The creative brief

Summer is a cumin in Berlin and my wife is busy planting the balcony so that we can enjoy our evening cocktails in a fragrant, colourful environment. Young plants grown in Dutch greenhouses do give you a really quick start but much patience is still required. As an impatient man, I thought about what I could conjure up that gives instant satisfaction for friends of the floral.

The technical brief

The mechanism was to be as simple as possible. A handle rotates a cam which friction drives a wheel perpendicular to it, so that the wheel and its shaft are both lifted up and down and rotated a little. Petals are attached to the other end of the shaft and as the shaft is lifted, the petals should open up to reveal an egg-shaped centre.

Petals & hinge

To get the shape of a petal I used a piece of plastercine pushed against a wooden egg. From this I made two templates in card, to mark up my lime wood for cutting on a bowsaw.

Plastercine petal and two card templates

First cut for petals

Second cut and carving for petals

Instead of trying to hinge each petal separately, I bent a piece of brass rod into a ring and cut two holders to grab the ring in a sandwich.

A hinge for 6 petals

And when this is all assembled it looks like this

6 petals hinged on a centre piece

The base mechanism

The base has four chunky dowel legs. Two of the legs have holes to take the 8mm dowel axle with its cam and its disc-shaped crank

Parts for the base mechanism

The assembled base mechanism

There is a short video showing the effect of turning the crank.

Youtube link “”

The flower and its “cage”

Adding a wooden egg into the centre of the petals completes the flower

The open flower

To push the petals up when the flower is closed, a wooden ring is required at just the right height. A certain amount of experimentation shows the correct height and some trimming of the outside of the petals gets them all to move synchronously.

A ring/cage at just the right height

Lessons learned

The flower jammed when open and didn’t want to close again. A lead washer fixed that.

Lead washer to increase downward force

It was caused by the vertical activating rod tilting due to the off-centre upward pressure from the cam. It’s a delicate balance between the diameter of the dowel and the diameter of the hole in which it moves. I used a 10 mm dowel in an 11 mm hole and that was too loose. Maybe a 10.5 mm hole would have been better, maybe I should have used a much slimmer dowel to reduce the surface area subject to friction? I will just have to try it and see in future.

What did the critics say?

My severest 4 year old critic asked “are those rabbit’s ears?

Rabbit’s ears?

It only has 6 arms so it can’t be an octopus


Something from outer space?


This finished piece has a very short narrative. Each turn of the crank opens & then closes the flower. That is not much of a story. Nevertheless my official tester played with it happily for quite a while. I think it is more something to entertain kids and is of less interest for adults. I had fun making it and learned a bit, so I am content.

The video

Video link “”

Download the images