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Author Topic: Building a set of walking legs, never made a robot before, what should I know?  (Read 10819 times)

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Offline Admin

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read these to help you in the right direction:
http://www.societyofrobots.com/actuators_servos.shtml
http://www.societyofrobots.com/microcontroller_tutorial.shtml
http://www.societyofrobots.com/sensors_accelerometer.shtml
http://www.societyofrobots.com/sensors_interpret.shtml

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Digital output ports = ports that servos plug into??

Yes. And not just servos, basically anything digital.

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Whats Input/Output pins for then?

A digital input reads in data from a digital sensor (or other source). Digital output sends out digital data (such as a square wave to control a servo). Most digital pins can be configured to do either.

Offline S. KarimTopic starter

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ah okay! um, stupid question: what if im purchasing analog servos? will they go into digital output ports?

Offline Ro-Bot-X

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Take a look at http://www.oopic.com/oopicr.htm. I think this will be a good choice since it has a free compiler (you can program it in C, Basic or Java), you don't need an programmer (just a serial cable) and it can handle up to 16 servos (just plug them in). So you will pay $80 for the OOPic-R, $80 for the (8) servos and build your own brackets. I think it can be done easy with a $250 budget.
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ah okay! um, stupid question: what if im purchasing analog servos? will they go into digital output ports?
Yes. The input is always digital, but internally they operate in a different manner.

Offline S. KarimTopic starter

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Take a look at http://www.oopic.com/oopicr.htm. I think this will be a good choice since it has a free compiler (you can program it in C, Basic or Java), you don't need an programmer (just a serial cable) and it can handle up to 16 servos (just plug them in). So you will pay $80 for the OOPic-R, $80 for the (8) servos and build your own brackets. I think it can be done easy with a $250 budget.
Yes! finally! this is the type of stuff im looking for. i have both a serial cable and a A-miniB usb cable so this will be good.

okay a few questions:

a ) it says "the first 4 can be analog in"...does this mean only 4 analog servos will work with this board? i plan to buy 8-10...

b ) where does the power supply go?

c ) this is ALL i need?? i can hook up servos to this and then program it, unhook my pc cable and itll work...correct?

d ) where do i purchase this?

Offline Ro-Bot-X

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1. "analog in" means input pins, you can connect 4 analog sensors like Sharp GP2D12.

All the pins can be set eighter input or output. If you connect servos to the pins, you will set them to be output. If you connect sensors, you will set them to be input. Actualy, if you connect servos, the compiller will set the pins as outputs when you configure the servos.

2. The 9V battery to power the board goes to the small 2 pin white connector on the right side of the board as you look in the picture. You can buy a ready made 9V battery connector. For the servos, there is an 8 pin connector just above the white one. You will plug the 6V servo power into the GND and +SP (pins 4 and 5 counted from the bottom). If you add to the board the optional 6V regulator, you can power everything from a 9V battery package (6 AA's). In this case, you have to install a jumper between pin 4 (+SP = Servo Power) and pin 2 (+MP = Main Power).

3. Yes, it's all that simple.

4. http://www.oopic.com/ordering.htm Any of the stores on this page have it.

Also take a look at this Hexapod walker and at it's code to get a glimpse at how easy it is to program.

Good luck!
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Offline S. KarimTopic starter

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awesome! sounds perfect. so i guess ill be purchasing 4 sensors with it along with my servos then?

and i noticed its $90, im gonna have to see if i can still get it with my budget.

okay what is this thing for...http://www.robotstore.com/store/product.asp?pid=1006&catid=11 - it says its a carrier but what extra things do i need for it to work like a regular robot controller?

Offline Ro-Bot-X

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You don't have to purchase sensors unless you need them. On the first 4 pins you can plug eighter analog sensors or digital sensors or servos. On the other 12 pins you can plug eighter digital sensors or servos.

The Mini Atom Carrier Board needs a microcontroller to function. It's called a carrier because you can use it with different 24 or 28 pins microcontrollers, like BasicStamp2, OOPic-C, BasicX... So you need to purchase in this case both the carrier and a microcontroller.
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Offline S. KarimTopic starter

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I think I do need them for ankle balancing.

How hard is it to turn the $50 tutorial's unit from controlling 4 servos to lets say 16 servos. I can't just solder in 12 more headers in random holes can I ?

Offline hazzer123

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Im not familiar with ATMega8 but i doubt they have less than 16 IO (input/output i think) ports on them. So you could control plenty of servos and have sensor inputs. at the same time.

You can't solder them into random holes. You would stick another 3 pins into the board, wire one of the pins to the ground, one to the power and one to a free I/O port on the microcontroller. Do this as many times as you need servos.
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How hard is it to turn the $50 tutorial's unit from controlling 4 servos to lets say 16 servos. I can't just solder in 12 more headers in random holes can I ?
Funny thing you mention this, because literally today I just added 6 more headers to my $50 robot board to handle more servos. Without counting the programmer pins you get 19 I/O (I dont think you can afford that many servos, anyway :P). I didnt use pins 9 through 14 originally, but they are easy to add on.

The advantage to using my circuit is that its already done for you, its crazy cheap, and a bunch of us have already built it so we can help you. Plus, Im writing tons of source code on it for beginners to use.

Offline S. KarimTopic starter

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Sounds good.

So what do I need to do after building that circuit to achieve 16 servos?

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So what do I need to do after building that circuit to achieve 16 servos?
Well, you need to add 6 additional male headers next to those pins exactly like you did for the other servo pins. Ill post pics of my upgrade sometime in the near future.

I just upgraded and uploaded the new source code to handle the additional pins for anyone to use.

Lastly, to use the analog pins as digital outputs like you want, change these two lines found in SoR_Utils.h:
Code: [Select]
DDRC = 0x00;  //configure all C ports for input
PORTC = 0x00; //make sure pull-up resistors are turned off

to:
Code: [Select]
DDRC = 0xFF;  //configure all C ports for output


Otherwise no additional work!

Offline S. KarimTopic starter

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That sounds awesome! So post the upgrade as soon as possible and I'll work on a 10 servo (? or was it more/less) microcontroller as soon as its up.

I think my plan now is to get the electronic brains last, since I have time for that and I dont wanna spend money on something now thatll be outdated in a month. Making my own sounds more fun anyways.

I'll be working on joints and building just for now (ill update you guys with servo info in a bit) so i'll take pictures of how its turning out.

What are some things I should be careful about when making legs? Any warnings you can give me will be greatly appreciated!

 


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