Earlier this year, Meccano released a collection of six Nano kits, that we featured HERE. These Nano-models are built using a minimum of parts and all the models are produced only using zinc parts. Having managed to get our hands on a set when they first appeared we took them to a couple of shows where they were a bit of a novelty.
Usually this sort of model will get stripped down to its component parts and added to our building stock. However while discussing them with some interested onlookers at one of the shows it occurred to us they might make the basis of a model kiddie’s roundabout.
The made up models were assembled around a 6 inch circular plate. It was found that with a bit of fiddling about securing points could be found and the models could be arranged alternatively air/road transport. At this point some consideration was made to how this model would best be mounted. A 5½ inch diameter hub disc, mounted under the circular plate, conceals a ball thrust bearing. I found the ball cages I had to hand were not as free running as they might be. All right for supporting a large mass but a bit of a hindrance on this small model. Instead I substituted the ball race with 25 loose balls. This works fine so long as you restrict the movement of the upper and lower bearing surfaces – otherwise you find yourself playing a new game; 25 steel ball pick up! You may think that using such a large bearing is a bit of an over-kill on such a small model but it was the only way I could think of the keep the roundabout running perfectly true.
The base needed to be made high enough to house the gearing and drive motor. Rather than build a heavy looking box for such a small model, a stepped structure built from strips and angle girders makes for an aesthetically pleasing stand on which the roundabout sits nicely.
Building in this manner can cause problems as the width of strips can vary, usually towards the plus tolerance. When a lot of strips are bolted into adjacent holes the extra width will compound and exceed the tolerance provided by the hole/bolt clearance. On this model, the strips are mostly new (ish) and it became obvious that orientation of the strips made a difference. It appears that there is a very slight chamfer on one side and a small, almost undetectable, burr on the other. Insignificant most of the time but in this case I found that bolting the strips with the bur against the surface being fixed to resulted in a misalignment by the time I had got to the outer edges that I could not overcome. If the strips were turned over and bolted down with the burr uppermost I could get all the strips to lay perfectly flat! I think what is happening is the burr is trying to bend out of the way but the surface that the strips are being bolted to is preventing that happening, that along with the fact that the burr will increase the friction between the strips and the mounting face.
The method I used in the end was to start in the centre and fix all the strips down working out from the centre hole and then one at each side, secured finger tight. Then use a drift to force the strips together before fixing the last ones in place. At this point all the fixings were tightened and the process was repeated for the other surfaces.
Now the fun bit! The column is fitted to the canopy first using angle brackets and bolted through the hub disc and a bush wheel. The bottom has a couple of angle brackets fitted and two long bolts are passed through them and just hang loose. These bolts are then carefully passed through the 6 inch circular plate, hub disc, two 3½ inch circular strips the top of the thrust bearing and secured with nuts and washers added by the use of a long driver passed through one of the holes in the bush wheel at the other end. This operation was probably the most complicated part of the whole model it required skill patience and a cool head – all properties that are thin on the ground in my case. After the first couple of attempts, Smokie left the room…
The sprocket portion of the trust bearing is then bolted to the base along with the bracket that holds the bevel gear drive. Bolting a couple of angle brackets to it by their round holes and doubled five hole strips stiffens this bracket nicely. Four small tyres are bolted to the base to act as non-slip feet. All that remained was to add the roundabout and tighten the grub screw in the top bush wheel and that is it assembled and ready to run once the drive has been sorted out.
My attempt at keeping the base low profile proved to be a hindrance in getting the drive arranged. Also the bottom of the thrust bearing excludes lots of the holes from being used to mount the motor. As the roundabout needs to rotate slowly, I decided to use one of the small compact motor/gearbox combinations. This is one of the motors I managed to get from Stan Leech last year. These have 3mm output shafts and require sleeving or special parts made in order to make them Meccano-compatible. I decided to use a band drive to connect the motor to the roundabout drive. This works but the snatch in the rubber band tends to make the roundabout run erratically. Running out of time (as usual) the roundabout was taken to the August TIMS meeting where it ran reasonably well but I was not satisfied with the results.
The rubber band drive proved too unreliable and the model could not be run for long periods without attention. The rubber band drive was replaced with a much more effective sprocket and chain drive. This involved moving the motor position to enable a conversion coupling (3mm to standard Meccano size) and short rod be fitted to the motor shaft on to this a small sprocket wheel was attached. The larger yellow pulley was replaced with another sprocket wheel and a suitable length of chain fitted. This modification worked well but it still needed a tensioner to prevent the chain bouncing about. Once this is fitted the model will run quite happily from a 6V lead/acid battery. The motor and wiring is protected by a 1A thermal cutout incorporated into positive connection to the battery.
Plonk ‘n’ play
This model is another one of our simple models that can be transported easily with minimal set-up time. These models have come to be referred to in our household as ‘Plonk ‘n’ Play’ models and they are exactly that. We can take them to a show, set up in no time and not have to worry about them. Makes a real change from having to baby-sit the bigger models.