Homemade automated system for heating the workshop using wood chips.
During longer sessions in the workshop, while it’s cold outside, it gets quite annoying to refill the stove with pieces of wood frequently. With this project that process got automated, the stove is fed automatically and can run for hours without manual intervention.

Specification

Fuel type: Wood chips, sawdust, paper
Storage capacity: 70 L
Temperature range:
Rotational speed:
- Auger: 50 rpm
- Agitator: 26 rpm

Open bottom oven door

Features

Agitator: Reliably forces chips from tank into auger
Regulates exhaust gas to defined temperature
Modes of operation:
- Always off
- Always on
- Simple temperature control
- Smart control (default)
Smart control:
- Attempt for optimal and fast regulation to target temperature of a very delayed system
- Fuel amount gets dynamically adjusted
- Detects important states of the fire or system and acts accordingly:
  - Fuel empty
  - Fire went out
  - Too much fuel
  - Burning in pipe
7 Segment display:
- menu to set target temperature and other parameters
- current temperature
- text notifications
Buzzer for acoustic notifications

Assembled control box

Components

Mechanical

Old furnace
Custom adjustable frame using 40x40x2 mm iron square tube
Steel pipe d=120 mm
Auger d=60 mm, l=900 mm
Storage tank using two steel buckets
Motor
- Type: Three-phase 400V
- Power: 90 W
- Speed: 1380 rpm
Gearbox
- Type: HEYNAU G2V39M
- Reduction: i=32
- Torque: 20 Nm
Custom coupling (motor -> auger)
Chain drive for Agitator
- Gear Motor: 16 teeth
- Gear Shaft: 49 teeth
- Chain 06-B (3/8x7/32)
Agitator
- 20mm shaft
- 2x 20mm bearing
- metal bar clamped onto flattened shaft

Built attachment without tank

Control

Custom strip board
Atmega8 microcontroller
3d-printed housing
Input
- Potentiometer
- 3x Momentary switch
Sensors
- Thermocouple in exhaust pipe with custom amplification circuit
Output
- 8 digit 7-segment display (via spi bus)
- 2x 5mm LED
- Buzzer
- 3x mosfet output for future extensions
- 12V contactor

Custom board inside the control box

Failed Attempts

Before the current, final solution, multiple approaches were tested:

Spring auger

Problems

Flexible and small diameter spring gets pushed away in tube, and does not convey the chips
Long spring tends to get stuck at the end and stats tangling itself

Spring auger

Pneumatic piston

Problems

Chips get stuck between piston and pipe opening often
Instead of conveying, the chips get compressed in the pipe (like a press for wooden briquets)
Limited force of the pneumatic cylinder

Pneumatic piston

Pneumatic agitator

Problems

Unnecessary noise (exhaust and valves are loud)
Unreliable - After certain time the Chips are stuck above the auger anyways
Manual intervention is necessary sometimes

Pneumatic swivel arm

Agitator with springs

Problems

Springs get bent by the permanent stress
Springs tend to build tension and throw chips out of the tank at certain fill level
Unreliable - Springs never reach down to the auger, thus can clog below

Agitator with springs