The motors(2)

I received a few days ago the new motors. Now I use 12 Volts, 90 rpm motors. You can see yourself in the picture the big different between the old ones (the little thing in front) and the new ones.

The new motors allow a fast movement while having a very good behavior at low speed.
I purchase these new motors directly in China here.

You can see them in action here:

The next step will be to use full rotation servos. This will ease the construction and keep the bill of materials shorter, therefore the cost of materials will be reduced. 

But this involves writing software to control them... hope to be finish this week end!

Keep Making!

Wiring up the elements

First things, first. We need to create a diagram of our wiring in order to prepare our job. Normally, an engineer creates wiring diagrams to indicate other people how to connect things together in the proper way. So, if I will wire myself... why shall I do a wiring diagram? 

There are a few very good reasons: 

1.- To keep track on what you did! Working a few hours per week, you shouldn't assume you will remember everything. 

2.- If you need to troubleshoot your design, you will need to check 2 things: the concept and the implementation. To visualize the concept you need a wiring diagram. 

3.- Obviously, if you need external help you need your wiring anyway.

So, do yourself a favor and create proper documentation of your projects!

If you're a beginner, I recommend you to use Fritzing. Once more, this software is easy to learn, to install and yes, it's for free! Here you have my Fritzing diagram:

CAUTION: When using library elements on Fritzing, please double check for accuracy. For example, the pin out of the Bluetooth Modem included in Fritzing is not compatible with mine. If you have a close look on the photos of real wiring you will realize the difference.

You can find the source code of this fritzing wiring here. It is not possible to preview this type of files. If you want to work with it, you must install Fritzing first and then download the file to your computer...  or you use the above picture!

Bill of materials:
1x Arduino Leonardo.
2x Motor Driver 1A Dual TB6612FNG
1x Bluetooth Mate Silver WRL-10393
3x small motors (I'm trying some different motor types. I will update this when I'm finished!)
1x Battery

Pack
4x Accumulators, to create 4,8 Volts.
1x +/- bus as explained here below.

Wiring Description:

I always create a + - bus for my projects. This is useful to power all the electronics we will install. It looks like this.

To avoid problems with the polarity, I use the 3 points plug I described here some time ago.

Bluetooth Modem: Imagine you are connecting 2 microphones with 2 loudspeakers. You must connect Data Source with Data Destination. Serial communication is the same: I connected the Tx Modem to Rx Arduino and also RxModem to Tx Arduino.

I used an "DiY plug" to connect it. This is the result

Drivers: The selected driver must receive 2 power voltages: one for the electronics and another one for the motors. I used a battery pack for the 7Volts, then I use the +5Volts from the Arduino Board to power the drivers and the modem. Here, a picture of the splitter board:

I wired together both "Stby" pins to control them with a single output. (Output No 2). 

Then I wire PWM, AN1, AN2 of motor1 to outputs 3, 4, 5. I repeat the same for motors 2 and 3 using outputs 6,7,8 and 9,10,11. I prepared the wiring of motor 4 on the driver's side, but I didn't connect it to the Arduino. 

This leaves us only 2 digital in/out's (12 and 13) available for other purposes. If I need more digital I/O's I will use alternative techniques to free some of them. But for the moment I prefer to solve the wiring of the drivers using simple techniques.

Phase 1: soldering the wiring.

Phase 2: Gluing the plugs to create a socket.

Observe that I bend the motor pins to allow me to plug / unplug them when the driver is in his socket. Believe me, it is always a help to have an easy way to disconnect motors...

Then we add the battery pack. The final result looks like this:

I needed some 2 "part-time days" to create the concept, figuring out how to put all the elements together, then soldering & wiring. So, this is something you can do in a single week end. If you are good at soldering, you may be finish in a few hours.

Wiring is finished. Now, the very interesting part of the project. The software! But you must give me some little more time for it. 

Keep doing!

Installing the main elements

The picture above shows the elements we need to fix on our wood board. Let's start with the motor/wheel.

To fix mechanical elements having not a "clear fixture point", I use metallic perforated band like this one:

I bend it in the form I need. This are probes No1 and 2 for my motors:

After some attends, it is easy to reach nearly perfect results. Here support No. 3:

As you can see, I bend the form that I need, then I saw it out of the strip.

You can purchase ready made supports, if you want. But hey, c'mon, we are makers, aren't we?

Now let's fix the elements on the board. I use metallic screws for the motor, nylon screws for the arduino board and hot glue for the rest of the elements.

I use those screws:

I  mark the holes with a hand drill, then I use a small cordless drill to make the holes. (One day I need to create an entry to describe my tools & workbench...)

We reach this:

Then, I glue the rest of the elements using hot glue. I always use plugs to connect the electronic modules. I'm not rich, so I expect to re-use them in other projects. I glue the plugs on the wood board, then I plug the devices on them. I fixed the Bluetooth modem in this way.

The final picture: 

Now, we must wire the elements, then we will upload some software on the Arduino. Things are getting interesting now... Keep reading!

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