Intro: Two Simple Drone Delivery Systems
In keeping with the current interest in drone parcel delivery systems I decided to take a try at making a simple system myself. I started out with the payload delivery container (PDC) suspended from the drone with a chain - I call that version Drone Air One. Next I tried attaching the PDC directly to the drone with a couple of machine screws and wing nuts - I call that version Drone Air Two.
My DJI Phantom II + drone is the power lifter for this Instructable, but it might be possible to adapt the same delivery system to other drones. The quad copter had no problem lifting the PDC along with a payload of almost one pound.
A simple homemade plastic bracket makes the link between the payload delivery container and the drone. The same bracket design works for both versions of the delivery system. I call this part the Link Bracket.
The automatic latching and payload release method is identical for both versions of the delivery system. So far I have created two videos about the systems. I put a little humour and drama in the videos to make them (hopefully) a bit more interesting.
Step 1: Drone Air One Video (parcel Delivered to Mrs. X)
I tested Drone Air One enough to confirm that the system works pretty well as expected. This video shows a "typical" delivery.
Step 2: Drone Air Two With "fail" Footage
The weather turned bad on me before I got a chance to give Drone Air Two a good set of tests. But right now I think that this version might be the way to go. But one significant disadvantage of this version is the limited range of view for the onboard drone camera - the plastic box blocks most of the downward view.
The failure scene at the end of the video was not put on... for some reason I was unable to gain altitude during this flight. My initial thought was low battery but the battery turned out to be ok. The crash landing damaged two of the four props. For now I will say the incident was due to pilot error.
Step 3: Parts Used for Drone Air One and Drone Air Two
Drone Air One parts
Plastic box with cover approximately 9 x 13 x 5 inches deep
1 wire coat hanger
2 small metal binder-type paper clips 3/4 inches long
3 small plastic zip ties
2 snap fishing swivels
5 cotter pins about 1 inch long
1 light duty link chain about 6 feet long
4 12 inch long steel wire fishing leaders
2 small split rings about 3/8 inch diameter
Drone Air Two parts
Plastic box with cover approximately 9 x 13 x 5 inches deep
1 wire coat hanger
2 paper small metal binder-type paper clips 3/4 inches long
2 10-32 x 3/4 RH machine screws and nuts
2 10-32 wing nuts
Step 4: Tools Used
Cordless drill with 3/16 twist drill (for 10-32 screws) and a 1/8 twist drill for the cotter pin clearance holes
Screw driver bit for the machine screws
Small diagonal pliers
Small general purpose pliers
Step 5: Payload Delivery Container (PDC) - Making the Link Bracket and Payload Base
The PDC is made from a plastic storage box selected to fit both the drone landing gear size (for Drone Air Two) and the wire coat hanger that forms a significant part of the payload support and auto release system for both versions of the delivery systems.
With the utility knife, score and cut-out the large central area of the box cover. This flat piece forms the base to support the payload. Next measure and mark the length of the link bracket that connects the drone to the PDC. The bracket is then cut from the existing perimeter area of the box cover. One of the photos shows a fitted link bracket for Drone Air One (with the swivel and chain attached).The length of the link bracket should be somewhat longer than the outside distance between the two landing gear legs. The curved profile of this part of the box cover makes a secure spring-fit in the landing gear when the link bracket set in place. To install the link bracket you need to spread the landing gear slightly to allow the link bracket to fit between the two landing gear horizontal leg members. The landing gear then holds the bracket securely in place with the returning spring action of the landing gear legs.
Before attempting to install the bracket cut-out a small notch at the center of each end of the link bracket to permit the bracket to fit all the way into the recesses in the landing gear. The center of the landing gear has a small structural divider that the notches must fit around. The little dividers in the landing gear prevents the link bracket from sliding forward or backward.
Step 6: Mounting the Drone on the PDC - (Drone Air Two)
Temporarily install the link bracket between the landing gear and mark the two mounting hole locations with the black marker. Drill clearance holes for the machine screws with a 3/16 inch bit. Reinstall the link bracket on the drone landing gear and position the done on the PDC making sure it's centered. While holding the drone in place mark the mounting hole locations on the PDC with the marker, using the holes already made in the link bracket as your guide. After drilling the two holes in the PDC install 10-32 machine screws in the PDC. Tighten up the nuts good and then make a test installation of the drone on the PDC. The PDC is now secured in place with 10-32 wing nuts making it easy to install and remove as required without the need for tools.
Step 7: Preparing Payload Support, Latch and Trigger Mechanism (same for Both Versions of PDC)
The payload support plate made earlier from the top of the plastic box is now secured to the wire coat hanger with three small zip ties. To do this mount the hanger on the box with the two paper clips, and then align the plate in the center of the PDC. Then mark the locations of the three sets of holes for the zip ties. After drilling the holes (a 1/8 inch bit is fine here) the zip ties are installed and trimmed.
The latch for the payload release consists of the curved "hanger" part of the coat hanger and a small rectangular slot cut in the plastic box. First mark the slot location and cut out with the utility knife. The sensitivity of the latch is easily adjusted by bending the curved hanger in or out. The trigger is really low tech in that it is just a wooden clothespin clamped on the box edge near the latch. Adjusting the location of the clothespin also plays a roll in the sensitivity of the payload release. I plan on changing the trigger in future tests. In a test or two I found that a heavy landing with Drone Air Two will trigger the release even without the clothespin in place. More work needs to be done with this part of the project as I would like to see a more controlled and softer landing trigger the payload release mechanism.
Step 8: Chain Link Between PDC and Drone (Drone Air One)
A combination of small fishing gear items make up the main parts of the connection between the drone and the PDC. The leader lines and swivels with snap links and the two split rings lets you put the assembly together pretty fast. First I made four small holes (1/8 inch or sized for the cotter pins used), one in each corner of the box. I fed the cotter pins through the eye of the leader line swivel and then I inserted the cotter pins in the box holes and bent them over to prevent removal. I then made a similar cotter pin connection to the center of the link bracket on the drone landing gear. That being done it is then just a matter of connecting the leader lines, swivels, split rings, and the chain together as shown in the photos.
Step 9: Upcoming Work on Drone Air Two
This photo shows the two props damaged in the crash landing. The crash landing as shown in the second video (above). My plan is to do more experimenting with the Drone Air Two payload trigger release system and also to get some better indication of the maximum payload that is practical to carry with the delivery system. I will also install prop guards on the drone.