Build log
Propeller guards a finger cannot pass.
A robot that flies in a home will meet hands, including small ones. We set Alkyon’s guards a simple test, and our first design failed it.
In short. Thin rings round the propellers looked like guards but bent into the blades under a push far gentler than a poke. A carbon hoop with grilles above and below holds well beyond our requirement in our model, and keeps the standard test finger out. It costs grams, and we chose it over our weight target.
The test we set
Two rules. A child’s finger must not reach a propeller from any side: we use the standard test finger from IEC 61032, a jointed probe the size of a child’s finger. And a guard must take a 5 N push, roughly a firm poke, without bending into the blades.
Why the first rings were not guards
Our first design hung a light ring round each propeller on two small plastic struts. We modelled it as a frame and checked the model against a textbook closed-form solution, and the two agreed closely. The answer was clear: a push far gentler than a poke bent the ring almost onto the propeller tip. Open rings also left the blades reachable from above and below.
What we tried
| Design | In the model |
|---|---|
| Plastic ring on two struts | Bends into the blades under a light push |
| Carbon hoop | Stronger, still short of the requirement |
| Carbon hoop on four struts | Takes the push, but the blades can be reached from above and below |
| Carbon hoop with grilles above and below | Holds well beyond the requirement, and the test finger stays out |
What it costs
Grams: with full guards, the concept is over our weight target. We chose the guards, and we keep working on the weight elsewhere. Grilles also cost some thrust; how much, a test stand will tell us.
What is next
These are model results, not measurements. Next we print the guards, push them with a force gauge, put the test finger to them, and measure the thrust the grilles take. We will write here what we find, along with the rest of Alkyon’s safety work. The other rules in its design: rules for a robot at home.