Author Topic: Building a set of walking legs, never made a robot before, what should I know?  (Read 10509 times)

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Offline S. KarimTopic starter

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I'm building a set of walking legs, before I build the upper body. This is what I think I need:

a) 8 servos. (waist, thigh, knee, ankle / per leg). dont know which ones are good though, there are hundreds of hitec / futaba servos on websites but i dont know what torque i need (since i have no concept of torque, i do know what it is though). the calculator on this website wont help, cause ive never purchased motors before and i dont know what power i require.

b) something to control these servos...will this work:

http://www.robotstore.com/store/product.asp?pid=676&catid=1563

or do i need something else with it? seems like it's a plug and code microcontroller, can anyone verify? i do know how to code in C/C++.

c) battery pack, dont know what voltage though, anyone can help?

d) balsa wood or something stronger, cutting tools, glueing tools.

Okay, I need your help, do I have the right ideas for equipment? I will document everything to show you guys how a beginner does this if you help me. I have a budget of $200-250 and I need links to reliable vendors I can purchase powerful/small servos for around 10 bucks a piece.

Oh and do I have my microcontroller concept right? All I need is that servo controller and I'll be able to make my robot walk right?

Thanks guy!

Offline S. KarimTopic starter

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bump!

dont wanna read first post?

simplified version: what do i need and what do i need to know to make a set of walking legs, that will support a future upper body?

thanks!

Offline S. KarimTopic starter

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Comon guys, any help?

I want to make walking biped legs, what do I need?

Offline Ro-Bot-X

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Get the Bioloid kit. There you have all that you need.

There is no cheap way to build a walker. Good servos cost big bucks. Take a look at www.lynxmotion.com and see what servos they are using for their Bratz kits. And there you will find servo controllers and batteries also. It you buy a kit, they will give you the Servo Sequencer software to make the robot move.

I don't have any of the parts required so I can't help you more. But a walker is not an easy project for a beginner, since it involves good mechanical, electronics and programming skills to make it work.
Check out the uBotino robot controller!

Offline S. KarimTopic starter

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Im looking to build this from scratch. I'm not a complete newbie, I lied in the post so you guys could give me directions as if I were a 5 year old.

I already have the ROBONOVA1 kit, so I know what's required already.

But I need help from you guys to see what I need from scratch. What recommendations can you offer me that are cheap but durable? There has to be a place I can get 10 servos for bulk for a reduced price.

Offline hazzer123

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If you only want to make the legs, with no plans of building the rest of the body in the future. Then the servos you can buy are cheaper since they dont need to haul so much weight.

Woops .. Ii just read that you do want to build a body :) so you will need the more expensive ones.

Its going to be difficult to find such strong servos at the price you want. The only place i can recommend is ebay. There was a post on here about a very cheap set not long ago.

For the frame, I have seen many robots built with brackets made out of bent sheet metal or acrylic. I think that this is a simple, effective and light way to hold the servos together.

If you can code in C, id say make your own servo controller. Just get a PIC16F876A or similar. You could use PICC LITE to code in C for the MCU and there are plenty of outputs. It has onboard USART to link to your computer so that it can do all the  calculations.

ermmmmm Thats pretty much all i have to say :)

See ya

[EDIT] - Oh yeh - there is a homebuild section in the Robosavvy website. You might get more info there. http://robosavvy.com/forum/index.php
« Last Edit: June 19, 2007, 11:53:53 AM by hazzer123 »
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Offline S. KarimTopic starter

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wonderful reply! thats just the type of help im looking for. i appreciate any links and info no matter how tiny!

servos:

lets completely scratch the upper body idea! what good servos would you recommend now? where can i buy 8 or more servos in bulk or individually, thats not -too- expensive? ill bump my budget to $150 for servos alone, can we work on something now?

brackets:

ive never worked with such materials before. where would i purchase this "sheet metal or acrylic" and what do I need to shape these things?

microcontroller:

im pretty new to electronics, i dont really want to make my own without any knowledge and i surely dont want to invest money into something i might mess up. ive soldered my own MCU before but with instructions...

can you -please- look at this following MCU: http://www.robotstore.com/store/product.asp?pid=676&catid=1563

now im not sure if im correct or not, but to make walking legs move, thats ALL i need right? am i correct when i say that the small microcontroller in that link is enough to make 16 servos work? or do i need other electronics with it??

thank you so much for the help. hopefully others with ANY input can contribute!

Offline rgcustodio

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can you -please- look at this following MCU: http://www.robotstore.com/store/product.asp?pid=676&catid=1563


That item is not a full MCU. It has an MCU but the I/O of the MCU is dedicated to controlling the servos only. As the name implies it is only a servo controller which communicates to a software running on a separate host (in this case a PC) via USB. Read the document and see if it's what you need:
http://www.parallax.com/dl/docs/prod/motors/PSCusbManualRevBv3_4.pdf

The documentation only states how to connect the controller to a PC with a USB port, it does not go into detail on how to connect the controller to an MCU. Verify this first if you need to connect the controller to a separate MCU.

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now im not sure if im correct or not, but to make walking legs move, thats ALL i need right? am i correct when i say that the small microcontroller in that link is enough to make 16 servos work? or do i need other electronics with it??

Yep it is enough to make 16 servos move. You must provide a power source for the servos. NOTE that, as I mentioned above, you will be tied to a PC unless you can connect the controller to an MCU via serial or something.
The best thing one can do when it's raining is to let it rain. - H. W. Longfellow

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Offline hazzer123

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Glad i can help :D

Servos -

Im guessing you are from the US since most of the people are on this forum. Here is what looks like a fantastic source for servos http://search.stores.ebay.com/Toms-RC-Simulator_Hitec-HS-servo-servos_W0QQfsnZTomQ27sQ20RCQ20SimulatorQQrefidZstoreQQsaselZ9159503QQsatitleZHitecQ20HSQ20Q28servoQ2cservosQ29QQsofpZ0

And also as always www.servocity.com. (Order from these and you get free sweets :))

Before you go and purchase something, i think you should go and learn about rotational moments and torque if you don't allready know much. Then do some pretty simple calculations and decide what is the best. It would be better use lighter, less "torquey" servos at places such as the hip rotating joint which don't bear much load.

Brackets -

You can buy brackets on the internet http://www.lynxmotion.com/Category.aspx?CategoryID=87, but for a peice of bent sheet metal they seem expensive.

To make them out of acrylic yourself, you would need a strip heater. They heat a line of the acrylic up makng it bendable. And a drill for the holes.

Out of sheet metal would require a sheet metal bender (not sure what the official name is :)).

Microcontroller -

Yeh that link looked awesome. Im not sure how good the supporting software is though. Says it supports keyframe animation which is good.

I think you would need a power supply with it, since there isnt any mention of one in the description.

Harry

PS - rgcustodio posted as i was writing
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Offline S. KarimTopic starter

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RGCUSTODIO & HAZZER123:

Aw man my hopes in a cheap MCU has been destroyed :(. It seems like that parallax servo controller would be all I need.

I want a brain for my servos...without being stuck to the computer so I can take my walking legs around town, so at the push of a button there will be a few seconds delay (which I can program in) and then it'll do the walking or whatever sequence I programmed it to.

I need a brain that controls 8 servos, not being tied to my computer all the time. What do I need? What would you recommend thats small?

Servos -

Great link hazzer123! Thats perfect, it'll save me a dollar or two on those HS322HD servos! 51oz/in torque sounds like an okay number, but I'm wondering is this enough to pick up an entire leg for movement? Do you know where I can find other links like this for better hitec servos for around the same price?

Brackets -

Wow, I saw that link yesterday. 13.00 for 2 brackets is waaaaaaaaay too much. I'm a hobbyist, not an money tree ;D!
« Last Edit: June 19, 2007, 03:18:30 PM by S. Karim »

Offline hazzer123

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If you can code in C/C++ then get a PIC18 or PIC24.  These have enough processing power for sequences. Also, i think it would be good if you had a small MCU to send out all of the signals to the servos, but with one of the better, faster MCUs actually telling the other what signals to send.

This means you wouldn't have to make a single controller worry about servo pulses while it does all the complicated maths involved.
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Offline Steve Joblin

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Yes S. Karim... Robotics can get to be quite an expensive hobby!.

If you want to create a simple walking robot, but don't want to spend tons of money on an expensive kit, you may find inspiration in creating a "home brew" version of an existing robot.  For example, Parallax makes the "Toddler" bipedial robot (http://www.parallax.com/detail.asp?product_id=27311), but at $250, it may be too expensive for your budget (though, it is actually a good value as it is well designed, made with quality parts, and is complete (robot, microcontroller, servos, sensors, instructions, tutorials, etc.).  If you study the manual and get real familiar, you may be able to figure out how to build one from scratch.  Harry Lewis (of Blue Bell Design) did just that and created a "home depot" version (http://www.bluebelldesign.com/AppMod2.htm).  This approach can reduce your costs significantly and you get the satisfaction of truley building it from scratch!

Offline S. KarimTopic starter

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Hazzer123:

What is a "PIC18" or a "PIC24"? Can i plug servos into it, a battery, some code, and it'll do what I want (im not sounding like a smartass btw, I just dont know if thats what it does, which is what I need)? I dont know if i've been making any sense in my last posts...but I want an entire package of whatever electrical components are required to make my servos work. I'm weak on the electronic side, so thats one thing I'd like to purchase pre built, unless it's super easy to make an 8 servo controller.

What am I saying in simple words? Im looking for a motherboard/brain that'll control 8 servos, (sensor inputs no required), is programmable and battery interchangable and can be taken for a ride on the other side of the planet and still work without hooking up to a computer.

Steve Joblin:

Yes I am a student with very small budget, but my school has purchased a ROBONOVA-1 kit for me. In the process of building that, I've realized I want to build my own from scratch. Therefore, the "TODDLER" which is amazing, ive read many articles about it on ROBOT MAGAZINE, is completely ... well ... useless to me compared to what the ROBONOVA-1 and I'm trying to do. And no no I dont want to use parts from my ROBONOBA-1, it's too precious to me haha im such a dork!



Offline hazzer123

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Ok PIC18 and 24s are microcontroller chips made by a company called microchip. www.microchip.com

They don't come with a board and all the pins to plug a servo into, but guess what - They are FREE. (Well in small amounts). Every month you are allowed to order up to 3 each of 8 different chips.

The advantage with the PIC18 and 24s over the older PIC16s is that they have a fantastic C compiler (Microchip C18). So you could wirte some simple code to send the pulses out to the servos.

To make it usable, you can make a simple I/O circuit using Pin headers in a strip board. It had got a little bit of electronics, but not much.

It is easy to hook a battery up to these through a simple voltage regulator.
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Offline S. KarimTopic starter

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Okay so the chips are basically memory? They can calculate fast and whatnot? Where do I get the rest of the things for the board? You're telling me stuff and it's all great but honestly I have no clue where to get this stuff...and Im confused about what I need, it's all a blur right now haha

Question for everybody:

I found HITEC servo for 10 dollars at 51oz/in. I find GWS STANDARD SERVO 10 dollars...at 111 oz/in. Whats up with that? Do I trust this?

Offline hazzer123

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Radioshack or Digikey are good suppliers (ive heard)

all you would need basically is a 20MHz crystal oscillator for the PICs timing. and 7805 5V voltage regulator to create a steady 5V for your electronics from your battery. Some pin headers to plug the servo leads into and maybe a couple of LEDs, resistors and capacitors.

If this seems a blur, you will need to do some reading up on PICs. You will be using a microcontroller like it if you are wanting to store motion sequences in the robots memory.

got to go now

see ya later

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Offline Steve Joblin

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S. Karim:  with all due respect, you are way over your head.  I suggest you take a step back and start small.  The chips mentioned are not memory, they are microcontrollers.

Why don't you start with learning about microcontrollers and how you can use them to control a servo.  Parallax has some very good kits that focus on teaching you (like their "What's a Microcontroller" kit (http://www.parallax.com/detail.asp?product_id=28152)).  You can download the manual for free!

Once you learn the basics, you can then take it a step further... maybe a robot that can roam around a room and use sensors to avoid obstacles.  Then you can start to kick it up a notch and learn how to make a walking robot.

I wouldn't be focusing on searching for servos just yet... I think you have a lot of learning to do before that!

Offline dunk

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hi S. Karim,
so PICs are microcontrollers. sometimes referred to as MCUs. (MicroController Unit.)
think of them as inexpensive single chip computers that need a minimum of external components to work.
typically just a regulated 5Volt power supply and one capacitor is enough for basic functionality. (although some parts need extra components.)

PICs are made by the company Microchip and come in a few variants: PIC16 PIC18 and PIC24s.
the other big microcontroller hobbyists use are AVRs made by Atmel. part numbers tend to take the form ATsomething. eg: ATMega16 or ATTiny12.

if you allready have some programing background then getting a PIC or AVR to control multiple servos would be fairly easy once you have overcome the initial learning curve associated with the basic electronics involved.

i'm not trying to convince you down this road, just trying to help with the language.

if you are interested in exploring this method, Admin's $50 robot project walks you through this technique to controll 2 servos. from there it would be a matter of scaling it up a bit.
http://www.societyofrobots.com/step_by_step_robot.shtml



as for your desired servo control product, sounds like something you can program sequences into via a computer, then unplug from said computer and play back when buttons on a remote are pressed is your ideal solution?
have you tried searching for something like that on some of the robonova type websites? i'm guessing that's how those guys must be doing it.
i can't imagine they are controlling the servos individually.

dunk.

Offline S. KarimTopic starter

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S. Karim:  with all due respect, you are way over your head.  I suggest you take a step back and start small.  The chips mentioned are not memory, they are microcontrollers.

Why don't you start with learning about microcontrollers and how you can use them to control a servo.  Parallax has some very good kits that focus on teaching you (like their "What's a Microcontroller" kit (http://www.parallax.com/detail.asp?product_id=28152)).
I'll look through it, but as I've hinted I'm not worried about electronics. I'm trying to learn the mechanical aspects of bipeds, not it's electronic components. Maybe this was the wrong forum to ask for supplies. I need a premade microcontroller that can handle 8-10 servos after being programmed, it shouldnt be too hard to ask for, I figured one of you guys would know a product to recommend?
Once you learn the basics, you can then take it a step further... maybe a robot that can roam around a room and use sensors to avoid obstacles.  Then you can start to kick it up a notch and learn how to make a walking robot.

I wouldn't be focusing on searching for servos just yet... I think you have a lot of learning to do before that!

I've already done the whole roaming robot using sensors thing, about 3 years ago. I'm way past that and I've built other robots previously. I was just never the guy to handle the electronic parts so I'm asking for help. Hopefully it's not too much to ask for. Regardless of me coming off as an electric noobie, I'm not one in terms of building mechanics.

All I'm asking is if anyone knows any links to supplies, please feel free to provide. That is all :D.

DUNK:

that made a LOT of sense. I see what pics are now, sounds good. but until I have a whole list of what and where I can get em to make my own robot brain I wont exactly tinker with it. admins project is cool, ill do it if you can tell me how to extend the project for 8 or more servo ports.

Offline Admin

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can you -please- look at this following MCU: http://www.robotstore.com/store/product.asp?pid=676&catid=1563

now im not sure if im correct or not, but to make walking legs move, thats ALL i need right? am i correct when i say that the small microcontroller in that link is enough to make 16 servos work? or do i need other electronics with it??

It isnt enough if you want sensors on your robot. You do want sensors, no? :P


You might want to check http://www.towerhobbies.com/ for servos. They tend to offer discounts if you buy servos in bulk.

As for your $250 limit . . . you should probably up that to $500 since as you are probably missing a lot of useful equipment and other misc stuff . . . Most of my robots are valued at about $500 each in parts (its a one time expense as I scrap my old robots for new ones). Because bipeds require tons of servos, you might need up to $1k (serious).

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admins project is cool, ill do it if you can tell me how to extend the project for 8 or more servo ports.

Ive been meaning to build a biped of my own for years now . . . I would probably use the ATmega644 microcontroller if I did. Most of my $50 robot tutorial can be used, with slight modification, with the ATmega644.

Offline S. KarimTopic starter

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sensors? not really, im just building a set of walking legs. what sensors could i possibly need? unless i wanted my legs to kick an object in mid air that im holding up, id require a camera and a camera port or something of the likes. is the MCU enough now to program something in, unhook from pc and replay what i programmed?

i doubt ill need 1k for a set of walking legs. i wouldnt expect you to say that...being the admin/master hobby robot builder and all since you're a pro at finding loopholes in prices.

im thinking 8-10 servos for the legs total. only thing im worried about is this MCU thing and materials to make the actual frame.

Offline Admin

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i doubt ill need 1k for a set of walking legs. i wouldnt expect you to say that...being the admin/master hobby robot builder and all since you're a pro at finding loopholes in prices.
I meant that price for you, not for me :P

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only thing im worried about is this MCU thing and materials to make the actual frame.
make light weight and rigid your priorities

Offline S. KarimTopic starter

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rigid priorities is definetly a good idea. but, not sure what type of wood ishould buy thats strong but easy to cut.

Offline Admin

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Consider carbon fiber, as well as thin bent sheets of aluminum, too. Id recommend designing it in CAD first (search the forum).

Offline S. KarimTopic starter

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i know what cad is, ill definetly design it before cutting.

and um, wheres a good place to get thin aluminum sheets. and what tools required to cut?


Offline S. KarimTopic starter

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wow, cannot say how much i appreciate the help :D.

ok i did a little bit of research and i found out (or im guessing) a servo controller requires a robot controller to work without a computer (since the robot controller is the computer its feeding off of now i guess).

ive looked all over, pololu, parallax, etc...where do i find a robot controller with built in servo ports (sensors arent a priority)?

Offline Admin

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where do i find a robot controller with built in servo ports (sensors arent a priority)?
just look for digital output ports 8)

Offline jsmoker

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Just some good to know background on Servos.  A servo has 3 wires, power, signal, and ground.  The signal is a pulse between ~1-2ms long.  The position of the servo is determined by the length of the pulse.  The controller you found just simplifies the timing task for you, but any microchip with output capable of hundreth of a milisecond output can do the same thing.

Stuff on microchips.  You seem new to microcontrollers as well.  I just want to make sure that you know to buy a programmer for your microcontroller as well.  It's a one time startup cost usually between $30-200, depending on the depth of versitility you're looking for.  Some simple ones are here http://www.electronickits.com/kit/complete/complete.htm?gclid=CJniq8T66owCFQhaZQodkHqO6w

I know you said you have some background in robotics, but you seem to have a lot of gaps in your knowledge base.  I hope you know what you're getting into.  Controlling 8+ servos in sink to walk without falling over is a task.  Good luck.

Just curious, but how are you planning on keeping the robot standing as it walks?  You mentioned you aren't going to use any sensors. 

Offline S. KarimTopic starter

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Admin:

Thanks! Digital output ports = ports that servos plug into?? Whats Input/Output pins for then?

jsmoker:

Thanks for the info. I'll look through the site you provided and ask if one I like is worth it in the next post. Well, I'm going to use ankle servos to tilt the robot and shift its COG to do the walking. What sensors should I get? I already have a ton of touch, encoders and IR sensors, laying around and about 2 cameras. I'm guessing I'll need an accelerometer or a gyro? Any info is appreciated! Thanks a lot.

And yes there are gaps in my knowledge base, that might be what it seems like on this forum but im not as dumb as i come off lol, ive stated before im new to electronics so i'm choosing to have noobie-instructions i can understand, rather than casual instructions that i wont.

 


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