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Monday, June 30, 2014

Over 2 years...

Wow time flies. It's been 2 years since my last post. Life... Graduate work is sucking most of my time currently. I need to start my thesis (in the field of cyrogenic fluid slosh dynamics) soon, which won't make doing side projects any easier.

Projects update:
-EHB and LITE are suspended until further notice. I'm currently in a small apartment with very little access to machine tools, which makes making things difficult. They will eventually be built and will be followed by some other similar projects I have in mind, probably a scooter.
-I'm working on my Level 3 certification rocket. It's going to be a half scale Phoenix missile.
-Also designing a huge rocket with some MIT Rocket Team cruft. More details on that closer to launch day (BALLS 2015)

I'll post a build log of my L3 rocket similar to my L2 rocket when it's complete.


Sunday, May 13, 2012

3 months....more ouch

Yeah...I haven't done anything on my boards. I got swept away by MIT's work load again. All my free time was spent leading the team that built this:

MIT DBF 2012 Competition Plane
It's our plane from the DBF competition this year. I am an aerospace engineer after all...gotta build some things that fly :P .

About DBF:
DBF (Design/Build/Fly) is an international RC aircraft competition sponsored by Raytheon, Cessna, and the AIAA. Every year in September, a new set of rules/missions are released, and 60-80 teams design, build, and fly a plane for those rules. The contest site location alternates between Tuscon, AZ and Wichita, KS. 1 plane is allowed, and the missions are usually very different, making it a complicated design/optimization problem. Also, weight is usually a HUGE scoring factor (in some years it's been the only one that really matters). Also, lithium batteries are not allowed...It's like Flintstones meet the Jetsons in that regard (NiMH battery tech meets top-of-the-line composite technology).
The missions this year were to fly as many laps as you can in 4 minutes, carry 3.75lbs of aluminum block for 3 laps, and carry 2L of water up to 100m as fast as possible and then dump it.

About MIT DBF:
We're a small team (~12) undergraduates, usually with one or two graduate advisers who help out here and there. No profs at MIT have the time to devote to helping the team out, so we're really undergraduate run.

About our plane:
Unfortunately, I can't tell you very much about our plane because DBF is SUPER competitive, and a lot of how/what MIT DBF does is secret. I can tell you what you see in the pictures though. This plane is the product of a semesters worth of design/analysis, and a semesters worth of building. (for a reference length: it's wing span is about 1.4m). It has composite reinforced (various amounts of carbon fiber/fiberglass/Kevlar...I won't reveal weights or locations) foam wing and tails. The airfoils are very precise thanks to the CNC foam cutters the Aero/Astro department has. The fuselage is made out of a honeycomb/fiberglass composite; we CNC milled our molds in house for this fuselage, and developed our own manufacturing processes. The propulsion system is: NiMH battery pack, Castle Creations ESCs with Axi Gold brushless motors, and APC propellers (different props for different missions).

More pics:


Filling with water.

The team.
How the competition went:
Not well. Fucking tornadoes. I'll start from the beginning though: The plane made it to Wichita via freight no problem. It was SUPER windy every single day there. First day, we successfully completed Mission 1 (the speed mission) in the morning with 6 laps, at the end of which, an ESC fried (it was a bad one...we weren't anywhere near the amp limit). Then we decided to call it a day and go do Mission 2 flight testing at a small RC airfield nearby. The next morning we successfully completed Mission 2 (aluminum block passenger mission) in 20+mph winds. We were sitting in the top 5 at that point (top 3 if you didn't count the heavy planes that had already finished all 3 missions, but were way too heavy to place in the final top 5). Then we were waiting around for our next turn (they cycle through everyone for flight attempts) to do Mission 3 when they closed the flight line due to some rain and high (30ish) winds. It's unfortunate...we designed our plane to be very fast, so it could have handled the wind. Oh well, we decided to go back to the hotel and wait for tomorrow, the last competition day. That night, 90 tornadoes ripped through Kansas, out of those, 10 hit Wichita, and 1 happened to go right through the competition site, wrecking everything. They had to cancel the competition; no reschedule, nothing. We were super bummed: 1000's of man-hours and 1000's of dollars went into that plane. But we went back to the small airfield and completed Mission 3 (2L water dump mission) in ~40s in 35mph+ winds. We did the math...if we had completed Mission 3 in anywhere close to that time at the competition, we would have won. It sucks...a lot. The judges decided to get rid of the 3rd cycle of flights in the competition (the one we did M2 on), so we ended up in like 12th (because we only had one mission score...), or something. The places are total bullshit this year; 1/2 the teams never even flew, and the ones who placed high would have placed much lower had half the competition not been canceled.
I'm just glad Tuscon doesn't have tornadoes.


I'd like to thank the MIT Edgerton Center, the MIT AIAA Chapter, the MIT GEL Program, Lincoln Laboratories, the Department of Aeronautics and Astronautics, Aurora Flight Sciences, and Lockheed Martin for their support this year, and hopefully in many years to come!

-Jed Storey
President, MIT DBF

Sunday, January 29, 2012

2 months...ouch

Needless to say (but I will say it anyways), I've been busy. Leading MIT's DBF team has taken up every bit of my spare time since november. Well, almost...

I got the hubcaps and spacers for LiteBoard's hub motors machined:



I did the spacers on the lathe, but the hubcaps I did entirely in the mill. I really like the mill method, rather than going from the lathe to the mill. It took a lot less time. I didn't check one of my drill bits though, and being a student shop, it was damaged, so the tip broke off in my part. I was lucky that it had gone most of the way through before breaking off, though, so I was able to get the tip out. I also decided to try loctite bearing compound this time, so I made the bearing holes slightly oversized.

Even though I haven't been building much, I've been gathering supplies: 2 hobbyking 80A car esc's, 2 more 6S 5000mAh packs (in addition to the 2 I have left over from ELB), all of the metal stock I'll need, 4 1.25"x4" colsons, a massive lipo charger and power supply, a $15 hobbyking 2.4GHz 2 channel radio, etc.

The next machining I'll do is probably coring out the colsons.

Left to do:

  • core out colsons
  • machine axle adapters and hubs
  • wind stators
  • order rotor plates
  • find/buy hall effect sensors
  • assemble motors
  • test motors/esc's
  • assemble massive lipo pack (6S4P)
  • laser cut grip tape design
  • assemble board
  • add lights
  • +more
Wow that's a long list :/ . I hope I have time this semester to work on it. I'll only be taking 3.5 classes to give me time for DBF and this, so we'll see how it goes.

Monday, November 14, 2011

Here we go!

I’ve been busy, but I’ve somehow found time to work on LiteBoard. Oh right…what is LiteBoard?

Now Presenting LiteBoard:
But first, some history: I want a light*, fast way to get around campus, which is the same premise and idea that evolved into ELB. Unfortunately, ELB turned out to be more of a prototype and a learning experience. Now I want a light*, fast, and polished product to get around campus. Sure, there are commercially (and cheaper) available options, such as a bicycle (can’t pick it up and take it to class…also not original and would get stolen), roller blades (no way…I’d kill myself on those), kick scooters (lammeee), electric scooters (lammeerrr), hub motor scooters (so not original)…but I wanted a longboard. So I came up with the EHB concept, and started acquiring parts for it. But once I did a weight build-up, I realized that EHB wouldn’t actually be much lighter than ELB, so I suspended work on it. I’ve been riding around on the mountainboard I bought for EHB for awhile now…I have to say, it is a great way to get around. It’s just slow: I can only maintain about 10mph.

LiteBoard is the V3 concept that I came up with after completing ELB. V2 is/was EHB, but even though it would address most of the problems ELB has, it didn’t address one very important one: weight. ELB weighs 40lbs. EHB is predicted to weigh 35lbs. Liteboard: 25 lbs.

Not enough time to do a rendering=screen shot.
Lite will be a 2WD hub motor powered electric longboard (actually a longboard this time, and not a mountainboard). Each motor will be ~1100W, producing ~3.9Nm of torque each. Lite’s estimated top speed will be ~25mph. The basis of Lite is this longboard:


Pending cool grip-tape design

Randal II 50deg 180mm trucks, ABEC11 97mm Flywheels, and a bamboo/maple deck I got off of ebay (it was incredibly cheap, yet very high quality. ebay=good source for longboard parts). The deck needed some modifications to use the massive 97mm Flywheels:

Initial cutout lines. 
1st try: didn't remove enough.
Second try: Now the wheels don't bite the deck when I turn.
I think it looks awesome...
Why did I need 97mm Flywheels? …

Detailed Motor design:


I couldn't get a good angle of the internals. The axle extension is not round, but keyed to fit with the hub that is pressed into the stator.
Since ELB ended up with about twice as much torque as I’d ever need, I decided to shoot for the same amount of torque/motor for LiteBoard, but cut the number of motors in half. I followed the same design process I used to design ELB's and EHB's motors: Start with simple calculations, move on to SolidWorks CAD drawings, import DXF's into FEMM, modify CAD, repeat...

FEMM pre-diameter shrinking.
The motor underwent one large design change as a result of FEMM. Turns out that pretty much the whole stator was saturated, so I wasting a ton of energy. I shrunk the magnets from 3mm to 2mm thick, and shrank the whole OD of the motor by 4 mm, and only took a .1Nm hit in the process.

Estimated Motor Specs:
Specification
Value
# Phases
3
Power
1100W
Voltage
6S Lipo
Max current
50A+
Torque (FEMM)
3.9Nm
No-load speed
30mph
Stator dia
55mm
Stator length
35mm
Teeth
18
Turns/tooth
4
Rotor OD
70mm
Magnet thickness
2mm
Magnet grade
N40
# Poles
20
Motor width
60mm
Motor OD
100mm

The high current, low voltage method was picked in order to use HobbyKing’s 80A car ESC, which is about 1/3 of the cost of an equivalent Kelly Controller, and about ¼ the size. It also has a sensored option that I plan on using. I will likely get some pretty serious I^2R losses, but I’ll try to keep wires as short as possible and pack the stator with multiple parallel strands of magnet wire (thinking 22Ga). 8 parallel 22ga stands has same resistance/m as one 13ga strand…idk, I’ll see how many strands I can fit.
The stators are Scorpion Power Systems 5535 18T stators. They come in their S5535 motor series, which are about $400 a piece…which is why I bought the stators directly from them again ($140 for both, free DHL express shipping). Yet again, they are very high quality:



I officially love these guys' work.
I decided to bite the bullet and go with BigBlueSaw for waterjetting my rotor plates. Turns out that 11*.125” =35mm to within a fraction of a mm…I got lucky there. 22 plates will run my $250…ouch! But I did the math, and if I spent the amount of time working that it would take me to machine the rotors, I would come out ahead if I just have them cut for me (and waterjetting them here is a no-go…it’s freakin’ expensive).

Batteries: While I thought about trying A123 cylindrical cells for this one (specifically a 7S7P pack made of their 26650 cells), it turns out that it won’t fit under my deck. So I went with lipo again. Specifically, I’m going to buy 2 more 6S 5000mAh 25C packs from HobbyKing, and using the leftover packs from ELB, I’m going to make my own, slim 6S4P pack (22.2V, 20Ah).

Control: At first I’ll use a $15 hobbyking 2Ch. 2.4GHz system. But I’m planning on doing something like this eventually.

Tires: So my last post suggested a Colson 4”x7/8” rubber wheel was my best bet. But that was before I shrunk the OD of the motor from 74mm to 70mm, which puts it out of the range of the 7/8” one. So I’m going to use two 4”x1.25” ones.

From left to right: 4x7/8 turned out, 4x7/8, 4x1.25, 4x1.5,4x2

Note the huge void.

After digging a bit deeper: MORE huge voids.
 Next I tried the 1.5" wide one:

Only 1" wide of plastic inside (after turning out visible part of hub).  Guess I'll be using the 1.25" wheels (more plastic for press fit).
I was able to cut the rubber on these.
Again: another void...

Here's a table of 4" Colson rubber wheel data for your reference.

Safety: I’ll have the same setup as I did on ELB. A contactor sitting in the main battery line that is actuated by a magnetic reed-switch from a magnet strapped to my shoe. This will act as a fail-proof way to make sure that if I’m not on the board (anymore…), it doesn’t keep going. I’m also planning on wearing a helmet with it.
The ultimate goal is have a very sleek, finished product that achieves all of my criteria (safe, light, reliable, fast, etc…)
Anyways, that’s the plan so far. I should be able to get a lot of it done over IAP…we’ll see.

Oh, and to leave you with a cliffhanger: it’s called “Lite” for more than one reason ;) . 

Thursday, October 27, 2011

Wheel Study

I'll explain why I'm studying wheels in my next post. But for now: I studied some wheels.

More precisely, I bought a whole bunch of small rubber-treaded wheels from McMaster so I could measure them (McMaster doesn't have CAD of their wheels, which is annoying). I needed to be able to core out ~73-75mm of the hub.
I bought these: 2337T35 , 2337T42 , 2337T37 , 2829T68, 2829T56 , 2439T42 , 2243T22

All 4in wheels of varying widths and materials. I got them in and measured their hubs and 5 had hubs that were large enough, and only 3 of those were reasonably priced or would work for me (2337T42,2337T35,2829T68). Interestingly, the wider the wheel got, the smaller the diameter of the hub...no idea why. I like the super soft tire (2243T22), but it was really rounded, and I'm planning on putting multiple tires on *ahem* something.

2 of the 3 wheels are mcmaster's "Rubber Wheel" series. They are black phenolic? hubs with black rubber tread. The other one is "Performance Rubber-Tread"...actually Colson Casters! Nylon or polypropylene? hub with grey tread.

The phenolic ones are easy to machine...not nice, but easy. Phenolic is probably the WORST smelling material I've ever tried to cut...mix of shit and rotting vegetation. In fact, I gave up after a few passes. Even though the wheels are a lot cheaper, it isn't worth dieing for...

So I tried the Colson. MUCH nicer. Super easy to cut, and NO smell. Found my wheel!

Saturday, October 1, 2011

More EHB stuff

While I really didn't have the time today, I decided to do a little work on EHB.

I finished designing the battery box:

I used SolidWorks' sheet metal tools to design it. It's contoured to fit my deck. I plan on waterjetting it out of 1/16" 6061 aluminum. The battery packs are 4s1p 5000mAh Zippys.

I also did a pretty detailed mass calculation. It comes out to about 35lbs...which is annoying because I was shooting for < 30lbs. The motors are ~13lbs, and the batteries and battery box are ~5lbs. Unfortunately, the four kelly controllers weigh in at ~7lbs. Add in the deck and the trucks, and I get ~32lbs. Grrr...

So at this point, I have 2 options: Keep the current heavy configuration, or give in and make it 2WD (soo not as cool...). 2WD will save me about 9lbs, which brings the total down to ~26lbs.

I guess another option would be to suspend work on EHB and start LiteBoard. Though that would mean my $500+ investment in EHB parts would just be sitting around until LiteBoard is done...

We'll see what happens. Heck knows, at the rate things are going (I'm swamped), neither may get done by the time I graduate.

Saturday, September 24, 2011

Update

Well...not much has happened. I've been swamped (work, classes, DBF, etc...).

I got my hands on a pair of Ground Industries Bionic Spring trucks...arguably the best trucks out there (too bad GI seems to be going out of business).

I also bought a bunch of metal stock (for hub motors and battery box). EHB will happen eventually...just not as fast as I'd originally hoped...so no, you can't ride it yet.