3d Printed Sugar Rocket

The Challenge

For my Product Development class, the professor has tasked us with creating a transport module that can bring an aluminum 2” x 2” x 1” payload (157g) as fast and as straight as possible. Below was the full criteria given:

  1. Design a transport system that can travel 10 meters as fast and as straight as possible (Straight being defined as the angular deviation from the starting point at a distance of 10 meters horizontally)

  2. The payload MUST stay with the transport system and cannot leave said system throughout the time of travel (i.e. throwing)

  3. A provided battery and motor set can be used, but other forms of propulsion are acceptable

    1. This motor can be controlled with any desired motor controller, but a MyRIO system will be provided to simplify the learning process.

  4. The team will have a budget of $200 to design their systems

To begin the design process, I began to thing of quick transportation methods and their pros and cons

1. Wheel based systems (4 wheel swerve drive, 4-6 tank wheel system, etc.)

Pros

  1. Readily available

    Parts to assemble a 4 wheel drive system (pulleys, gears, tires, gearboxes, motors) are cheap and can be found at any hobby shop

  2. Mechanically simple

    If a wheel were to fail or a gear/sprocket were to break loose, the problem would be easy to diagnose and fix

  3. Active course correcting

    If the transport vehicle were to veer off-course, it would be simple to steer the vehicle back to 0 degrees of deviation

Cons

  1. Frictional losses

    The motors would not be in their most efficient configuration if some of the force they generated went to slip experienced by the wheels on the floor, friction between the gears/sprockets and, possibly most crucially, will need to move the weight of the transportation system (battery, motors, controller) along with the payload

  2. Imperfect steering

    If both motors were used, one per each side, there would be slight discrepancies between each motor’s spinning speed which can exacerbate the angularity issue. Steering can also be too quick/imprecise for operator control

2. Pneumatic systems (Pressure rocket)

Pros

  1. Lightweight

    By omitting the use of motors, the force generated with this method can be focused solely on propelling the payload to the finish line

Cons

  1. Precision

    It will be extremely difficult to ensure the transport module crosses 10 meters at a specific angularity

  2. Pressure

    Handling pressure with enough safety to comfortable perform in front of my peers will require a lot of thorough planning

3. Rail Systems (Trains, Gondolas)

Cons

  1. Rail system

    This rail system will need to be transported to wherever the tests are being performed. This environment may make the rail system not perform as intended. This rail system also significantly increases the size of the transportation method

Pros

  1. Angularity

    The use of a guidance system will ensure that the transport module will maintain an extremely small angle of deviation

  2. Low friction

    Using a gondola can give significantly less frictional losses when compared with a floor-based transportation system

  3. Lightweight

    The propulsion method can be placed off the transportation module, reducing the weight of the module to improve speed

4. Chemical based (Rockets)

Cons

  1. Imprecise

    If the rocket were free-flying, it would be hard to keep the system flying straight

  2. Complex

    This design would require an understanding of rocketry and a reliable method to prepare it

  3. Dangerous

    I’m dealing with explosives — need I say more?

Pros

  1. Compact

    A rocket based system would pack the most amount of energy in the smallest space possible, ensuring the transportation module is as light as possible




The decision

After laying out all the methods I considered, I ended up using a hybrid of two of these systems: The Rail System and the Chemical Based system.

The rail system ensures that the transport module would satisfy the 10m distance and a small angle of deviation. The added complexity of having to design this system outweighs the downside of having to set this up.

The chemical based system, however, just sounds AWESOME. I have an excuse to make an explosives? And it’s for class? Sign me up.

The design phase

With a general design language solidified, it was time to conceptualize the system. To better organize the project I decided to split it into several different subsections:

  1. Braking (Eddy current system)

  2. Propulsion (Rocket Capsule)

  3. Nozzle performance

  4. Rail system

Braking

While difficult, I didn’t perceive the manufacturing of rocket motors to be too difficult. To add a stretch goal to this design, I wanted to incorporate a passive braking system to this design. I took inspiration from roller coaster design for this idea. Roller coasters implement an eddy current braking system as a reliable safety system. These systems are completely passive, utilizing the power of eddy currents from a magnet to an electrically conductive material and incredibly simple since this eddy current effect can be experienced just by sliding a metal on a magnetic surface. Eddy current systems also provide proportional braking resistance. A heavy system will be slowed down at a similar rate to a lighter system. This will ensure that if the braking system works for one configuration of the transport module, it can also work for a newer iteration with a different mass.

The difficulty of this system comes from calibrating the distance of the metal to the magnet and also the cost/weight of the metal + magnet system.

Since the payload that needs to be transported is aluminum, it can be the braking mechanism present on the device, therefore adding no additional weight to incorporate a braking system.







Propulsion

To ensure this sugar rocket design would be successful, the motor would need to produce as much power as possible in the limited space it has. A successful rocket motor needs to have the right oxidizer and propellant, the right ratio and coring pattern and a nozzle that can redirect the exhaust gases to achieve maximum thrust.

The chemical compounds I opted to use for this design were Potassium Nitrate and Sorbitol. These two constituents were selected since they make up the basics of a type of rocket fuel called Rcandy. Rcandy is easy to make since the two ingredients can be melted in a pot then poured into the motor housing. Sorbitol is becoming the de facto standard for sugar rockets, replacing sucrose as it has a lower melting point speeding up the manufacturing process and also is less prone to crack in larger motors, resulting in a less efficient burn.

A commonly used ratio in the sugar rocket community is 65% Potassium Nitrate and 35% Sorbitol by weight. This is the formulation that I decided to go with for this sugar rocket.

In terms of coring patterns, there are a lot of different designs one can go with depending on the type of burn they are trying to achieve. I want a large initial thrust to overcome the friction the transportation module is going to experience and once that has been achieved, a longer, more consistent burn is desired to ensure that the module is going to keep accelerating until the finish line. For this requirement, the slotted core pattern is used as the surface area is much greater in the beginning, thus increasing overall fuel that can burn and then it transitions over to a cylindrical shape which is a balance between thrust and time burned.

Finally, the hot gases generated by the Rcandy need to be redirected into a nozzle to give the most amount of thrust possible.

Michaelangelo Parkinson