Frameless Scale

Finished rails (load cell mounts). Two go under the hive, one on each side.

End view with end cap and closure strip removed.

Goals:

• Parts cost under $100 and are readily available.
• Low thermal drift and creep.
• Low power consumption.
• Overload protection.
• Automatically resumes operation after power failure.
• Can be built by 15 year old student (9th grader) using hand tools.
• No soldering.
• No lethal voltages.

Design Features

• No frame: no welding, no bending.
• Load cells are mounted in metal strut readily available from electrical or industrial suppliers in aluminum. galvanized or painted steel.
• Only straight cuts and drilled holes.
• All electrical connections are made with crimp plugs or terminal blocks.

Design Flaws

1. The M6 Cap Screws stick up and require a spacer or mortising the bottom board (Use counter sunk flat head screws?).
2. The leveling feet form the over limit protection and are not for leveling. If they are used to level, the over limit protection will break.
3. The feet stick out from the rail and can damage the load cells if dropped or if improperly packed for shipping.

Material List

A detailed Parts List with part numbers, suppliers and prices is available in pdf.

Strut is available from different manufacturers with different brand names: Unistrut, Superstrut, etc. It is available in galvanized steel, aluminum, and fiberglass. Closure strips are available in steel, aluminum or plastic.

If the scale will be shipped via UPS or USPS, even though the aluminum is more expensive, it will be cheaper when shipping expenses are considered.

Block Diagram

Block Diagram

Enclosures

Several enclosures can be used.

HX711 with screw terminals and metal shield installed connected to H5 on the Pi. H5 is no longer used as it was dropped from the B+.

Exploded parts diagram.

Parts Detail

Assembly