Spray and Fly Away

Building a rig to stabilize the sprayer can be rather cumbersome. The sprayer doesn't really have any place that you can safely clamp down on the hold it in position. It is also rather heavy and in my case, had to be mounted at an angle to be on any use. Cable tieing the sprayer onto a rigid sheet could work, but it will be useless if you can't remove the sprayer to reload it without cutting the cable tie and reattaching each time.

 

In my build, I took advantage of the flexible and spring properties of FR4 fiberglass sheet to hold the sprayer onto the rig. The bracket which holds onto the body of the sprayer was built using multiple strips of 10mm wide 1.5mm FR4 arranged like below:

The bottom strip is designed to be the same length as the diameter of the sprayer. It acts as a seat for the sprayer hence its position is carefully chosen to so the sprayer is tilted to the right angle. Precision isn't really that important however. It is mounted by bolting to the long strips with a right angle extrusion on each side as shown below:

The two side strips have a slot where the top strip goes. These slots are made by drilling adjacent holes then filing. Fiberglass manufacturability makes this easy, just drill three holes and wedge the excess web out then needle file to finish.

To get the right length for the top strip, insert the bottle between the two long strips first, bend the two long strips so that they wrap around the bottle snuggly. Then measure up a suitable length of strip and mark holes to hold the two long strips apart at the correct distance. The snug fit around the bottle is what allows to bracket to hold the it so securely.

 

The bracket is hinged to the base plate. The hinges are aluminium angle extrusions double bolted to the base plate. The hinge shaft is just an M3 bolt with a nylock nut tightened just enough to provide some freedom.

 

Actuator Mechanism

Fitting the servo will require cutting a large rectangular hole in the base board to fit the body through. With fiberglass, it was as simple as drilling around the perimeter and using a hammer to punch the middle out, then using file to finish. Sorry I don't have a picture for this.

The servo horn that I am using for this has a 3mm hole drilled out where the cable for the mechanism goes through. One of those eye rivet thingies that come packaged with servo was inserted into that hole to make the hole more wear resistant.

A cable tie was used as the cable to transfer the movement of the servo to the release trigger. I have tried steel cable and other forms of string. Steel cable had a habit of plastically deforming a various times and I found it difficult to fix at ends. Many forms of string were too stretchy for this application. A 3mm hole needs to be drilled into the release trigger of the sprayer for the cable to go through.

Play around with the mixer on your radio transmitter, to get the servo ranges correct. You want the servo horn to be as perpendicular to the cable as possible throughout the whole travel. Obviously you want to have enough travel for the release trigger to go all the way down.

Add a cable tie stub to allow the cable tie to actually pull on the release trigger. The position of this stub is based on where the sprayer is seated and the release and engaged positions of the servo you have just set on your transmitter. Make sure the sprayer is seated properly before finalizing the position of the cable tie stub. Pull it through too much and you'll have to use a new cable tie! I used another cable tie to ensure the sprayer is fully seated back. The two bolts around the handle prevent the sprayer from rotating.