- final project
- ∨
grow a tetrahedron - ∨ move a human the sick stick
- ∨ thursday
- ∨ friday
- ∨ saturday
- ∨ sunday
- ∨ monday
- ∨ tuesday
- ∨ bom
i was going to make a tetrahedral sculpture, something recursive and self-similar, that can can unfold into a tree.
but i didn't find a satisfying mechanism to both unfurl and refurl
source: wikimedia - ruggiero
playing with mechanisms
now i got one week to make a final project
( see parkinson's law )
so let's move
move a human
always wanted to make a kickstick
( gondolier style / punting on a skateboard )
some cool people from rise robotics made the first kickstick
they're folks from mit (aaron and some other rise co-founders)
and kyle, parker and jeff from risd
i want to dumb it down a bit and
make a wizard skate stick for myself
jen ordered me a BLDC
10s of dollars > about $90
got here thursday
50A flipsky 6354 190KV BLDC
• Max Power: 2450 Watts
• Max Current: 65 Amps
• Max Volts: 12S
• Max Torque: 7Nm
• M4 screws
Hole depth = 5mm
1/4in plate = 6.35mm
need M4 at 10-12mm length
40A ESC
these were stocked at archshops
• Max Cont Current: 40A
• Max Burst Current: 50A for 10 seconds
• Input Voltage: 2-6 cells li-XX or 6-16 Ni-MH/Ni-Cd battery
• BEC: 5.5V/5A Switching BEC
• PWM: 8~16 KHz
$26.95
wiring diagram
source
got some motor dimensions
dxf file
picked up some 1/4" aluminum plate offcuts
thanks will
designed a motor mount
M4 bolt holes, holes for drywall screws
made a quick file to waterjet
file on the OMAX
thnks shah
triage: don't have time to design a new board
so gonna use the motor driver board from wk 10
only need VCC, GND
one pin for pot, one pin for pwm to ESC
pin 3 > PA02 - ANALOG
pin 5 > PA04 - ANALOG
motor driver traces png
that'll do
note to future jerome: just get a $3 servo tester, it'll do the trick
POWER
i wanted to use a lawn mower battery - 60V 5Ah
but it was too big
ESC voltage of "2-6S" means two to six 3.6V cells in Series
so that's 24V max
a dewalt 20V powertool battery is perfect!
B+ pin is hot, B- pin is GND
anthony is the saviour who bestowed his wisdom and patience upon me
first tested with a Leonardo > basic pot to servo sketch
then powered by dc power supply before trying battery
EECS has great drawers of lugs, terminals and junk
then tried a sketch from former fablabber who made a centrifuge
servo ESC sketch
the ESC has a start-up sequence to map the potentiometer values
ESC start-up
DC power supply (not cranked yet)
And Anthony thus wroteth:
"Driving servos with SAMD chips. The typical arduino servo library doesn't (unless updated in the last year) work on SAMD devices. That being said creating your own PWM to set servo position is straightforward in software. It's perhaps a little clunkier in hardware though Neil has done most of that for you here and there is a nice library for the SAMD21 that uses hardware interrupts. Also a number of other choices that you can find on the good ol' google."
Library for my SAMD21
servo sketch (new library)
then tried my SAMD21 board
needed that new library
but the sample sketch was a bit hairy,
so anthony helped me with that too
combo'ed with the Loop from the first basic sketch
here's the sketch
and we're mobile
solder and heatshrink connections
gotta cast a tire
i found a vaccuum hose adapter thats the same size as the motor
and hot glued it onto a mug
i had some leftover urethane from molding/casting week
16 hrs later: goop
one edge didn't seem to set well
it was too soft / wrong durometer
makeshift mold with leftover reoflex
gunk
time to put it together
gonna use a wooden hand rail,
leftover from a home renovation
it has a nice flat face
1 1/4" exterior screws
zipties
yellow tape
sick stick... assemble!
countersink some holes
triage: gotta find a tire
kyle suggested 1/4in square o-ring's
i went to home depot to see if they had any o-rings
but instead found some rubber flex plumbing
this flex joint was nominal 2x2in
and fits so snug!
it cuts really easily with an olfa knife
flex joint for the wheel
cuts easily with a knife
kyle on video
kyle helped me 3D print a file
found this dewalt battery holder STL online
edited it in Fusion: removed the rear for the power pins
• Import Mesh >
• Generate Face groups >
• Convert Mesh (parametric)/
• Now its editable as a Solid object. Export STL.
edited stl
tuesday
i couldn't help but go skating this morning
and i took a tumble right before the final review
• busted the power switch
• 3D printed battery holder split
• the ESC seems to have error codes
was able to bypass the switch with alligator clips
it was rideable again
but then the tire started slipping off
twas a fun night! woohoo htmaa!
front
side
• bldc motor (50A) ~ $90
• ESC (40A) ~ $27
• SAMD21 mcu (VCC,GND, 2 pins w/ PWM)
• Dewalt battery 20V ~
• tire: 2" rubber flex joint (plumbing)
• 10K potentiometer ~
• rocker switch for power ~
• M4 x 12mm bolts for motor mount ~
• drywall screws to attach plate to stick ~
• 1/4" aluminum plate to mount motor ~
• tape, zipties
• stick ~
• check out VESC (avoid RC startup sequences)
• use a $3 servo tester to avoid milling a board
• try a finger throttle or slide potentiometer
• recess switches to survive impact
• some donut-like thing to protect hardware from falls
• glue tire to motor
• learn how to program "braking"