Weekend Update

The pile of parts on my shelf is starting to resemble a scooter.

This weekend went off to a slow start, but, among other things, progress was made on the scooter.

Dimensions for the rear caddy platform and fork were finalized through the magic of Draftsight (solidworks for noobs).

Totally legit.

As you can see, I've been very thorough.

All that's left in terms of parts is getting the fork and rear platform sent out for water jetting. The only concern I have is the motor mount, which, considering I don't have any reference material, has been left out of this sketch. Not a problem as some creative milling can probably fix any clearance issues.

Trolling will be courtesy of a jasontroller, which will eventually be abused  modded for the purposes of increasing output wattage via decreased shunt resistance.

An in-depth how-to can be found here: http://yameb.blogspot.com/2013/07/cruscooter-and-minijasontroller-or-how.html

Power, originally coming from some derpy li-polys off of hobbyking, will be replaced by some A123 LiFePO4 cells that I'll have to weld together and arrange log style. I should be able to barely fit in a 10S2P pack (~36V and 5Ah).

Hub machining was a great success; I managed to mill down the ends of the rear hub to accommodate for the 4" aluminum u-channel.

Before

After!

To be continued.

Derpy photo shoot

Now that DOHLAC (Derpy/-oneTesla/Hot Long/Ass Coil) lives at home, I finally decided to take pictures.

Bad lighting is bad >__<.

Specs:

Half bridge of 60N65s kept well within spec to avoid damn-I-blew-the-bridge-again syndrome (up to 75% duty cycle at 340VDC)

Gate drive provided by a pair of UCCs and feedback courtesy of question-mark antenna.

Secondary:

2.5" x 10" PVC, 32AWG wire

fRES @ 316kHz

I can probably push the coil to give more spark, but due to my unwillingness to replace the bridge, it'll be kept at a lofty 7.5". 

Long pulse widths for fire-y streamer goodness.

Longest spark on this run from a nice straight streamer. Top-mounted breakout point seems to distribute the E-field in a nice symmetric way that promotes longer sparks. 

Special thanks to Bayley and Kramnik for helping me troubleshoot this thing at one point or another.

...!

80kW of hot long sparks coming soon.

Project Dump

Working from nine to five doesn't seem to be helping my projects.

Part 1: The still imaginary scooter 

After learning how2mill, I set out on machining one of the few components that didn't require the motor or battery (which I have yet to order): the fork!

I should learn how2CAD at some point too.

After rough sketches and some trigy math in the comp book, I sadly discovered that If I were to set the axle in line with the handlebar shaft, I'd end up with a scooter nose-up. Not to worry though, as forward offset fork is here to the rescue! Combined with some derpy angle finagling by cutting away part of the  rubber 'shock absorber,' I'd achieve a scooter that is both aesthetically and structurally sound. Well, aesthetically sound at least. 

The resulting hunk of 1/4" thick aluminum resembled something slightly too angular for my taste, but as the first thing I've ever milled, I think it turned out ok. 

Part 2: Derpy Coil lives!

Also known as "Long Hot," Derpy coil has finally come to life after scraping the secondary base feedback scheme. 

Here's how the troubleshooting adventure went:

1. Coil is completed, run off a variac at low power. Nothing

2. Scoped across primary: looks legit. The primary waveform only goes to shit when it's running off of its own feedback. 

3. Add turns to secondary base feedback CT and hope it doesn't reach saturation. Nothing.

4. Remove high-pass filter. Poopy sparks appear. 

5. Feed the coil a 316kHz offset sine wave. Success! Kind of out of tune 2" long sparks appear.

6. Abort secondary base feedback, go to antenna: nothing.

7. Give up on this driver board and repopulate another one (without secondary base feedback junk attached).

8. ???

9. Success!

Here it is playing Solfegietto by CPE Bach. Spark performance isn't quite impressive as duty cycle was turned down to maintain note clarity. Modified oneTesla interrupter pulse widths were overlapping each other, which you'll notice when the really low notes start playing.

After Bayley reflashed the interrupter for true continuous wave output, several things happened:

Hot Long finally got hot and long.

Then the bridge blew after getting to ~140VDC. 

The number of primary turns then grew to 27.

Then the bridge died again, but at ~200VDC.

Failure is probably due to transients - further testing will resume after TVS is added and primary current is scoped.

UPDATE: 8/18/2013

Long Hot will no longer endure CW abuse and will continue to live life happy at 75% duty cycle, occasionally pushing out the odd midi file. 

-oneTesla Lives!

After weeks hours of deliberation, I sent out -oneTesla to OSH Park, hoping to receive a functioning board.

But, oh, I got so much more.

Dat gold plating.

It might have been the fact that this was my first fabhouse board, but, damn. That looks sexy. The board features silkscreen, gold through-hole plating, and purple solder mask, making it quite the specimen.

A fully populated "Derpy Coil" with secondary base feedback tentacle.

Look! The inverter is inverting...!

It even does that inverting thing.

Power testing to come soon...

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!

√−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: http://www.hobbyking.com/hobbyking/store/__18175__Turnigy_Aerodrive_SK3_5055_280kv_Brushless_Outrunner_Motor.html

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...

-oneTesla

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)

ERMAHGERD ETCHED BOARDS

Minuet 1.x

Time to go solid state!

For my first solid state coil, I decided to go with something on the moderate side of complexity, basing it off of Steve Ward's mini SSTC schematic: http://www.stevehv.4hv.org/SSTC5.htm

Operating Principles

Tesla coils are resonant air-cored transformers.

A primary inductor is coupled to a secondary inductor, resulting in a voltage step-up that allows for the breakdown of air after the secondary exceeds air's dielectric voltage (~3 × 10⁶ V/m). 

By using an air cored transformer, Tesla coils avoid the pesky core saturation that would otherwise limit the magnetic field and the resulting high voltage. 

The simplest variation of a Tesla coil, a spark gap coil, consists of the following:

SGTC Schematic
Source: http://enterpriseprogrammer.files.wordpress.com/2012/07/tesla_coil_circuit_diagram.png

When the primary tank capacitor reaches the voltage neccesary to arc across the spark gap (literally two electrodes separated by air), an LC circuit is formed that exhibits a resonant frequency.

Spark gap Tesla coils (SGTCs) and Dual resonant solid state Tesla coils (DRSSTCs) use two resonant tuned circuits (The primary and secondary) to more effectively transfer energy from the primary to the secondary coils. This is achieved by the phenomenon in which at resonance, impedances and reactances effectively cancel each other out.  

Given the resistive nature of the primary and secondary, the oscillations at the resonant frequency in both sides of the transformer will undergo decay and display waveform damping. This damping effect produces distinct RF "cycles" that are offset by 90 degrees. It's during each cycle that energy is exchanged through the changing magnetic field.

Simple solid state Tesla coils only have a secondary which is coupled to a primary inductor. The primary inductor is then driven at the resonant frequency of the secondary. 

Being driven at resonance requires current to flow back and forth in the inductor at a resonance frequency (simulating AC). In a solid state coil, this is achieved through transistors assembled in either a half-bridge or a full bridge (H-bridge) with the primary inductor acting as the load. The resonant frequency of most secondaries is around a few hundred kHz and bus currents and voltages linger around in the tens of amps and 240V (bus voltages will vary from topology to topology), this puts quite a bit strain on the transistors, limiting the field of options down to two types of transistors: MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors); the transistor strain is limited by the fact that most of the oscillations are induced in pulses i.e. the coil is kept in operation in short bursts to prevent overheating. Spark production is also noticeably different when driven in an "interrupted" mode as opposed to continuous duty. 

More often, IGBTs are favored over MOSFETs because they exhibit diode-like voltage drop while MOSFETs exhibit a resistive drop that increases with current.

Dual resonant variations of solid state coils include a tank capacitor in the primary side circuit, creating, like a spark gap coil, an LC circuit while in operation. The addition of a capacitive element to the circuit also cancels out the inductive reactance of the primary coil, thus allowing for currents orders of magnitude greater than regular SSTCs to propagate within the primary.

Tuning

Spark gap coils are tuned via physical parameters: the inductance of the primary, the capacitance of the tank capacitor, etc. 

In solid state coils, the resonant frequency is maintained by some sort of feedback mechanism. SSTCs generally use antenna based feedback (literally reaching into the electric field produced by the secondary), which induces a changing voltage as the field changes, while DRSSTCs required primary feedback as the secondary is out of phase with the primary. SSTCs are unable to use primary feedback because the current isn't effectively measurable due to the lower primary currents found in SSTCs. 

Construction:

Minuet 1.x was intended to be a single-boarded audio modulated SSTC; unfortunately, it's had a hard and very confusing life.

Evolution (to be added when I bother to take some pictures)
At one point, it did produce sparks, albeit only in continuous wave operation:

6'' sparks run continuous wave

The board since exploded after the addition of a fiber-in jack to more reliably interrupt operation. Maybe duty cycle issues?

If any good came out of this project, it's the list of things you shouldn't do

The project was abandoned in lieu of -oneTesla (negative oneTesla) 5/29/13. 

Herp Derp

me:  ben, I'm in school

get me out of here

halp

halp me

 Ben:  hue hue

 Sent at 10:23 AM on Monday

 Ben:  I'm at home

 me:  T^T

Spark Gap Tesla Coil 1.0

Conceived during a summer that probably could've gone to better use (Junction, whyyyyyyy did I attend you???), SGTC 1.0 was what first got me into the whole business of shooting lightning.

Long exposure is best exposure.

Design Considerations:

Modularity

- At some point, I want this thing to shoot monster streamers, so being able to swap components would be nice.

Reliability

- Demos are far more fun when things work.

Sexiness

-Hnngggghhhh *ahem*

Construction breakdown:

Chassis

-Two sheets of HDPE held up by threaded rod columns

- Fan bolted onto a piece of plexi that was subsequently ziptied onto the threaded rod (farming hard)

Secondary

- Donated by the Daniel Kramnik

- 4" diameter, 2.5'~ tall

- 24 AWG???

- Resonant frequency ~555kHz

- Added toilet flange for increased mounting stability to chassis

Primary

- 1/4" copper refrigeration tubing wound spiral-style

- Added supports for sexiness

Topload

-  Some very sad aluminum ducting wrapped in even sadder aluminum tape. Not exactly my best handiwork.

MMC

- Scavenged Panasonic metal film caps

- Rated for ~8kV 

-Capacitance: ??? (something in the 0.005uF range)

NST

- 9kV, 30mA (problem, MMC?)

Spark Gap

- Zinc-plated hardware (a bad idea)

- Cooled via muffin fan (a yummy idea)

Here, have some pictures media!

Note: bleed resistors help
 prevent accidental electrocution

Protip: when laying the primary,
 go from the center outward 

mmmm, HDPE

Results:

14"~ streamers