Magic Forest

Big Brother

Click here to see the Library of Big & Little Brother Images

Introduction

The Big Brother project started in 2005 whilst Jezza Bear was watching TV with Al Bear. There was some very clever scientist telling everyone that would listen that ornithopters were a fantastic machine used by insects and brought to life in the drawings of Leonardo da Vinci. The scientist then, as a finale to his fine talk pulled out a model ornithopter and proceeded to fly it around his head. Jezza Bear was mightily impressed by the scientists ornithopter but noted that he obviously had a machine that had been mass produced using light weight plastics and polythene. He also noted that the mechanism that was being used caused an asymmetric flick to the wings. Note that Big Brother was never designed in a view to flying more as a concept model for the later Little Brother KTS project.

The Challenge

To create a flying machine that simulated bird wing movement ( an ornithopter) but was able to have smooth movement.

Constraints

No Budget

Items used

  1. Coffee Stirrers
  2. 4mm MDF
  3. Motor from redundant 1990's video camera
  4. Various cogs and clips from video camera
  5. 2mm thick dowels from PC cleaning equipment
  6. SupaGlue
  7. Twine

Build Time

6 hours

Method

 

The upper mechanism

The main difficulty that presented itself from the beginning was the issue of the smooth motion required to get the wing blades to move smoothly. The diagram on the left shows a schematic overlay of the wing coupling on Big Brother. The upper wing joints forming a triangle are fixed and the lower (in the current shot) is fixed to the cam. You will note that the distance between the couplings at the low stroke and high stroke is 36mm but at mid point the distance between the central coupling and each out joint is 30mm.

Due to this issue Jezza Bear saw fit to cut a slit in the wing blade (circled in blue on the left) with a length of 6mm, the difference between the maximum coupling distance and the the shortset coupling distance. The couplings were made by drilling a 2mm dowel into MDF and then feeding the blades onto them. The blades were kept in place my minute aluminium washers found in the video camera.

Lower mechanism

This is where a simple cam mechanism worked an absolute treat. This part required a bit of trial and error but it was finally worked our using some graph paper, a compass and my trusty metal ruler. The trick is to ensure that the three arms creating the cam are cut to specific lengths so that the upthrust and down thrust do not create a jam at the lowest and highest points. The measurements Jezza Bear used are:

  • Arm A - 20mm
  • Arm B - 52mm
  • Arm C - 73mm

Note that there is no real need for the white polythene cog behind arm A but it was a good support. Behind the system shown is a small cog which inturn is attached to a small 6 Volt motor. This motor was absolutely fantastic, it was taken from an old video camera in the lens housing. It appears the motor was used focus the lens. Not a fast motor but had a very, very strong torque.

Notes

You will note that Big Brother appears to be held together with twine. The reason for this was that the motor that was used was so powerful and with such a high torque that it had a habit of grinding over the gears. The twine was introduced to increase the tension on the cogs connecting the motor to armature A's axle.

This was one of the most successful KTS projects to date.
  Here is a very video originally recorded on my mobile phone in MP4 format but now rendered into an animated gif file. The film has been speeded up 4 x and the graphic quality reduced dramatically to assist download time but you can certainly see the smooth flapping produced by the linkage.
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