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MR1 Hexacopter Project 6/2/11

Posted on June 2, 2011

       Hello Everyone!! I am glad you could join me again for another episode of the MR1 Hexacopter build. I am going to try and build a landing skid assembly for my hex that will allow me to use the copter for FPV or First Person View flying with the use of a live video link. I already have some experience in this field with the aid of my Video Cub and Sail Cam Aerial Video Platforms or (AVPs for short).
       I have always been interested in flying by the camera as it is the closest thing to actually being up in the sky. Multi-rotor AVPs have proven to be the most versatile and stable video platforms to date allowing the pilot to fly through incredibly tight spaces with precision accuracy. I can only hope that I will be able to get a shot at doing some FPV work with this copter although it will greatly depend on how stable the flight characteristics will be.
       To get moving in the right direction I will need to build a sturdy set of landing skids that will leave enough clearance for a video downlink system as well as permit an unobstructed view for the camera system. I will also need to leave clearance for a camera stabilization system should it be required however I am hoping that the hex will fly stable enough that it won’t need any assistance in keeping the camera stable.

       To build my skids I will be using some .25” x .065” wall 6061 aluminum tubing that has a T6 temper rating (McMaster-Carr Cat# 89965K233). Although expensive it will be the lightest and strongest material with a tensile strength of 42,000 PSI!!!

       I plan on building my skids in sort of an unconventional way making each side out of one piece of tubing. My hopes are that the one piece design will be stronger than a conventional helicopter style skid in where the two skids are supported by a pair of cross rails. I shaped out a proposed skid template that I could use to model my skids after as seen below....

       Using the template I was able to bend up my first two bends. I marked out where the bends were started in relation to the hand bender’s “start” mark so they could be easily duplicated on the second skid.

       I finished up the last two bends while keeping the tubing as close to the template edge as possible. Note: I used 110° bends for the upright legs. The skid overall length is 11.5” and the uprights are 9.5” tall (total) with 1” tall tangents bent at 20°.....

       I trimmed off the excess tubing and rounded the edges of the cuts....

       I am going to mount my skids to the outer four booms so that they can be supported directly over their locations. This will save weight in the long run as I won’t have to use more skid material to cantilever out from the main hub.  The skids will mount to the booms with four mounting blocks that will clamp around the booms much like the motor mounting clamps.
       To make my mounting blocks I will be using some 1/2” x 1” black Delrin (
McMaster-Carr Cat# 8662K41). I cut out four pieces 1.25” inches long on the bandsaw.....

       I used the belt sander to clean up the saw marks.......

       The next step was to center up a Delrin block in the mill vise so that all four blocks could be drilled in the same spots....

       The first hole I drilled was the 1/8” hole for the clamping screw. This was drilled in at .170” from the edge (to center of the hole) in the center of the block. All four blocks were drilled the same way at this time....

       The next hole was for the landing gear skid. I drilled this with a 6.3 mm drill bit (.2480”) so the landing skid tubing would fit tightly. The hole was positioned .25” back from the edge (to center) and centered in the block....

       The next hole to drill was the 1/2” boom clamp hole which was positioned .550” from the 1/8” hole side edge to center of the 1/2” hole (also centered in the block laterally)...

       Now that the blocks were drilled out I could cut the clamping slot in the 1/8” hole side to complete the blocks (not shown)....

       I test fitted the blocks onto the skid tubing and then drilled some #43 (.0890”) holes through both the blocks and the tubes near the “tops” of the blocks. I then tapped these holes with a 4-40 tap to install a short screw to secure the skids into the blocks (not shown). Note: You can see the clamping slots in the blocks in the picture below.
       I weighed the skids and blocks before installing them on the airframe and came up with 167 grams (5.89 oz)........

       And now to test fit the skids on the airframe. I installed the blocks on the four outer booms and then secured them with some 4-40 18-8 stainless steel screws and locknuts.

       I secured the skids in place with some 4-40 x 3/8” long screws (McMaster-Carr Cat# 91783A108).

         I used some .25” ID x .5” OD black silicone tubing pieces to act as skid protectors (McMaster-Carr Cat# 51135K192). I pushed the 1” long tubing pieces onto the skids using some dish soap before mounting the skids....

       I now have the basic airframe ready and boy is it strong!!! That’s a good thing because it will need to support 26 ounces of batteries before too long. I am planning to power my new hex with 9000 mAh of batteries so that I will get a decent flying time. Considering that the copter could possible pull 100 amps at full thrust I will need all the battery I can get :0P
         I do not fly a ton of electric aircraft but the few that I do have mostly use 2250 mAh x 11.1 Li-Po (Lithium Polymer) batteries. This is a really common size Li-Po and nowadays are pretty cheap considering what they cost several years ago :0P Since I have a ton of these batteries I am going to run four of these packs in parallel to run the six speed controls.
       I have never run Li-Po packs in parallel so this will be a learning experience although right now I will need a battery tray that will support the cells underneath the MR1. I am going to build a battery tray that is suspended under the main hub that will also double as a payload platform for camera equipment and such. For this I will be using 3/32” FRP (
McMaster-Carr Cat# 8549K53) for the bottom piece as it will resist flexing. I will also be using some 1/16” thick FRP for the top plate....

       I cut out a 6” x 4.375” of the 3/32” FRP for the bottom and a 4.75” x 3.875” piece of the 1/16” FRP for the top. A 1/2” x 4.875” long piece of 3/32” FRP was cut for a battery stop as well...

       I centered up the top piece on the “payload deck” and offset it to one side as seen below. The two plates were then taped together and then drilled for four support screws (9/64” for 6-32 screws) at 4.3” center to center apart from each other (to leave room for the four battery packs). Of course the tray could be custom made to fit any configuration of pack you may be using....

       I rounded off some of the edges on the plates and then drilled out four additional 9/64” mounting holes for the payload deck to mount to the airframe hub. I also drilled out the battery stop holes (1/8”)......

       I will be using some 3/16” OD rigid aluminum tubing (seen below) for screw spacers on this project. This 3003-H14 alloy aluminum tubing has a wall thickness of .022” which will be perfect for 6-32 and 4-40 screws to pass through (McMaster-Carr Cat# 8978K113).

       I cut out two spacers .6” long for the battery stop and trimmed down two 4-40 screws to 1-1/8” long (from the 1-1/2” long ones I have)...

       The spacers seem to work well just as long as they are not tightened up too much otherwise they start to deform.....

       The next step was to cut out four more 3/16” spacers at 1.6” long for the top piece supports. I used some 6-32 x 2” long 18-8 stainless screws for added strength (McMaster-Carr Cat# 91783A159) along with some 6-32 locknuts (Cat# 91831A007) and #6 washers (Cat# 92141A007)......

       I completed the assembly by adding a Velcro strap to hold the cells in place. At this point the battery tray assembly weighs 138 grams (4.87 oz)..............

       The next step will be to mount the battery tray to the airframe hub but not until the next episode of the MR1 Hexacopter project ;0)

Till then work safely my friends!!

Don R. Giandomenico

 

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