pip and an associated slot in the lid.
  • Magnet - The tab features are suppressed, and the outer wall is expanded in order to accommodate holes for gluing magnets. The magnet dimensions should be what calipers report. There are separate parameters to specify the slack for both the diameter and the magnet height. There is also a parameter buffer_thick_mag which specifies how much distance should be included around the magnet so that it doesn't touch the edge of the part. Update 7-Oct-2023: This buffer is only added to the sides of the magnets on the outer edge now. The chamfer on the overlap provides sufficient clearance. This should save space, time, filament to at least some degree.
• Cut Grip (added 7-Oct-2023)
  • No - Produce the box without recessed grip area
  • Yes - Cut a recess in each of the side walls of the box (lower half) to aid gripping. This produces a sausage/capsule shaped (cylinder capped on each end with a half sphere) cut that grazes the side of the box. The cutting shape is centered in the z axis at the midplane of the box. There are three parameters that define the cut.
    • The grip_cutter_axis_offset parameter defines how far from the edge of the box the centerline of the cutting shape will be.
    • The grip_cutter_axis_start_offset parameter defines how far back from the front and rear walls should the cutting shape endcaps be.
    • The grip_cutter_radius defines the overall radius of the cutting cylinder and half spheres. This value should be larger than the first parameter (axis offset) or the cutting shape will miss the box completely.

Design Intent / Future Work

There are several additional options that influence the part but are probably not exceedingly useful at this point. Configuration parameters specifying the minimum width, depth and height are included in the calculations that produce the part.

My original intent was to include the ability to define multiple sections. Each section would be a grid of cells for a specific battery type. This would be a generic method of generating the popular AA / AAA combination boxes as well as one box that could hold a variety of the odd coin type batteries.

When combining multiple different sized storage grids, there needs to be a way to align them into a single rectangular volume. The idea was that setting minimums would be an easy way to get things aligned. Unfortunately, I've found that both Fusion360 and OnShape have issues with creating configurable arrays of parts where both the number as well as the type of subpart could vary.

The minimum width and depth features are active, but only come into effect when the minimums specified are larger than the most compact design possible. The most compact (i.e., best) design dimension is the size of the cut in that dimension times the number of cuts combined with the number of walls in that dimension times the minimum desired wall thickness. The minimum height parameter is used to calculate distance between the top and bottom plates, but the cut is based on the battery height and slack. If the minimum width or depth parameter specifies a larger size, the wall thickness in that dimension is expanded such that the cuts are evenly distributed across that dimension.

Another feature I've considered adding is a recess along the side of the box say 5 mm tall and 2mm deep that would provide a more stable grip for those who may have weaker fingers. (Update 7-Oct-2023: This has been added, but as described in the update text above.)
 

7-Oct-2023 Update:

• Reduced some of the excess magnet spacing so that the magnetic latch configurations are smaller/faster at least to some extent.
• Added a configuration option that creates a recess in the bottom box along the sides to make lifting it easier for those with less grip strength. The "Cut Grip" parameter has no impact on the lid.
• Uploaded the v14 Fusion360 file.
• Updated the STL files that have magnetic latching to bring in the space savings. Added STL files for magnetic latching with the grip. Use the non-grip lid file, only the box file changes.

The major differences include:

• Uses Fusion360 configurations feature - All battery types are in a single file (*.f3z)
• All sketch constants have been made parametric.
• Some additional battery types included.
• Lettering is omitted.
• Choice of traditional rectangular cuts, cylindrical cuts, and half-disc coin battery cuts
• Lids can be secured using the tab with pip design from Duncan's design or by gluing magnets into parametrically configured holes.
  • The parameters default to 6x2 magnets (that actually measure 6x1.6) and with 0.2 mm slack for both diameter and height.
• Measurements of object dimensions are intended to be exact. Those that prefer a tighter or looser fit can set the user parameters that include the word "slack". If your batteries actually deviate from the specified measurements, then it's appropriate to alter the dimensions directly, or create a new battery type.
  • This is particularly useful for batteries that have a protection circuit included that increases the physical size beyond the specs (18650 batteries)
• The ability to add an additional wall thickness of material around the storage volume. Thus, a storage volume consisting of 2 cell columns in each row normally had only a single divider separating the two cells. If the "Outer Buffer" option is set to Yes, then there will be a total of 3 dividers - the standard center divider as well as one on the left and the right. The same applies to the "depth" dimension.