pic: Blue Lightning 578 presents KateGleasonOne

[CD47-Bot]

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[Scooter]

How do you actuate the telescoping action in the arm?

[Ayu]

are those suction cups on the end?

[KenWittlief]

one of our mechanical engineers came up with the idea for the telescoping arm - I dont think its ever been done on a FIRST robot before - there is a plastic chain inside it that only bends in one direction.

to extend the arm we push the chain into the bottom tube with a globe motor. The arm has three sections, and it reaches up 9 feet from the floor.

those are commercial suction cups on the end - the hose runs up inside the chain, and we use a commercial vacuum pump that is piston actuated, driven by a fisherprice motor (had to remove the original motor from the vacuum pump)

the arm raises and lowers with a van door motor on a half gear

the front roller pulls balls into a curve scoop that stays in contact and sends the balls straight up into the net (we might replace that with a clear box)

not seen is the Analog Devices gyro sensor that we use to generate a compass heading, for auton mode and to drive with closed loop steering
and we have contact switches on the front to tell when we hit something

and IR sensors on both sides with pinhole openings so we can tell when we are near the beacons and its time to turn towards them

BTW - this is a photo from a couple weeks ago - we have triwheels on the bot now.

[Scooter]

Which gyros are they? Are they the ADXRS150's or are they accelrometors (like the ADXL250's?

-Bill

[KenWittlief]

the ADXRS150EB (eval board version)

when you pull the joystick trigger and close the loop it goes where you point it like the whole bot is one of the hitec servos - its SOOOO nice to drive that way

even with our little 1 inch castors for front wheels :^)

[ngreen]

Looks really nice Ken and team.

Question: Can your suction grab a bonus ball? I know it is easier to knock it out but it would be cool if it could.

[KenWittlief]

good question - havent thought about that - we push the 10 point ball off with the suction cups, I guess we could try to capture it instead

theres 3 of them, they are spaced to get a solid grip on the 2X ball, but we could give that a try - thanks for the suggestion :^)

BTW - if you put them on your forhead and turn the pump on, it will give you a nice hickey - dont ask me how I know that

[Scooter]

Originally Posted by KenWittlief

the ADXRS150EB (eval board version)

when you pull the joystick trigger and close the loop it goes where you point it like the whole bot is one of the hitec servos - its SOOOO nice to drive that way

Yep...good times...I've had to use those on several occasions (I am working on an inertial autopilot unit for RC helis right now...have 3 sitting on my desk)....

What do you mean drives like a hitec servo? How so? Does the stick just give the controller a position command? Do you only use it for rotation, or do you use it for linear motion, too?

-Bill

[KenWittlief]

we closed the loop on steering last year by looking at the joystick1 X axis as a desired turn rate, and compairing it to the actual turn rate from the gyro sensor

it worked very well, esp keeping the bot straight going up the ramp- but the thing that didnt sit right with me was, when the commanded turn rate was equal to the actual turn rate, you ended up with no error signal - so there was no obvious way to command the motors to keep turning (if you were turning)

this year for auton mode, we create a compass heading with the yaw sensor by initializeing a variable to 32,000 - then we add the (sensor>>2 -127) to that on every loop of the code - so when the bot turns right, the accumulator goes down, when it turns left it goes up - and we use that as the relative actual heading of the robot

this let us use a straight PID loop to steer - if we want to be going straight we take the error from 32,000 and scale the error signal to be the X axis command into the one joystick equation

then it hit me one day. In normal mode, you can create another variable, desired heading, and init it to 32,000 as well - and when the driver moves the joystick add the x axis signal to the accumulating desired heading - and it will generate a desired (sorta like a projected heading) and we could compair the compass heading, and have the same kind of PID equations we used in auton mode

so in auton mode, the SW has preset desired headings, like go straight (32000) then turn left 80° (new desired heading is 29500) ect

and when the driver closes the loop it starts at 32000, clears the compass to 32000, and as he moves the stick left and right its changing the desired heading in realtime

all you have to do is get your gains right for your drivetrain - I think we are dividing the error signal by 8 - and limit the commands to the 8 bit range - and it works so nice

what I mean by steering like a hitec servo is, its like you connected a servo to the x axis of the joystick, thats how the robot turns - you nudge the stick slightly to the left and that desired heading starts accumulating to the left, and the robot slowly and precisely turns to the left

you hold the stick straight and push it forwards and the bot move forwards, dead straight.

[ngreen]

If if worked fast enough that could be a quick 80 pts. Watching practice round the bonus balls didn't get touched in 95% of the matches.

I want the job to reset the bonus ball.

[KenWittlief]

I dont think we would take the time to try to acquire other 10 point balls off the tees - think about it, it would take several seconds each to aquire them, and drop them into our hopper

in that amount of time we could get 5 or 6 5 point balls from the floor

from watching the games so far, it looks like being able to focus on the biggest bang for the buck, as it were, is whats going to win the game - I think for us that will be sweeping the 24 balls off the floor and getting them to the HPs - if there are 10 pointers scattered in there, thats great, but we will not go out of our flightpath to chase them.

[ngreen]

Yeah I wouldn't either. In my robot's case where we can only move basically one at a time I was looking at ways to maximize that potential, ie if you can move one 10 pt faster than 2 5 pts move the 10 pt. We can't do it. I didn't realize the bar was that close to the top of the bonus balls.

I've got better strategy ideas than that though. I keep those secret because they are more robot specific. They're easily countered enough so they can be used for a couple matches.

[shadowfox32]

Originally Posted by KenWittlief

theres 3 of them, they are spaced to get a solid grip on the 2X ball

do you have any pic of that which you woul be willing to share? It would be quite a sight too see, reminds me of basketball players holding the ball with just there hands.

[KenWittlief]

no I dont have any photos holding the 2X ball - but it has a death grip on it, and we can reach between the PVC pipes on the goals to get the 2X ball, so we dont have to reach over the top like lots of teams are having problems with using claws

Ive seen several teams on the webcasts with claws, when they place the ball on the goal, then open the claw, it pushes the pvc pipes out and the 2X ball falls off the goal.

Our arm was originally centered between the drivewheels, so when you held the 2x ball straight up and did a victory spin, the ball rotated in the air perfectly, like the earth spinning on its axis

but we had to move the arm forward a bit to match the C.G for hanging from the bar.