The Official Armortek Forum - World leader in one sixth scale metal kits

Mark designed and installed a recoil system in the prototype Sherman I'm rebuilding, using a simple servo and linkage system.

The linkage was very bent and the servo gears stripped when I bought the tank but I don't know if that is evidence of self destruction or because the barrel is the obvious point by which to lift the turret - something to bear in mind with any recoil system

I've just picked up a suitable servo so will be able to rebuild it once that arrives. Until I get it fitted I don't know what the stroke will be - does anyone know the correct stroke for a 75mm Sherman

To replicate the dual speed of the recoil, I will be using a PIC microcontroller to step the servo as quickly as possible on the shot but ease it back for the return. I know this is quite simple in theory but I have yet to see how the system behaves in practice

Adrian.

Adrian, That sounds very promising. Will you let us know how it turns out?

Alan, I don't have a video of the recoil mechanism i have in my Tiger. Looking at the Tamiya system I am sure it would be quite easy to make a larger unit with the most basi of machines if one could source the gears. The other proble is that the motor must run just long enough to complete one turn of the large gear to reset the mechanism. I suspect that the brain for this is the Tamiya DMD unit, so it may be possible to design in some micro switches to stop the motor, rather along the lines of car windscreen wipers that always stop in the stowed position.

Hi guys,

The Tamiya recoil can work without the DMD/MF electronics.
The start/stop of the movement is controlled by a micro switch. This microswitch is bridged for 0,5 second to start the motor, at the end of the recoil movement the micro switch breaks the circuit again and the motor stops.
However, without the DMD/MF there is no synchronisation with the sound and flash unit.

I just watched the video of Adrian's Sherman recoil unit. The action looks perfect. http://www.youtube.com/watch?v=pQSiuzfaQz0

The setup is elegant and not too complicated, its also fairly compact. I wonder if this could be duplicated in the Tiger?

Alan

Check this out: http://www.thedecoy.org/1/6th/plan/buil ... 100298.jpg

Might be adaptable to the 5kg. Although that was more than I thought...

If this approach doesn't cut it, I would (will... ) use a two-spring approach. The gun would be controlled with a flip switch. When flipping the switch in one direction, the gun would be "loaded". That is, the main spring would be pre-tensioned with a reasonably powerful electric motor. Flipping the switch to the other direction would "fire" the gun by releasing the main spring and sending the gun backwards with great speed. At the rear turning point, the main spring would be disconnected from the gun and the much softer return spring would return it to the original position. All this moderated by a gas damper (like in the kitchen drawers mentioned previously) with an appropriate stiffness. Maybe like those used for station wagon rear lifting doors. It'll be a fun project!

Cheers,
/Chris

I have just recently replaced my Futaba recoil servo with a much more powerful version, which is a S3306 with 24kg of torque. This retails @ £39.99 This comes with an extra large output arm which gives much more movement.
As you can see I use a separate receiver which enables me to use a 6volt battery.





The correct barrel length when extended.392mm Thanks to Roland for this data.

I have just got into Picaxe programming and it has to be the simplest way to do it. I'm using a 2 RX system in my tank with the turret having it's own power and rx so there are no leads between the hull and turret. I am also using a modified version of Thomas's rx control on the benedini system.

This means I can sniff the RX in the turret on the channel which RX control is operating. Using a Picaxe servo board, available as a kit, I can connect the rx control channel and sense the pulse width so that it activates the servo when the main gun button is actived. A very simple program which winds the servo full swing at full speed then goes full travel in the oposite direction in slow mo. I haven't got it all sorted yet but, it has been tried and the principle is sound.

The beauty is that if it doesn't do exactly what you want, change the program until it does.

Yup, the PICAXE is ideal for these sorts of control projects

The Sherman recoil took a few iterations but seems to be running smoothly now.

And with the new SM layout boards, the RC plugs are about the largest part of the circuit

Adrian.