Something Different

There's more to life than building things. Please enjoy this semi-serious cover of John Lennon's Imagine with my friend Seti on vocals and me with the keys.

TOBL: It's Working.

It's working, it's working. It = TOBL and here are some stats:

• 6 wheels
• 18 gears (think about it...)
• 84 oz/in Torque
• iPhone-controlled via TouchOSC app interface
• OSC/Serial communication
• 8 zip-ties
• Top speed of 0.413 mph (my personal favorite)

After much adieu, TOBL has been captured on film with my new camera -a Pansonic Lumix DMC-ZS7. It's about to make this blog a whole mess snazzier, 9.1 megapixels more snazzy to be exact. Henceforth, all videos shall be shot in 720p HD, like this one (fast-forward to 2:34 for wall flips):

Kind of dark but I still recommend watching in 720p.

Now held together by 8 zip-ties, thats 4X as strong as last time!

One of the finishing touches on TOBL was trimming the servos. However, PWMShield V1.0 is not yet wirelessly-updateable and in the monotony of disconnecting and reconnecting all the controls hardware, I vaporized yet another trace. This board should be renamed "GhettoShield" after all the loose wires I've had to solder to busted traces. The circuit works fine though, and using it saves $33. After fixing the trace the servos were trimmed.

Can you spot the latest exo-trace?

I don't talk about software very often, and that's because I don't know much about it. I do like to share the code I use though, isn't that the point of the whole open-source movement? After all, most of the communication software for TOBL was "taken" from this iPhone-controlled tank and this SFE tutorial (Thanks to both!). I modified bits of this software and wrote the rest to interface this existing code with my TouchOSC layout and electronics. In order to return the favor here is the Arduino and Processing code. You'd think a wireless iPhone-controlled robot would have denser code than ardWINDo, but take a look, it's surprisingly compact.

This project was a lot of fun. It's rare that you can take an idea and bring it into fruition exactly the way you imagined it. My initial goals were to make it iPhone-controlled and able to drive after rolling over -TOBL does both of those things. It wasn't cheap, I would estimate ~$250 including redundancies, but TOBL is an awesomely fun desk toy and an even better platform for playing with software, different sensors, and whatever else.

I also learned that servos are great for being servos, but not so great at being drive motors (especially modified micro-servos). For future projects I will venture down the new and exciting road of custom motor-controllers. Time to start playing with H-bridges...

TOBL: Testing

Done with my first exam of the semester and feeling like it's time to get back to TOBL, however briefly. I still don't have a camera to record test footage but that may change soon. Until then, here is the little guy in his most primitive form a.k.a. being held together by two whole zip-ties.

Yup, two.

So far testing has been limited to some laps around the apartment, during which I have already broken yet another spline gear. Reassembling the HS-81 plastic gear servos has worked out well. One of the wheel gears was a little tight, but has since been fixed. So now the plastic gears should last longer than 10 minutes.

Since the servos were modified they don't center very well. I suspect this is because the resistors that replaced the potentiometer do not match exactly. However, I did trim them in software and even after wearing the battery down a bit the neutral point doesn't drift much. As often as I ramble about servos I've learned my lesson and my future projects will likely use motors, for drive purposes at least.

Speaking of future projects, my V1.1 XPWMShields are finally in. Somehow they were delivered twice? Go figure. I think the perfectly good V1.0 board will remain on TOBL as not to have wasted $33 and shipping. I'll be able to comment more on the functionality (namely wireless uploading!) once I get some new Nanos to test them.

On a side note, I've recently started working at the Micro Robotics Research Lab. I thought I was into making things on a small scale...not even close! This lab concentrates on MEMS, fabrication techniques, and small scale robotics in general. For example, one team is designing a similar wireless communications board to XPWMShield, except that the board is approximately 1cmx1cm! Very cool stuff. Technically I'm working there for a program I'm in, but we'll see what happens. As for TOBL I will try to acquire a camera asafp!

XPWMShield V1.1: ...??

According to UPS tracking my Advanced Circuits order was delivered yesterday at 12:47pm and signed by a fellow named "WILSON." It's true, I could see the truck out my window! Regrettably, somewhere along the 100ft path from that truck to the front desk of South Campus Commons 1, the package was vaporized. It was never logged and nobody knows where it is. All I can say now is WIILLLSSSOOOOOOOOOOOOOOONNNNN!! And some four letter words which I already shared with the elevator and don't need to be shared here. I'll wait a few days before re-ordering, ugh.

TOBL: Teaser

What happened to TOBL?? Well it's alive, better than alive. In an effort to actually finish the thing before returning to school I focused more on the building and less on the documenting. It was close but I had to take it back with me to school:

What's up TSA?

I used 1-1/2" Dubro tail wheels for the drivetrain, mainly because they have ridiculous grip and aluminum hubs. To my surprise, the smallest outer diameter of the hubs was ~0.401". To support the steel standoffs I bored them out to 3/8", so that's like 0.013" wall thickness or less at the very center. We're good though, the two halves didn't torque themselves apart on the lathe. The hub diameter just barely supported the gear-mounting holes as well, but they don't post these dimensions online so not my fault.

This just looks goofy.

Small snack for the mill.

After making those aluminum plates I thought lasering some out of acrylic would be cooler. It was good milling experience still, I guess? It took a few tries to adjust from the gears' theoretical to actual pitch diameter -in the end an extra 0.02" radius. The servo-gears are also not properly supported i.e.they are cantilevered off of the spline gear. So they wobble, just a little. Enough though that the servos stalled and stripped some teeth internally. This was actually a good wakeup call because the stronger HS-82MG motor wasn't designed with the HS-81 plastic gears in mind. New gears are on the way, enough to bring two HS-81s to life.

Not even including the set that actually made it to production.

Look for test footage next post! (waiting on parts in the meantime :/)

XPWMShield V1.0

After a long wait (it says 2010 on the board because it was sent out last year!) XPWMShield has arrived from AdvancedCircuits. And with a bag of microwave popcorn in the packaging? Awesome company.

XPWMShield V1.0

This revision of the board lived a short life. I only got it yesterday, soldered on all the components today, and just broke it five minutes ago. Before that though here's V1.0 in all its glory, running off a 1300mAh, 7.4V, 2-cell, LiPo battery I got off HobbyKing:

She lives.

Need a better camera.

Just as I was going to test the wireless, one of the leads from the battery touched the bottom of the board, contacted a pin/via and blew up a trace coming out of the voltage regulator. Great. But at least the $34 Arduino Nano and $24 XBee are alright.

As it turns out the diode I put in between the XBee DOUT and Arduino RX was disabling radio communication. I put it there so that the software could be updated wirelessly without having to remove the XBee. So, I removed the diode and soldered a wire in its place -the same for the busted trace.

Ghetto wiring aside I can't complain, it works really well. With some minor revisions it's time to order more for future projects!

TOBL: Quick Software Update

There was an issue controlling both servos at once. With one fader value being sent over to the Arduino one servo would work fine. With both, that same servo would tweak out. After isolating the error to the Processing side, it turns out the float defining the fader values was preventing the second fader from registering. With that cleared up the code finally works as intended*!

* The interface needs some work to be more user friendly. For example, a deadband at the neutral position so you don't have to land the fader on the exact pixel that corresponds to STOP. Also, there's a point - about halfway through the range - where there's no noticeable change in speed. Playing with the fader ranges in the touchOSC editor should fix that. My only other complaint is a little lag in feedback due to the speed of wifi. On the other hand, it can be controlled from anywhere in range of the network aka college campus, so we'll let that slide.