[FTC]: Do Servo's reset during start up?

[jbbjjbt]

I have submitted a question to the official Q and A for clarification under the section Robot Inspection. I think based on question 6 the servos can be powered on before the match.

I agree that the "glitch" occurs when the servos are powered on. My experience is it always goes to or toward the center position. So maybe glitch is not the correct term.

I think if the servos are not continuously updated during the disable period between when you start the autonomous program on the NXT and when the FMS start the autonomous game period, that the servo will power down and the glitch will occur when the servos get power even if you set all the positions to zero. This is my experience.

[PhilBot]

Originally Posted by jbbjjbt

I have submitted a question to the official Q and A for clarification under the section Robot Inspection. I think based on question 6 the servos can be powered on before the match.

I agree that the "glitch" occurs when the servos are powered on. My experience is it always goes to or toward the center position. So maybe glitch is not the correct term.

I think if the servos are not continuously updated during the disable period between when you start the autonomous program on the NXT and when the FMS start the autonomous game period, that the servo will power down and the glitch will occur when the servos get power even if you set all the positions to zero. This is my experience.

I feel the need to clarify a few things here...

When I say "Power on the servos" I mean "Turn ON the 12V with the power switch". You have to do this before the match starts otherwise your robot will not move (as the same 12V runs the DC motors). This is when the "glitch" occurs.

Next, you say "if the servos are not continuously updated during the disable period..". OK, there really is no IF here. The program templates clearly show that the servos must be disabled if the program is getting a disabled state from the FMS (which IS the case between starting your autonomous program, and the start of the actual 30 second auto period). You can verify this yourself by downloading the FMS and trying it yourself

To disable the servos, you call the "FTC Move Servo" VI and set the "Enabled?" input to FALSE. This does not actually power down the servo, but it does stop sending pulses to it, which has the effect of shutting down the control loop inside the actual servo. This will cause the servo to droop if it's under load from your manipulator.

When the match begins, the FMS send an "Enable" state to the NXT which is interpreted by YOUR program to mean "Start the autonomous sequence". At this point you can start sending commands to the servo with the "Enaled? set to true.

Now, if the first position you send is a 0 then the the servo will probably jump to the middle, since "0" isn't an actual position. A position of Zero means go to the last commanded position (which in this case has never been done.).

Bottom line: only use Zero if you want to reissue a prior command (like in a refresh loop that doesn't know what the last command was).

I'd recommend you figure out where you want the servo to be when you start your autonomus sequence and send that position as soon as you get enabled. If you do that, there will be no "glitch" or any other unwanted movement at the start of teleop.

In our case, we assume that the servos that run our puck-picker-up will have drooped to the ground, so when auto is enabled we pick them up and keep them out of the way during auto.

[jbbjjbt]

Again I'm hoping for more clarification, but from the official Q & A Section 9 Robot Inspection Question 6:

A:

It is possible to have your robot "initialize" servos prior to the enable that signals the start of the autonomousportion of the match. It is as straight-forward as inserting the code prior to waiting for the enable signal.

So I incorrectly said we're powering the servo in the disable section of the code. We're powering the servo (to keep it in one position) in the section of the autonomous code where the bluetooth command is read. This seems legal to me based on the above Q & A. We haven't changed the disable section.

But during the beginning of the match before the autonomous is enabled essentially we are turning on the servo where the blutooth is read and the disabled code section is turning off the servos many times a second. Hence it does jiggle but stays where we need it.

[PhilBot]

Originally Posted by jbbjjbt

A:

It is possible to have your robot "initialize" servos prior to the enable that signals the start of the autonomousportion of the match. It is as straight-forward as inserting the code prior to waiting for the enable signal.[/color]

But during the beginning of the match before the autonomous is enabled essentially we are turning on the servo where the blutooth is read and the disabled code section is turning off the servos many times a second. Hence it does jiggle but stays where we need it.

The original Q & A implied (to me) that you could set the servo position ONCE before starting to wait for the enable. Thereby truly being "disabled" before the match. But that's just my interpretation.

Note that the Q & A was written well before the new templates were created. I hardly think that rapidly enabling and disabling the servo is what they had in mind when they created the new template..... All that jittering is just going to draw attention to the fact that you are driving the servo while the robot is meant to be disabled. Any "field safety" gained by disabling the servos is lost by you reenabling them right away.

If you really feel like arguing on the day, it I guess it's up to you, because there don't seem to be any clear rulings regarding software other than "Use the templates". It may just fall on you to convince the inspector that your robot is "safe".