A Recap

It’s probably quite obvious that we haven’t had a chance to work on the quad for quite a while recently. As a matter of fact, I had forgotten this blog even existed… But not to worry! Plans are on the drawing boards for some good changes to our machine that should make stable flight much easier. Following the massive slew of smart phones with accelerometers and all other sorts of motion detecting features, you can now get BoB’s (break out boards) at Sparkfun containing not two, but all three axis gyroscopes, triple-axis accelerometer, and triple-axis magnetometers… that’s a single 9DOF BoB for about what we paid for our accelerometer and dual-axis gyro alone. Which means we will very likely be replacing all of our sensor boards with one beautiful new board.

Matt also wants a redesign due to the still seemingly present vibration issues (I like the idea of the memory foam Nic- sorry, just got that comment- I am just worried that our vibration is a really high frequency that may not be cancelled by the firmer foam? Worth a shot though!) So, new positioning sensor boards, new mounts, and while we’re at it, why not throw in a custom printed PCB? (Time to learn EagleCad). In all, the guts of our new quad should be almost brand new by the time we get back to test flights.

But let’s back up a bit further. Since we’ve been gone, our “roll cage” was developed. It really turned out to be more of a box the electronics sit in. Four threaded rods act as our posts on the four corners, and with a plywood battery casing and phenolic top, we’re set.

Finished Gut Casing

For your imagination’s sake this post has lots of pictures.

Battery Plate

This plywood plate is what supports our battery, which is encased in the pink foam you see below:

Battery Casing

Our most exciting new addition to the quad (that I don’t think I’ve covered) is our new motors (I’d link you to them, but I’ve lost the bookmarks, I believe they’re Hacker A20 20L). These are supposed to give us much less vibration, and hopefully be more reliable than our first four (one who’s shaft we bent, and two other’s bearings we shot). Anyways, they have a square mounting base as opposed to the three triangularly oriented holes of our others, so I just drilled a second hole in our shafts, and sandwiched our motors on. I would give pictures, but sadly it’s currently not accessible. Here’s a shot of the new motor alone though.

New Motors

If I remember correctly, these came with gold “banana” male/female connectors that you had the option of using. We went with them, and soldered them to our power supply cables and the motor’s cables. Now, the upside to using these motors is that they come with many different mounting brackets, and axle options. The downside is that the mounting point for the motor is where the axle extends out. This means you have to mount your motor with your axle sticking through the mount. Well, that’s a problem, because the axle isn’t too long to begin with. So our solution (and many other people’s across the internet) is to take the motor apart and actually flip the axle so it extends out the opposite end of the motor. This is a very simple task, and everyone claims it works just fine, but I still have some reservations about it. The motor comes apart in two parts. There’s the outside shell with the magnets (blue part in picture), and the inside coils, which are mounted to the black end cap with the wires protruding. The whole blue casing then spins, turning the axle that extends through the stationary black cap with the wiring. The axle is press-fitted, and held with a set screw into the opposing black cap (which spins with the blue casing), and the only part that holds the entire assembly together is a tiny C clip that fits in a groove on the axle protruding out of the wired black cap. Remove the C clip, and the two halves slide apart (with just a little resistance from the force of the magnets). To flip the axle, you remove this C clip, then separate the motor, unscrew the set screw, and hammer the axle out of the press-fitted black cap. You then flip the axle, hammer it back in, and the questions start. First off, the set screw has a groove cut into the axle just for it (so the axle will have no chance of sliding in or out if the press-fitting fails). Flip the axle around, and guess what? The groove is in the wrong place. So, you can just screw the set screw in and pray for it to hold I guess… Second, that little C clip that’s the only thing that holds the two halves of the motor together, well, it’s got its own groove too, and obviously the groove won’t line up with its original spot either. Luckily, however, the wider groove for the set screw ends up being in about the place of the C clip. So if you’re careful, you can align the axle just right so that the friction from the black cap backing it and the side of the groove it’s in holds it in place. It’s a very loose fit however, which again worries me. I’m not saying it won’t work, I’m just saying, if you try to work with these motors, be careful. So, best case the set screw holds, the C clip doesn’t fall off, and our quad flies miraculously. Worst case, the set screw or C clip fails, and since one half of the motor is attached to the quad, and the other half is attached to our props, and both have opposing forces, we get halves of motors everywhere.

That’s our news for now, come August Matt and I will be in the same town again, and our posts will certainly become more frequent.

~Will

To be or not to be, That is the question…

If by “to be” you mean a flying quadcopter, and “not to be” you mean a pile of charred ashes…

Due to the worry that we will end up with the latter if we continue using the battery we have, we are looking into investing in a new LiPo. After spending the past hour or so perusing over some witty banter between many flight hobby enthusiasts on the topic of “puffy LiPos” and the dangers included in using them, I have come to realize that yes, it is potentially dangerous to operate with puffed packs, but many people have been doing it with no consequences. While it is true that you must keep in mind your craft could go down in flames from any possible overpuffing and consequential bursting and venting of the pack, or puncturing and burning of the pack, in reality, you can minimalize these events from occurring by just being careful. Not operating a pack that is puffed so badly that it holds pressure, meaning not operating a pack that is puffed and hard, and any added pressure could burst. Monitoring puffed packs during current draw, to be sure they don’t become puffed enough to burst and vent. Monitoring the packs as well for heat, it appears 140F is the “bad zone” for LiPos, so letting batteries cool before they reach that point is always a good idea. And in general, just being careful with them. From what I have read, yes, there have been catastrophic failures, where houses burn down, but LiPos seem to only have a bad name from a few cases. Plenty of other people have blatantly cut into their packs, knowing what to expect, and yes, when charged, you should get a fire, but if you are prepared, it shouldn’t be the end of the world.

A note to anyone on disposal of LiPos: From what we have found, they are landfill friendly, once discharged completely. This can be done numerous ways, some people hook them up to a power draw, and just let them drain, then they will cut them open and submerge them in a saltwater solution for a few weeks, and dispose in a landfill. Others simply place the whole battery in saltwater. The water conducts slightly, so it drains slowly directly through the contacts, and eventually you have a completely dead battery. Now, whether you need to cut open the packs and re-submerge, I don’t know for sure. I would imagine the battery should be fine as-is, and ready for the landfill. Keep in mind these are all the “safety conscious” people. Personally, I would prefer (and there are plenty who do this) to set the battery in a firesafe area (nothing that can catch flame within at least a few feet), and puncture the pack (adding water optional), as fully charged as possible. BE CAREFUL THOUGH! This can be extremely dangerous, and while LiPos don’t seem to be as bad as their reputation, I am not responsible for giving you an idea that you carry out dangerously on your own.

On that note, we are still worried about our pack. It appears puffed, and while this whole time we have been thinking it was just an air bubble between the cells and the covering shrink wrap, we are getting nervous that in the case we are wrong, and the battery does catch fire, and it happens to be on the quadcopter at that time, we would be down a very fun toy… So tomorrow morning, we are very carefully stripping the shrink wrap off of the cells to compare them and verify if any or all are puffed, or if it truly is just an air bubble.

Also on the agenda for tomorrow is adding the LCD screen we bought a while ago, which means soldering plenty of tiny pins, my favorite! And adding a roll cage to the quad, so upon a collision with the ground (something we really don’t want to have happen) the two sheet metal strips bent into two U shapes, and crossed over the electronics, will take the brunt of the force, and the electronics themselves will not.

~Will

…Not Taking a Break

Well, as the school year winds down, and we go into a state of shock realizing how many tests we’re about to take… we need not study! There’s work to be done!

So, last weekend Matt and I met up again to get a little more minuscule bits and pieces sorted out. He had been complaining about the switch that pulls the reset line high or low to put the PIC in programming or run mode, saying “It won’t reset to programming mode, I put it in programming mode, but it doesn’t make contact, and I think the switch is broken…” Needless to say, the whole time I tested it, it went into programming mode perfectly fine.

… Well, except for when it didn’t… and then he rubbed it in my face, but all in good fun. So, first on our agenda was changing the switch, which we had come up with an ingenious plan for: There is a pin on the PIC that is a reset line, pulling it high will reset the microcontroller. I just so happened to have a reset button from a computer… a very special button. It was a double poll double throw switch (DPDT)… but a momentary push switch, so it had two feed lines, and then each feed line would go to one of two leads depending on if the button was pressed, or released. This would be perfect, we figured! We would put the reset line on one side of the button, so when you pressed it, it would automatically reset the whole PIC, as well as the choosing line on the other half of the button, which would pull the pin high, to put it into programming mode. After plenty of redrawings of the schematic, and Matt realizing when you flip the button over, the pins also happen to flip (left is on right, right on left now) (again, I’m just teasing him, he’s extremely smart) we finally reached a final draft. There would be two options, you could press the standard reset button on the PIC, to which the choose line would always be pulled low (momentary second button) and so you would reset the PIC into run mode, or you could press the new button, which would use the secondary reset line to reset the PIC, and also pull high the choose line, leaving it remaining high for a fraction of a second after you released the button via a capacitor so as the PIC booted, the line would remain high long enough for it to recognize the fact. This would be perfect, no more Matt flipping a semi-broken switch and pressing a button, and pressing a button but realizing he forgot to flip a switch, etc. etc. However, as we pulled our precious one-of-a-kind switch out of the breadboard (which we had to… jerry rig to make fit, see picture below) one of the pins broke off… and that was the end of that. No amount of pleading with my parents to just let me have a quick look in their computers to see if the power switch was the same kind, because I could easily replace it! It only needed two of the six pins! (which ours still had) helped.

Testing the New Switch

You see, breadboards are designed for ICs, the middle slot is wide enough to accommodate the two hole gap between the pins of a standard IC so the rows of connected pins can span outward in either direction, but not short the two pins on opposing sides of an IC together. Sadly our switches hole spacing was 3×3, so there was only a one hole gap in the middle. We couldn’t span the breadboard’s built in break in rows, so we had to come up with a way to still momentarily test the switch. It turns out an IDE ribbon cable (for hard/CD drives before SATA) butted up against the breadboard gives an exact one-hole-gap. So, as ridiculous as this may look, and as ridiculous as it felt, it worked!… Until we broke the pin off.

Without a momentary DPDT switch we had to dig up the next best thing, which turned out to be a normal DPDT. We decided against making the design any more complicated than need be, and just replaced the old SPDT we had been using that had broken.

Among other accomplishments during our meeting, we added landing gear (cut a pool noodle into two inch long sections, and zip-tied to the bottom four corners of the quad, pictures to come later), modified an adapter for Matt’s new “fancy” battery charger, watched it balance the cells automatically, charge them, etc. We deduced that despite our fears, the Lithium Polymer battery pack we have been using is not going bad (we were quite releived), and swapped out a propeller blade, since someone’s feline friends enjoy chewing… (to clarify, not mine)

Propeller we replaced

Good thing we bought extras!

Finally, we realized that our 12V to 8V power supply was heating up a little much. To be sure we weren’t drawing too much load or harming it in any way, we tested current draw with certain sensors plugged in and unplugged. Determining everything should be fine, and we had no shorts, we just added a nice heat-sink.

New Heat Sink for 12-8V

While this next photo is a little blurry, it shows the perfect placement with which we planned to fit the heat-sink, right around our USB plug for the PIC. Yeah… that’s right… planned… like everything, right?

As if it were designed to fit...

~Will