lego seismometer

Building a lego seismometer

Bill of materials

Bricks
4 x 2x3brick
2 x 2x4 brick
2 x 1x12 brick
2 x 1x10 brick
2 x 1x8 brick
2 x 1x2 brick
1 x 2x8 brick
1 x 1x1 brick
plates
4 x 2x6 plate
3 x 2x10 plate
4 x 1x6 plate
2 x 2x4 plate
2 x 2x3 plate
4 x 1x2 plate
2 x 2x2 plate
2 x 1x1 plate
2 x 4x6 plate
2 x 1x4 plate

smooth plates
4 x 1x2 smooth plates

Non-lego components

1 x spring steel leaf spring (25mm x 0.152mm x 150mm)
1 x 14mm diameter magnet
1 x 5mm diameter magnet
2 x 20mm x12mm adhesive tape (eg kaptan 0.03mm, or packing tape )
1 x coil (1200turn  22mm id 10mm high)
1 x spacer 0.5mm thick for assembly
1 x 3mm thick 50x50mm square steel washer

Instructions... there are two seperate lego parts which are hinged together with the thin tape acting as weak flexures.  The leaf spring is clamped between adjacent lego pieces

when making the hinge piece, use a strip of card or plastic 0.5mm thick as a spacer to hold the two halves of the hinge the right distance apart before adding the tape (a double thickness of kaptan or packing tape seems to work OK as a hinge)    

The gap between two adjacent lego pieces is 0.2mm, so the 0.152mm thick leaf spring is a bit loose on its own.   If you add some tape to the ends then it forms a nice tight interference fit.  

The final assembled unit needs a mass of about 70-100grams to balance if the spring is in a nice semicircle shape.  There is a fine trade-off between spring length, armature mass, and natural period.  I aim for about 1 second natural period.   

Not shown the magnet/coil arrangement for sensing (15mm diameter button magnet stock to armature and 1200 turn 22mm id coil on the base, damping with 22mm copper pipe and/or resistive load)



Lego assembly instructions (missing all non-lego parts)
The base

The leaf spring is placed vertically between the two 1x8 bricks

The hinge tape is stuck to the two 1x2 plain plates sticking out to the right 

The armature