Minibot Control

[E2207]

Our team was thinking our using a limit switch to activate the minibot as it reaches the pole. Our minibot looks like a claw, so when the switch is triggered when the minibot ias its pushed onto the pole, it closes the claw by actuating the 2 servos to close in. it would also start up the 2 motors we have. when the minibot gets to the top, another limit switch will be activated and shutoff the motors (while still providing power to hold the servos against the pole and send the minibot back down. Is it feasible to wire thses all together without a tetrix motor controller and servo controller, and nxt brick? How? could you possible show a wiring diagram?

[EricH]

I think it's quite possible.

Run two parallel circuits. Each has one locking switch to detect the pole, and the motor power circuit has some form of locking switch to detect the target.

Your locking circuit would be one switch (say, a light switch) to indicate the pole plus power to the servos. Ideally, there would be a second switch to indicate closing of the clamp and shut off the servos so they don't damage themselves.

Your motor power circuit would be a similar circuit to the locking one, but the target sensor would be on top, and would need to lock to the "motor off" position to prevent climbing back up.

You could also use a single switch for pole detection with both circuits going through it.

[E2207]

Introduction to circutry 101----me. I know what your talking about, it seems possible form what your saying. I just need to visualize it.

[EricH]

I've attached a quick sketch. The left-side target detector would be normally closed--it would open if the target were hit, and stay open. The right-side jaw closed would be normally closed--if the jaws are closed, it opens. The central switch is the pole detector.

[E2207]

Originally Posted by EricH

I've attached a quick sketch. The left-side target detector would be normally closed--it would open if the target were hit, and stay open. The right-side jaw closed would be normally closed--if the jaws are closed, it opens. The central switch is the pole detector.

Which means that although both jaws are open in order to attach the minibot to the pole, but the circuitry is wired so that when one jaw closes and activates the switch, it closes both?

[EricH]

Originally Posted by E2207

Which means that although both jaws are open in order to attach the minibot to the pole, but the circuitry is wired so that when one jaw closes and activates the switch, it closes both?

I was thinking that the controls would be like this: When the pole is detected, the main power (both motors and jaws) turns on. (You could hold the minibot down until jaws close.) When the jaws close, their power is cut off (servos can hold their position pretty well; no sense in stripping gears). Should the jaws open again, the switch (say, a standard limit switch) will turn the power back on and the servos will close the jaws more firmly.

Meanwhile, the motors are pushing the minibot up the pole. When the minibot hits the top, another switch cuts the power to that circuit and then latches down (how you do this part is up to your imagination), keeping power to the motors off. The minibot slides back down.

[klmx30302]

We are using a "latching" limit switch to prevent the minibot from climbing during retrieval. once it hits the top it must me manually reset so when the minibot hits the top it cannot move anymore.

[Joe Ross]

Originally Posted by EricH

Your locking circuit would be one switch (say, a light switch) to indicate the pole plus power to the servos. Ideally, there would be a second switch to indicate closing of the clamp and shut off the servos so they don't damage themselves.

I think you will have trouble running a servo with just switches.

[Chris is me]

It's certainly an interesting problem to get a minibot to power off when a top mounted limit switch hits the target - wtih enough delay to actually depress the target's button and not immediately powering back on when it slips down after shutoff.

[EricH]

Originally Posted by Joe Ross

I think you will have trouble running a servo with just switches.

I'm just going with the OP's desire to avoid the NXT. It'd be a lot simpler if that side of the circuit was something other than servos.

[E2207]

Our team was thinking of using a plunger mechanism to close the jaws, instead of the servos.