Design Stage

So, I’m trying to keep this as informative and useful as possible for anyone that has questions about things we used that they think they may need, or possible problems they come across that we have solved so that building a quad can be possible. First of all, the battery. It has connectors on it that look like long metal hollow rods:

Connectors on Battery

Well, our problem was that we never bought the “specified” connector to use with them, they sell in packs on sparkfun as lightweight connectors, good for airplanes of course. We have our own box of crimpons lying around as it is, and tested them, finding that one fits perfectly in the connectors on the battery, the male and female are made to match, so both work with the battery, only thing you need to do is cut around the plastic on the female crimpon that you supply because the ones on the battery have shielding all the way to the tip. The female has its own shielding that does interfere. Easy fix.

Crimpons

Crimpons with battery

We are now planning out our frame design. We decided to set the motors on the beams so that the propellers did not extend past the tips of the beams. We also added a quarter inch, so that the beam is a full quarter inch farther out than the tip of the propellers. This will give us some confidence knowing that we would have to be past ninety degrees turned over for the props to touch the ground, otherwise the beams will touch down first, stopping the copter from its fall (something we hope to never have to deal with anyways).To connect the motor to the beams, we will drill a single hole in the beam, and allow the other two screws to extrude on the outside of the beam up to the plate we are using. The plate is a triangular metal or plastic (whatever we have on hand) plate that has three uneven holes drilled in it. The mounting plate included with the motor is interesting in the uneven holes it has. Two are closer together to each other than the third making an isosceles triangle instead of an equilateral triangle. This allows us to use one hole through the beam to secure the odd hole, and compress the beam between the other two closer holes, which fit perfectly on the outsides of the beams we bought. The triangular plate we use will sandwich the beam between itself and the motor mounting plate. The screws supplied with the motor are not long enough to extend past the beam the way we need them to so we can put the second plate on. We are going to get those from a local hardware store, just bring with the nuts provided, and make sure you can thread them on the screw you buy, and make sure your new screw is long enough to traverse from the head of the screw, through your first triangular plate thickness (depending on material you use), through the beam, through the motor’s mounting plate, and finally into the nut enough for you to tighten and secure it. If you feel nervous about using regular nuts, and believe they may vibrate loose, feel free to get lock nuts, just be sure they, again, thread on to the screw you are using. There is plenty of room between the motor and the motor mount for lock nuts to be used.

Just to make it more fun it seems, the manufacturer let the shaft extend out the back of the motor (through the mount bracket) so that it is not countersunk, or even flush with the bottom of the bracket. This is done by them to allow enough extra shaft to easily secure their E clamp that you put on the bottom of the motor to hold the bearing and the bracket to the motor. Unfortunately, this means if we don’t make a hole for it to fit in, it would rub on the beam and create friction (a bad thing in this case). Easy fix: drill a countersink hole for the shaft to fit in, just deep enough, and wide enough that it won’t have to touch the shaft. Better fix: as to not hamper the strength of our beams, make a second triangular plate, one that will sit between the beam and the motor bracket, this will have four holes and will keep the beam as strong as possible. We will use the PCB plastic for our triangular plates, because it is extremely light weight, and quite strong. Try to find it without the holes drilled into it, just the straight up plastic is best.

Now for the dimensions, using all of the parts we have, we found our ideal location of the motors to be almost exactly 5 – 1/4 inches in from the end of the beam to the center of the hole in the upper plate for the shaft extension. From there, it appears that the hole we need to drill for the odd  screw on the mount plate is 1 centimeter in farther from the center of the shaft hole to the center of the new hole. According to Google calculator:

(5.25 inches) + (1 centimeter) = 14.33500 centimeters

So you can measure directly from the end of the beam to the hole you will drill as 14.335 centimeters. (Don’t you love the use of different units? We don’t work for NASA yet, so it’s OK). To make your triangular plate, lay the plate under the bracket, and mark with a sharpie or easy marking devise where the holes are, careful not to move in between marks, and drill on the marks. We are going to use a 1/16 inch drill bit for our screw holes, and a 9/64 inch hole for the shaft area you will drill in the top plate.

If none of the above made sense, hopefully a few drawings may help, also check out later posts with pictures of the finished frame.

To mount the propellers on the motors: The motors come with two locknuts that fit the shaft, we will use one of them. The props come with a countersunk nut hole in one side, without the prop savers, we would put one lock nut on the shaft, then the prop which would fit over the nut, and the nut slot would be what ensures the prop turns whenever the motor does, then the second nut would be sandwiched on top to hold the prop on the motor shaft. This is nice, but if you strip the nut hole in the prop, the prop is useless. With the prop savers, we place the prop saver on the shaft, let it slide all the way down. These come with an extra part that you would use if the prop had a larger hole, ours doesn’t so don’t worry about it. We need the smallest extrusion on the prop saver facing upwards, the nut hole fits over this perfectly. Screw in the prop saver to the shaft, careful not to over tighten, it’s only plastic, but be sure it won’t turn separate from the motor. Next slip the prop over the shaft, the hole on it is just small enough to not fit perfectly, but if you spin it you can thread it down the shaft. Stretch out one of the rubber bands provided to be sure it will not snap the first time you put it one, then gently ease it from one screw over the shaft and prop and around the other screw. Finally, thread and screw one of the lock nuts provided on the shaft to keep the prop from falling off if the rubber band does break. It should look like this:

Motor with prop attached

Rubber band alignment for prop savers

~Will