BatteryTube.foocad

A protective case for 18650 batteries (and other sizes).

Adding machine screws

This case can also be used to electrically connect to the battery.

Set holeDiameter appropriate to a machine screw
Set extra to account for the height of two screw head heights
Insert a screw in the body and the cap with the bolts on the outside.
Screw the cap on tightly (which makes the electrical connection to the screw).
Connect wires between the plastic and the bolt (ideally using a spade/ring connector, but bare wires would also work).

The cap can now be used as a switch! Unscrew slightly to break the connection.

Note. PLA isn't a good choice when using this technique, because when under stress, it deforms over time, and therefore the threads will deform, and the pressure reduces (leading to a higher resistance connection).

Remember that litium battries are dangerous, and a short circuit can lead to a fire. Don't leave any bare metal exposed.

FooCAD Source Code

import uk.co.nickthecoder.foocad.smartextrusion.v1.*
import static uk.co.nickthecoder.foocad.smartextrusion.v1.SmartExtrusion.*
import uk.co.nickthecoder.foocad.threaded.v2.*
import uk.co.nickthecoder.foocad.cup.v1.*
import static uk.co.nickthecoder.foocad.cup.v1.Cup.*

@Data
class BatteryTube : Model {

    @Custom
    var size = Vector2( 18, 65 )

    @Custom
    var thickness = 0.8

    @Custom
    var baseThickness = 1.2

    @Custom
    var capHeight = 10

    @Custom( about="Extra z space within the tube" )
    var extra = 0

    @Custom( about="Optional hole in the base and cap" )
    var holeDiameter = 0.0

    @Custom
    var clearance = 0.5

    meth thread() = Thread.forRod( size.x + (thickness + clearance)*2, 2 )
        .rodChamfer( 1 + thickness/2 )

    meth caseDiameter() = size.x + thickness * 2 + clearance

    meth hole() : Shape3d {
        return if ( holeDiameter > 0 ) {
            Cylinder( baseThickness * 3, holeDiameter/2 ).centerZ()
        } else {
            null
        }
    }

    meth threads() = thread().threadedRod( capHeight - thickness ).threadsOnly()


    @Piece
    meth body() : Shape3d {
        val shape = Circle( size.x / 2 + thickness + clearance )
        val main = Cup( shape, size.y + baseThickness + extra,  thickness )
            .baseThickness( baseThickness )
            .outsideBottom( Chamfer( thickness/2 ) )
        val threads = threads()
            .topTo( main.top )
        return main + threads - hole()
    }

    @Piece
    meth cap() : Shape3d {
        val thread = thread()
        val solid = Circle( thread.diameter/2 + thread.clearance + thickness )
            .smartExtrude( capHeight )
            .bottom( Chamfer( thickness/2 ) )
        val inside = thread.threadedHole( capHeight - baseThickness )
            .chamferStart(false)
            .translateZ( baseThickness )

        return solid - inside - hole()
    }

    @Piece
    meth both() = body().rightTo(-1) + cap().leftTo(1)

    @Piece( print="both" )
    override fun build() : Shape3d {
        val body = body().color( "Orange" )
        val cap = cap()
            .rotateX( 180 )
            .bottomTo( body.top + 3 )

        val battery = Cylinder( 65, 18/2 )
            .bottomTo( thickness )
            .previewOnly()

        return body + cap + battery
    }
}