The Most Useless Machine EVER!

Step 2: How Does It Work?

Inside the box is an geared motor powered by double A batteries and two switches: a toggle switch on the top of the box and a micro-switch inside. That's it.

The switches are positioned to be limit switches for the motorized arm. The toggle causes the motor to reverse, while a micro-switch powers down the circuit when the arm finishes retracting back into the box.

When idle, the circuitry is fully powered down. The toggle is “Reverse” direction, and the micro-switch is being held in the off position by the servo arm.

Keep in mind the micro-switch is wired up so that it works completely opposite from a normal switch like you would find in a doorbell. By using the common pin and the normally closed pin the micro switch is “OFF” when it’s button is being pushed.

When a person turns the toggle switch to the forward position, it also provides power to the motor causing it to rotate the arm towards the toggle switch.

As the arm moves away from it's off position it releases the micro-switch providing the backup power needed for the motor to retract after the toggle switch is turned off.

When the toggle gets switched “OFF” it actually reverses the motor’s direction. The arm reverses direction returning towards it's 'OFF' position. When the arm runs into the micro-switch it stops.

The toggle switch needed is a Dual Pole, Dual Throw (DPDT) toggle switch. This type of switch is actually a pair of switches which operate together (Dual Pole) and both are On-On (Dual Throw).

Comments

[lukeD]

what if you are faster than the robot, and turn it off by yourself?

[Frivolous Engineering]

Same as if the machine switched it: the arm retracts back inside the box.

[sirfag]

thanks mate it works great exept i need a box

[Hack/Slash]

I just bought a nice little box over at Lowes. It's a kids "build it yourself" Jewelry Box. It only cost $8. It's precut pieces that you just tack together. May be a little tight with all the wires.....

[Pierce 93]

I just finished mine, and I have to say the box was the hardest part, well making it look good was hard anyway. (I made mine from scratch.) I think going SaskView's route might be better.

[KenCan]

Awesome!
How about:
- a rubber finger or glove to cover  the wooden arm?
- a doll's arm lashed to a shortened wooden arm?
- a dime store rabbit's foot?

please try and then post, somebody! I'm creeped out already

[Troyboyd]

 made me laugh so hard xD

[muskogee]

can i do this with a continuous rotation servo? i have one frome my boe bot

[Frivolous Engineering]

Yep! 

I was calling it a modified servo and didn't make it very clear.  I've made some changes to the 'ible to correct this.

[Football viking boy]

I thought this was soooooooo funny!

[judobrian]

Is there a secret to getting the geometry of the push arm down?  Its the last thing Im stuck on and my project is complete.  I've been creating 1/3 circles off my servo 'arm' but it never seems to quite do the job....  The one in the images above seem to be more of an "L" shape...  Thx

[TheMONKEY]

I messed with it for awhile till I figured out it was a resister to make my servo go down farther After that my first arm worked great

[Frivolous Engineering]

No secret, just a lot of fiddling around.

I've added a  'step 8'  to the 'ible.  Hope this helps!

[compukidmike]

Great instructable! I just built one for myself yesterday! I would like to point out for those of you who don't want to build the electronics portion or don't have the parts, it can be completely eliminated. I modified the servo for continuous rotation (by removing the internal stop) and then soldered the red and black wires directly to the motor inside the servo, bypassing the electronics inside. Now it's just a motor with a gearbox. This allows you to use just the two switches to make the motor change direction and stop. I attached a schematic of how I hooked it up(the resistor represents the motor).

Overall, great instructable! And thanks for the idea!

[compukidmike]

For those that have asked, here's a pic of the inside of the one I built. I also attached a video of it in action. The lid of my box is very thick, so It wouldn't open easily the way SaskView's did, so I left it opening the way it came. It still works just fine, as seen in the video.

[judobrian]

What degree of rotation does your servo get?  I notice when I run mine (not in the box yet, but just the circuit by hand) I only get ~90 degrees of travel.  Is this normal?

[tww1fa]

 90 degrees is considered the "standard" servo movement with control pulses between 1 and 2ms. However, most servos will actually handle about 120 degrees without a problem by going out of the 1-2ms range for the control pulses.

[judobrian]

Thanks for the reply!  Looks like my servo is working properly  I have another question, is there a trick to getting the white piece off here?  I'd like to remove it and attach my swing arm but undoing the screw doesn't do much.  Should the metal piece screw out or pull straight out?  I dont want to mess with it without knowing how to do it properly because its the most $$ piece of this project.  OR should I just trim down the white piece?  I need to align it better anyhow....  Thanks in advance

<img src="http://imgur.com/BDOKC.jpg" alt="Hosted by imgur.com" />

[tww1fa]

 Followup on my earlier reply - I didn't notice the link to the photo. From what I can see, both the metal bit and the white plastic gear thing should just pull off once you remove the screw in the middle. It might be somewhat tight but nothing else should be holding it in place unless someone glued it. Note that the shaft is probably 3/16" - 1/4" into the white thing, so there might be quite a bit of friction.

[judobrian]

yeah, sorry I didnt post the pic properly and couldnt find a way to edit my comment. 

Ok so if I pull the metal bit and the plastic gear straight out I should be fine.  Thanks!  I just wanted to make sure it wasnt attached to anything on the inside (obviously once I remove the screw holding it in).

Appreciate it!

[tww1fa]

 By "white piece" you mean the little arm with holes in it that fits on the servo shaft? To remove it it should be sufficient to remove the screw and pull. I don't know what "metal piece" you're referring to unless you're using a servo with a metal shaft... usually the servo shaft has teeth and the servo arm fits over the shaft and screws in place. You can pull the arm off, turn it a few degrees until the next tooth engages and push it back in. That's how you get coarse adjustment on the arm.

[patrickmccb]

 every thought of making a kit? if not i would love to :D

[compukidmike]

I thought about it, but I don't have the time or resources. Go for it!

[patrickmccb]

here is the DPDT switch  http://search.digikey.com/scripts/DkSearch/dksus.dll
here is the servo www.hobbypartz.com/kahaoubrmo14.html

[compukidmike]

Very nice! I like how fast it is!

[patrickmccb]

 thanks alot for the picture and schematic of yours. First time i modified a servo but it worked out ok :D.

[Frivolous Engineering]

Sweet!

[HHL]

Isn't the third switch more useless than the machine itself?
A power switch for a machine whose sole job is to switch of itself.
Or am I missing something here?

lol

[compukidmike]

There are only two switches. S1 in the schematic is a DPDT(Double Pole Double Throw) so in effect, it is two switches in one, allowing you to switch two things with one lever.

The other switch is so that the servo stops when it retracts.

[wwslubs]

Hey, I have good soldering skills but I'm not very smart when it comes down to electronics, especially schematics.  Would you mind explianing where and what I need to solder/connect or provide a link that I can learn how to read this?  

[compukidmike]

Here's a link showing what all the different schematic symbols are...
http://www.kpsec.freeuk.com/symbol.htm

I don't want to just give you a link, so I'll try to explain it. I've attached a photo of the insides of mine showing how I connected everything. Keep in mind that the battery or servo connections may need to be reversed if the servo goes the wrong way when you try it.

If that doesn't help, let me know and I'll try to explain it better.

[tmcalhoun]

Hello i have a question on the SPDT switch. Is there a wire going to the middle of it and then to where?

[compukidmike]

I pulled the switch out of something else, so it already had wires attached. The middle wire isn't attached to anything.

[tmcalhoun]

Great. I finally received my servo in the mail and put my box together. It works Awesome. Thanks for the easy work around of the electronics. Now what else to do with a servo. I bought 2.

[patrickmccb]

 made it and works :P, thanks for the schematic.

[wwslubs]

First, are the lines shown correctly pointing to where you soldered them?  Two, for the dpdt switch does it matter if the switch is reversed, or due I have to solder them to specific pins?  Three, I am modifying a servo for the motor, do I have to resolder the wires directly to the motor and can I just leave them the way they are?  Four, do I just not use the white/yellow wire from the servo after modifying it now?

Thanks for all the help and I hope this helps other people with the same questions.

[compukidmike]

1) The lines are pointing to where I soldered them. 2) Most DPDT switches should have the pins in the same place, so it should work as shown. And yes, it does matter which pins(the only change you could make would be swapping all three wires from right to left side of the switch). The only thing that can go wrong is that the motor goes the wrong way when you flip the switch. The easiest way to fix this is to reverse the connections to the servo, or to the batteries (not both). 3) Yes, resolder the wires directly to the motor and don't hook the white wire to anything. 4) You can even take it out if you want.

I apologize if this still doesn't make sense. I'm not that great at explaining things. If there's anything else I can help with let me know.

[wwslubs]

Where should I solder the wires to the motor then? Also will a hitec hs-311 work if i modify it?

[compukidmike]

When you take out the 4 screws, the bottom of the servo will come off, revealing the circuit board. The motor leads are usually soldered directly to the board, and are probably the biggest things on the board. They will normally be on the opposite side of the servo from where the wires come in. You need to solder the wires to these two motor pins.

As for the HS-311, here's a site that shows which hitec servos are easy/difficult to modify... http://www.servocity.com/html/rotation_modification_difficul.html

If I get a chance I will open mine up and take a pic for you. Or if you have already opened yours, you can send me a pic and I will show you where to solder the wires.

[wwslubs]

Im using your technique with the modified servo