Let’s recap. My Altoids Drone recently underwent a huge redesign; dropping the bottom half of the tin to create an integrated underbelly with rotor arms and battery compartment etc. The next step was to construct the new design in metal.
Using a single hole-punched sheet to mount the motors proved very flimsy. The motors would be stable but likely the metal would bend and shear off in a crash; not good if you have to build a whole new undercarriage every time. With that in mind, I revisited some of my original motor-mounting ideas, as well as a few elaborate new ones.
With a CNC router for easier, more accurate cutting, a wrap-round approach could work very well. However, hand-cutting is too inaccurate to reliably grip the motor with some form of locking part (bear in mind thin metal tears). Additionally, any design could easily bend open or deform so this approach was not practical. The final nail in the coffin was that the design with motors was of similar weight to the wooden frame trial; my motors are too heavy so we know from the outset it won’t take off.
The wonder of crash-kits
Try as I might, I was unable to find the motor’s specs. Good drone and helicopter motors give you the lift they can produce in the specs, so you know these are meant for flight. Any specs of motors comparable to mine did not have lift specified. In short, these motors are meant to produce torque under load, not high speed and weight efficiency.
Finally, I bit the bullet and went back to the shop with the crash-kits from whence my rotors came and bought the motors too. Now my motors, rotors and battery come from a G-Force Hubsan X4 drone. The X4 weighs just under 400g, so I now also know my own weight goal is the same 400g. Thankfully these new motors are cylindrical and so could be mounted into a rubber washer. As such, my new arm design simply had to crimp the washer, not the motor.
I also added legs to the arms to protect the motor wires and stand the drone a bit higher. The bridge under the base of the arm is now moved forward to allow it to be crimped rather than fixed with adhesive, making the join structurally strong. Here’s the shiny new drone with the tin lid on.
Wiring the motors – My motor wires are now considerably shorter, only reaching to the their respective corners. But, this has an upside. It’s important that if anything happens I can replace the motors without re-soldering my Arduino every time. Keeping weight low, the plan is to use female connector contacts crimped to the motor wires (these wires are tiny so need crimping). That way, the Arduino wires can simply be plugged in rather than soldered.
Space – At this point the total depth I have to house everything (apart from the battery) is the depth of the tin lid, approximately 8mm. It’s going to be cosy!
In the next post, I’ll start to plan my electronics and look at how it’s all going to wire together.