So I was trying to figure out what M3 fasteners to order at Mr Metric, and fell into the standard state of confusion when offered too many choices I didn't understand. So, here's the relative price breakdown of a standard piece (or close; I didn't bother to confirm that the M8 piece I randomly selected was available in all the materials). Sorted by price, with the different sizes marked with ***. All the items reference standard DIN439B.
Note that Mr Metric has a huge price break at 101 pieces, so be sure and pick that number and not 100.
class size type price ----- ---- ---- ----- STEEL CLASS 4 ZINC M8X1.25 Jam Nut Steel 4 Zinc .04 STEEL CLASS 8 ZINC M10X1.25 Jam Nut Steel 8 Zinc .05 *** STEEL CLASS 8 M7X1.0 Jam Nut Steel 8 .05 *** BRASS M10X1.5 Jam Nut Brass .15 *** STAINLESS STEEL A2 M8X1.25 Jam Nut Stainless Steel A2 .15 STAINLESS STEEL A4 M8X1.25 Jam Nut Stainless Steel A4 .21
An interesting Instructable about quadcopters. It doesn't actually have a lot of details about building one, but has some good low-level technical stuff.
An overview of the math of controlling brushless motors and gimbals.
Sainsmart sells nice looking Arduino clones and other interesting electronics. PLA too!
jj604 has a neat 1S/2S brick made from a LemonRX receiver and 1.7g servos.
And the longer explanation. We want to mix two switches (3 position and 2 position) so that they map smoothly over the range of one transmitter channel. This will allow us to use a combination of the two switches to control something the the Ardupilot Mega flight modes. We'll use the 3 position switch and the Aileron D/R switch in this example.
There's a lot of slop, but we basically want to get the approximate midway values here.
-100% -67% -34% 0% 32% 65% 100%
| | | | | | |
| -84% | -51% | -18% | 15% | 48% | 81% |
| | | | | | |
| 1 | 2 | 3 | 4 | 5 | 6 |
We start by mapping the 3 position switch. By specifying just the switch, we get the values (-100, 0, 100) in positions 0, 1, and 2. That's not quite what we want; we want the values (15, 48, 81) so that it corresponds to positions 4, 5, 6 in the diagram above.
We can do that using a Curve. We'll use curve 1. First we set the curve type to "3 points". Fill in the point values to 81, 48, and 15 as shown.
Then set the first part of the mix to 3POS, Curve 1 as shown. Note that multiplex is ADD. As you toggle the switch among the three positions, the mix will follow the curve and fill in 15%, 48%, and 81%.
So, that takes care of three of your positions (4,5,6).
To get the other three positions easily, we'll cheat a little bit. We can do this because we don't need to hit the midpoints exactly -- we just need to hit somewhere in the range.
Now, we're going to cheat a little to get the other positions. We can do this because we don't need to hit the midpoint of each position exactly... we just need to be between the high and low points of each range.
So, we look at the low three values, and note that they are close to being the negatives of the top three values (-84 : -81, -51 : 48, -18 : 15).
So, we add the the channel mix the AIL switch. This will give us -100 and 100 for when the switch is on or off (or vice versa). So, we set Multiplex to MULTIPLY, and that gives us a handy way to multiply by 1 (keeping the positions we already have) or -1 (giving us the approximate positions we want for 1,2,3).
Here's the Companion 9x simulation. You can see that as we toggle the buttons, channel 5 outputs the desired values for all the positions.
Here's the finished OHD (One Hour Drone). We'll tidy up the wires, but for now we'll just tape everything down to test it out and tune it up. We might put a cover over everything for protection.
Here's an update on the One Hour Drone (OHD). It was bare again after Andreas used it as a parts donor. Second generation drone enthusiast Alexander and I wanted to refurbish it and kit it out with new electronics. We had discussed tossing the Wago-attached power distribution unit, and that's what we did, replacing it with a Hobby King PDU.
We had to pry off the top plate of the quad (the down side of super-gluing everything together!) but managed to do so without mangling things too badly. This height looks about right for the PDU to be safely ensconced in the frame.
It turned out we didn't have any spare 4-40 1'' bolts. We got some 6-32's in a bulk pack coz they were a ton cheaper. They turned out to be too big for the motor mounts, so we had to drill out the motor mount holes with a 1/8'' bit.
The battery died in my tiny DSO Oscilloscope. Opening it up showed a 1S LiPo of undetermined amperage. Pay close attention to the smallness of the battery wires!
I had a spare 1S battery. It was fitted with a JST connector, so I snipped that off. The wires were huge compared to the old battery.
I'm pleased to say I got it soldered with no problem. It's the closest work I've ever done with a live battery and I'm happy to say nothing was shorted. I was really sweating it out though!
I'm putting this picture up partly as reference for battery orientation, and partly coz I'm pleased with being able to make this connection successfully.
As many of you know, I'm a proud member of the Concord Model Engineers. You might not know that I'm the Secretary as well, in charge of taking and circulating the minutes. The club has a lot of great guys who are exquisite craftsmen as well. Each month I get to see things that (by my standards!) are flying works of art that belong in a museum. So, I'm going to experiment for the next couple of months... take picture of the Parade of Planes and other interesting things, and post them here along with the minutes of the meeting. If you're in the East Bay, you should stop in for a meeting!
LemonRX is a new manufacturer of DSM2 (Spektrum) compatible receivers. They've been getting lots of good press about their performance, build quality, and price. At 2.5g, they're about as light as can be.
They come as bare boards, so I wanted to toughen them up a bit. I started out by quickly applying the smallest dab of hot glue to the antennas.
Next, I cut some 3/4 inch heatshrink tube to a length that covered the exposed electronics and a bit past the antennas. I cut two slits in the side for the antennas to go through.
Here's an interesting article on tracking planes via the ADS-B signal, using a $20 software defined radio. The author, Clayton Smith, has done an excellent job in integrating the application into Google Earth so you can see the location of the planes there.
I've ordered the radio, and will try building the software once it comes in.
Much thanks to coworker Drew who told me about Mr. Metric, which has great prices on (as you might have guessed) metric parts. They've even got M2 sizes. Various grades, etc. $6 flat rate shipping, and free shipping over $50. Example price: M3x8 stainless steel socket head screw (pictured), $.06 each in quantities of 101.
Update: I don't recommend KOVA fasteners from India, no matter how many times they leave spam in the comments below! Update: and Udehra too! Update: three times, Udehra stop it! And Indian Cutting Tools!
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