75mm Gun Stabilisation

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Adrian Harris
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75mm Gun Stabilisation

Post by Adrian Harris » Sat Apr 20, 2019 3:22 pm

Since the M3 was announced, I knew I wanted to build a gun stabilisation system for the 75mm.

This is the first attempt. It's pretty crude but works as a proof of concept.

75mm Stab.jpg

https://youtu.be/mqdcfCmrEyI


I need to speed up the response, but get into stability issues with the current system when I try. I think this because the Arduino UNO I'm using isn't quick enough. I've ordered a 32bit ARM Cortex board as an upgrade, to see if that has the power to keep the servo in sync with the gyro.

The final code will either:

1) Use a transmitter stick to control the elevation, and when there has been no input for 1 second, the stabilisation will kick in.
2) Use a transmitter switch to enable and disable the stabilisation.

Not sure which yet.

I'm also looking at ways to create a recoil system for the 37mm gun. Until the Motion Pack is released, I won't know exactly how it needs to interface but I think it should be relatively easy to incorporate, using what I have already manufactured.

BTW, this is a Male Sponson from the Mark IV, which I have assumed will be controlled in a similar manner to the M3 75mm sponson.

Adrian.
R.I.P Margaret I.L.Y

Vince Cutajar
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Re: 75mm Gun Stabilisation

Post by Vince Cutajar » Sat Apr 20, 2019 3:41 pm

Very interesting Adrian. It seems both of us have been playing with the Arduino this week. My project is for the recoil mechanism and it is looking very promising.

Did you put any "delay" commands in the code because I think that can slow down the running of the programme a lot?

Vince

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Re: 75mm Gun Stabilisation

Post by Adrian Harris » Sat Apr 20, 2019 3:55 pm

No, there are no programmed delays in the code. I haven't really delved into it too deep yet, I wanted to the basic premise working first.

Are you going to try and control the recoil with timing, rather than relying on the switches ?

I wonder if it needs an opto or hall effect transducer to detect the relative position of the spiral, as that could be used to get the motor to switch off at exactly the same point every time, rather than using the barrel position.

Adrian.
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Re: 75mm Gun Stabilisation

Post by Stephen White » Sat Apr 20, 2019 4:01 pm

Adrian, great to you your prototype for the Chieftain stab......

Have you attempted to mass balance the barrel? That would help although if you add recoil, the mass balance will change. Are you using a "6-axis' IMU? I found that rate gyros alone were ineffective. Ideally, a setup would include rate gyros, accelerometers and GPS so that the barrel can reference a specific point in space.

The AlexMos controller boards for camera gimbals look promising and I believe he does a 64bit version.

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Re: 75mm Gun Stabilisation

Post by Adrian Harris » Sat Apr 20, 2019 4:15 pm

:lol: :lol: :lol:

I've not checked the balance of the system but the Mark IV Male has quite a short barrel and quite a lot of gubbins at the back, so it won't be any where near as bad as the Chietain with a metre of barrel hanging over the pivot point.

It is a 6DOF board but I'm only using one of the "freedoms" as the system I'm replicating only had gyro stab, not full GPS etc. Adding the accelerometer to the mix might assist with the stability of the stabilisation but I need to get my head round how to incorporate that.

Looks like Chieftain will be a challenge but it's been done in 1/16th so no reason we can't get there with 1/6th. Just need bigger motors :lol: :lol:

Adrian.
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Re: 75mm Gun Stabilisation

Post by Vince Cutajar » Sat Apr 20, 2019 4:20 pm

I'm using a stepper motor and an A4988 driver which I can put to "sleep" when the stepper is not in use. Stepper turns 360 degrees and goes to sleep. If it stops where I want it to stop then I don't need any holding current. At the moment, I was thinking of using the microswitch which is triggered by the servo. I would have liked to use the signal that goes to the servo to trigger the Arduino but have no idea what sort of signal is going to the servo.

More research required.

Vince

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Re: 75mm Gun Stabilisation

Post by Adrian Harris » Sat Apr 20, 2019 4:33 pm

Vince, you have a PM :D

Adrian.
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Re: 75mm Gun Stabilisation

Post by Jeffrey Goff » Sat Apr 20, 2019 9:00 pm

Why not use a gimbal stabiliser, as used on drone cameras,
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Re: 75mm Gun Stabilisation

Post by Adrian Harris » Sat Apr 20, 2019 10:14 pm

Jeff, they tend to use brushless motors mounted at the axes of rotation, which would entail a complete redesign of the gun mount.

The assumption is that this gun will use a servo for elevation, so this system should be a drop in.

Adrian.
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