This is sort of a different kind of Instructable... While the "destination" was a really cool costume for a sweet young lady who uses a power chair, the "journey" was teaching a small class of 10-12 year olds about how Engineering isn't about following a recipe but about identifying a problem or opportunity and solving it by applying the principles discovered by scientists.
For background, I teach a class for an educational non-profit where the students learn first principles engineering concepts: DC Circuits, Mechanical Advantage, Electromagnetism (simple motors and solenoids), Motion transformers, and Design thinking. Then they find a problem or opportunity to apply their idea to. Being so close to Halloween we wondered how we could find a way to incorporate the assistive device for another kid their age into a really cool costume so they could go Trick-or-Treating together where the device would become the most enviable part of the costume.
I got in touch with a friend who volunteers for another local non-profit for sensory impaired. She put me in touch with a local family who was having a tough year. The young lady (the same age as my students) with CP uses a power chair and her father hand-makes her costume every year. We recognized an opportunity to include her with our class shenanigans and give her dear old dad a break on costume fabrication this year.
Step 1: Design Thinking
We got the whole team together and interviewed our customer. We took measurements of the normal arrangements of the structures on her chair, as well as got a look at what type of mobility the chair has.
We found out that our customer loves dogs and wanted to go as a dog for Halloween. Our brainstorming led us to a Dalmatian driving a firetruck.
We set up some requirements to ensure the costume was safe and didn't restrict mobility, because it was also a STEM class I included some design challenges.
- One was to take one kind of motion from the chair and convert it into a moving element of the firetruck.
- I also challenged them to include electrical circuits to control additional features of the costume.
Step 2: Research and Excitement
I stopped by the local firehouse on the weekend and told them what we were up to and asked if they could ambush us during class for some hands on research. I invited our customer and her father as well, and tipped them off to the surprise. Shout out to Spotsylvania Fire and Rescue Station 4 for showing up with lights and sirens blazing and two fully loaded trucks!
The students and firefighters traded questions and answers relating to the purpose and patterns of lights/sirens for the project. Do particular paint schemes mean anything? What are the essential elements of the pump control panel on the engine truck?
And also generally geeked out for a while, I mean they ARE firetrucks after all and firefighters are awesome!
Step 3: The Truck
The truck was super simple. Used foam insulation board as the walls, and furring strips to make a basic box frame. The back end has a shelf for the battery bank to rest on. The four corners had dolly wheels (we wanted it to be able to spin as well as roll since that is how freely the power chair moves.) We used PVC piping to connect the fog machine output to the clear tubing (with UV lights) on the side. This was our fog fire hose. The clear tubing is available in the PVC section of hardware stores. Additional PVC components were spray painted silver. Some were functional connectors, others simply looked like elements of the pump station on the actual truck.
Artistically we wanted a Halloween themed firetruck so instead of sparkly red, we painted it pumpkin orange and used glitter spray paint to add that shiny element. It was actually our customer's idea to name it Engine 1031 for October 31st.
We used some fluorescent yellow/orange to create the warning pattern on the back and added some jack-o-lantern features to our rotating dome light.
We found some good warning stickers, reflectors and fire safety plaques to spruce up the rest of the truck. Our goofy ladders had modified gold glitter writing turning Spotsylvania Fire Department into "Transylvania Fire Department."
Step 4: Electrical Elements
Of course flashing lights came to mind for this vehicle. We found 12V emergency vehicle flashing circuits on Amazon (meant for automobile grills) and procured 20 sets of 3 LED light bars half red/half white.
We experimented with black-lights and fog in class and made the determination that we wanted a fog element on the firetruck to act as if it were the fire hose. The refraction of both the black-lights and flashing Red/Whites off of the fog really added to the overall dramatic presence of the firetruck.
The hose was lined with 12V UV LED strip lighting.
We found an amber rotating dome light with cigarette lighter adaptor for the back. We knew that car voltage is 12V so we cut the cigarette adapter off and wired it off a 12V DC battery.
On the front of the truck is a rotating "fidget spinner" light that has three separate beam lights. We used UV LED flashlights, removed from their casing and mounted them to a "fidget spinner" looking base. Since this was intended to be a spinning element we had to power them locally by putting three AA batteries, wired in serial for 4.5V, but physically mounted one on each blade for balance. The three UV Light clusters were wired in parallel off a single on/off switch.
The flashers, dome, and UV LED Strip were powered off separate 12V batteries with switches mounted in the command center (reachable by our customer while driving). For the fog element, I found a mini-fogger at Walmart (tis that time of year). The mini fogger ran off 120V AC. To solve this we connected a 12V to 120V DC/AC converter to a lawnmower battery. The heating element was a big current draw and induced a pretty substantial voltage droop on the battery and would shut down the DC/AC converter on under-voltage trip. To fix this, we added two more 12V lawnmower batteries in parallel which was jusssst enough to keep it running. Although that fogger did suck the batteries down pretty quickly so it was used more for showing off than for a lasting effect. We moved the fog machine switch from the machine up to the command console with the other effects.
Step 5: Motion Elements
For our design challenge we still had to convert motion from the power chair to motion on the truck. Since we determined the safest way to maneuver was to use moving straps to anchor the power chair to the truck frame equidistant front and back, the available moving element was the big wheel on the chair. Having learned about gears, linkage, pulleys, cam shafts and other motion transformers... the class devised a way to couple to the power chair wheel using pegs into the wheel hubs. That peg wheel, mounted to the truck frame adjacent to the wheel was then connected by pulley (found in the appliance and lawnmower sections of Lowes) to two gears (woodgears.ca online creator/template maker) that would mesh orthogonally (reversing the direction of rotation didn't matter). The second gear was again connected by pulley to the "fidget spinner" mounted through the truck frame. Used nails to adjust tension on pulleys and spray teflon to lubricate gearing. When it was all said and done, we wound up disengaging the tire peg portion because there was a little too much free play in the system and binding up could cause some components to torque off their alignment or the frame completely. But motion transformation still worked!!
Step 6: Trick-or-treating
The best part by far was getting a big gang of kids to go trick-or-treating at our local mall (they were having a trunk-or-treat). The firetruck was a hit, and everyone we met (or almost ran over) was so inclusive and complementary. Everyone had a great time.