The last post covered a one-day build of a prototype quadcopter using a wooden chopstick frame, a battery and motors. It achieved a hover above the table but nowhere near lift. Since then, I’ve been doing some research about calculating how much lift I need and what types of motors or rotors etc. You may have seen this video, which I highly recommend looking into anyway. After watching it, I realised I don’t have the motors’ specs, make or model (remember, I salvaged them from servos) and as they are generic, finding the specs to do any real calculations is guesswork at best.
So, where next?
Thus far, the factors I have been toying with are:
- Upgrading my motors
- Going for bigger rotors
- More powerful versus less powerful, smaller and lighter battery.
Basically, I focused on what I could electronically manipulate to improve performance. Additionally, my new design sketches focused on building a surround for my tin, so as to be minimally invasive to it, as shown below.
There are lots of practical considerations like how do I mount my components inside? Do I leave it opening or cut a hole for replacing the battery? Do I construct a frame with arms, or four separate arms? If separate, how do I ensure everything is secure and flush? All these considerations play off against space, weight and complexity so in short, too many questions and not enough answers. To escalate the situation, I searched lots of drone manufacturers and hobbyists to see what motors, rotors and batteries they use etc. Finding that my motors simply aren’t used, the possibilities of buying lots of new parts opened up.
After a good step back and a deep breath, I realised that my problem is indeed weight. Everyone else uses plastic; I’m working with metal. So, time to think outside the box, or at least with half the box. The lower half of the tin is the heavier by far. Removing that bottom half and using the hinges / clasp as a mount-point means that once again the world is my oyster.
Back to the drawing board
Without a bottom to work around, it was now possible to have a single frame unit based upon a flat sheet, providing both rotor arms and the main chassis. A battery compartment or sleeve could be incorporated by design as well as using the original tin hinges to mount the lid. Back to Excel (yes, it is my drawing platform of choice and I know it’s weird) to put together some more paper concepts. This was the result.
The new version incorporates the Mk III arms shown in the preliminary designs post, with additional flaps to join the lower edges, increasing rigidity. When folded, the centre plate forms a battery slot underneath the drone. A plastic layer will be fixed on top, covering the battery slot and insulating the chassis for mounting components. The design needs access for wiring the battery and rotors so that the tin lid will lie flat, but it sufficiently demonstrated the concept.
With the battery dimensions checked and a few fine adjustments made to the hinges, the tin lid could then be fit to see how the overall design worked.
The new design gives me a number of options to explore:
- Different metal thicknesses (an aluminium tin will be used for the next stage)
- Recycling the metal from the original tin bottom
- Using plastic, such as a 3D printed solution
- Using a one-piece design or making removable arms and battery compartment
If I do end up using a 3D printed base, it will be done by a print shop nearby so a quote may be a determining factor here. There are some advantages, such as low weight and making clip-on motor mountings rather than using screws or glue.