OpenServo.com

erebus · Joined: 01 Apr 2008 Posts: 10

I have been struggling with openservo for about 2 months now.

I am part of a group with Case Western Reserve University using the servos in a team biorobotics project. We are making 2 to scale cockroach legs that will be several times larger than the actual legs.

The original plan was to use a blackfin ez kit and labview to communicate with the servo using the blackfin's twi.

A majority of the 2 months has been assuming that the blackfin was the problem and so I had no reason to bother you all with this.

We purchased a handful of openservo boards from pendragon. I will copy those emails to this forum when I am allowed to post urls. They were not purchased under my name, but they were purchased by Case Western.

After getting fed up with labview and blackfin we purchased a usb-i2c device to test the servos. It is a FTDI FT232R module. After purchasing it I noticed in previous posts you thought about using those and then decided instead to make your own boards. I am sure you will suggest I just buy the osif board. But I am only using the usb device to test to ensure the boards work and they should work with any i2c.

When I plugged the servos into the USB to ic2 converter and ran their example labview and C++ programs it showed no devices on the i2c hub. A troubling thing is that it shows the same status regardless of whether the usb converter is in the computer or not. I emailed the FTDI guys to try to get some help with that.

The next problem is that when I put 7 volts across the gnd and Vdd ports of the openservo board that has been put together with a servo it doesn't resist movement. This lead me to think that maybe the boards weren't flashed and need to be flashed and whatnot. This would be a bit of a pain for me.

This project has gone to hell in a hand-basket. The plan was to just use openservos for nice current feedback and extra control, and th blackfin and labview for a nice user interface. And then everything would work perfectly. Currently nothing works and I have no results.

The current plan is to put linux on the blackfin and still use that twi to communicate. But we have had these servos for a month or more and we haven't gotten them to so much as twitch.

Help would be greatly appreciated. For starters how can I tell if my boards work, and why wouldn't they resist movement with 7 volts across it?

Thanks,
Jesse

ginge · Posted: Tue Apr 01, 2008 10:21 pm Post subject:

Hi Jesse,

It sounds like you are having a bad time with this Sad

erebus · Joined: 01 Apr 2008 Posts: 10

I am aware of the power issues. I had a variable power supply when testing if the servo provided any grip on the motor when powered.

I also have a battery that is 6.6v or so that I was hooking up to the servo for power and just sharing the common ground with the clock and data input from the usb converter.

Tomorrow or maybe Thursday's plan is to get a scope hooked up to the usb thing and see if it can find some other i2c devices.

ginge · Posted: Tue Apr 01, 2008 11:13 pm Post subject:

ok, fair enough. But remember, there will be no servo movement until you program some parameters!

Good luck,

Barry
_________________
http://www.headfuzz.co.uk/
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erebus · Joined: 01 Apr 2008 Posts: 10

Ok well we have had minor progress. I now have uClinux running on the blackfin, and when I use U-boot and probe the valid addresses when i have nothing plugged in i get no output but when i plug the servo in i suddenly get a large number of valid addresses. So at least it has had an effect on something. Never mind that both 0x10 and 0x20 show up in valid addresses, (I'm not sure which is the default).

I have in frustration told my boss to order a osif board.

However, while I wait for it to come I have questions that I think should be easily answered.

How do i write to /dev/i2c-#

I have read a lot on the topic and I am confused as to what goes into this thing.

I read two webpages on outputting to i2c with the dev/ interface, but I can't post links yet because apparently my previous two posts have not been approved as legit or somesuch.

I don't really want to write a Kernel module. I would much rather just output a buffer with a read or write command but it seems to want me to pick an adapter in the dev/ folder to output on. Isn't there some code developed already to output on the i2c output in linux for the open servo? I thought about just putting 0 in as my number and hoping but I didn't want to frustrate myself if that didn't work.

I looked through the whole cvs. It is hard to know what folder leads to what exactly for generic library code.

So, what files should I download/what code should I write which will very simply allow me to read and write from the dev/i2c-# output thing in linux?

Also, when I get the osif what files do I download to use your pre-made functions? I thought I saw a get_position() function and others written for it, but I can't find them in the cvs.

In the end I plan on ditching the blackfin and just using the osif and creating a sweet opengl visualization of the leg while its position is manipulated by the servos and by people. But, until that osif board gets to me I would like to poke at the servos some with the blackfin.

Thanks,
Jesse

erebus · Joined: 01 Apr 2008 Posts: 10

superservo looks like what I want, but the readme doesn't tell me everything I need to know really. Am I at least right that I need superservo?

ginge · Posted: Mon Apr 07, 2008 8:32 am Post subject:

erebus · Joined: 01 Apr 2008 Posts: 10

Thanks for the quick reply. Could you please send the example using fread/write and the more comprehensive interface you mentioned.

I changed my profile so you can send emails now. Just include the example code in an email.

Thank!

ginge · Posted: Mon Apr 07, 2008 9:07 am Post subject:

I can't post up the newer version of the code for some hours (at work at the mo) but there is an older, albeit functional version of the source on my web site. I will mail the latest and greatest to you later on.

http://www.headfuzz.co.uk/?q=openservolib
Download that library and look through the code, specifically i2c_func.c

The readme in the file has an overview of the basics, but the /dev/i2c interface is not particularly well documented in this. Here is a quick rundown:

Initialise the dev-i2c interface. Pass in a pointer to a string of the interface. E.g "/dev/i2c-0"

erebus · Joined: 01 Apr 2008 Posts: 10

major success finally. uClinux is working with the blackfin and i figured out how to load the i2c module so now the servo is communicating using your code!

It can get position fine, I havent set the pid stuff so set pos isnt working yet. Do you have your newer version of your code to post? that would be great.

Also, how long does an osif take to get to the US I ask cause we ordered one and the business wouldn't respond.

Thanks

ginge · Posted: Fri Apr 11, 2008 8:43 am Post subject:

Great news!

erebus · Joined: 01 Apr 2008 Posts: 10

I'm not sure how they tried to contact you but I will find out.

The servos still don't move. I am using futaba s3102 servos. Which should run off 4.8 volts. I am feeding them 6.0

here is their site

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXH291#tech

i am setting the maxpos and minpos and the gain values. Any thoughts on what I'm doing wrong? I am still reading positions fine. What exactly do the gain values do? I tried looking them up but it wasn't well documented on the site? I set them all to 10 is that too low? too high? prior to setting them to 10 I just tried using the "safe" default values. still no movement. Whats wrong?

erebus · Joined: 01 Apr 2008 Posts: 10

the person who tried to contact you was Alan Pollack. He said he tried emailing you through your webpage. He also said he ordered an osif this past Tuesday or Wednesday. Can you confirm that? Still no luck on the movement.

My code looks like this

openservo_add_adapter("gumstix",0);
openservo_add_servo(0,0x10);

openservo_start(0,0x10);
openservo_configure(0,0x10,MAX_SEEK, 304);
openservo_configure(0,0x10,MIN_SEEK, 26);
openservo_setpos(0,0x10,305);

while(1){
//print out stuff
}

that isnt copy pasted but written from another computer so forgive a typo but it does compile and run.
I can read current and pwm and pos and speed. Current is at 9, pwm is 0 pos is static and speed is 0. What am I missing?

erebus · Joined: 01 Apr 2008 Posts: 10

found a major error in your code for writing to the servo. in your file i2c_func.c in your function i2c_block_write8()
you make a call to i2c_write() but you pass the wrong value into it. you are passing your cmd_addr variable, you should be passing your tmpwr variable.

kbb · Joined: 01 Jun 2007 Posts: 180