Hi Aussie Kev and Bertus, yes it is an hysteretic oscillator. This is the only configuration that gives a 50-50 duty cycle and it uses the least amount of components. The two 10k resistors with the 1uf capacitor gives a frequency range of 30 to 6o hz. The signal from this goes through a 33k resistor into the LM13700 mod chip. The 555 is capable of suppling 200mA, so I don't think a load impedance of 33k will bother it. I have been using this circuit for months without any trouble. Maybe you had some iffy 555's  Kev?

Have you seen this topic?    

Hello!   I was just wondering if anyone could assist me in making a name plate for my dalek. I tried to design one using SketchUp but I kept messing up on it.   If anyone who knows how to design and 3d print And could send me an STL file. that would highly appreciated.   Best Regards Mason

I took a cue from Acrodome and used roller blade wheels. cheap if bought second hand and easily found. For one price you get eight wheels in case one or two of the bearings are shot.