sábado, 26 de enero de 2013

Tipp 2. fixing the grippers of your third hand

When you use use a lot your "third hand" you turn the grippers to different positions quite frequently. Thus, it is possible that the fixing of the grippers wears off. They wont support in position any part / board having a certain weight. 

To solve it, I just solder them! Grippers are made on a soldable alloy. The arm is not soldable, but if you apply the soldering iron for a while, the soldering material will flow between the two parts. Once cooled, they are fixed forever!

The motor (1)

You can take 2 ways when choosing the motor. The easy one and the not so easy.

The easy one is to use a normal servomotor configured to infinite rotation (sometimes called full rotation). A normal servomotor controls the POSITION of his axis. This means, it turns until it reach his commanded POSITION. But it is possible to modify this kind of servomotor in such a way that it turns to a certain SPEED but never reaches is command position. You can do this my "fooling" the control installed into the servo. You interrupt the position feedback. Therefore, the servo keeps turning and turning but never reaches is target position.

There are different ways on how to do this. Have a look here and here.

You can also purchase a ready made continuous servo. For example here.

Working in this way allows you to directly connect the servo to your controller. No additional electronics are needed. Less wiring and therefore less complexity. This is the way I used for my first prototype.

But there is a draw backs in this approach.

Servomotors are a combination of a DC-Motor + Electronics + Gear. The included gear has a big reduction ratio. Therefore, the original motor (high-) speed is reduced to a small one at the output. This is necessary to increase the output torque of the servo. Low speed is good at the beginning as it let's you clearly see what's happening. But very soon you will want more speed.

If you purchase a DC Gear Motor, you choose the Gear ratio. So, you can select a faster or slower motor.
Have a look here to see a selection table that shows 2 motor types with different Gear Ratios.

In motor (2) I will show you the combination DC Motor + Drive. Things will be faster there!

The Wheels

This is an important choice. There are plenty of omni-wheels available on the internet, but I recommended those ones.

The contact (yellow) material is rubber, not plastic. Therefore, these wheels don't slip on nearly any surface, even over glass or similar. The elements conform a perfect circle. This allows a nice turning. There is no "bumpy" movement due to uneven sections on the wheels.

The central axis is designed to fit LEGO elements, but there is a cylindrical cavity (9 mm diameter / 8 mm deep) that allows you an easy adaption to any possible motor axis you may need to connect.

You can purchase them here: http://www.holonomicwheel.com/index.jsp

viernes, 25 de enero de 2013

Things are moving!

After some time, here I am back again. I received the materials, I put them all together... and this is the result:

I created an App to control it via Bluetooth. I used App Inventor to write it.( http://appinventor.mit.edu/ ) Here you can see it on working:

Give me some more time and I will explain you the parts & processs, bit to bit!

viernes, 11 de enero de 2013

Tipp1: Prepare an easy power plug


Sometimes you need to prepare a plug to connect different battery packs to a certain connection plug. If you use an intermediate "Easy plug" with just 2 connections you may change the polarity. To avoid this risk, I prepare them using a 3 pins header / socket in this way:

If you connect the 2 sides correctly, everything works fine.

But if you connect them in the wrong way, nothing happens! Just the 0Volts are connected.

Furthermore, you can easily recognize what's the right way.