Maker Faire NY 2012

I spent the last weekend at a DIY 3D printer convention Maker Faire NY with the MITERS crew showing off some projects from the past year, as well as some older ones. Last year was my first time attending a full Maker Faire, although I've done the Cambridge Mini Maker Faire several times. Armed with a better understanding of exactly how many little kids with inattentive parents were going to try to touch, climb on, and ride the sharp and dangerous projects, I came better prepared this year:

Yes, tinyKart made it down again, this time with a new license plate. Getting it down was a little trickier than last year, since we had to bring nine people plus all the projects in one minivan and one Jeep. That meant going a step further than the two-piece configuration that made it down last year. This year, tinyKart was packed entirely flat and stuck in the back of the minivan along with all of my other small projects:

And I just sat in the seat the whole way down.

I almost didn't bring tinyKart this year, but I'm sort-of glad I did because it was able to finally get a tiny bit of "track" time on the Power Racing Series track at Maker Faire. The Power Racing Series is a relatively new racing league for modified Power Wheels-style cars. tinyKart is obviously not a modified Power Wheels, so it was ineligible to win any races. (Although as some places seem proud to point out, it was apparently eligible to lose them...) 

Still, it was fun to get a little track time in an ultralight kart that was never really designed for anything of the sort, which weighs 55lbs and can be brought down in the back of a minivan. If you want to see what it actually can do, here's Max taking it for some laps with little traffic to slow him down:

It's a viable go-kart with handling that is way better than it should be, given the custom and very flexible chassis. I got to run some laps in the wet and it was quite amazing. By the second day of the Faire, it had incurred a bit of race damage and was down to one wheel drive and a single disk brake. Then, it started raining. No matter, it was still awesome:

So, tinyKart is a little broken after this trip. It's been due for maintenance anyway, so this will be a good motivator to fix it up and finally put on new controllers. Other than that, it needs completely new spindles, since two of them got bent up in brushes with the track barriers. It also needs a new belt and a new steering linkage. (The part which is called a "fusible" in French for reasons I now understand more completely.) And some of the non-structural front frame got beat up. No major structural or powertrain damage though.

Kinda glad we kept those corners in the design.

Of course there were also many copters at this year's Faire. Here's the selection of MITERS flying objects that made the trip down:

From left to right, there was 4pcb (which didn't get to fly since it's mostly an indoor copter), my versatile Talon Quad, Nick's feather-light tricopter, and Banks' Derpcopter. There were several other groups with flying things at the Faire. One that particularly caught my eye was the AeroQuad booth, which had several nice FPV frames:

Generally, it was too crowded to fly around, but there were a few opportunities to do so at the field near the AeroQuad booth. My brother and I also decided to head in early on Sunday to get some aerial video before the crowds showed up. Of particular interest was the (real) Titan rocket, which is a bit over 100 feet tall. Here's some GoPro video from the Faire before it opened on Sunday:

The Talon has been flying great with FFv1.2s motor controllers and the modded KK2.0 firmware. It's mostly limited by my piloting skills and lack of FPV equipment at this point.

Photo credit: Matthew Honickman.

I also brought Pneu Scooter, and as luck would have it the rear tire got a leak the week before Maker Faire just like last year. So just like last year, I took the entire wheel/motor assembly apart, cleaned everything out, and replaced the wheel. I also took the opportunity to extend the phase wires so they would not have to be cut every time I need to replace the wheel.

After the wheel change, I also tried and failed to get a 3ph v4.0 controller in Pneu Scooter for the Faire. But since I ran out of time, I went back to the trusty v3.1 and it worked with no problems for the entire event. It's by far the best way to get around the venue when it's crowded.

That's it for the project updates, but here are some more pictures I collected from the Faire:

Chibikarts and hexarideablepods.

Ground clearance?

Runs on two D&D motors.

MITERS won an editor's choice award from Make.

I hope those are all used metro cards.

One of these things is not like the others...

Ben's scooter hauling most of MITERS back to the cars at the end of the Faire.

World Maker Faire: NY 2012

 

All packed up and ready to go to World Maker Faire 2012 in New York! Come find me and the rest of the MITERS group in Zone B, or just follow the gradient of ultralight go-karts, scooters, quadrotors, and Tesla coils. But unfortunately...

Cambridge Mini Maker Faire + Kramnikopter

A couple weeks ago I went to the Cambridge Mini Maker Faire. It's a smaller event than the full-scale NY Maker Faire I went to in September, but it's much closer to home. In fact, it's within walking distance, so I decided to kart everything over.

Yes, kart.

It turns out that tinyKart makes a pretty good hand truck. Also along for the ride was Pneu Scooter (ziptied to the frame), Twitch, and 4pcb (in the seat). Unfortunately, the Mini Maker Faire is too crowded for the vehicles to be effectively (or safely) demo'ed. And it was too windy to fly 4pcb.

So that just left one option:

Balloon Twitch.

You can see how windy it was by how far the balloon is deflected. The balloon was my way of making sure that nobody stepped on Twitch accidentally, but it also made the robot a lot more "interactive". And by that I mean that several little kids were teased.

Sorry for the blue video...forgot to turn off manual white balance...

You can find more photos from CMMF 2012 in the Flickr pool.

I was really looking forward to demo'ing 4pcb, since it drew so much attention at the NY Maker Faire despite not actually being flyable at that point. It's small enough not to pose much of a safety risk, but micro quads really don't like wind. In general they're twitchy and hard to fly. Giant hexrotors have the opposite problem: they're very stable, but too dangerous to use anywhere near people.

To fill the gap in my flying things fleet, I decided to put together a Turnigy Talon frame from Hobby King. I got to fly one that was put together by Daniel Kramnik (of Tesla Coil fame) and was very impressed with the quality of the frame. For $34, you get a real carbon fiber + aluminum frame. Add to that four $7 motors, four $14 ESCs, and $18 battery, a $3 bag of props, and $15 control board, and you get a complete mid-size quadrotor kit (bring your own radio) for $154.

Kramnikopter!

Here it is with 4pcb propped on it for size comparison:

The Talon frame is very impressive, even without considering the cost:performance ratio. It's stiff and light and it looks amazing. It also seems very durable - you'd have to crash pretty hard to break it and the landing gear is nice. When you take into account the fact that it's $34, it is one of the best deals I've seen.

The motors, on the other hand, leave something to be desired. They are the most inexpensive of an already low-cost/low-quality brand name, which means they have some issues. Mostly, I ran into axial alignment problems - the can and shaft are poorly constrained. They are also not balanced. If I were to replace one component right now, it would be the motors. They do look cool, though. 

For what it is, the KK board is an impressive deal as well. It's rate-mode only, so it can't do self-leveling, position hold, altitude hold, or any other more advanced features. 4pcb flies in self-leveling attitude mode, so returning the sticks to center means it tries to go to level (zero angle). So it took some practice for me to learn how to fly Kramnikopter in rate mode, where returning the stick to zero means zero angular velocity. You can see me learning the new input mode a little at the start of this video:

After filming the first half of that video with it, I decided to go ahead and attempt to fly my HD video camera. I have a long history of attaching my camera to things that move, but this would mark the first time that it's actually left the ground. The mount I made was pretty simple:

Kramnikam v-1.0

On one hand, the camera flew and survived. But it's not quite a cinematic experience yet. This camera weights exactly 300g, and it's just a little bit too heavy for this combination of motors and props. The resulting flight is very close to being unstable, since the motors are almost maxed out. The more obvious problem is that my initial vibration isolation solutions (foam tape, felt) didn't help much. So, lighter camera and softer mount seem to be the next steps. For now, I have a really nice medium-sized quad to play with.

Maker Faire NY 2011

Last weekend I went down to the World Maker Faire in New York, along with some of the other builder-types from MIT and the Summer Engineering Workshop crew. Needless to say, we were responsible for most of the rideable objects on our side of the Faire:

I've been to the Cambridge Mini Maker Faire twice, but this was my first experience with one of the three World Maker Faire events. While the Mini Maker Faire probably attracts a crowd of a few thousand, the World Maker Faire numbers must be in the several tens of thousands. First off, I was amazed that a handful of people actually knew me from my blog, so here's a shout-out to the people who came by my table to say hi. I'm not as famous as certain people, but it's cool to meet my blog readers in person.

Also present was Max H., who brought TOBL to show off, and most of the tinyKart crew. A large sampling of the MITERS builders came down from Cambridge as well to show off a pair of sound-reactive EL shutter shades, giant Tesla coil driver, 3D printer, battlebot, tankboard, hub motor kick scooter, eddy current clock, and rideable freakin' hexapod.

For my part, I decided that I would attempt to bring five projects. First, my three Maker Faire veterans, Pneu Scooter, Twitch, and SegStick. Additionally, I brought 4pcb, which turned out to be an attention-getter even though I did not even attempt to fly it. I would say that quadrotors are the new Segways - the current obsession of every random tech-savvy person. But in fact, Segways are still the new Segways. For some reason, no matter what else I bring, I can't escape the Segway people. Then again, I've said a few times that the quadrotor is just two Segways and a FIRST robot, so maybe it's all inherited from one parent class of silly self-stabilizing objects.

So before I get angry, Yes, it does have an angular rate sensor, commonly known as a "gyro" for historical reasons. No, there is no mechanical flywheel keeping it balanced. No, it does not use a Kalman filter. And yes, it runs just fine on an Arduino, and it doesn't even use that much of its processing power because the code is very, very simple...much simpler than you want to think.


And that's all I want to say about quadrotors and self-balancing platforms. But here are the Maker Faire recaps for the more interesting projects:

tinyKart:

That's tinyKart in the trunk of a Ford Fusion. I loaded it into the trunk myself in about 10 minutes. It involved taking out 12 cap screws and sliding the two halves apart, then flipping the front half over so that the steering wheel rested in the seat. The back half weighs less than 40lbs and the front half weighs less than 20lbs. There was even enough extra room in the trunk for Tyler's monster Tesla coil driver.

In terms of making an ultralight, ultra portable go-kart, I consider this trip a huge success. We like to make things that don't exist, and an ultralight electric go-kart is something new. There is the Razor Ground Force, which is the same weight (55lbs) as tinyKart but there really is no comparison. Which brings me to my next point:

tinyKart is absolutely freaking awesome as a go-kart. 

Just look what reverse did to this dude's hair...

We drove it all weekend and it is actually amazing to me that we built such a thing from scratch. It's a totally different experience from Cap Kart and most other go-karts I've driven, and it's more fun than any of them. "Sprightly" might be a good word. I really don't know. It darts around in ways that defy its narrow tires and flex-y frame. The acceleration is good too, despite the lack of more formidable brushless motors. The trigger throttle just makes it even more of a unique experience. And the brakes are so good that I worry about bending the steering wheel from the deceleration force. I really would not change a single thing about the mechanical design...it's pure win.

"If it's going to break, it's going to break now." -Max

It even does things it shouldn't, like off-roading. We took it on slippery grass and dirt, and it was even more fun than on asphalt. The flex-y frame doesn't mind at all and the 17mm aluminum wheel axles, which are probably the weakest link in the structural loop, survived both the shock load from bumps and side load from drifting.

Pretty much the only things that isn't 100% perfect are the controllers. Maybe I just have a high standard for motor control...well okay, I definitely do...but the Kelly controllers just aren't quite up to the task of driving full load into these motors. They cut out occasionally, leaving you with half power for a second or two. I'm learning the acceleration threshold that works, but the motors can handle more power so I feel the urge now to give tinyKart a set of controllers that can, too.

Pneu Scooter:

A few days before Maker Faire, Pneu Scooter got a flat rear tire. I knew it would happen eventually because the front tire got a flat about a month ago. Unfortunately, the 6" pneumatic casters are not conducive to easy tire/tube changes. I thought they would be, which was one of the motivators for using pneumatic tires in the first place, but as it turns out, barring special tooling, it's easier to change the entire wheel. So changing the rear wheel means taking apart the hub motor. But, really, Pneu Scooter has been ultra-reliable, so this is more like scheduled maintenance than a design flaw.

Could use a cleaning while I'm at it...

So I opened the motor for the first time since it was built. The process is pretty simple. The only tricky part is getting the three phase wires out, since they are soldered to connectors. To fit back through the bearing, they needed to be de-soldered and shoved back into the axle slot. Here are some pictures from the teardown, with everything dirty but intact:

Windings.

Outer spacer.

Dirty rotor.

Awesome adapter ring.

After taking off the adapter ring, I could get a good look at the rim and tire to see where the damage occurred. I suspected that the tire and tube had been punctured by screws that hold the ring onto the plastic rim. (The front tire suffered a similar failure.) Sure enough, I found a bunch of slashes like this:

I guess the screws were wearing through the tire and eventually the tube over time. The solution is so simple that I have no idea why I didn't do it in the first place.

Duhhhh...

So I put the motor back together with the shorter screws and Pneu Scooter was back up an running in less than three hours...

...which is great, because it actually came in really handy during Maker Faire. Not only was it the only one of my vehicles that I actually felt reasonably safe letting the annoying little kids ride, but it turned out to be the best way to get from the Citi Field parking lot to the Maker Faire itself. There were shuttle buses, but they were crowded and only took you about 60% of the distance anyway. So, I just took the scooter instead.

Twitch

Twitch also had some lingering wheel problems before Maker Faire. Specifically, the press fit holding the custom aluminum hubs to the plastic Vex omniwheels had failed on one wheel, making it hard to drive. It's happened before and I've resorted to epoxy for a quick fix, but I wanted to make a more permanent solution before the Faire. So, I manned up and got on the lathe...

...and then the mill...

... to turn out some new hubs that will actually bolt onto the wheel instead of relying on a press fit into flimsy plastic. The six-bolt pattern lines up with the spokes such that 1/4-20 screws rest against the inside surfaces to positively transmit torque to the wheel. I only put on one new hub for now, but I have the full set for when the remaining press fits fail. 

As I was doing this, though, some other problems revealed themselves. One of the linkages had a stripped-out hole, and one of the servos that drive the linkages was also damaged. I suspect both were symptoms of the wheels running into hard stops while the servo continues to drive the linkage. So far, I've only been calibrating the servos by hard-coding in soft-stop values, but they change every time I take the robot apart and put it back together.

Twitchguts, if you don't remember.

I decided that after replacing the servo and fixing the linkage, the best way to prevent this problem from happening again would be to just write the damn trim software the way it should be written.

Now the servos each have a software-settable minimum and maximum value. Through some coding trickery I was able to "or" the calibrate state with the normal drive states (forward, sideways, omnidirectional) so that you can trim the servo end positions while in any one of the states. This is useful since the servo maxima occur in the forward state and the minima occur in the sideways state. And just for extra software hacker cred, I save all the trims to a text file that automatically loads when the program starts up.

Twitch was, as usual, a constant source of entertainment that filled in the gaps well while the vehicles were charging. Part of the fun of Twitch is that nobody (or very few people) have ever seen a robot move the way it does. I am finally able to drive it in the way that it deserves, making smooth state changes and combining rotation and translation in ways that just look cool. It took a lot of practice, but I feel like Twitch is finally living up to its potential. And on that note I'll just leave this here...