Monday, July 29, 2013

Maker Faire Detroit!

My first Maker Faire, and in the Motor City, no less.

July 26th marked the first day of Maker Faire Detroit and all of its insanity: lots of fire, homemade jet engines, (one)Tesla coils, giant dragon-sculpture-things, and of course, the wonderful community of makers to name a few.

I was there on oneTesla business, showing off demo coils and whatnot, but for me at least, the excitement lie in the other exhibitions.

(side note: oneTesla won editor's choice!)
The oneTesla team.
 I also happened across Paul Kidwell from the Geekgroup: their youtube series on SGTCs is part of the reason I'm coiling today, and as you can imagine, I was screaming like a soldier at a KPOP concert.
My expression does not do justice to the fangirl trapped inside omgomgomgomgogmomg
Enough words. Photodump!

Monday, July 22, 2013

√−1 Scooter

As part of my last free this summer, I've taken up the task of building a personal scooter to transport me around campus and to MITERS.

Design parameters:
  • 5-8 mile range
  • cruise speed of 20mph
  • reliability
I used Charles Guan's instructable as a guide in how to succeed not to destroy everything.

Among the most useful "steps" was the motor page as, having no previous EV experience, sizing up a reasonable motor alone would lead to either utter disappointment or too much scooter for any sane person to handle.

To safely fulfill the 20 mph (8.9 m/s) cruising speed, I'd need a motor with the following output wattage:

P = Force(drag)*Distance/Time

Substituting in air's density at STP (1.1839 kg*m^-3), and my drag coefficient at 1 into the drag equation gets me 38.0N, which translates to 338W. It's recommended that this number be less than 15% of the max motor input as ideally, only half of the input wattage goes into mechanical output. 

This would mean I'd need a motor rated for ~2.3kW. 

Hot damn.

With waterjetting out of the question, I ran into the idea of constructing the entire chassis out of u-channel to avoid racking up costs (the actual theoretical budget for the project is around ~$400). 

Going for $47.06, three feet of 4"x2.25" McMaster u-channel seemed to fit the job. 

At this point, several issues arise with trying to build a suitable motor into the frame of this form factor.
  • Outrunners of the correct wattage tend to be either too big for the frame, or run at voltages that would cause battery costs to be too damn high.
  • Having an outrunner too long/large would mean having to machine out the appropriately sized  hole in the other side of the chassis while mounting the motor to the frame. 
  • Batteries are expensive.
  • Ideally, the motor should completely inside the chassis to avoid gunk acquisition that would otherwise limit its lifespan.
This meant downsizing the motor from the previously melon-esque Turnigy SK3 63mm motor to the following:

Running the system at 36V also means an overall cheaper system and a happier wallet.

This did mean, however, my safe cruising speed would take a fall to 18 mph (hardly slow).

After settling on the motor, I could finally go shopping for the other assortment of parts I'd need to make this scooter scoot. The BOM can be viewed here along with the drag equation conveniently available in table form.

More to come...

Tuesday, July 9, 2013


Pronunciation: "ne-guh-tive wan-tess-luh"

This summer, I'm working as a slave for oneTesla, a start-up founded by three MIT students: Bayley, Heidi, and Kramnik.

The recent bout of employment happened to coincide with my recent quest to get a "singing" SSTC working, and so -oneTesla was born.

Conceived from its namesake, oneTesla, -oneTesla is the SSTC derivative of the DRSSTC. The conversion process involved, to name a few things, removing the tank cap, fiddling with the feedback, and some trace rerouting.

DISCLAIMER: I do not recommend that you undertake this path as an alternative to purchasing an actual oneTesla kit. Trust me. The amount of pure butthurt incurred in troubleshooting alone is not worth the minuscule monetary sum that you'd save.

I started out with this very humble chassis and fan assembly, orphaned from Minuet 1.x:
4020, some lasercut acrylic, and HDPE (currently smothered in electrical tape) machined on a lathe. obligatory zip-tied fan included.
The original plan involved simply etching a oneTesla. It went less than swimmingly. For the longest time, I was under the impression that the optical receiver on the board was dead. Four hours later, I tried the interrupter on a oneTesla unit and it also didn't seem to work, and it turned out that the interrupter was just running out of batteries and the LED on the output just wasn't bright enough. Oh, and this was after I accidentally shorted +12 to ground, frying a few traces.

Important lessons learned:
1. Humans are not manufacturing houses.
2. Traces are not magical.
3. Always check the battery to your opto-coupled interrupter.

Version 1.1(6/10/13)

After receiving the board file for one of the original oneTeslas (meant to be etched), some more finagling occurred, which lead to the creation of another functional board.

Results: 3" of spark run at ~8% duty cycle.

Not bad considering the low duty cycle. Too bad that the bridge fried itself a few times before I could reflash the interrupter to increase the pulse width.

To be continued...

UPDATE (7/22/13)

New and improved -oneTeslas with secondary base feedback have been sent to the fabhouse. ETA July 29th.

UPDATE (7/30/13)