Let's Make Robots!

Chair bot

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What do you do when your 6 year old is excited to share his idea : "Let's build a robot!" Well obviously you start building a robot with your son! At least that is what I have done. This robot will be a humanoid torso on a swivel (office) chair base.

 

Video of chair base before torso was added:

http://www.youtube.com/watch?v=bWLt67l7shY&feature=player_embedded

 

Video of head turning:

Now with Pan and Tilt!

https://www.youtube.com/watch?v=3Qzw7Va9V2Q&feature=player_embedded

(old) http://www.youtube.com/watch?v=WxfH0qB_MCo&feature=player_embedded

 

 

Build Blog:

http://chronofish.com/blog/tag/e1/

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So I now have color tracking working on board the beagleboard computer.  I also have servo control (via Torobot servo controller).

However, when I try to run both the USB camera and the USB servo controller together at the same time the results are aweful.

I can usually make about 3-5 servo calls before the system resets.  If I don't connect the camera I can control the servos for hours. 

If I don't use the connect the servo controller, the color-tracking will work till I tell it to stop.

 

But as soon (or shortly after) as I use both, the computer restarts.

I'm wondering if the servo controller (or servos more specificlaly) is causing a noisy power supply and making the Beagleboard trigger it's protection circuit (causing it to reboot).

Thoughts?
CF

This is coming along very nice.  A very interesting project.  I can't count how many old office chairs I have pitched over the years.  Never even occurred to me what a nice robot base those would make.  Good luck with it and please keep us up to date.

Since I can't see the details I'm just guessing. I did do a pan/tilt for a camera many years ago and these worked for me.

I'm thinking perhaps 3 things.

  1. Upgrading the servos isn't a bad thing. Underpowered motors can cause jitter.

  2. For smoother action, perhaps some ball bearings in the bracket and the servos.

  3. Perhaps a PID loop for acceleration and deceleration would make the end-points smoother.

However, it looked like you had a lot of jitter in be center. That would be the dead band in the servo. Perhaps with a digital servo that could be dealt with, but I really don't know. I thought the dead band was supposed to protect from that sort of jitter.

A question: how often per second are you updating the servo position?

Once my 3d printer gets here I get to do these experiments and I get to see if my own advice is any good. :)

I have created a simple web interface that allows me to control the servos through the Beagleboard.  It's been fun to see all this come together.  The power system has been key.  I can switch between a transformer or batteries at will and switches and digital voltage display have been a great way to monitor what's going on with power and I have been able to "see" how one system effects the others (It's clear I need better isolation of the modules).

 

Anyway I have replaced my simple head turning with a pan and tilt mechanism.  It's pretty brute-force right now.  The "turning" servo has a simple platform connected to its control horns that holds the "tilting" servo.  The tilting servo has a bracket that tilts around it. 

This bracket holds the video camera and eventually the helmet.  With just the bracket it's pretty smooth.  But with the camera on it's pretty choppy.  You can really notice the torque after a quick turn.  Tilting up is slower than tilting down.  This can be balanced out a bit, but will cause the turn-torque to be greater.

 

Additionally I am using cheap SG90 tower pro servos.  So there is a lot of jitter.  I am wondering what the best option is here.  Ditch the direct mount Pan/tilt mechanism, upgrade the servos, or both?  

Here are the latest videos:

UI + head move + commentary :) (2:00)

UI + head move (1:00)

UI + speed control + power + head move (1:45)

 

 

After frying a battery last year just before showing the robot off, I decided a more robust and safer power system had to be setup.  This system now has a single power source, main power switch, emergency power disconnect, and switches for each sub-system.  It also gave us an opportunity to add some much-needed bling!  You can see more of the details at my Half Built Blog.

 

Power On and Regulated

it is a nice project, i like it..

Great project for you and your child, looks like RAD went on a RADical diet :-) Head movement is pretty cool, I always thought of putting a sonar sensor in one of my RAD heads in the "nose" for distance but getting the head to move with a motor or servo didn't look easy on the regular body. Keep,us posted, bet your kid is having a blast with it. Stephen

Ha! I like it!

We were able to present our robot at the Mini-MakerFaire in Rhode Island!

 

During setup one of our drive batteries shorted out and fried.  So we were not able to demo how it moved.  But we did have video to show at least.  We were able to demo the head movements, so that was fun.  It generated a lot of interest and I left with a very tired jaw (from talking to everyone wanted to engage)

 

On the way to the MakerFaire

Good start! That chair base will make it nice and stable. You might need an ultrsound range finder on each spoke to prevent it crashing into things.