The first method is to rotate a screwed rod quite fast. This in turn will work on a slide. This solution often fails because of excessive vibration, and the need to provide a motor nearby.
The second method uses co-axial cable. The best that I have come across is Philip Edwards method of using bicycle brake cable inside curtain wire or similar. Quite a good method, with excellent push pull, and the motor actuator can be at a distance.
The third way to is to use wire or inelastic string. A drum is attached to the motor, which rotates at a suitable speed. The cable is wrapped around the drum with enough turns to prevent slippage. The two ends of the two cable are then run up to the actuator, which is a small trolley running in guides. This can then in turn be connected to the simulated hydraulic ram. It is essential that the cables are tensioned properly. This system works very well, and is very powerful, but there may be some vibration caused by excessive friction in the pulleys.
Now I know that the Action Engineering system did not work at all well. How well I remember, some years ago, a wonderful road grader model using this system, with pipes running everywhere, and it did not work. That model is still waiting for a suitable alternative.
We have been assured by Alan Partridge that a miniature hydraulic system cannot be made to work because of the small size of the components etc. There was an article about it in CQ in December 1997. The flow in a tube increases as the fourth power of the radius. Your house has 1/2" pipes, but an 8 or 10 inch main can supply a whole town. A JCB or similar digger may have 1 inch armoured tubes, but a model one tenth scale will hardly work. The mass of the bucket has come down by 1000, but the flow by 10,000.
But a hydraulic system can be made to work in our scale if two double acting cylinders with pistons are linked by strong plastic tubing. If one piston is actuated, it's linked mate will follow the movement exactly (master and slave). Being double acting, the slave piston is pushed on both the forward and backward strokes. Marvelously simple! All you need to do is to drive the master piston with an electric motor. One way this can be done is with a screwed rod telescoping inside the piston rod (to save space). The screwed rod is short, and is driven by an electric motor with speed control. The contained fluid should be brake fluid from which water vapor has been vacuum extracted. All connection should be very tight, and there should be no contained air bubbles.
For those who want a simpler system, you can do the same thing with medical 5cc syringes and drip set tubing! But here you have only a single acting system and rely on a vacuum effect for one of the movements. This might not be a drawback. Fill the system with water, and off you go! The problem is that the throw of the piston is rather small. But it works!
One final word. Has anyone tried using pneumatics? I have seen many examples of air systems, but never on a Meccano model. They are very good for bang bang actuators, with end to end movement. Commercial examples are very expensive. And they are linked to a programmable controller. But there is no reason why a simple system could not be devised for the Meccano system. Other systems have used air for actuation.
From Howard Somerville:
The system I am endeavouring to perfect will be suitable for small to medium-scale models. It uses sleeve pieces for cylinders, fishing wire inside Meccano spring cord as Bowden cable, and two new Meccarep parts to enable the cord and fixings to be concealed INSIDE the cylinder.
From Bob Galler:
There is a company on the web you might look up and ask for their catalogs. They make real miniature industrial pistons and valve/controls. Find them at www.clippard.com. Never used them for models but
have used them for industrial design.
From Howard Somerville:
Thanks for the info, Bob. Clippard do indeed sell miniature hydraulic components of the right size for Meccano. Please, somebody, make up a kit from them and market it!
From: Philip Edwards:
Suggests using bicycle brake cable inside English net curtaining. You will find that after stripping off the white outer jacket of the net curtain cable, the resultant spiral form will fit nicely into a Meccano boss/coupling.....
Cables running around pulleys has been known to work - especially with Teflon coated steel fishing line as the cable. Was that what you were implying?
From: Philip Edwards:
Bowden cable is definitely the way to go. In the world of Meccano backhoe excavators, my CAT 235 uses it; Tony Rednell's Hymac models kind of use this technique - they work on cables running around small pulleys; Paul
Jones' CAT 245 works the same way. These are all BIG models and throw lots of power around. As for my CAT, the model has now been running for a little over 10 years and I had to replace the first cable earlier this year. I use
English 'net curtain railing' for the outer jacket and bicycle brake cable for the inner. Lots of car grease give a smooth operation. For models, the efficiency of Bowden cable is acceptable, as far as I'm concerned. Who needs messy hydraulics ?
From Fred Culpepper
There are three styles of cylinders available from Clippard that have proven to be useful in model construction. All of these cylinders can operate in either the pneumatic or hydraulic mode. The first of these is the Stud Mount. This cylinder is 5/8" in diameter, 4-15/16" long with two ports on the side and one on the end. It has a threaded section at the front of the cylinder (the end with the piston rod) similar to the mounting system for a potentiometer. On the 9SD-2, the thread is 15/32-32 and is supplied with a matching nut. This threaded portion fits the center hole of the Meccano 137 thus requiring no modification of the Meccano part. Since the #137 fits on the end of the Boiler, #162, this allows the cylinder to be enclosed in the Meccano Boiler to mimic the real thing in such models as a steam engine or pump.
The length of the cylinder (9SD-2) exactly fits the length of the Meccano Boiler with a threaded (port) hole (10-32) matching the hole in the Boiler End. A 10-32 screw in this hole will allow the cylinder to firmly mounted in the Boiler. A slight reaming of the center hole of the Boiler End may be necessary to fit the cylinder within the Boiler. The result is a securely mounted cylinder within the Boiler assembly. A clevis (obtainable from Clippard) to fit the diameter of the piston rod (3/16") is the only additional part needed to mate this cylinder to Meccano models.
If another mounting arrangement is desired, then a mounting bracket can be easily constructed from sheet metal, or a suitable hole drilled in a standard Meccano part such as #51. Clippard can also supply several styles of mounting brackets for this size cylinder.
The stroke (working length) of the piston rod in the 9SD-2 is 2", certainly sufficient for most applications. The bore (inside diameter) of the cylinder is 9/16". The cylinder is made of brass with a matte finish. This is a double acting cylinder in which a positive pressure is required to move the piston in either direction. Usable pressure for pneumatic operation is in the range of 5 to 20 pounds of air pressure.
The force factor for this cylinder is 0.22. Therefore, when using 20 pounds of air pressure, the output force of the piston rod is 20 x 0.22 or 4.4 pounds. This cylinder design is available with piston rods of various lengths. Those lengths found to be suitable to Meccano are 2" 4", and 6".
The second type of cylinder useful in Meccano construction is the block Mount. This cylinder has two blocks, one at each end with a tapped hole (10-32) for mounting. The #3BD-2 is 1/2" wide, a suitable size for Meccano components. The mounting blocks at each end of the cylinder present a problem, however. It will be necessary to drill two holes for 10-32 screws to fit the mounting holes in the blocks. These holes (center to center) by no means match Meccano.
An alternative is to fashion a mounting block as an adapter. Metal or plastic rod with a square-section of 1/2" has a neat appearance. This adapter can then be drilled and tapped with a series of holes on 1/2" centers to function with Meccano. A piston so mounted can find many applications in Meccano models.
The force factor of 0.10 does limit the usable amount of work that can be performed with the 3BDS-2 cylinder. With 20 pounds of air pressure, the output force of the piston rod is only 2 pounds. This is a result of the inside diameter of the cylinder which in this case is 3/8".
The third type of cylinder which has proven useful is the clevis mount. The one most suited to Meccano is the 3CD-2. This is easily incorporated within a model and can cause the model to function much like the full-size mechanism. These pistons function the same as the large pistons found on hydraulic operated machinery. Because of the clevis mount, they are free to swing in a limited (but satisfactory) arc. The clevis mounting piece is easily fashioned from Meccano parts.
The 3CD-2 is also available in a series of piston rod lengths. The 1", 2", and 4" lengths are the most useful to Meccano. The diameter of the bore of the cylinder is 3/8" giving a work factor of 0.10. It has an outside diameter of 1/2" and a length of 4-13/16".
Perhaps the most versatile of the cylinders in the 9SD-2. Clippard has block mounts and brackets for their cylinders as well as clevis forks with a threaded stud to convert any cylinder to a clevis mount. It is a bit large for the Meccano scale, but it is quite powerful for its size and easy to work with.
There are several precautions which must be followed in working with pneumatics and hydraulics. First, only "hydraulic oil" may be used as the lubricant for air operation, and as the medium for hydraulics. Second, never exert any lateral force on the piston rod. It must move easily in its end seal. Any lateral motion may break the seal and the result is a leaking piston.
Hose barbs are also available from Clippard for their valves and cylinders in 1/16" and 1/8" sizes to fit flexible hoses with these inside diameters. In most low power applications, the 1/16" inside diameter hose is adequate. This size hole allows the hose to be easily hidden within the Meccano structure,
See the Clippard site at
Http://www.clippard.com
There has been some discussion in the past on the making of Bowden Cable for use in Meccano models. I have used a method of making this cable that is effective and utilizes the Spring Cord #58.
This is not original idea, I discovered it in reading some Meccano literature years ago. For the outside jacket, use the Spring Cord. It has the advantage of easily being fixed within the standard hole in Meccano bosses where it can be fixed using a grub screw.
For the inside cable I use plastic coated 80 pound test fishing leader. It slides within the Spring Cord with little resistance. There is also available "connector sleeves" which permit making excellent eyes for the ends of the fishing leader.
Over the years, several of these Bowden Cables have been made up for models and retained for use in the future. They are a part of what I call my "Meccano Plus" collection.
Fred Culpepper USA
| return to previous page |