Intro: How to Build a Epic Multicopter Frame
Multicopters (particularly quadcopters) are gaining immense popularity, and DIY multicopters are all the rage. While most components need to bought due to complexity, frames do not, and making one can be a cheaper, more customizable option to those found ‘on-the-shelf’.
There are many great Instructables on how to make a frame, and aside from making the frame from chocolate or old jeans, most involve the use of a 3D printer or some form of CF (carbon fibre).
I live in Australia, and for me (student) 3D printers and CF parts are study-induced hallucinations. The aim of this instructable is to show you that you don’t need high-end materials or tools to make a durable, lightweight frame (and how to make said frame).
So, how to make a multicopter frame that’s lightweight, cheap, and doesn’t need anything your local hardware shop won’t sell?
The answer is wood, good ol’ pine. . . . ply.
For those who don’t know, ply consists of layers of timber, each with the grain aligned perpendicular to the layer before (see image).
This makes use of wood’s good directional strength, creating a material which is strong in every direction.
Because there are already many videos and instructables on how to configure the electronics I will focus on designing and making a frame.
Step 1: Materials
So, what will you need?
Paper (stiffer the better)
Drill (and associated bits)
Jigsaw, Bandsaw or Scrollsaw (or Coping-saw - which will take ages, but is much more affordable if you don’t have one already)
Hacksaw (for alloy tubing and motor mounts)
File (for neatening cut alloy)
3-9mm plywood (thickness depends on the size of the frame)
Aluminium square tubing or C-section (again, size depends on the frame, and the motor power, 12mm is good for 650g/motor load, 16mm is good for 1.5kg, 20mm does 2.5kg+)
Bolts and nuts - generally M3 or M4 (again depends on frame size, you figure out what’ll work for your frame)
Lacquer/paint or superglue – yeah superglue. (Model aircraft Dope is good, but is harder to get and more expensive)
Step 2: Design!
Take your stiff paper and fold it in half then sketch away, treating the folded edge as the centre of the frame. This ensures that your frame will be symmetrical L/R.
Quads don’t need to be symmetrical F/R. e.g. a ‘deadcat’ or H-frame - a wider spread on the front arms prevents propellers from getting in video or photos shot from the craft.
If you do want your quad to be completely symmetrical, fold the paper into quarters. If you’re making a Hexacopter or Octacopter, you can use a completely circular frame design or adapt off a circle or oval.
I find it’s a good idea on small frames to add pieces to the lower plate (or upper) to attach cameras, Rx’s and video transmitters. If you decide to add ledges you can either add them in the ‘copy to ply’ phase, or make separate upper and lower templates.
Decide on the type of arms you want, one pair as a single piece or all separate arms. On a quadcopter, you generally have all four arms separate and foldable. A-symmetrical frames require separate arms, which are more common even on symmetrical quads.
For a (DIY) symmetrical Hex or Octa, one pair of arms is generally solid, to provide a mount for landing gear.
Once you’ve designed plates with enough space to secure arms properly and mount your hardware and undercarriage, start marking holes for the arms and any other bolt-on parts.
When it comes to mounting arms, I like to have around 1.5x the arm’s thickness as the distance between each mounting hole, with the arm continuing half that distance either side. For example, on a 12mm arm I’d have 18-25mm hole spacing, with 9-12mm from the outer hole to the end of the ply, and the arm continuing round the same distance past the inner hole (possibly a little less).
For creating the holes, mark them and then cut or punch them out with the template folded to ensure symmetry.
Step 3: Paper to Ply
Pretty simple really, all this step requires is a pencil, some extra hands, and the template.
First, cut out the shape taking care not to cut any crucial folds. Once the shape is cut, unfold it and trace it onto the desired plywood.
If you decided not to add protuberances for batteries, VTXs or RXs to the template(s) you can add them now, basic pencil and ruler stuff.
With light items like VTXs or RXs, it’s not necessary to have the weight balanced symmetrically, however with batteries or cameras, it’s a good idea to approximately counterweight them e.g. Gopro @ the front, Bat @ the rear. Image 3 shows an underslung battery at the rear, further back to counter the narrower spread of the rear arms.
On a Deadcat frame, the COG should still be in the centre of the motors, which is generally not in the centre of the frame.
Now is also the time to add holes – to save weight. As can been seen on the frames featured, ply has been removed to reduce weight, it’s surprising how much you can remove, especially with a single piece arm pair for strength.
Step 4: Cut, Sand & Coat
Now that the design has been transferred to the plywood, fire up your tool of choice and start cutting away!
I tend to use the ancient jigsaw that I have, however if I can I use the scrollsaw at a local tech facility. Scrollsaws are definitely easier to use, and you can cut the tight corners more easily without needing to drill them first, however they are more expensive and have a more limited task scope. If you’re on a budget, the hand tool equivalent of a scrollsaw, a Copingsaw, is good but takes ages.
After cutting, drill the holes for mounting the arms and other hardware that may require it. It’s best to drill holes with a press drill, otherwise just take it slow with a hand drill.
If you decide to buy commercial arms for your quad, you may need to make different upper and lower plates, and make cutouts as seen above, for alignment ‘things’ – this is a pain, and commercial arms cost money so it’s generally better off to go for DIY alloy tubing. Such cutouts generally involve lots of drilling, chisels and tiny files. Messy.
Once you’ve cut out the plates, you’ll find that they look a little rough, take the time to sand them back, using a block of wood and some sandpaper, I generally use 80grit, then 200grit to finish up.
Onto the coating…
While you can certainly just go straight ahead and use the plates raw, or simply give them a lick of paint, several coats of good thin lacquer or model aircraft dope will soak into the frame, improving rigidity and strength, with the added bonus of waterproofing it. If you can’t get Dope or don’t have lacquer, super-glue actually works well, simply add it liberally, then spread thin. If it all the desired coating soaks in, a further coat can be used, finishing all coatings with a light sand. Once prepped like this, you can paint the frame with colour.
To thin a lacquer, add 40% turpentine or water depending on the type.
Step 5: Alloy Arms
I'm assuming that you’ve decided to go full-blown DIY, want to make your own arms and have bought the required aluminium square tubing based on your Multi’s weight, and some 3mm alloy plate (for motor mounts).
Motor mounts simply have the three or four motor mounting holes drilled (M3) and a M6 to M10 hole drilled in the middle of the four, to accommodate the bottom of the motor’s shaft. They then taper to the arm, and generally secured with another 2 or three bolts, typically M3 or M4 with nylocks.
Once you have the motor mount size, decide on a frame size if you haven’t bought electronics yet or base it off the size of your props if you have. Calculate the required length of the arms based on a minimum of 10mm clearance between the props and the frame plates, and/or 25mm between prop tips.
Common frame sizes are 250, 350, 450, 570, 650 for quads, and 550, 650, 700, 800 and 900 for a Hex (all sizes in mm)
As an example, if you had motors and props decided and wanted a minimum frame size; 16’’ props on a Hex would need a 430mm span motor to motor, with a diameter of 825mm. This includes the plates, arms, motor mounts and prop-tip clearance.
Once you have made your arms according to your design from step 1, mark and drill them to align with the holes you made in the plates earlier, attach motor mounts then bolt the bird together using the M3 or M4 bolts and Nylock nuts!
Add electronics and you can 'make it fly'!
Step 6: Undercarriage - an Instructable for Another Day!
Undercarriages are diverse and there are many designs, a few of mine are pictured.
To avoid rambling on forever, I’m going to do a separate instructable on making a custom landing system at a later date. For now my advice is skis, as seen in image 1. 12mmx2mm flat alloy and 10mm angle-alloy.
Update - my landing gear 'ble is up! Check it out and throw any questions or ideas you may have in the comments.