Using tape to trigger sensors


#1

my team is trying to find a way to set a point on the launcher that it can detect, allowing it to fire and pull back to that point by pressing one button. one idea we had was placing black tape along the bottom of the slider and a strip of white tape at the desired point. we would use a line sensor to detect the white tape and pull back to that point. however, we’re not sure if this would count as using non-vex parts. if it does, is there an alternative that is legal? thanks


#2

Yes, you should be allowed to do that, Rule R7 a.


#3

Actually, <R7>a now says the following: “Any material strictly used as a color filter or a color marker for a VEX Light Sensor or Vision Sensor.”

I don’t know if a Line Follower would qualify under <R7>a, so if you get a nitpicky inspector, you might get in trouble. (Somebody should ask in the official Q&A, but then be prepared to wait 3 weeks for an answer. LOL.)

However, I’ve seen kids use pieces of white plastic to do exactly what the OP is asking about. And that would surely be allowed under <R7>e.


#4

you could use white and black zipties or antislip mat too.


#5

Or just a potentiometer to track the position of the catapult axle.


#6

think they’re using a puncher, but this could work as well. you may have to gear down the potentiometer so the shaft doesn’t exceed the potentiometer’s rangle.


#7

Couldn’t the puncher hit one of the limit switch arms bent into the correct position while its retracting and this input would stop the motor? There would need to be enough travel in the arm to absorb any slop in the system so you didn’t inadvertently refire the puncher but that may work


#8

but then you’d need a way to prevent it from sliding back from the rubber bands. either a brake motor hold, or just use a a ratchet


#9

You could use the white rope, and the black anti-slip mat.


#10

sorry I didn’t reply right away, but thank you so much for the answers!!! it will really help us knowing we can do that


#11

If it starts in the same position every time at the start of the match, they could also just use an encoder. Slightly larger than a vex potentiometer but still smaller than the space it would require to gear it down.


#12

we are actually currently using an IME. however, if we disconnect during the match it will permanently fire the rest of the match due to the value resetting, or won’t be able to fire at all. the main issue we currently face is actually a lack of sensors. we have no bump sensors, limit switches, or sonars to use. hence asking about a light sensor.
I’m hoping the light sensor will work, but mounting it may be tricky, since the puncher we use is very similar to the one in the tutorial by 574C


#13

Yeah, true. I didn’t think of that.

Seems odd but the girls have had zero issues with the puncher on their robot. They are using a 32 tooth gear on the rack and two torque motors. Theres lots of rubber bands on the unit, but it draws back full speed and takes just over a second to pull back an shoot. This has been an advantage for them as they don’t take so long to fire as others. I see lots of robots that have a much longer puncher and they take forever to fire. We have not had any motor or PTC problems all season. With the puncher at least.


#14

We’ve used a limit switch that, when triggered, stops the catapult. When you press a button it cycles (shoots, and pulls back down to the same spot. It seems to work well for us.
-4004Y YNot!


#15

V5 or Cortex based robots?


#16

We’re currently using Cortex, but a good friend of mine uses the same system for V5


#17

How are you locking the puncher in the retracted position? Just motor power or do you have a ratchet of some kind?


#18

We have a ratchet gear, but it currently isn’t working like we would prefer. We have the legacy motors set to 10 power once the limit switch is pressed. This is plenty to hold the catapult in the retracted position. We have, I think, 10-15 strong rubber bands on the catapult, if this tells you how much power it has when it shoots


#19

@10-15!!! GEEZ! Shooting to the next field!:grin:

I’ll have to mention this to the girls. There have been times they were lining up to shoot, and although our pull back is quick, this would make shooting a bit quicker. We may have to try this before US open. They’ll have to pull some ultrasonics off (aren’t using them right now anyway) to get another input.


#20

We actually put an IME on one of the 2 cortex puncher motors and just made a loop that when you pushed a button it resets to 0 and runs to x then goes to motor hold 10 power (plus they have a ratchet on to back that up so the motor doesn’t potentially burn out). Works well and simple - no extra sensors required! It’s not perfect and will eventually need reset when using extensively (we have a separate button that runs while pushed to reset and as a backup) but does well for the length of the match.

We tried a limit switch but the puncher kept eventually knocking the metal arm off - could have been resolved, but IME ended up working just fine so we went with it.