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Servo Motor Help
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Servo Motor Help

by Iceman086 on Tue Mar 30, 2010 5:00 am

Hello all.

I am currently in an Art Design class in college and I am looking at making a set of Steampunk Goggles that have Iris Aperture's built into them. What I am looking at doing is motorizing the iris's so that they can be opened and closed at the push of a button (the button would be attached to the goggles somewhere). Currently I am looking at using this little servo motor (http://www.hobbypartz.com/topromisesg9.html) that I just picked up to control the opening and closing motions. Due to the lack of space on the goggles I am not going to be using a circuit board if i can help it. A servo motor seems like it would be the right choice for this project because the iris only needs to move a small amount in order to open and close.

The three lines on the servo are the Positive- Red, Brown- Negative and Signal- Orange

My Questions:

1) Can the servo run using only a momentary switch (I.E. a simple push button from Radio Shack)?

1.1)If so, do I just need to attach the orange Signal line into the button or do i need a specific kind of button?
1.2)Or would I need to have a switch that controlled the direction (toggle switch) and one that controlled power going to the motor (a momentary switch)?

2) When the signal line no longer is receiving a signal does the motor return to a neutral, "centered" state or will it remain at the angle that it stopped at?

I will try and have a drafting of the Iris posted in the next day or so when I can edit it a little bit to make it more web-friendly as well as a picture or three of what this all will be installed in.

Any help will be greatly appreciated! I can also give plenty of other details for any questions that anyone has for me about the project.

Thank you all very much!
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Re: Servo Motor Help

by adafruit_support_bill on Tue Mar 30, 2010 6:34 am

1) Can the servo run using only a momentary switch (I.E. a simple push button from Radio Shack)?


No, the servo requires a pulse-train signal for control. This is actually pretty easy to do with an Arduino http://www.adafruit.com/index.php?main_page=product_info&cPath=17&products_id=50
Or even one of the smaller clones like a Boarduino. http://www.adafruit.com/index.php?main_page=index&cPath=19. Servo control commands come standard with the Arduino library. You could hook your button to one of the Arduino digital inputs and program whatever servo action you want.

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Re: Servo Motor Help

by Iceman086 on Tue Mar 30, 2010 9:46 am

Thank you for replying so quickly!

Humm... Well I might be able to work one of the DC Boarduino's into the mix but I have never worked with any kind of circuit board before. Is there a tutorial floating around some where?

Also, would there be another solution, like using the circuit board from an mini RC Car like this one?

http://www.radioshack.com/pwr/product-reviews/Toys-Games/Radio-controlled/XMODS-custom-RC/XMODS-Custom-RC/p/3348289-XMODS-Nissan-GTR-RC-Car-Kit.html

I have one currently and have taken it apart a few times to look at its innards. It has 2 motors in it and has 2 lines that run to each (red and blue) but I don't know if one is for high speed and one is for low speed or if one is positive and one is negative.

Thank you for your help so far! I really appreciate it!
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Re: Servo Motor Help

by adafruit_support_bill on Tue Mar 30, 2010 11:27 am

LadyAda has a tutorial for running the servo via the motorshield:
http://www.ladyada.net/make/mshield/use.html

But you can also do it with just an arduino (or any variation such as the boarduino) :
http://itp.nyu.edu/physcomp/Labs/Servo

The car electronics won't help. Those are plain DC motors, not servos.

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Re: Servo Motor Help

by Iceman086 on Tue Mar 30, 2010 1:30 pm

A DC DC Boardunio would probably work the best due to my size restrictions on this project because I might be able to hide the board in the strapping for the goggles. My biggest concern in all of this is how close all of this is going to be to the eyes and face. It is one reason I was trying to avoid using a board all together (aside from time/space constraints).

It looks like the Tutorial you linked should still work for the DC Boarduino, I think. I have only had a chance to glance over it.

If this doesn't work, would you need a board to control a stepper motor as well? Something like the Small Stepper Motor?

My only other question is, how tall is the DC Boarduino once the parts are attached? I have the length and width dimensions but I didnt see a height (most likely because its an open source board with interchangeable parts). I am trying to mock things up as best I can in order to avoid issues later on.

Thank you very much for your help!

P.S. The board can also be programed to turn on and off several LED's if I added a switch to do so, right?
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Re: Servo Motor Help

by adafruit_support_bill on Tue Mar 30, 2010 2:55 pm

The tutorials will work for the DC BoArduino also.

A stepper motor would require a motor shield and a full-size Arduino like the Duemilanove. The shield is designed to stack on top of the Arduino and the pins would not line up with a BoArduino. I think you are better off with a servo for this application anyhow.

I don't have a BoArduino handy, but I'd estimate that it is about 1" tall as pictured. You would not need the pins on the bottom, so you could save some height by eliminating them.

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Re: Servo Motor Help

by mtbf0 on Wed Mar 31, 2010 11:38 pm

tallest thing on the dc boarduino is the voltage regulator, which you may not need. how do you plan to power your device? if you don't use the regulator, you also get to eliminate a couple of tallish caps and the power jack. next is the processor itself which can be lowered by soldering it directly to the board, which you may regret if you should let the smake out of it.

for power, i'd suggest a pocket full of minty boost.

don't know where blinking leds fit into the steampunk aesthetic, but, sure, an arduino can blink a passle of them.
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Re: Servo Motor Help

by Iceman086 on Wed Apr 07, 2010 5:44 am

Its been a while since I last updated and I wanted to do so. I recieved my servo's, metal, circuit board and cable. As for the power source of the whole thing I was hoping to use 3V watch batteries due to their slender size. I would put a few of them in series to power the whole thing. I wanted to make a quick video though of the Lighting Instrument Iris that I am modeling mine after. So, here it is!

http://www.youtube.com/watch?v=jAWElOSiMoM

I also wanted to post a few pictures of the goggle piece that the servo and smaller version of the Iris will be fitting into, once I have it made.

Image

This is actually made of PVC pipe fittings that I have doctored up pretty good. I cut the fittings down on a bandsaw and then used a heat gun to soften and bend it a bit to get the shape that it became. I had to cut notches in it to allow the piece to bend in the correct direction. I filled in the notches with a small wedge shaped piece of PVC and some Bondo Car Body Filler. The Tape represents where I will be putting a brass jacket over the PVC and possibly doing some acid etching and inking some into the pattern that would be on it.

Image

Image

Image

You can see in this picture where the servo would sit inside of the goggle. It will be walled off in order to keep moving parts, like those in the servo, separated from the wearer's face.

Image

Image

This is a reference picture that helped me to understand just how the Iris would work. From there I dismantled the one in the video that I linked above and scaled down the design so that it would fit into the PVC fittings.

Image

This is a picture of the draftings that I did in ACAD for the iris. I printed them off and created a working model in paper. Right now I am using the new Parametrics feature of ACAD 2010 to model the iris from the above picture. The idea behind using the Parametrics is that it will allow me to see what degree of movement will be required in order to fully open and close the iris. The servo's that I have move 60 degrees, so thats the number that I have to shoot for.

I will begin assembling the circuit board sometime this weekend. The only thing that I am not sure of is if it is possible to not install the breadboard pins on the board so that it will have a slimer profile. I have the same question about the DC power unit. Can I not solder it in and instead solder in a switch that would control the flow of power to the board? If I did that what would need to go where?

Thank you for all of the help and opinions so far!
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Re: Servo Motor Help

by adafruit_support_bill on Wed Apr 07, 2010 6:25 am

I'm assuming that the circuit board you are talking about is a DC BoArduino. You can leave off the connectors and pin headers and solder any connecting wires directly to the appropriate holes.

If you can put together a 5v battery pack, you can leave off that big voltage regulator and the filter capacitors too. Your power switch can go anywhere between the battery and the board.

I don't know if you will get much runtime out of watch batteries. A servo will probably suck them dry in no time. CR-123 cells pack a lot of power in a fairly small size. If you find you need to go to an external pack, you can still get cloth-covered wire for the proper effect. http://www.radiodaze.com/wire-cloth_covered.htm

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Re: Servo Motor Help

by Iceman086 on Wed Apr 07, 2010 12:17 pm

Yes, I am using the DC BoArduino. Would I just need to find the Positive and Negative lines and skip the ground when I connect the battery line to it?

I also looked up the CR-123 batteries and saw a few things about them exploding. Sadly that makes it a bit of an issue IMO. I know that given the application there is a very low possibility of it happening but even so. I also don't need it to work for very long even if I only get about 20 minutes worth of work out of the batteries thats all that I really need for the time being. I can always upgrade the batteries later.

The servos require 3.5-8.4 V with a stall out voltage of 4.8 V. So I am guessing that if I used 2, 3V batteries batteries in series that it would be enough to power it, even for a short time. I could use 3 or 4 and put in a resistor to lower the voltage that goes through it, couldn't I?

The following link is an idea for a battery, though I will need to mock it up when I get home to test the size. I know that I will need an extra resistor to two to help regulate the voltage. I will still have the power switch in there as well. Will the battery below work though?

http://www.hobbypartz.com/83p-800mah-2s1p-74-15c.html
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Re: Servo Motor Help

by adafruit_support_bill on Wed Apr 07, 2010 1:01 pm

also looked up the CR-123 batteries and saw a few things about them exploding.


You have to be careful charging the rechargeable version, but most of the CR-123's are non-rechargeable. Safety during charging is a general issue with lithium batteries, particularly Li-Ion cells. LiPo packs like the one in your link from HobbyPartz are somewhat safer, but still have been known to fail explosively. You can find similar sized rechargeable packs that use NiMH cells which are quite safe.

So I am guessing that if I used 2, 3V batteries batteries in series that it would be enough to power it, even for a short time.


6v is enough voltage, the question is how much current they can supply. Watch cells are designed to power devices which draw maybe a few micro-amps over a period of a couple of years. Although I have seen other button-cells like LR-44's used in small devices with lamps and motors. But as you say, you can always upgrade the power supply later.

Your microprocessor is going to need a 5V source. You can acheieve this two ways:
1) find a 5V battery pack (4.8V may be close enough, but I've never tried it) and eliminate the on-board voltage regulator circuit.
2) use a 7-17v source and let the on-board regulator regulate it to 5v.

7.2v packs are easy to come by. Either way, you can power the servos directly from the pack. A resistor is not a replacement for a voltage regulator, but unless you go over 8-9v, I wouldn't worry about trying to regulate the voltage to the servos.

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Re: Servo Motor Help

by johngineer on Wed Apr 07, 2010 1:45 pm

Bear in mind the board and batteries don't need to be near the servos. You could rig it so that you could have a mintyboost sized enclosure at the back of the strap (i.e. behind your head) and just run the control wires along the strap to the goggles themselves. This would not constrict as so much with regards to size and space needed.

Just a thought.

Incidentally, what are you going to make the aperture blades out of?
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Re: Servo Motor Help

by Iceman086 on Wed Apr 07, 2010 3:12 pm

I was wanting to make the entire thing self contained within the goggles (except the battery pack and board on the sides). The main thing that I want is to have the buttons that controlled the opening and closing on the goggles themselves... Though it would be easier to just make an enclosure thats wrist mounted and run lines up to the goggles from the backside of the goggles it wouldn't be quite as fun. The idea of being able to control the opening and closing of the iris's from the goggles themselves seems more fun, to me anyway.

I will give alot of thought to the enclosure idea though. I might be able to get away with that and get a better aesthetic look.

The blades will be made out of 24g Brass and 24g Nickel Silver. The idea is to alternate them so that it gives a nifty spiraled effect of different colored metals. I am in the process of making a Die out of tool steel to use in a hydraulic press so that I can punch the pieces out of the brass and nickel silver.
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Re: Servo Motor Help

by johngineer on Wed Apr 07, 2010 3:21 pm

Iceman086 wrote:I was wanting to make the entire thing self contained within the goggles (except the battery pack and board on the sides). The main thing that I want is to have the buttons that controlled the opening and closing on the goggles themselves... Though it would be easier to just make an enclosure thats wrist mounted and run lines up to the goggles from the backside of the goggles it wouldn't be quite as fun. The idea of being able to control the opening and closing of the iris's from the goggles themselves seems more fun, to me anyway.

I will give alot of thought to the enclosure idea though. I might be able to get away with that and get a better aesthetic look.

The blades will be made out of 24g Brass and 24g Nickel Silver. The idea is to alternate them so that it gives a nifty spiraled effect of different colored metals. I am in the process of making a Die out of tool steel to use in a hydraulic press so that I can punch the pieces out of the brass and nickel silver.


Well, you can still have small switches mounted on the goggles with wires running to the brain in the back.

The alternating brass alloys will look cool too. Good luck!
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Re: Servo Motor Help

by Iceman086 on Fri Apr 23, 2010 6:09 pm

Sorry to Necro-Post but I have a few updates and questinos.

I got the RT-Blanking Die for the blades made and all of the blades punched out. I will have the iris assembled by monday and hopefully motorized by the end of the week.

Right now my issue is, How do I connect the power source to the board? Above it was said to leave the DC power connector off but would it be better to connect it and find an old DC connector that I can cut off and connect to the batteries? Or, Which holes would I need to connect to the power holes on the board? (Just not sure which it is since there are 3)

Also I didn't put on the power regulator that is on the side. Below are some pictures of what the board currently looks like. My apologies if they are a little bit blurry.


Image

Image

I am not quite sure what to solder in next either. Here is a link to the DC Boarduion that I am following.
http://www.ladyada.net/make/boarduino/solder.html

Any suggestions would be much appreciated!
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