Science project rotating disc

Our son is going to do a science project to test higher gravity effects on plant growth.
We are thinking of a disc about 1m in diameter rotating about 60rpm should give the seedlings about 2g’s at an angle. We were going to 3D print holders for the seed pods at the correct angle.
The fun part will be getting a 1m disc spinning at ~60rpm for a few weeks.
We originally thought of a record player but I think it would be too fragile.
Our latest version is an inverted ceiling fan with the disc mounted to the blade holders and the body of the motor mounted to a sturdy base.
Anyone have an old ceiling fan they would be willing to donate?
I’m checking the auction site but haven’t seen any in a few days.
We could do some cool Arduino control stuff to monitor the rotation speed and maybe even control the fan (would need some PWM that could handle mains).

Anyone have any other ideas?

Have you thought about the plant part? Germination requires time and various environmental parameters, like temperature, water, light, etc. Gravitropism is known to influence tap root development and orientation of the embryo, however, once a shoot starts, light, day-length, hormone levels, consistent moisture, etc would be challenging with a jiffy seed pod. As far as the botany goes, I think in-vitro lab technique would be much more agreeable, controllable, and, most importantly, measurable. Development of a tap root is visible in agar, moisture is constant, nutrients, etc.

I’d get a large, autoclavable tube (tissue culture bottle) and use MS basal medium agar (Murashige-Skoog agar) + IBU-K. It’s fun botany lab 101 stuff. Looks super cool to grow a test tube plant, too. Very mad science…


I think I might actually have a fan motor in my cellar, I'll let you know when I get a chance to check.

Regardless of the biology, you are going to have a very real experience with a rotating imbalance.
No mater how hard you work to maintain even weight distribution one plant will grow differently from another and throw the weight out. Or you water one a little too much.
Rather than adapting a fan which must be balanced or it shakes your house, go for a bike wheel and axle. It’s designed to take a beating.
A 27" or 700C bike wheel could spin faster to make 2G’s or you could add carefully balanced outriders to achieve the 1M seed swing diameter.
It’s not crazy fast or out of spec for a bike wheel of almost any diameter to take that kind of load. You will need to frame the thing to take the generated imbalance forces.
Anyway it’s done the dang thing will vibrate at 60hz or faster. It’s gonna get annoying on a wood floor…Mount it to a concrete pad.

Fun stuff.

Yes we were thinking a bike wheel based turntable would be more rugged. We would then have to connect a motor to spin everything, but the Arduino part would be much easier. Not looking for large acceleration, just maintain ~60RPM. Working with mains electricity makes me a bit nervous for an unattended high school experiment. :flushed:
I’ll do some more sketching and brainstorming tonight. Of course everything needs to be done in a week or so, couldn’t work on it during Spring Break when he was off school . . . . .
Perhaps a study of salinity or chlorination affecting growth (where nothing needs to spin around) might be more in order.

There’s a lot of cool research regarding acoustics and plant growth. The sound of running water causes roots to grow toward the source, hence why we often end up with root clogged sewer pipes even if the trees are far from the pipe. One experiment I know of is putting one plant on a speaker playing bass-boosted water sound, and another on a speaker playing white noise.

Or you guys could cheat.

Not “cheat”, “dry lab”!


Thanks for all the input. I think he has settled on an angled light experiment. How various angles of light affect plant growth.

Should be easier to control everything.

if you used a bike wheel could you add dyna beads to help it ‘auto balance’ the tires in reaction to the variable plant growth?

Yes, but this would be testing the effect of plant growth on wheel spin, not wheel spin on plant growth!

if the plant throws up hot dogs on this tilt-a-whirl, does it hit the plant next to it?

(really hoping that D Velzy answers this for me, with estimates of vectors and velocities at this rotational circumference and velocity)

hmm… IDK how much this helps, but here you go Lorin

SpinningPlantsVomitingHotdogsCollisionCriteria.pdf (2.71 MB)

The answer depends entirely on wheel size, plant height, and number of plants on the wheel. There is no dependance on angular velocity unless you begin to consider the plants having a dimension normal to the plane of rotation and having gravity act on the hotdogs in that direction.