Minibot switches and soft landings

[WarehouseCrew]

I have two questions that I would appreciate help with. What specific electrical switch is working to turn the minibot off after the top pole sensor is successfully tripped (but not turning off without triggering sensor)? We have one push button switch from Home Depot that takes about 7 pounds of pressure to turn it off. The fuse may trip before this works.

Secondly, how do you make the minibot come down the pole to a "soft landing"? I've read that some teams are using reduced power on the motors to provide a braking action after the top sensors is reached. How is that done (eg. my switches are only on and off, no 1/2 power option) and is there a risk of burning up the motors?

Thanks.

[wevets]

This circuit (click on image to see it enlarged):
10461
(sorry for the bluriness) will make the robot come down the pole slowly. The robot takes off up the pole when S1 is closed. When S2, a SPDT switch, is thrown by contact with the top of the pole, it takes the battery out of the circut and connects the motors so that they act as generators into a short circuit load. (Note that the motors are not internally shorted, a bad thing.) This provides "dynamic braking" as the robot comes down the pole gently by gravity. It works quite nicely.
When taking the robot off the pole, open S1 then reset S2 to arm the minibot for the next run.

[Mr V]

I can't help you if your switch will or will not trigger the sensor before turning the machine off w/o seeing your design. Much of the problems reported with minibots not triggering are with extremely fast and light minibots that do not keep the trigger held long enough for the system to register it.

I can tell you how to make it fall back down the pole slowly. Use a "3-way" "common household sw" or a 3 terminal "limit sw" to short the motor terminals together making the motor into a electric brake.

To wire either you connect the COM, common, or odd colored terminal to the terminal on the motor you want to be (+). One of the other terminals goes to B(+) and the remaining other terminal goes to B(-) and the motor terminals you want to be (-) when in the "on" position.

In one position the sw will connect B(+) to motor (+) and in the other it will connect motor (+) to motor (-) making it act as an electric brake.

If you are using 2 switches then place the "on" sw between B(+) and the off/brake sw.

[WarehouseCrew]

Thanks for the help. We will try this.

[Andrew Bates]

You don't necessarily need to make your minibot come down slowly. Our minibot hit the top, turned off, and then free falled down to hit either our deployer or the platform. Our minbot hasn't had any issues with this.

[boomergeek]

Team 241 uses a high friction hinged flap over the top of the kit-of-parts limit switch. When the hinged flap hits the plate, it absorbs the energy in the friction on the hinge. The bottom of the flap then strikes the limit switch and the minibot starts down the pole in brake mode. The small spring in the limit switch is not strong enough to push the high friction hinged flap up. After the minibot comes down you manually have to put the flap back up and off the limit switch to be ready for the next race.

Our hinged flap is just a piece of angled aluminum connected to the minibot with a screw and TWO nuts as the hinge. The first nut is tightened until the hinge gives the right amount of friction, the second nut is tightened while securely holding the first nut in place. This will keep it from loosening.
The flap can also have a stop under it to assure the limit switch does not absorb the full blow of the tower plate. The stop can just be a well placed screw and nut.

[DonRotolo]

What specific electrical switch is working to turn the minibot off after the top pole sensor is successfully tripped (but not turning off without triggering sensor)?
I saw team 75's minobot with a KoP microswitch limit switch, where they bent the lever into a "C" or 'hook' shape so when it is pressed down, it 'latches' under the body of the switch and keeps the switch "off". Since it's a SPDT switch, they use the NO contact to short out the motors as described above.

[JB987]

Team 241 uses a high friction hinged flap over the top of the kit-of-parts limit switch. When the hinged flap hits the plate, it absorbs the energy in the friction on the hinge. The bottom of the flap then strikes the limit switch and the minibot starts down the pole in brake mode. The small spring in the limit switch is not strong enough to push the high friction hinged flap up. After the minibot comes down you manually have to put the flap back up and off the limit switch to be ready for the next race.

Our hinged flap is just a piece of angled aluminum connected to the minibot with a screw and TWO nuts as the hinge. The first nut is tightened until the hinge gives the right amount of friction, the second nut is tightened while securely holding the first nut in place. This will keep it from loosening.
The flap can also have a stop under it to assure the limit switch does not absorb the full blow of the tower plate. The stop can just be a well placed screw and nut.

How did you turn 1 limit switch basically into a 3 way usually used to produce the break mode?

[Al Skierkiewicz]

I know it is hard to read this in the rules for the minibot, but you can modify the light switch so that a plunger mechanism turns the switch off when it reaches the top. You can also use a lever to increase the pressure placed on the switch.

[Mr V]

How did you turn 1 limit switch basically into a 3 way usually used to produce the break mode?

The KoP limit switches are in essence identical to a "3 way" sw. How to make it so the off position if brake is detailed in post 2 and 3 of this thread.

[boomergeek]

The KoP limit switches are in essence identical to a "3 way" sw. How to make it so the off position if brake is detailed in post 2 and 3 of this thread.

Here's a marked up diagram...
(I always tell students to use a continuity meter (ohm meter with a beep mode) and flip the switch on and off to make sure they know which terminal is the common before wiring anything- sometimes its easy to get confused by the markings).

[kws4000]

UNTESTED: We have applyed a 'brain bucket' to our minibot...lime green...got us the imagery award at GVSU/West Michigan comp last week...Amen. Thats all I can say.

[Vermeulen]

You don't necessarily need to make your minibot come down slowly. Our minibot hit the top, turned off, and then free falled down to hit either our deployer or the platform. Our minbot hasn't had any issues with this.

We also did this. We had a small latex tubing cushion on the bottom, but removed it due to deployer issues. Our minibot never had any problems with this. On a semi-related note, you don't want to have the minibot contact the deployer if at all possible. I've seen red cards being given because of this.

[Brandon Holley]

We also did this. We had a small latex tubing cushion on the bottom, but removed it due to deployer issues. Our minibot never had any problems with this. On a semi-related note, you don't want to have the minibot contact the deployer if at all possible. I've seen red cards being given because of this.

Can you provide a rule that would indicate this is a red card/yellow card/penalty?

-Brando

[cgmv123]

<G22> HOSTBOTS may not contact their ALLIANCE‟S MINIBOT while any part of it is above the DEPLOYMENT LINE.

[Andrew Bates]

<G22> HOSTBOTS may not contact their ALLIANCE‟S MINIBOT while any part of it is above the DEPLOYMENT LINE.

At least in our setup, when the minibot can touch the deployment, the minibot is not above the deployment line.

[cgmv123]

That should be legal.

[Vermeulen]

@Brando

Hm, I guess I was misreading rule G22 as not being able to contact the hostbot after any part crosses the deployment line, and not as long as any part is over the deployment line. In that case, I don't know what our partner's red card was given for during that match, we just assumed it was a G22 violation.

[boomergeek]

@Brando

Hm, I guess I was misreading rule G22 as not being able to contact the hostbot after any part crosses the deployment line, and not as long as any part is over the deployment line. In that case, I don't know what our partner's red card was given for during that match, we just assumed it was a G22 violation.

If a deployer swings the minibot down, like a drawbridge, and as it comes down if any portion of the minibot is above the deployment line and simultaneously within the vertical cylinder of the tower and in contact with the deployer- independent of whether it is in contact with the pole, I think the referees will rule it in violation.

Here's a whole thread on it...

http://www.chiefdelphi.com/forums/showthread.php?t=92381&highlight=deployment+cylinder

[waitwhat?]

I have two questions that I would appreciate help with. What specific electrical switch is working to turn the minibot off after the top pole sensor is successfully tripped (but not turning off without triggering sensor)? We have one push button switch from Home Depot that takes about 7 pounds of pressure to turn it off. The fuse may trip before this works.

Secondly, how do you make the minibot come down the pole to a "soft landing"? I've read that some teams are using reduced power on the motors to provide a braking action after the top sensors is reached. How is that done (eg. my switches are only on and off, no 1/2 power option) and is there a risk of burning up the motors?

Thanks.


Here is a little tip. McMaster Carr sells "Manual Reset limit switch" Part # 7336K51. Works like a charm. This will also allow you to create this circuit with EASE.

This is exactly how our minibot is wired....

http://img191.imageshack.us/img191/9329/minibotwiring.jpg

[Ed Law]

Here is a little tip. McMaster Carr sells "Manual Reset limit switch" Part # 7336K51. Works like a charm. This will also allow you to create this circuit with EASE.

This is exactly how our minibot is wired....

http://img191.imageshack.us/img191/9329/minibotwiring.jpg

Is that considered a legal switch according to the rules and all the Q&A?

[Vikesrock]

Is that considered a legal switch according to the rules and all the Q&A?

Yep, it is marketed as a "limit switch" so it is allowed.

[Al Skierkiewicz]

Is that considered a legal switch according to the rules and all the Q&A?
Yes it is. The McMaster catalog lists it as a "limit switch" and it is the application for which it is most used.

[TheCommander]

We did something a little different.

I took the Tetrix switch that is legal, took out the dremel, put on a cutting wheel and removed the on half of the toggle so that it is flush when the switch is in the off position. Now it only toggles to the off side, but can be reset to the on position.

We mounted the switch at the top of the mini-bot and when it hits the trigger it toggles and turns off the mini-bot. It can be mounted by cutting out a rectangle that is 1 inch by 1/2 inch and pressing the switch in. We designed the mini-bot a little more on the rugged side, so when gravity pulls it back down the pole it can withstand the impact.

The added bonus is that it mounts easily, is sturdy, looks nice, and the red on the switch lets you know the mini-bot is armed.

This just seemed like the simplest solution for our design and application.

[krudeboy51]

wouldn't the highlighted area on this pic cause the fuse to blow?

[11douglash]

What we did is find a 4 way light switch (i believe). Basically, it was a switch that flipped polarities. Then there was another switch that triggered when the robot hit the pole.

Our minibot went up, flipped the polarity switching switch, powered down, hit the bottom, and then, due to the mechanical way the wheels were rotating, fell off, and thus broke the switch that kept it powered, and turned off.

[penguinfrk]

This was the circuit diagram for our minibot.

10548

When we short the motors, the current generated when backdriving will go through the circuit again the opposite direction. The result is a fairly slow terminal velocity when it falls.

Hope that helped.

[sumginazu]

I saw team 75's minobot with a KoP microswitch limit switch, where they bent the lever into a "C" or 'hook' shape so when it is pressed down, it 'latches' under the body of the switch and keeps the switch "off". Since it's a SPDT switch, they use the NO contact to short out the motors as described above.

I did the same thing with a simple momentary switch when designing the minibot my team used. The latch worked perfectly, but we had to be careful in ensuring that the switch consistently contacted the top plate - it didn't during one practice run, which ended with a burnt out motor.
Our minibot usually stayed at the top after it had finished its run because it did not weigh enough to backdrive the motors, which ended up being okay. Unfortunately, the minibot's momentum occasionally caused it to fall off the pole once it hit the top plate, and twice it hit the ground hard at the end of a match. We needed to repair it both times. As long as your minibot has a reliable method of attaching to the pole and it does not "free fall" after it hits the top, it should survive a trip back down. You should certainly test it to make sure, though.