Let's Make Robots!

Gipsy, son of Sticky

As seen in my previous post, first attempt to build a quadrupod ended with a jump from the desk.
Hopefully, I learned a lot and I was ready to launch the next experiment.

My wife just received this very nice material from a friend and there’s enough for me too :)

I think the best english translation is paper foam board, but you will see it later.

This time, I choosed to get a step further and build a 3DOF quadrupod.
As usual, as I don’t have 3D software knowledge, I draw my ideas.
Very quickly, thanks to the foam board, I was ready to try real parts:

from thoughts to real

Easy to cut, strong enough, first leg parts were quickly ready:

one leg kit

I had to get back servos and servo horns from the poor Sticky.
Bye Sticky, you were very useful:

good bye sticky

Using the hot glue gun once more, I started to assemble the legs:

new femurs horn glued

When a leg is ready, I thought it my be good to check the 90° position of the servos:

align servo

Quite a lot of work, but that was fun:

4 legs

I quickly cut a platform and here is the first shoot of Gipsy:

structure ready

And there, I learned another lesson: glue is good, but you have to screw horns on the servo.
Until now, I just pushed the horn, but here comes the first true physical constraints.
So, I carefully use my cutter to get back all horns, screw them and glue back.
No true difference to see, but hey, I’ve done it! :)

same structure but horns are screwed now

Then, I started to plug all 12 servos to my DFRobot Romeo board.
Which bring me to my next lesson: always put a proper code on a board before switch on :)

Never plug the board before having initial code

No harm, but I thought I was stupid because I didn’t initialized all the different 12 ports used.
To be honest, I believe there’s also an electrical issue, as I was only USB plugged.
As I didn’t meant to move all servo at the same time for the moment, I thought USB was enough.
Obviously, this is not the case.

Next step will be to determine if this is an electrical issue.
I’ll add an external power source as in Gary

Also, I started to study the way I’ll code the movements. It looks harder to move a 4 legs bot than one with 6.
It’s a matter of balance and you need 3 legs on the floor to keep a stable state.
But I start learning anyway, even if at the end I code an hexapod ;)


I'll try to keep updates on LMR but if you want more about me and my experiments, I have a small blog on heroku.

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Cool, that looks promising. That material seems to be good for such use. 

Yeah, upload the right code before switching on the board and use an external power supply for moving that many servos. The USB will just not have enough juice. Well done so far, keep us updated and don't forget the video...also if the video only shows a jittering creature :-)

I didn't had video and wasn't sure if I will connect a board at first. So I put this in a blog post.

Of course, any further step will switch this to a full "Robots" entry with video.

The power is always a source of confusion to me.

This time, I knew that USB won't provide enough, but I thought I could plug and start some tries servo per servo. It looks that I was wrong in a very visual way, far better than a simple bug in a Java application for example :)

So, I added a 4AA pack, but this still behaves in silly way.

But, I took current measurement and I had only 4.4V on the servo pins on the Romeo board.

My Turnigy TG9z are given for 4,8 to 6V, I guess it doesnt' help. I will try with a 5 pack but I need to take it from Gary, or try with my Turnigy 2200mAh 2S but I have to order some XT60 plugs and wait.

Weird... I tried with a Arduino R3 with IO expansion V7 from DFRobot.

I could not try with all servos but it looks more reactive and stable...

During the trip to the office, I remember that the Romeo board has some switches to manage the 2 motor drivers and it looks it was linked to 4 pins... I'll have to digg it.

Edit: it was bugging me, I took some time at the office to read the Romeo wiki.

There are 2 problems that I had both I think:

- the motor control pin jumpers that prevent proper use of the pins 4,5,6 and 7

- there is a specific servo power select jumper that I didn't use and I pluged my AA on the motor power pins, not the servo power pins

On the Uno+shield solution, I pluged power to the servo power pins... I really have to improve my thoughts, I'm on the bad path to burn a board or a component if I don't follow the right schemas.