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Post by swanrail on Oct 12, 2007 17:39:02 GMT 1
I have now modified my servo, includes microswitches and tested OK. This picture shows the microswitches fitted. With the barbette: The under side of the rotating gun carriage: Guns ahead: and the guns to port: The guns now move about 180 degrees in total before hitting the microswitches. This coyuld be expanded by judicious placing of the microswithches. The guns will stop at any angle in range when the joystick is centred. One channel is used for the forward guns and another for the aft guns. This is necessary so that all four guns can point in the same direction, not possible with single channel control. I have stayed with the mechanical lifting gear, an electronic one would be better as the guns could then be raised lowered in any position, but have no idea on how to do this. Has anyone else??? Now ready as soon as Hachette reach the turret section to fit the gear permanently.
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Post by markus on Oct 12, 2007 18:18:24 GMT 1
maybe something like this ?? or as speed controlled version:
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Post by swanrail on Oct 12, 2007 19:21:44 GMT 1
Hi Markus, the speed control of the servo works pewrfectly, and it stops whereever I want it! The neutral position will be dodgy with two servos, so am thinking of fitting a variable resistor to tweak the neutral position so that both servos line up with each other. (else one turret will turn while the other is stationary.) Have thought of your idea to lift the guns before, but rejected it as there is no space under or over the revolving disk deep enough to fit a mini servo. (max space on mine only 4mm.)
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Post by markus on Oct 12, 2007 20:36:33 GMT 1
Hi Markus, the speed control of the servo works pewrfectly, and it stops whereever I want it! The neutral position will be dodgy with two servos, so am thinking of fitting a variable resistor to tweak the neutral position so that both servos line up with each other. (else one turret will turn while the other is stationary.) Have thought of your idea to lift the guns before, but rejected it as there is no space under or over the revolving disk deep enough to fit a mini servo. (max space on mine only 4mm.) you can bring all servos into the same (exact) neutral position if you replace the potentiometer by 2 resistors with 2,7kilo ohms each. these have to be wired parallel to the switch contacts. not enough space? maybe a mini servo fits between both gun barrels ? maybe one gun barrel mounted directly on the servo's axis ? cheers markus
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Post by swanrail on Oct 12, 2007 21:16:53 GMT 1
Unfortunately, I had already fitted the resistors instead of the pot, but due to very slight tolerance differences, the neutral point is still slighlty off. To cure this, I placed a 100k pot across each arm, and tweaked them one at a time until I found true neutral, then removed the pot not affected, leaving the tweaked one in service. Measuring my servo, I needed to fit 4.7k resistors to simulate the original pot. (miniature resistors fit easily with room to spare). There is still not enough room to mount even the smallest of servos anywhere on the gun mounting disk, max space ANYWHERE is 13mm by 13mm by 4mm!!! (my mini servos measure 22mm by 28mm (this includes the arm) by 11mm)
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Post by markus on Oct 13, 2007 12:28:59 GMT 1
what do you think, swan ?
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Post by swanrail on Oct 13, 2007 20:14:35 GMT 1
Yes that look good Markus, how is the other side of the servo set up with the gun barrel?
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Post by markus on Oct 13, 2007 20:58:19 GMT 1
...how is the other side of the servo set up with the gun barrel? not at all - one barrel is fixed on the servo axis, the other barrel is simply fixed on the 'motorized barrel' markus
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Post by markus on Oct 14, 2007 13:05:53 GMT 1
....Measuring my servo, I needed to fit 4.7k resistors to simulate the original pot... normally potentiometers in servos have a TOTAL resistance of 4,7 kilo ohms. if you want to simulate this, you'll need 4 resistors with 4,7 kilo ohms each using resistors with 1% tolerance will provide a simulated poteintiometer exactly in centered position
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Post by swanrail on Oct 14, 2007 17:24:14 GMT 1
hI Markus, the pots in my servos are actually 10k ohms!!! I used 1% tolerance resistors but there is still a very slight discepancy, which to match two servos in different gun turrets needs to be tuned out. The actual value of the resistors is not critical, as it is the actual voltage in the centre which is fed to the comparator, and this requires very little current. Anywhere between 2.7k and 10k per resistor should do, as long as they are matched. Ref the lifting servo, the guns need to be 12.4mm apart, my servo, which is the smallest I have been able to find, measures 20mm!!! A possibility is to strip a servo completely, attach the second gear wheel to the gun barrel and drive it from the motor gear. The motor can then be fitted inbetween the barrels (my motor is 13mm overall) and the electronics glued to the base section. There will be a need to fit limiters, one at 0 degrees and the other at 30 degrees, and as there is no space for microswitches a simple pin and plate system at each end would suffice. Fancy having a go???
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Post by markus on Oct 14, 2007 19:09:17 GMT 1
hI Markus, 1. ...Ref the lifting servo, the guns need to be 12.4mm apart, my servo, which is the smallest I have been able to find, measures 20mm!!!... 2. ...a simple pin and plate system at each end would suffice... hi don! 1. this is not a problem if we drive only one of the barrels and glue both barrels together (see previous pics) 2. yep, that's what i call an idea !! think it's worth having a go, but i'll wait for amati's turret parts before i start motorizing them markus
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Post by Mark on Oct 15, 2007 2:18:25 GMT 1
As the song goes, In the year 2525........
I like Markus' sugestion about cutting the breech off one barrel, and pivoting off the servo arm, but you might need to support the far side pivot point to make sure the two barrels lift evenly.
Any thoughts about what to use as the material that seals the gap between the barrel and the turret body ?
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Post by swanrail on Oct 15, 2007 17:13:06 GMT 1
Hi Mark, think that I will wait a while to see what turns up: such as the barrels, how long, can they be pivoted? (they might be short and just stick into the turret top!!), what material are used in the turrets, wood, metal, a combination of both??? I am currently concentrating on getting the turning operation suitable to fit the model. Not sure that Markus idea of using a servo to lift will work until I know how much clearance we have under the turret top, etc etc. I am hoping to shortly publish the models dimensions interpolated from the diagrams in the Anatomy book, it looks very tight at the moment. Now at a scale of 100:1, no problems!!!! (except it would not fit in my workshop)
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Post by swanrail on Oct 16, 2007 22:04:23 GMT 1
The mini servos came from : www.servoshop.co.uk, and were bought as a pack of four. (HiTec HS-55) I originally bought some microswitches from Maplin, but although they were the smallest they do. they were still too big. Then found a pack of 50 microswitches for sale on e-bay, which are the ones in my pictures. The cases meaure 12mm by 8mm by 4mm.
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