3D Printed in Line Twin Cylinder Engine

This instructable was created in fulfillment of the project requirement of the Makecourse at the University of South Florida (www.makecourse.com).

The in line twin cylinder engine has many applications across various industries including powersports for which there is an entire class of racing devoted to this engine known as the Motoamericas twins cup races.

3D printer requirements:

• Capable of 220 degrees Celsius nozzle temperature
• Heated bed preferred
• minimum build volume 150mm X 120mm X 125mm (width X depth X height)

Printer Used: https://flsunofficial.com/products/super-racer-sr-...

PLA: https://www.amazon.com/Printer-Filament-SUNLU-Dime...

Assembly Lubricant: https://www.amazon.com/Royal-Purple-Max-Tuff-Synth...

12 Gauge copper wire: https://www.amazon.com/PHAT-SATELLITE-INTL-Protect...

Fasteners:

• M4 x 0.7 x 25 countersink flat (10)
• M3 x 0.5 x 12 (8)
• M3 x 0.5 x 16 (4)

Electronics

• Arduino Uno: https://www.arduino.cc/en/main/arduinoBoardUno
• Breadboard: https://www.amazon.com/Breadboards-Solderless-Bre...
• Wires: https://www.amazon.com/TOAPPNER-Multicolored-Brea...
• IR receiver with remote: https://www.amazon.com/KOOBOOK-Infrared-Wireless-...

The engine block houses the entire rotating and oscillating assembly of the engine.

The design features an open front for ease of viewing for the rotating crankshaft assembly as well as the oscillating piston assembly

On the rear of the engine block are marked out regions for the Arduino and breadboard to be mounted.

On the sides of the engine there are holes for the input shaft of the DC motors as well as holes for the M4 fasteners that hold the motors to the engine.

On the underside of the engine there are pre-marked holes for the M4 countersunk fasteners that will hold the crank journals to the engine.

The Engine base serves a dual purpose. its main purpose is to lift the engine off of the table to allow the crank arms of the crank shaft to rotate without colliding with the table. Its secondary purpose is to collect any oil that may drip down if the user opts to utilize any kind of low-viscosity lubricant such as engine oil.

The base also serves as a conduit for the IR receiver to be wired to the front of the engine such that it can receive unobstructed signals from the remote.

This base also contains the second mounting point for each of the DC motors.

This part should be printed with a relatively wide brim to prevent the corners from lifting from the build plate

The rotating assembly of the engine is responsible for delivering the power from combustion to the output shaft of the engine in a real engine. In this case it will be moved by the DC motors mounted on the ends of the crankshaft.

The crank shaft is best printed on its sides with supports for 45 degree or more overhang. Concentric style supports proved to be relatively easy to remove compared to the other options.

the piston is best printed upside down to avoid the need for supports on the hollow interior.

The connecting rods are best printed upright to avoid the need for excessive supports. it is strongly suggested to use a large brim for the connecting rods as they are long and slender and are therefore prone to lifting due to the small contact surface at the build plate. If bed adhesion issues continue, use a raft.

The electronics housing is responsible for concealing the control system of the engine.

This part should be printed upside down (large planar face down towards the build plate) to eliminate the need for supports.

The housing should also be printed at a fine layer height (0.15 mm worked well) to eliminate the need for support in the overhang. The need for support is eliminated by the fillet radius which is large enough to support the next layer if and only if it is printed with a fine layer height.

The concentric pattern for the base layer paired with a brim proved to be effective at preventing the lifting of the corners.

Using a brim is highly recommended for proper build plate adhesion for all parts.

Print all parts in the orientation such that they require the minimum amount of supports and those supports that are required are able to be easily removed.

The concentric style of support proved to be one of the easier ones to remove.

The concentric style base layer also proved to work well at preventing lifting of corners.

A base layer height of 0.3mm and a layer height of 0.2mm worked well at ensuring proper bed adhesion and yielding a good surface finish.

If desired, add a skin layer to the top of the print in a slicer to further improve the surface finish of the top layer (suggested for the engine block, base, and electronics housing to ensure flat mating surfaces)

Bill of materials:

• Block x1
• Base x1
• Electronics housing x1
• Connecting rod x2
• Rod cap x2
• Crank shaft x1
• Piston x2
• Central crank journal x1
• Outer crank journal x2
• Stepper motor housing x2

Start by sanding down any rough mating surfaces to a smooth finish. 120-220 grit sandpaper is ideal for PLA.

It is suggested to use the assembly lube on all mating surfaces.

Start by assembling the connecting rod, rod cap, and crank shaft together. The rod requires two M3 x 0.5 x 16mm fasteners.

Once the assembly of the connecting rods with the crankshaft is complete, the pistons can be added. Line up the radial through hole on the piston with the hole on the connecting rod. Insert a piece of 12 gauge copper wire with the insulation still intact slightly smaller than the diameter of the piston through the piston to secure it to the connecting rod.

The rotating assembly is now complete and ready to be installed into the engine block.

Refer to the assembly video at the beginning of this instructable for guidance.

Start by sanding the semi-circular bearing surfaces where the crank shaft will rotate on the underside of the engine until they are smooth.

It is suggested to use the assembly lube on all mating surfaces.

Take the rotating assembly from step 8 and insert it into the engine block through the underside starting with the pistons.

Once the crank shaft is seated in the block, take the central crank shaft journal (the wider one) and install it using the M4 countersunk fasteners (do not over tighten as there is great risk of stripping the fragile plastic threads).

Do the same for the outer crank shaft journals.

Once complete, the top end of the engine is ready to be mounted to the base.

Refer to the assembly video at the beginning of this instructable for guidance.

Take the engine from step 9 and place it on the engine base.

Locate the stepper motors and the two stepper motor housings.

Insert the stepper motors into the stepper motor housings and fasten the motor and housing assembly to the engine by first aligning the output shaft of the motor with the rectangular keyway in the crankshaft.

Finally, fasten the motor and housing assembly to the engine block and engine base with the M4 countersunk fasteners.

Repeat for the other side of the crank shaft.

Refer to the assembly video at the beginning of this instructable for guidance.

1. Start by removing the three (3) wires from the breadboard that connect the IR receiver.
2. Proceed by running the wires for the IR receiver through the small hole in the back left corner and then through the holes in the corner rib supports in the engine base. Ensure there is sufficient wire length to reach into the breadboard.
3. The wires can now be soldered to the respective terminals on the IR receiver.
4. These solder joints should be insulated with shrink wrap (preferred) or electrical tape.
5. The Receiver can now be positioned in the bottom left corner of the opening of the engine base.
6. Using a hot glue gun, glue the wires leading up to the receiver to the engine base to secure the wires.
7. Using a minimum of 2 holes on the rear of the engine block, mount the Arduino using the M3 x 0.5 x 12mm button head screws.
8. Using the adhesive backing on the bread board, adhere it to the marked recess in the back of the engine block. If no adhesive backing is present, use 3M double sided tape to secure the breadboard.
9. Proceed to fully assemble the control circuit in the following step.

The control system for this engine consists of an Arduino Uno, two 5-12V DC stepper motors, their respective driver boards, an IR receiver, and the IR remote.

Please reference the wiring schematic for a complete circuit diagram.

Note: the IR receiver will need to be soldered to the wires as it does not go on the breadboard as depicted since obstruction from the electronics housing will prevent it from receiving the signals.

The Arduino sketches have been attached for convenience.