3D Printer Quirks
1. The printer refuses to print anything thinner than 1.2mm horizontally LOL.
Context: we needed a holder with thin walls so that it is flexible to allow for the magnet to be inserted and taken out easily.
2. The printer can print thinner floors and ceilings than walls because 1 step vertically is smaller than 1 step horizontally, due to the property of the filament.
3. The first few layers at the bottom will have thicker walls and smaller holes as each line of filament is flatter and hence takes up more space. This is likely due to the flatter surface it is printed on which allows the melted filament to spread further. Found this out after a screw wouldn’t fit nicely and even broke through a print even after adjusting generously for tolerance.
Arduino is Cool Y’all
We learned how to use Arduino to make and soldering from Jeremy. We also learned more about circuits and microprocessors.
Suspension vs Shock Absorbtion
A suspension system should do the following:
1. Suspend a body from the body experiencing the shock while still having the two bodies being connected.
2. When the shocked body experiences a change in height, the suspended body must also have the same change in height because the distance between them cannot increase or decrease forever e.g. if the shocked body is pushed closer to the suspended body, the suspended body should move further from the shocked body by the same amount, if not the eventually they will hit each other.
A shock absorbtion system should do the following:
3. The suspended body should take longer than the shocked body to achieve the same change in height to reduce the acceleration it experiences for a more comfortable experience on the suspended body.
4. The suspended body should not oscillate once the system reaches even ground (again, for comfort).
Points 1 and 2 are easy to achieve since there just needs to be a force equal to the weight of the suspended body when the it is at equilibrium position and a restoring force when it is not at equilibrium position. This can be acheived by using magnets to repel the 2 bodies. When the magnets are too close, the magnetic force is stronger and they repel each other further away, and when they are too far, gravity is stronger and pulls them back together.
Point 3 is also easy to achieve. When the shocked body changes position relative to the suspended body, the equilibrium position changes, and there is a change in potential energy (PE) of the suspended body. This PE is converted into kinetic energy (KE) which moves the suspended body in the direction of the equilibrium position. Since the process is not immediate, it takes longer for the suspended body to achieve the same change in height.
However, point 4 is difficult to achieve as mostly the change in height of the shocked body is quick, giving the system additional PE. This will cause the suspended body to oscillate as the extra PE is converted to KE while it is in equilibrium position.
Initially we believed the solution was to make the equilibrium position such that the shocked and suspended bodies were as far away as possible from each other, so that there is more time needed for the suspended body to reach the new equilibrium position. However, the larger separation allows for more oscillation. If the equilibrium position was such that the spearation between the two bodies was small, the bodies are essentially rigid, and acceleration of the suspended body would be equal to the shocked body (no shock absorbtion). We thought it was a balancing act between oscillation and acceleration, but turns out the solution was something we have forgotten from our A-level education: damping.
We needed a way to remove the additional energy; a damping force. Normally this would be friction/heat, but since our project is on magnets, we thought it would fitting to use electromagnetic induction to remove the energy by converting it to electrical energy using magnets and a conductor, and then heat.
From our previous education, ideally we would want critical damping (the suspended body returns to equilibrium position as soon as possible but also does not oscillate). This is probably the most difficult part to do.
Testing
Obviously, we need to test our product. However, suspension and shock absorbtion needs to be tested with separate parameters due to how different they are.
For suspension, as long as criteria 1 and 2 are satisifed, so are we.
For shock absorbtion, more things need to be considered.
So turns out there is this thing called ‘transimissibility‘ which is the change in height of the suspended body over the change in height of the shocked body. For a working shock absorbtion system, this parameter would need to be less than 1. This makes sense since having the suspended body move less than the shocked body would reduce acceleration.
2 things affect transmissibility: rebound speed and bump frequency.
If the bump frequency is equal or close to the natural frequency of the system, transmissibility is high due to a phenomenon called resonance. However, bump frequency can vary thorughout a journey, so a general solution is tough.
A high rebound speed will work well for high bump frequencies and vice versa. Unfortunately, as stated, bump frequency can vary throughout a journey, so a general solution is tough.
Luckily, we will not tackle transmissibility in this project as our tests require the same change in height of both bodies eventually.
Another thing that was previously brought up is the time it takes for the suspended body to return to its equilibrium position without oscillating further. This can be measured by letting the system experience a shock and recording the process.
Engineering is TOUGH
As Physics students, we study the theory and assume the ideal/simplest cases. However, this experience made us realise that in the real world, there is so much more to consider. We can no longer say “let the length be x”. Rather, we have to measure the length and work from there.
When designing, we have to think about what we want something to do, how that something would work, what components would it need, understand how nuts, bolts and screws work so that we can think of how to put the components of the something together, designing the components accounting for the nuts and bolts and 3D printer tolerance, testing, redesigning so on and so forth. THIS IS HARD WORK.
RESPECT ENGINEERS Y’ALL.