How do you aim your shooter?

[Salik Syed]

just wondering how are all you other teams plannign to aim your ball shooting mechanism?

[sanddrag]

We have a custom turntable driven by sprocket, chain, and globe motor. It rides on steel and teflon balls. It has about 160 degrees of rotation. On top of the turntable is a tilt mechanism actuated by the van door motor and driven by sprocket and chain. It can go from 0 to 45 degrees.

Of course, all this is just theoretical. We have not even started building it yet.

[Donut]

For control of the rotator, we will be using a joystick to rotate back and forth manually, or will allow the camera to rotate it to face the goal (we have a switch that allows us to change between manual and automatic control). For the speed (we are adjusting speed not angle), we will use a series of 4 push buttons to change a desired speed by small or large intervals for manual control, and the camera will once again change the speed based on automatic control.

Mechanically, the speed control requires nothing extra than what we already had (one of the big CIM motors driving one flywheel), the rotator control will be done using a van door (or window) motor, driven by either a chain-sprocket connection or a belt drive (not sure which).

[Pat234]

We are using the camera linked to a globe motor to control the tilt through a 30 degree range of motion and the pan angle will be controlled through the drive train to line the robot up accordingly. These both will be controlled through the camera while on offense however the drivers will have some capability to override the camera controls.

[kawelch]

Luck and prayer

[Jared Russell]

Complete auto aim.

[Sachiel7]

We plan to allow the possibility of manual control, but we are focusing on having fully automated aiming utilizing the camera, to shoot on the fly.

[Spindash54]

Aim? Who needs to aim? We just hit the fire button and relax...

[bbehnke]

for our angle adjustment we are using a cam (off-set center circle) to move a plate up and own and for yaw we are using a lazy suzan design and a automatic aim from the camera. the only thing manual is when you want to shoot the balls into the goal and winning the game

[Salik Syed]

So it seems many teams ARE going the automated aiming route...

[Madison]

Originally Posted by bbehnke

for our angle adjustment we are using a cam (off-set center circle) to move a plate up and own and for yaw we are using a lazy suzan design and a automatic aim from the camera. the only thing manual is when you want to shoot the balls into the goal and winning the game

How do you compensate for the cams varying radius as it moves? The rate at which your pitch changes is never constant.

[Alan Anderson]

Originally Posted by M. Krass

How do you compensate for the cams varying radius as it moves? The rate at which your pitch changes is never constant.

Many things are nonlinear in this system. Camera tilt angle is not proportional to distance. Distance is not proportional to the required pitch angle. Pitch angle can be, but is not necessarily, proportional to the cam position.

Fortunately, the nonlinearities are all irrelevant if you forego detailed computation and just make a simple lookup table that converts the measured camera tilt directly to the desired pitch adjustment. Creating that table is as easy as moving the robot forward and backwards, measuring the camera tilt, and manually tweaking the pitch adjustment until it works the way you want.

[DjAlamose]

Originally Posted by Alan Anderson

Many things are nonlinear in this system. Camera tilt angle is not proportional to distance. Distance is not proportional to the required pitch angle. Pitch angle can be, but is not necessarily, proportional to the cam position.

I don't know where you got this from but good luck then.

We have our robot fully automated for just about everything. All you need are the equations for speed, angle, height, and distance. Once you have those the RC can control the robot fully based on where it is. In reality you dont need the camera if your robot can keep track of where it is on the field at all times (much easier to use cmucam).

But we plan on haveing 3 different modes for our shooter, fire, off, and store. Can't give details other than 270 degrees, 4 balls per second, and 2 shooting angles. Pneumatics and window motors will be used for aiming the shooter as well as the small cim motors which will provide the speed for throwing the ball, vary that and you can send the ball just about anywhere.

[Jared Russell]

Originally Posted by DjAlamose

I don't know where you got this from but good luck then.

We have our robot fully automated for just about everything. All you need are the equations for speed, angle, height, and distance. Once you have those the RC can control the robot fully based on where it is. In reality you dont need the camera if your robot can keep track of where it is on the field at all times (much easier to use cmucam).

But we plan on haveing 3 different modes for our shooter, fire, off, and store. Can't give details other than 270 degrees, 4 balls per second, and 2 shooting angles. Pneumatics and window motors will be used for aiming the shooter as well as the small cim motors which will provide the speed for throwing the ball, vary that and you can send the ball just about anywhere.

Finding a reliable ball kinematics equation that takes into account spin and air resistance is VERY hard to do on the RC (but not impossible). And that's not even taking into account the trig needed for angle adjustments and converting the x and y coordinates of the target seen by the camera to angles. Try doing the math yourself - in order to get a full-fidelity representation of what your camera sees, you not only need to convert between pixel offset and angle (which is fairly easy), but also take into account that the 2D space represented by the camera's data feedback is in actuality a representation of 3D space. To combine all of these factors together, you have to use some matrix math.

It is MUCH simpler to use look-up tables, and in addition they are always going to be faster. They do all the dirty work of physics for you.

Our team's solution is to slave camera pan to the turret (turret rotation controlled by a feedback loop) and use a constant camera tilt. Then, a look up table for flywheel speed is indexed by the y pixel offset of the target. With the right choice of camera tilt angle and lens, you can see the goal from pretty much anywhere that you could realistically shoot from. It really doesn't get much simpler than that.

[Parker]

[quote=sanddrag] On top of the turntable is a tilt mechanism actuated by the van door motor and driven by sprocket and chain. It can go from 0 to 45 degrees.

You might run into problems shooting close to the center goal with only 0-45 degrees of rotation. If you want to aim at the lower goal just turn down the speed of your shooter.