AP_Gripper: Servo Gipper enhancments

[lthall]

This PR improves the functionality of the servo gripper.

1. uses the servo trim to define the initial conditions during startup
2. applies the "regrab" variable to provide an automatic closing after a set time
3. shortens the delay
4. uses the update gripper code to be consistent with EPM

[lthall]

AutoClose

[rmackay9]

as discussed on the call we should add an AUTOCLOSE parameter instead of overloading. The name is just a suggestion.

[IamPete1]

Looks like the state tracking is not updated, did this work?

[IamPete1]

Sorry to be annoying. I think the re-grab function should be moved up to the front end. Currently it only works for the servo backend.

The re-grab also gives the wrong messages in some cases because the state has already changed out sync with a switch. For example if I have released using a switch is see "Gripper load releasing" then after the regrab timeout I see "Gripper load grabbing". Then I want to open the gripper again, so I move the switch and see "Gripper load grabbing" again even though the gripper is already grabbed.

Happy to help on the re-work. I also think we can save some flash by removing code duplicated in both backends.

[lthall]

I have added functionality to deal with the messages but I think the rework is beyond the scope of this PR. I would suggest we get this in and then rework it in a separate PR. I don't immediately see how to do regrab in the front end or if it is even appropriate for the other type of gripper.

[rmackay9]

I'm happy if @peterbarker and @IamPete1 are happy..

[andrefreitas97]

Hi @lthall! Shouldn't the gripper come back to neutral position if i move the RC channel to the middle position? This is not happening at the moment i am testing my gripper servo :(

[lthall]

Hi @andrefreitas97. The gripper is open or closed. The only time it looks at the neutral PWM setting is when it first starts up.

[andrefreitas97]

@lthall oh I understand! The reason i asked that question is that i am developing a gripper that deploys two objects with one servo. If the servo is in the middle position it grabs both objects. If the servo is moved to one side object 1 is released and object 2 is still grabbed. If the servo is moved to the other side it releases object 2 and grabs object 1. Thus I would need the servo to stay in the neutral position while my rc switch is in the middle and to move to the sides when I select high or low position in the rc switch.

Can you give me some directions to which files in the code should I work in order to make this happen? Thanks

[lthall]

This is ideal case for LUA scripts.

[andrefreitas97]

Oh ok I will investigate that. Thank you for your help!