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.
For your imagination’s sake this post has lots of pictures.
This plywood plate is what supports our battery, which is encased in the pink foam you see below:
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.
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.