Sunday, September 30, 2012

Airgun Target Stake

Airgun Target Stake

I love shooting paper targets.  There's nothing more challenging (or frustrating) than trying to get 5 or 10 shots into a little tiny group.  But once in a while you just want to have some fun and hear the satisfying ping of lead hitting steel.  So I decided to build a new airgun target.  I had the idea of supporting some empty CO2 cylinders with magnets; hoping they would go flying when I shot them.

the parts

At first I was going to orient the cylinders on a horizontal plane on some sort of rack.  I decided to go with a vertical spike instead because it would take up less storage space.  I looked through my scrap pile and found a 1/2" x 28" control rod from an old radial arm saw.  It had a nice knob on top that would serve as a handle when pushing the rod into the ground.  It is made out of some odd alloy I think.  It feels, machines, and corrodes like aluminum.  But it attracts a magnet and sparks when you grind it.  Not sure what it is but it seems resistant to rust so it should be perfect for a ground spike.

boring the recesses

I was going to just epoxy the magnets to the side of the rod but I was afraid I might shoot the magnets and break them.  So I machined 6 recessed holes in the side of the rod spaced 1.5" apart to hold and protect the magnets.  The magnets were supposed to be 5/16" in diameter, but they were just a bit larger, so I ended up using a 3/8" end mill to make the holes.  The holes are too large but they serve their purpose.  I really just wanted to get this thing made in one evening; function over form this time.

ready for paint

Next I ground the end of the rod into a point on a belt sander to make it easier to stake into the ground.  Then I cleaned the corrosion off the rod with a scotch-brite pad.  The magnets were fixed into place with some JB Weld.  A few coats of paint and it's done.


It functions just as I expected.  Really nice action on the cylinders when you hit them; very satisfying.  This new target should provide hours of shooting fun in the backyard this fall.  Check out the video to see it in action.

Wednesday, September 26, 2012

Silent Pellet Trap

silent pellet trap

I do a lot of target shooting with my airguns.  One requirement is a safe backstop that will stop even the most  powerful shots.  It must hold up to thousands of shots.  Additionally, you don't want your pellets to splatter on impact spreading lead fragments all around as they do when they hit a hard surface like steel.  And lastly, it would be nice if it isn't too loud, especially if you shoot indoors.

.22 caliber bullet trap

I was using a steel trap designed for .22 caliber rimfire bullets.  It is plenty strong enough but the pellets do splatter on impact and this thing is LOUD.  Sounds like a gong each time you hit it.  I came across this trap design online that seemed like the perfect solution.  The trap is filled with duct seal putty.  The putty catches the pellets silently and almost unharmed so there is no lead splatter or bounce back.  Looked like something I could build.

my inspiration

I don't really like to work with wood and I didn't like the idea of a stray pellet hitting the wood and damaging it, so I decided to go with steel.  I started with a 9" x 12.5" x 4" breaker box.  I cut a 8" x 9.5" opening in the front cover and fitted a cardboard backer behind it.  There were a few small mounting holes in the back of the unit, so I cut a piece of tough aluminum from an old street sign to fit the back and riveted it in place.  That way, even if I shoot through the putty, there is no chance of a pellet going through a hole in the trap.  I used an old steel carry handle I had lying around and riveted that to the top to make it easier to transport.  Then I put a few rubber feet on the bottom.  Finally, I filled it with about 10 lbs of duct seal.

carry handle
filled with duct seal
(and a lot of pellets)

It worked great just like that for many months.  Then, one day while the in-laws were cleaning out the garage, I acquired an old portable movie screen.  I didn't know why I was keeping it, but I was sure I would find a use for it.  Turns out, it made a great stand for the pellet trap.  I removed the screen and the handle that adjusts the height of the screen.  I mounted the handle on the back of the pellet trap.  The handle slides up and down the stand when you push the red button.  Release the button and it will hold position at any point.  The target center will adjust from about 2 - 5 feet high.  If I don't want to use the stand, I can just slide the pellet trap off the top of the stand and use it alone.

height adjustment handle

target stand

The pellet trap works great. Targets are held securely behind the front plate.  The duct seal will withstand thousands of shots.  When it is too full of lead, I just pick out the old pellets.  Then I knead the duct seal like clay and press it back in place for a nice even surface.  Good as new and ready for a few thousand more shots.

Monday, September 10, 2012

American Girl Dog House

My oldest daughter asked me to make a dog house for her American Girl dog "Sugar".  With her birthday just around the corner, how could I say no?  Still don't have a table saw in my arsenal yet so this was all done by hand.

blueprint from my daughter
(note requisite sparkles)

wood from an old wine box
(knew there was a reason I saved that)

pieces cut out

glued together

painted and sparkly

all done!

I left the inside unpainted just to show the origins of the wood.  I think the wine box motif inside is kind of cool.  Hope she likes it!  You can see the other one I built for her little sister here.

Saturday, September 1, 2012

ArduPilot TX Flight Mode Switch

flight mode switch (image from seller)

I have posted several times about modifying my FlySky FS-TH9X radio.  I modified the radio for use with an ArduCopter multi-rotor UAV that I built.  The ArduCopter is controlled by the ArduPilot autopilot flight system.  The ArduPilot has several selectable flight modes that change the flight characteristics.  For example, the "Alt Hold" mode will automatically maintain the current altitude of the UAV.  "Loiter" mode holds the UAV in it's current location.  While these modes improve the flight experience, they are somewhat difficult to program and select.

Normally the six flight modes are selected based on the position of two switches on the transmitter; such as the three position flight mode switch and the two position aileron dual rate switch.  3 x 2 = 6 possible switch combinations for six different modes.  While this setup works, there are two problems.  1)  It is somewhat difficult to program the switches to work properly with the flight modes.  It took me several attempts to get it right.  And 2), it's not that easy to remember what switch settings correspond to which flight modes.  Luckily I found a simple solution one day while searching eBay.

The idea of this system is to replace one of the potentiometers (pots) on the transmitter with a six position switch.  The switch is then wired to four miniature pots.  The resistance of each pot can be adjusted separately.  With the four pots and a positive and a negative lead, you can have six different resistance values for each position of the switch.  Those six values can then be easily adjusted to correspond to six flight modes by simply adjusting the pots.  The result is easier programming and selection of the flight modes. 

parts in the kit

pots glued together


While the switch can be purchased preassembled from the same seller, I opted for the DIY kit.  Assembly was easy.  I started by gluing the four pots together with cyanoacrylate glue.  Then I folded the leads down on each side of the pots and soldered them together.  I found a piece of scrap ribbon cable and peeled off six wires.  The six leads of the ribbon cable were soldered to each of the tabs on the switch except the "brown" labeled tab.  That tab is soldered directly to the radio wiring.  The four center wires of the ribbon cable were soldered to the four center leads of the pots.  The outer wires (labeled "red" and "black" on the switch) were soldered to the outside leads of the pots.

wiring diagram

outside leads soldered together

finished switch assembly


The seller suggests mounting the switch in place of the "pit trim" pot.  However, I use that to control the vertical angle of my FPV camera.  So, I decided to mount mine in place of the hover pitch pot.  I desoldered the pot and removed the nut holding it in place.  I then soldered the red and black (+ and -) wires go to the "red" and "black" labeled tabs on the switch.  The center wire of the pot (yellow in my case) was soldered to the "brown" labeled tab on the switch.

back of TX removed

close-up of hover pitch pot to be replaced

To mount the switch I opened up the hole with a 9/32" drill bit by hand.  Then I drilled a 7/64" hole for the tab that prevents the switch from spinning in the hole.  With the switch installed I secured the micro pot array with hot glue.  The shaft of the switch was too long for the cap that is included.  I cut it shorter so that the cap would mount flush with the radio case.  I then reassembled the radio (without screwing it together).  To make sure everything was working.  I programmed channel 8 to use P1 (the designation for the hover pitch pot) and turned the switch to each position.  With the main screen displaying the value bars for each channel, I could see the values for channel 8 change as I turned the switch.  Looks like it works; time to program.

Turns out the fit was a little tight.  When I tried to close up the case, the pot hit one of the switches on the other half of the case.  I had to bend down the pot tabs and trim some plastic off the corner of one of the switches to get everything to fit.  I added a piece of electrical tape over the pot just to prevent any shorts.

new switch installed


The switch is programmed with the Mission Planner software (see step 3).  With the TX paired to the software through the APM, select the "Flight Modes" tab.  Positions 1 and 6 should correspond to flight modes 1 and 6.  Turn the switch to position 2 and adjust the pot that is wired to that tab.  Select Modes 2-4 until you see the PWM value change in the software.  Adjust the pot to get the ideal PWM value.  Repeat for switch positions 3 and 4.  When you are finished, turn the switch though all of the positions.  You should see all six flight modes get selected as you turn.  Set the modes that you want from the pull down menus and reassemble your radio.  You are done.  It took me less than 5 minutes to program and I got it right first time. Big improvement over original method.

programming the flight modes

Before, I had to remember the correct switch combination and move two switches to get the flight mode I wanted.  And, I had to pray that I didn't accidentally flip one of the switches while I was flying.  Now to change flight modes, I just turn one rotary switch to the correct labeled position.  Now if I could just get my Arducopter to fly right!

installed switch with label