Getting the ripple tank working

I woke up in the night last night and figured out how to make the ripple tank work. I added a large blob of Blu-Tack to the motor's load:

This slowed it down enough for the wavelength to be big enough to see when I drove the motor through 3V and controlled the speed with a potentiometer:

I put a ruler into the water so that I could measure the wavelength.

I'd say that the wavelength is 1.5 cm. I used a strobe to freeze the rotation of the blob of Blu-Tack. That said 8 Hz. Using the wave equation, wave speed = frequency x wavelength so wave speed = 8Hz x 1.5cm = 12cm/s. I had hoped to time a wave going down the screen but it would take about a second to cover the distance shown in the picture so the timing would hardly be reliable. I think filming in slow-mo is the next adventure!