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Allan, as promised a couple of photos of the tool clamps.
I opened up the mounting hole with a 2mm drill and used a 2mm slotted CSK screw (because that's what I had) and a standard 2mm nut. You may notice that I slightly countersunk the mounting hole. Like this you can use the original holes in the hull roof or you can drill 2mm holes if you intend to shift things around.
You can also use 1.6mm CSK screws and avoid drilling the clamps to 2mm but then if you use the original holes you may need to use a spacer under the nut.

Hope this helps.

Vince

Vince

It very much does help.

Many Thanks Allan

I have been slowly assembling the recoil mechanism to see how it goes together. Had a little problem with the mounting of the cam to the motor. The hole in the cam where the motor shaft passes through was under-size. Opened up the hole and reamed it 6mm.
Then noticed that the hole for the grub screw in the bush that attaches the cam to the motor was only partially tapped. Quickly fixed that also.
Otherwise it all came together nicely and it seems that one can assemble it out of the turret and then when tested and calibrated fit it in the turret with four bolts which is a good thing.

The only thing that got me stumped (for now) is how to adjust the micro-switches. There's nothing in the manual which tells me who to do it. Good thing I made a note when I was doing the bench test of how the micro-switches affect the motor:

• Both switches undepressed - motor runs

• Both switches depressed - motor stops

• One switch depressed and the other one undepressed - motor runs

I think I can figure it out if I sleep on it.

Vince

Well, after sleeping on it, I figured out the micro-switch logic and went to the workshop to test my theory.

I still had to fit the micro-switches and soon encountered a snag when trying to do that. The micro-switch close to the servo is sitting too low. The servo arm cannot activate the micro-switch.
Temporarily fixed that by stacking nuts on the screw. Later on I will make proper spacers instead.
Eventually I got things working -- sort off. At least the theory of how the micro-switches work was correct but the problem is I can't get the motor to stop where I want it. Spent the whole day adjusting the micro-switch which stops the motor but always seems to overshoot. I have tested both micro-switches with a multimeter and they work perfectly when you hear the "click".

I don't know what else to do. I am really frustrated. Has anybody actually made this recoil unit work??

Vince

vince not my strong point electrics, the metal tabs on the micro switches can be bent in to a more precise on-off position, does this help you. some forum member with more advice will come on, regards simon manning.

Would the servo arm and switch align if the servo was installed from the rear, rather than fed through the hole ?

I don't have one of these new recoils, so can't comment, but on the animatronics for the Mark IV< some servos were installed through the holes from the front and some were bolted to the back of the plate. You do need to shave off the central buttress so that the servo sits flat against the plate.

Adrian.

If nobody has a better solution, you could put a button magnet on the cam and have it move the arm. That way, the angular position of the cam would trigger the switch, rather than the slowly changing amplitude of the cam at the end of the turn, which I suspect does not provide enough accuracy.

Hi Vince

Yes, I came across all the problems with the recoil that you’re experiencing! Have PM’d you with my opinion of this recoil system!!

Thank you gents for the replies and comments.

the metal tabs on the micro switches can be bent in to a more precise on-off position

Simon done that but next time I will be a bit more drastic. As it is I decided to get myself some new micro-switches.

Would the servo arm and switch align if the servo was installed from the rear, rather than fed through the hole ?

Adrian, it is installed from the rear.

You do need to shave off the central buttress so that the servo sits flat against the plate.

Done that as it is also mentioned in the manual.

you could put a button magnet on the cam and have it move the arm

Christoffer, that is an interesting idea. I have to investigate how feasable it is to incorporate with the current mechanism.

Thanks Phil for your comments. At least I can console myself that it's not me doing something wrong.

The micro-switch which is causing all my problems is not the one close to the servo but the other one which should switch off the motor when the barrel is fully extended (cam at the apex). I have noticed that if I activate the micro-switch manually I can stop the motor wherever I want but if I let the mechanism activate the switch it overshoots the apex and starts another recoil cycle whatever adjustment I make.

So my suspicion is that either the switch is mechanically defective (reason why I'm getting new ones) or the position of the switch is not correct.

Vince

Could you post a picture of the troublesome switch please ?

Adrian.

Adrian, it's not much to see as the switch is covered by another part of the mechanism.
Vince

Vince Cutajar wrote: ↑

Tue Mar 26, 2019 9:17 pm

The micro-switch which is causing all my problems is not the one close to the servo but the other one which should switch off the motor when the barrel is fully extended (cam at the apex). I have noticed that if I activate the micro-switch manually I can stop the motor wherever I want but if I let the mechanism activate the switch it overshoots the apex and starts another recoil cycle whatever adjustment I make.

So my suspicion is that either the switch is mechanically defective (reason why I'm getting new ones) or the position of the switch is not correct.

The switch is probably working correctly. The challenge is that the motor will carry on for a fraction of a second once the switch is tripped. That is why you will need to bend the metal tabs that trigger the micro switch . Getting the point right is trial and error, but that is why the limit switches have metal tabs that can be bent.

With regards to the other limit switch (the one next to the servo), as you have probably already done Vince, if the two are not aligned then use 1 or 2 washers as spacers.

Kian

Yesterday spent another whole day playing with the recoil mechanism with no success. Noticed also that the voltage between a fully charged battery and a half discharged battery changes the place where the cam stops. Basically at the end of the day I gave up and started thinking of Plan B.

Today I had some spare time and half-heartedly I gave it another try with the same results. Then I had one of those moments (a rare occurrence). What if I reduce the tension of the spring? Added a piece of wire to the spring to reduce the tension.
OMG! Started getting repeatable successes. It's starting to look promising.

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I will continue testing it for the next couple of days to make sure it is not a fluke. After that I can drill a line of holes close to the spring rear anchor point so that I can get various spring tension settings.

I will still continue working on Plan B though as a backup. It is a strong Nema 17 stepper motor controlled by an Arduino and programmed to turn one revolution at a time. Problem is that I'm no Arduino expert.

Vince

The problem with stepper motors is that they're energised all the time, to hold position, so:

1) they can get very hot if run for long periods
2) they waste battery capacity continuously, rather than just when in operation like a normal motor.

I looked into using a stepper motor to operate the elevation on a Sherman - with a view to stabilisation - but the continual current draw was a killer.

The gearing in the current motor will be helping to hold the cam in position. If you use a stepper motor and are able to disable the power to it when it is not in use, the motor will have no braking effect, so driving the tank around may dislodge the cam, making the barrel retract.

Adrian.

Points taken Adrian.

The cam has a notch when the barrel is in the fully extended position. I can maybe introduce an RC switch to remove power from the stepper when not in use. Just a thought.

As it is the spring mod is still looking good. Fingers crossed.

Vince