Autumn 2018 Newsletter
Autumn 2018 Newsletter
Issue 168
This was one of our informal quarterly meetings where our members showed off their latest Meccano creations.
At around 2:00pm we had a short committee meeting, followed by the Model Tour in which members were invited to give a short talk about their models — in particular their entries for the Secretary’s Challenge!
Report written by Peter Clay
The newly-rebranded Royal Greenwich Get Together was held this year on 30th June in the pedestrianised streets near the old Firepower Museum in the Royal Arsenal Riverside area, instead of on the field as in previous years.
The following members attended (apologies if I’ve left anything out — I’m doing this from memory):
- Brian Leach: Dinosaur, as always roaring, walking and swishing its tail etc. to the delight of spectators; Mantel clock with Heath Robinson drive to the back; Snakes and Ladders game.
- Brian Elvidge: Three-wheeled car with suspension; Tractor with tipping trailer (I think the former was based on a Märklin plan).
- Chris Warrell: Othello game which several people played; Dalek; Bicycle; Humanoid robot; Submersible with manipulators.
- Peter Clay: Baby Meccanograph. It produced designs but the breeze prevented them being displayed. We were given a gazebo, and it transpired later that we could have had side panels for it!
Our stand on № 1 Street
Our stand at the Royal Greenwich Get Together
Our Make It With Meccano workshop had several children (and parents) involved.
The Make It With Meccano tables
On the whole a good day, and very hot. Although there were various stalls for food and drink etc. there were none of the attractions they had on previous years on the big field. However, there were wartime displays and a stirring marching band.
Report written by Peter Clay
The following members attended this event on 7th July (apologies if I’ve left anything out — I’m doing this from memory):
- Brian Leach: Dinosaur, as always roaring, walking and swishing its tail etc. to the delight of spectators; Mantel clock with Heath Robinson drive to the back; Snakes and Ladders game.
- Brian Elvidge: Three-wheeled car with suspension; Tractor with tipping trailer (I think the former was based on a Märklin plan).
- Chris Warrell: Othello game which several people played; Dalek; Bicycle; Humanoid robot; Submersible with manipulators.
- Peter Clay: Baby Meccanograph. It produced designs but the breeze prevented them being displayed.
- Adrian Ashford: A hand-cranked windmill, boat and a battery-powered cement mixer.
We were as before in the school hall with tables and (child-sized!) seats. Unfortunately, due to the England vs. Sweden World Cup match, the time of the event was put forward by an hour to 11:00am to 2:00pm. This may have led to fewer people attending, with the hot weather keeping them outside. The day still went well — our models were well received, and the Make It With Meccano workshop had several participants.
Henwick Primary School did well, having plenty of tables ready and laminated signs made for us, and we got a free lunch and drinks!
Written by Brian Leach
Inspiration
This was a combination of things. One was an eccentric drive on a turntable to a spitfire plane built by Dick Watson. The turntable would turn-stop-turn showing all the sides of the plane.
Also, my fruit machine reel mechanism from 2008 was not very random and that has bugged me.
The pseudorandom motion mechanism
Eccentric Drive
The left-hand gear is the eccentric gear and is fixed to its eccentric rod. The middle gear which is hanging and speeds up or slows down depending on where the eccentric gear is in its cycle. It also goes up and down. The right-hand gear just provides a fixed point for the output.
Pseudorandom motion mechanism detail
So that’s a speed up/slow down but it is not random. By using four eccentrics with different gear ratios form the common motor, we can get varying cycles of speeding up/slowing down.
Gear Ratios
The four gear ratios must not have any factors in common. I chose:
- 16:1 — 4:1 and 4:1
- 21:1 — 7:1 and 3:1
- 25:1 — 5:1 and 5:1
- 19:1 — Epicyclic gearing: 60-tooth Gear Wheel for stationary gear; 57-tooth Gear Wheel for output gear.
The number of input revolutions for all the eccentrics to be in the same position again is 16 x 21 x 25 x 19 which is 159,600. At a modest 500rpm input that takes over five hours!
We still have the four eccentric outputs. These need to be added together. Three differentials used in reverse achieve this.
Pseudorandom motion mechanism detail
The output is interesting. All the eccentric outputs could be moving in which case it turns quickly. One or more could be stopped in which case it turns slowly. Occasionally all are stopped in which case it stops. That is rare, occurring only about once a minute. When stopped it quickly transitions to fast because all the eccentrics start moving again.
The uses for this are limited — a Meccanograph; maybe a fish or something similar moving in a mobile; or fruit machine reels.
See more photos and a video of this mechanism.