Absolute encoding using a limit switch as an index

I’ve have been working on a scoop system for my demo robot. It uses a small turntable like device constructed from a high strength 36 tooth gear supported by two layers of polycarbonate. As part of this design I wanted to use a quad encoder and also create some type of indexing system using a limit switch. This is what I came up with.


The motor is driving a 12 tooth gear that then drives the 36 tooth HS gear. A second 36 tooth standard gear transfers the motion to the quad encoder. A limit switch is mounted behind the encoder and is activated by a 3/8 screw (slightly shortened) in a shaft collar.


The 36 tooth HS gear has four 1/2 inch standoffs attached that are then connected to the scoop system, the scoop is able to rotate continuously through 360 deg. Software monitors the limit switch and sets the encoder to a known value when the limit switch is activated and the motion is clockwise.



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Great pictures as usual.
Are you aiming for the 1000 point autonomous?

Will the scoop be supported on the far side, or is the full weight of the scoop supported by a cantilevered axle from a ~1" support?

Metal or plastic pinion?

Do you expect the 36t axle hole torque limit to be a problem?

Have you checked the precision or repeatability of the limit switch?
Operating in only one direction (as you have planned) will help,
but pessimal reverses near the trigger-point could throw it off.

This setup uses 3 digital inputs, and uses interrupts for counting location.
Did you consider two potentiometers, modified for continuous rotation and mounted with offset zero locations? (2 analog inputs, no interrupts)

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Not with this one, the students are still working on that.

Here it is in context (not the final arm assembly). It uses a second drive on the other side but without the encoder and limit switch installed. It would have been easier to use an IME but that was not the point really, it’s just for fun and demonstration purposes.



Not really, the 36 tooth gear has four screws that rest on a couple of layers of polycarbonate. I generally don’t like a cantilevered setup but there’s no choice here to achieve what I wanted. The polycarbonate supports the gear so there is no bending of the axle and it is driven directly by the 12 tooth metal gear.

Not yet, there is some hysteresis going between on and off but in reality it will only be used once during calibration when the robot starts up.

We will see what happens.

This is not for a competition robot, I’m building one to use for tutorial purposes.

It currently has 5 IMEs (4 drive, 1 arm position)
1 gyro
1 accelerometer
3 line sensors
1 sonar
2 limit switches for arm position limits
1 quad encoder for the scoop
1 limit switch for the scoop.
and the ability to add pots on the arm system as needed.

The goal is to add all available sensors for programming demonstrations.

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