25 Oct Stability – Lesson 2
An arrow is designed to be stable in flight. If it is made too short it will wobble, too long and the additional weight will make it fall. It is given fins on the end to keep it pointed straight and most of it’s weight is located at the tip. A properly designed arrow will fly true and hit it’s target. The same needs to be done with a camera trolley that rolls on rope.
Many mechanical components need to be integrated to make it stable. Center of gravity, length, weight, solid bearings, zero friction etc. What we see on the market are many ‘drone’ cable cam systems (trolleys that have everything onboard including batteries and motor and operated by wireless control) that are too short in length. When operated one can see a ‘dogging’ of the trolley, a type of vibration caused by a lower frequency swing back and forth along the axis of the support rope. These designs are to attract the buyer to a kit that fits conveniently inside of a small case. Unfortunately an unstable platform is useless for film and all the buyer has received in the mail is another toy (albeit expensive toy) to give to their kids.
Trolleys need to have length. The actual length depends entirely on the weight to be carried and center of gravity. The more weight and lower the centre of gravity the longer the trolley needs to be. Think about a sailboat with a mast. On the ocean the boat seems rather stable in calm seas but climb the mast high above the deck and the smallest movements on deck translate to larger distances up high. Doing maintenance at the top of a mast during cruises is a dangerous proposition! Now try climbing to the top of a 100 foot sailboat that only has a 20 foot mast… not so bad!
Oscillation of the support rope or drive rope (induced by the nature of rigging) causes the trolley to bump and swing. This in turn throws the camera at an increased rate depending on its distance from support rope and centre of gravity. At STSCC we have developed software that takes the weight and centre of gravity and calculates exactly how long our trolley needs to be and what counter weight measures we need to implement. In turn our trolleys are configurable to ‘transform’ their shape to match the requirements.
As we learned in lesson 1, some vibrations cannot be seen by the naked eye and by calculating exactly what we need we can better guarantee a faster resolution to unwanted camera shake.
The image is of a properly balanced STSCC trolley taking into account length and centre of gravity. The head is a Bradley Engineering 236 Gyro.