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Help building robotic arm from scratch


#1

Hi -
I’d like to make a programmable robotic arm as a learning project with my kids using the Fez. I’m a newbie to this site, so I apologize up front if these questions have already been covered.

I’ve seen the sample Robot Arm Project under the Projects tab called RobotArmMP3, and I was wondering the following:

  1. Can someone please recommend a basic robot arm Technical Drawing for the standard shoulder, elbow, wrist, and grip movements along with a Parts List? I’d prefer to do it from scratch, to learn how to program the dc motors and servos, and when to use which - instead of buying a robotic arm that has been pre-assembled.

  2. Might not be the right place to ask this, but here goes … Has anyone noticed that at http://www.tinyclr.com/hardware/1/fez-domino/ each of the following parts are available to be purchased - the Domino, the component shield, the LEDs, and button, but the FEZ Domino Starter Kit which contains all of them is not available until July 8th??

Thanks for your help. Really looking forward to getting going on my project - this all looks very cool!:expressionless:


#2

Hi Chris,

Sure. First of all you said you would like this as a learning proces for servo/dc motors.
You can buy the parts for a robotic arm, but still program it yourself.

If you would like to build your own arm, the best thing you can do is search the internet for images. You can learn a lot from them.

If you are planning on buying arm parts, without servo motors, please make sure to buy high torque servo motors. I have made a mistake with my robot and therefor it has a hard time to stand up and it will cost me more money. If I checked well, it would have saved me money at this point.

For information about servo motors, you can check the servo page which I added: (but I guess you have seen this)
(link removed)

Also, here are some images which might help you planning:

First of all, this is the way your arm works. It uses 3 servo motors (4 if you would like a gripper)

Here are some images where you see the servos mounted and operating:

these are nice images of how a wrist works:

Gripper:

This is a video which shows the operation of the servo motors:

If you need more help, just ask!


#3

The easiest way is to use one of the many robot arm kits. Those have servos built in and then you can control those servos directly or use a servo controller board.
This is a good website http://www.lynxmotion.com/
This is the project with a video (link removed)
Note that this is a very old video this is why it is not using FEZ :smiley:

Looks like we have an error on website. The component shield is not in stock. We will have them next week I hope.


#4

Not really useful here, but still impressive video about robotics arms, to me : http://www.youtube.com/watch?v=SOESSCXGhFo


#5

What about this one? http://www.youtube.com/watch?v=uIuRc1r_N34


#6

here is a good one to follow if you are looking to go on the cheap and want to do it all yourself.
http://forums.trossenrobotics.com/showthread.php?t=4117


#7

I looked at each of your links, and wanted to thank you for so much detailed information. I will have some follow up questions I’m sure this weekend.


#8

Ask as much as you want. Don’t forget to take pictures :smiley:


#9

Hi Robert,
Again, thank you for your very thorough posts. My background is primarily database applications (.Net / Sql Server); the hardware world is completely new to me. I have a couple of more specific questions, that I wonder if you can please help me with -

1a) Are servos, and servo boards interchangeable? E.g., can a Parallax Servo Controller run HiTec servos, and vice-versa?

1b) Someone I met wants to sell me this for a deal: http://www.parallax.com/DesktopModules/CATALooKStore/Skins/Parallax/cat_image.gif - and I was wondering if it is compatible with the one selling on TinyCLR, at: http://www.tinyclr.com/images/products/TCLR-RP0016_large.jpg

Would it work fine, or might I run into a firmware issue, where the MicroFramework library specifically points to the one sold here? I remember seeing somewhere on here that Arduino Shields should run reliably on the Domino, but don’t know if that would include something like a 16 servo controller board.

  1. One site that sells HiTec servos says that the servo “can operate 180° when given a pulse signal ranging from 600usec to 2400usec”. I can’t find any information related to how many usecs the above controllers send, or even what a usec is in the first place :-/ . Have you seen any performance issues related to the data pulse wire not being sent the proper amount of usecs to a servo?

  2. Last question - Lynxmotion - what a site! Detailed pictures, hardware parts lists, manuals, complete with springs to keep everything working harmoniously. Unfortunately the basic skeleton of just the most basic aluminum arm, before adding the muscles and brain to move it, I believe is around $150 - out of my price range. Are there some good sites (not ebay) dedicated to old electronics projects or kits that the owners have since outgrown? Or any other alternatives I might consider?

Thanks again,

  • Chris

#10

Hi Chris,

1a) All servos use the same signaling methods, so all boards are compatible with all servos. I wrote a blog posting on this, here: http://www.chrisseto.com/wordpress/?p=129

1b) I don’t know the details of that Parallax board, but it is entirely possible that the GHI board uses a different interface scheme.

  1. Depends on the controller. Again, look at my blog posting to see how a servo operates. There might be a way to configure those timings into the controller though. More likely, the controller will use a “standard” set of timings, like 1000, 2000.

#11

Generally this is trues BUT there are still a few oddball hobby servos around that have non-standard connector pinouts and/or cannot be modified for continuous rotation (which is probably not important in this case.) The chap who has been posting about his turtle bot happened upon some of these non-standard servos. As Chris says they all use the same PWM control scheme though.

The link to Parallax does not seem to work so I’m not sure what your asking about being compatible.


#12

Sorry - the link was broken. I was wondering if http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/346/Default.aspx?txtSearch=servo+controller compatible with : http://www.tinyclr.com/images/products/TCLR-RP0016_large.jpg ?

If I am assuming correctly, the firmware that runs on the Domino sends signals to the servo controller board, isn’t concerned with which particular controller board is attached, and it shouldn’t be an issue, (from Chris’ blog) just a matter of tweaking the signal sent through it to each particular servo.


#13

I would say they are but I am not 100% sure. Also, the parallax board is USB so you will need to make changes on our code to use USB instead of using UART.

These boards take serial commands to generate the servo signals so what you see on Chris’s blog has nothing to do with the commands the board accepts.

Why not just connect your servo directly to FEZ?


#14

Since the two board serve the same function I would say they are comparable. Since they are both USB based the question would be the access to a driver for the device that would run on a Domino. GHI does a great job of having drivers available for the add-on boards it sells, so my first choice would be to go with the one from GHI. (You know you can also get support for it right here on the forum as well.)


#15

Yeah, I second getting the one from GHI. Besides, it may be that the Parallax board has a USB to serial adapter onboard, or it could be something more complex. Plus, it’s discontinued.

Besides, if you go with the GHI option, you will already have a driver written for you!


#16

You could buy the SSC-32

See the project page:
(link removed)


#17

I was just browsing a prototype site that overs cases etc and found a kit to build robotic arm.

http://www.ponoko.com/showroom/ClementFletchersPlace/open-source-robotic-arm-2674

maybe that is something you interest in.


#18

Funny thing i have one being made by them right now… Was gonna try a inverse kinetics with fez to control it.

Comes out to be 65 bucks to be made and cut out of 3mm Acrylic


#19

Which servos will you use?


#20

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2&Product_Name=HXT_10kg_Servo_(metal_gear)55g/10kg/_.16sec