Cass & Theo: Stem IMPACT Project Semester 2

Create/Trial and Error

Step 1: Prototyping

Prototype with Lego EV-3

Needed stability so we added rubber band

Added 2 proper rubber bands for max tightness

Rough measurement of seedballs

This prototype helped us get hands-on and understand how the final design would work. Obviously, the motors were far too slow, and we couldn't really attach one wheel to the other to stop bowing because they would break. It was much more helpful than just making a sketch, which already exposed challenges that could have arisen. It's also less wasteful and faster than immediately going straight to 3D printing.

Step 2: Finding motor and power source

These motors were too small

Found correct motor

Flattened spin shaft for design

Power source found, motors connected in series

We went around the class to find suitable motors and a power source. We landed on some very powerful drone motors and a power source Mr. Brown said would work fine for testing.

Soldering Motors

Adding Solder

Connected to negative

Connected in series, both on negative so motors spin opposite ways

We soldered the motors together "permanently" in series and connected negative to negative so they would spin in opposite directions from each other, so the flywheel would actually work. My (Cass') soldering job was very messy compared to Mr. Browns, but it would be fine for now.

Step 3: Attaching wheels to motors

First, we wanted to fix the motors to the plastic Lego rims. We thought about designing the same + shaped axle that LEGO uses, but with a side that would fit the motor top bit, but we didn't really know how to do that. We tried hot-glueing the motor spin shaft to the inside of where the axle goes on the normal LEGO rims, but because we couldn't make it perfectly centred and straight, there would be lots of dangerous wobbling.

Connection Point with well fitting measurements and clearance so motor fits nicely

Lego rim 3D design on Computer

Design with removed infills and motor attatched

Theo designed the LEGO rims on Tinker Cad with a hole for the spin shaft, which fit well and seemed to fit the wheels well. Now we could move on to mounting the motors

Step 4: Mounting Motor and wheels

3D Model V1:

First design, Fixed mounted motors

Design on computer

Space between wheels

Although the design worked, and the motors fitted, we realised that having the motors/wheels at a fixed distance from each other would mean some seedballs would work and others wouldn't, due to the fact that they aren't all uniform in size. The setup was also a bit awkward, and because we sanded the holes before we took off the stickers, the motors slid up and down, which caused rubbing.

3D Model V2-New design:

For this new design, we pivoted our idea for how to mount the motors. Mr. Brown helped us come up with the new idea, which included a spring so each seedball would stretch the motors apart the distance needed for them.

Hole for motor was too small

Tried sanding but no luck

Problem 1: Nubbin Stringy

Problem 2: One of sides stringy and wont sit flush

Problem 3: Cutout sides go over

The problems were because of the 3D model and not including enough clearance for things to fit in, and the inconsistencies of the 3D printers, which caused stringiness on the little nubbin that would be for the spring, and the overhangs also caused stringiness.

3D Model V3:

For the third iteration, I increased clearance so the motor can fit, flipped cutout sides so stringy problem is less and for aesthetic purposes, removed nubbin, changed nubbin to a sunken hole for a screw, and centered all holes and cutouts.

Print was too small again, not enough clearance

Tried sanding but still didn't fit

Hole for screw and nut worked very well

Screws, bolts, nut, and spring used

This version basically solved all the problems except for the motos fitting, which was quite frustrating, but other than that, the design was essentially finalised.

3D Model V4:

For the fourth iteration, all that was needed (hopefully) was increased clearance, even more so that the motor can fit; we went from 35.8 mm to 36.25 mm circumference, which is 7.5 mm clearance from the circumference of the motor.

Print was a bit warped needed sanding

Had to tape bottom to maintain heights

All put together with stronger spring for more resistance

New power source because old one was not getting along with motors

This model fixed all the issues before, meaning the mounting and spring mechanism was how we wanted it, but as we solved one problem, another arose. Because of the inaccuracy of the original rim 3D print, the tires experienced a lot of centrifugal force, and they expanded and stretched when it was spinning. The new power source worked very well, though. We got Mr. Brown to re-model the rim in Fusion 360 rather than Tinker Cad.

3D Model V5:

Mr. Brown more accurately modelled the rim using a pre-existing one from the internet. He used that to get measurements, and double-checked in real life also. Let's hope that if the tire fits better, it won't expand to such a degree.

Glueing wheels to new rims

New rims on wheels

Mr. Brown re-soldering

finished test

Final test with new rims with tires glued on and better wiring

Although there is deformation and stretching of the wheel in the centre, they don't come off of the rims and that central deformation may actually improve the grip of the wheels on seedballs.

With the wheels glued, some improvements on soldering and changing of wires one half of the project was essentially complete and ready for testing once the feeding mechanism is finished.

Step 5: Feeding seedballs into wheels

Sketching and research

We looked at lots of hoppers and dispensing mechanisms, like gumball machines and tennis ball launchers. Sadly, there is not a lot of time left for us to complete this project, so we decided to just go for a PVC pipe for testing.

We found a 1 inch pvc pipe

We got Juma to saw it in half on the table saw

Now we had 2 half 1 inch pvc pipes to act as a ramp for the seedballs

The ends were quite sharp so we sanded it down a bit

Now we had a ramp for the seedballs, we just needed a way to mount it to the design so they were always at the perfect angle and position to be fed into the flywheels. Because we had very little time left, we just decided to make the holder out of cardboard and hot glue.

Finding what angle we wanted

Top view

Gluing it

Final w step

We found a cardboard cylinder that seemed like it would hold the half pipe well. First, we decided what angle we wanted, how far the end should stick out, and how much we should cut off. Once we decided on all of that, we just hot-glued it and added a little bit more cardboard at the front so it was a bit higher. Because we now had a way to feed the seedballs, we could test it all out.

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