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Unread 11-05-2018, 12:46 PM
Ophbalance Ophbalance is offline
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Autonomous - How do you know the "thing" in intake

I've been tasked with mentoring our team from "woo! We crossed the line!" to "woo! We did the thing! And took that thing to the other thing! And then we flung the thing!".

I'm curious how folks determine that you've captured the "thing". For last years game that was power cube. I grasp that you can use NavX to figure out where the things are and program some routes to them. I grasp how you can use vision to pinpoint the thing and drive to it. But how do you know when you actually have the thing where it needs to be in the intake system?

I've had some thoughts, and what seems likely is to:
  • Something like a garage door sensor. Break the beam and you've got the thing
  • Momentary switch. If the thing has made contact, well it's where it needs to be
  • Measure the load on the motors doing the intake. If the load is at whatever value for XX amount of time, we know that the thing has been onboarded

Anyone care to share what they did in previous years? We' like team 6004 to approach the season with a successful preseason, and I think this would be a strong approach to getting our budding engineers into the gear.
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Unread 11-05-2018, 12:52 PM
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Re: Autonomous - How do you know the "thing" in intake

I find that this limit switch, which has been in the KoP for many years, is extremely useful for detecting game objects. The long arm, adjustable angle, and durability are key. With the power cubes, for example, if you had a "standard" roller claw, you could place one of these in the back, or have one on each side and it would trigger when the cube was captured. Personally, I like the idea of using two or more in many situations - it gives you the chance to teach the students about series or parallel wiring, and you can often increase the dependability of the system that way.
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Unread 11-05-2018, 12:55 PM
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Re: Autonomous - How do you know the "thing" in intake

On 340 this year, the back of our intake was a polycarb plate with small rectangular cutouts for 2 IR sensors.

They were pretty fragile so having a backup was nice. We 3d printed mounts that were attached to the polycarb by double sided tape (and later in the season, lots of electrical tape...).
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Unread 11-05-2018, 01:00 PM
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Re: Autonomous - How do you know the "thing" in intake

Quote:
Originally Posted by Ophbalance View Post
I've had some thoughts, and what seems likely is to:
  • Something like a garage door sensor. Break the beam and you've got the thing
  • Momentary switch. If the thing has made contact, well it's where it needs to be
  • Measure the load on the motors doing the intake. If the load is at whatever value for XX amount of time, we know that the thing has been onboarded
These ideas are exactly what we've come to use every year. While a limit switch is always a great object, we've become very happy with the use of distance sensors and other (as you put it) "break the beam and you've got the thing" sensing tools.
I would also deff agree that the use of your motor control feedback is something that few teams utilize, but is of great use when wanting to know what is truly happening to your robot, not just if your intake is holding an object.
Honestly, the best method for ideas from my code team has come from ideas that they learned while in FLL all those years ago. And if your students didn't have that experience, bring it to them with the use of possibly having a mindstorm kit for the simple purpose of gaining understanding of how one can work with things in a simple, yet very high level thinking.

Cheers!
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Unread 11-05-2018, 02:05 PM
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Re: Autonomous - How do you know the "thing" in intake

We used two photoelectric sensors on our intake to detect if a cube was in or not. When picking up the second and third cubes for autonomous, we only continued with the routine when the sensors said the cube was in. This can be seen in our match videos (the LEDs on the robot blink when the sensors detect a cube -- this also helped the driver know that he had a cube when the robot was on the other side.)

A picture of the intake with the two sensors can be found here: http://prntscr.com/leqdsh
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Unread 11-05-2018, 02:26 PM
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Re: Autonomous - How do you know the "thing" in intake

1296 has used VEX bump sensors (aka limit switches) in previous years. They are cheap and easy to program, but mounting bump plates on to them can be a challenge depending on your design.
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Unread 11-05-2018, 02:33 PM
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Re: Autonomous - How do you know the "thing" in intake

We used a beam break sensor to detect cubes in our intake for the purpose of triggering LED strips as a signal for the drivers. I don't believe we used the sensors in autonomous, but we had code written to do so.

I believe 254 had similar sensors on their intake this year.
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Unread 11-05-2018, 03:44 PM
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Re: Autonomous - How do you know the "thing" in intake

548 prototyped using the 873M analog ultrasonic sensor from FIRST Choice. We ended up not using it, but it would have worked on the cubes.
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Unread 11-05-2018, 04:02 PM
Dan Katzuv Dan Katzuv is offline
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Re: Autonomous - How do you know the "thing" in intake

We used a proximity sensor at the back of our Gripper system.
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Unread 11-05-2018, 04:16 PM
Peter Salisbury Peter Salisbury is offline
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Re: Autonomous - How do you know the "thing" in intake

Quote:
Originally Posted by Prateek M View Post
We used two photoelectric sensors on our intake to detect if a cube was in or not. When picking up the second and third cubes for autonomous, we only continued with the routine when the sensors said the cube was in. This can be seen in our match videos (the LEDs on the robot blink when the sensors detect a cube -- this also helped the driver know that he had a cube when the robot was on the other side.)

A picture of the intake with the two sensors can be found here: http://prntscr.com/leqdsh
These seem really nice because they look easier to mount than the IR sensor mentioned by Justin, while accomplishing the same non-contact sensing. Though I bet they are more expensive. Would you be able to share where you bought them?
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Unread 11-05-2018, 04:27 PM
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Re: Autonomous - How do you know the "thing" in intake

I think for many teams this process doesn't require any game-piece sensors.

Every year, the vast majority of teams that can meaningfully score in autonomous only score one game piece, and usually they start holding the game piece. Such an auto doesn't need a sensor to detect a game piece since you place it in your robot before the match.

I think for most teams who pick up a second game piece in autonomous, the game piece usually starts in a known location, so you can just make a guess and assume you have the piece. It's very possible to write a two or even three cube auto without know whether you've picked up the second or third cube.

This isn't to say you shouldn't have a sensor, just that you don't need to have a sensor to be successful.
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Unread 11-05-2018, 04:28 PM
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Re: Autonomous - How do you know the "thing" in intake

On 423 we used this beam break sensor from Adafruit a few times. They were easy to mount, easy to wire, cheap, shipped quickly, and didn't fail us. I would definitely recommend.

I've also heard good things about this distance sensor, but don't have any personal experience with it.
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Unread 11-05-2018, 04:39 PM
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Re: Autonomous - How do you know the "thing" in intake

Yup, those are the ways, and I've used them all.

Sharp makes some great IR proximity and range finding sensors, available at a number of sites, including pololu. 3946 used the shortest range "binary" one to detect gears for STEAMworks, and a longer range one to detect boulders in STRONGHOLD. Ultrasonic sensors which are capable of resolving the short ranges needed to detect when you have a game piece are much more expensive than IR ones; on the other hand, for longer ranges and larger objects (how far away is the wall), inexpensive ultrasonic sensors are viable.

We had IR "interruption" sensors both of two pieces to detect various game pieces, and a single piece to detect a "curb feeler" in Recycle Rush.

Limit switches for totes in Recycle Rush, and motor current in POWER UP.

All in all, my favorites are the IR rangefinder and one-piece interrupts, because they are relatively easy to install in a place where they won't be struck by the game piece or other robots or other parts of your own robot (e.g. inside or behind a structural member) and are less subject to misalignment than the two piece version, and much less than limit switches. With motor current, you have to code around motor startup spikes, through requiring a spike to last a certain duration, or ramping the voltage, or something similar.
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Last edited by GeeTwo : 11-05-2018 at 04:42 PM.
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Unread 11-05-2018, 05:34 PM
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Re: Autonomous - How do you know the "thing" in intake

Quote:
Originally Posted by Jon Stratis View Post
I find that this limit switch, which has been in the KoP for many years, is extremely useful for detecting game objects. The long arm, adjustable angle, and durability are key. With the power cubes, for example, if you had a "standard" roller claw, you could place one of these in the back, or have one on each side and it would trigger when the cube was captured. Personally, I like the idea of using two or more in many situations - it gives you the chance to teach the students about series or parallel wiring, and you can often increase the dependability of the system that way.
+1 for that limit switch; it was great when 4901 used it in 2014. If I'm doing a mechanical limit switch, it's that one. Though I'd probably want to try to use a Talon SRX's current sensing function first these days.
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Unread 11-05-2018, 05:59 PM
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Re: Autonomous - How do you know the "thing" in intake

Ribbon Switches from these wonderful folks are some of my recently-discovered favorite sensing devices for intakes. It's like a long limit switch. Useful if you don't know what orientation your thing comes in at, you just need to know when the first part of it touches somewhere.

They can make custom lengths, or (at least in our experience) were pretty good about sending samples of standard lengths.
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