Sunday, February 27, 2011

Tricopter Weekend Update

When Josh and John were out riding, I was soldering up a storm. All three motors and ESC's are now in place. It turns out that's a lot of soldering. (at least for me)


I believe I know how I'll wire the power connections to allow the gyro's to arm before the ESC's. I'll post a schematic if it works. I'm planning on connecting a UBEC to the battery connection on the receiver, and put a switch on the power leads for both the UBEC and another switch on the three ESCs in parallel. Hopefully it'll work to first switch on the UBEC, let the gyros arm, switch on the ESC's, then once the ESC's arm turn off the UBEC.

I also have not pulled apart the HK401b gyros yet. The online guide on the Hobbyking website recommends checking the internal solder joints and then reinforcing the circuit board with epoxy and double stick tape. I might just try and fly it without doing this first. There doesn't seem to be any rattles internally in the gyros. I might rig up a separate platform for the gyros to further insulate them from vibration- everything I've read so far indicates they cannot tolerate much. I'm thinking a small plywood daughterboard mounted on rubber grommets would work well.

I'm hoping to be able to complete the linkage between the tail rotor servo and pivot tomorrow.

With any luck it'll be flying this week....

Tuesday, February 22, 2011

Tricopter Start- At Last!

Literally months after ordering all the electronics, and perhaps a month after finishing machining the motor mounts, I've started on my first Tri-copter build in earnest. I'm basing my build after this knowledgeable Swedish fellow's build: http://www.rcexplorer.se/projects/tricopter/tricopter.html

I think this will make a fantastic camera platform- maybe even FPV someday. The motor struts are 1/2" OD aluminum tubes purchased from Lowe's. They appear to be a fairly soft alloy- it'll be interesting how well they stand up. They were quite cheap, though. $4 for a 36" length. My initial build is using 18" long struts.

The two body sections are 1/8" liteply cut to the plans on RCExplorer's website.  I'll probably cut lightening holes in the plywood body to save a few grams. RCExplorer uses fiberglass printed circuit board material for his components, but since I don't have easy access to that material I'm just using 1/8" plywood.

Eventually if this system flies well and proves fun, I'll upgrade the structural components to carbon shafts and a lighter weight body.

The motor mounts are my own design, machined from delrin scraps. The rotating tail motor mount uses the 1/2" aluminum tube as the bearing surface. It seems to work pretty well, with minimal slop.

Structural Components


I'm attaching the struts to the baseplate with 1.25" long 4-40 screws, also from Lowe's One nice feature of this design is the right and left struts will fold after removing a screw from each side. This will make the craft nice and compact for transport.

Unfolded, flight configuration (DX6i for reference)
The motors will mount at the end of each strut. The electronics will mount on the plywood, with the battery being suspended below the bottom plate. The rectangular "platform" towards the bottom of the photo is a prime place to mount a camera- that'll be the 'front' of the craft during flight. I have an old Canon SD300 that might get flown...

Folded, Storage configuration

Exciting stuff.... Perhaps it'll be flying in a week or two!

Sunday, February 20, 2011

P-51 in Snowstorm

I thought it would be cool to fly a camera in the snowstorm yesterday. From my back door, the wind seemed light and manageable. Even from the lake surface at the bottom of the hill it seemd fine. Boy, was I wrong! As soon as I took off the P-51 was getting bounced around like crazy. It was all I could do to try and keep it under control let alone fly a nice pattern to try and capture video of the storm..


Monday, February 14, 2011

Invisible Fence Troubleshooting

Our invisible fence for the dog went on the fritz a month or so ago. Specifically, somewhere on the property the wire broke and the loop indicator buzzer went off signalling a break. Until this past week, our dog didn't notice and it wasn't a problem. Sometime over the past week Sophie noticed the fence wasn't there anymore and started wandering the neighborhood- a big problem. Luckily the weather was great this weekend allowing me to try and fix the fence.

An invisible fence consists of a single strand of wire that is buried around the perimeter of your property. A box uses this wire to set up an electric field around the property at a certain radius from this wire. Your dog then wears a collar, and when the collar enters the field it first warns the dog with a audible tone, then if the dog continues it gives a nice jolt. Sophie was only shocked once- after that the audible tone was plenty. The fundimental problem with fixing these wire loops is that you don't know where the break is. In our case the fence encloses about a half acre and because of all the snow isn't really accessible.

There are some commercial products you can buy to do this, but the cheapest is over $50 and requires ordering online. There is another method using an RF choke placed across the output terminals of the box, but this method doesn't appear to work with the Petsafe Sportdog invisible fence setup we have.

My first step was to dig up the wire in four or five spots, and I tried to use a non-contact voltage probe to see if the wire at that point was energized or not. This didn't seem to work that well- it seemed to be very inconsistant and was potentially giving both false positives and false negatives. The probe indicated one section of fence was bad, and after cutting it out and laying new wire on top of the snow the fence circuit was still broken.

My next step was to purchase a continuity tester. I thought I could cut the wire in several locations, then use this device to detect if there was a break in each individual wire segment.


Unfortunately after I got home I realized that you needed two wires for this device to work. I wasn't about to lay out a huge wire segment just to let this tool work. So back to Lowes' went the tool.

So, finally I decided to make my own continuity tester. I thought I could use the fence wire and the ground to complete the circuit. I thought since a battery's negative pole is the electron source, and the electrons flow back to the positive pole, I'd design the circuit using a positive ground. Afterwards I did some internet searching and it looks like a negative ground might be a better design. However, it worked.

I used a two AA battery holder to generate 3V, then attached an allegator clip to the negative lead and a long nail to the positive lead. I then pressed the nail into the ground (after first thawing it with a heat gun) and attached the negative lead to one end of a fence segment.

For the continuity indicator, I soldered a 100k ohm resistor to the LED cathode to limit current. The aligator clip attached to the resistor. I then attached the grounding nail to the anode. When I pressed the nail into the ground and attached the aligator clip to the fence wire the LED lit if the fence wire was unbroken. This method seemed to work. After some trial-and-error due to poor grounds in some locations I was able to locate the break and string new wire on top of the snow.



Invisible Fence Continuity Tester Schematic
  




   The home made tester worked OK- but the LED was rather weak when used for the longer wire runs. (probably 150 feet or so). Perhaps it'd be better if I switched the positive ground for a negative ground. I think another option to try would be a slightly more complex circuit using a transistor switched LED, where the fence lead would only deliver a "high" or "low" signal, and the transistor would be powered directly from an attached battery.

Saturday, February 12, 2011

Moonie Lake Flying Club Video



Great flying today at the lake. Too bad John was busy. This might have been the last good weekend of the year. Saturday it was 38+ degrees and sunny- about the most pleasant weather you could imagine for flying on the lake. I didn't even have to wear gloves and was perfectly comfortable.  I'm guessing all the melting this week will turn the lake into a giant puddle of slush.