I'm currently working on about six different parts of the robot. There are wires everywhere as I test different things. Many times I find myself revising one component even as I design completely new ones. I;m still going to try to have the robot ready to start being mobile by this June (2012). Hopefully it will be smooth sailing from here. Mostly I just have to get everything hooked up in a way that the robot doesn't need some umbilical connected to an external power supply. I have found that powering the robot is not the difficult part; it is providing the correct amount of voltage to all of the smaller components that require less than a few volts and very few amps in order to function. If I were to connect them directly to the 12 volt car battery they would overload due to the extreme amperage. My savior has been the small car chargers that can convert 12V 75A to about 5V 4A which is perfect for powering small electronic devices like the Arduino. In about a week I will post again and show the wires all neatened up.
The image above is one of two 12 volt car adapter chargers that I disassembled to put into a single container. These were just some old chargers that I was able to recycle to use on the robot because they can directly convert the 12 volt, 75 amp power source from the robot's battery into a voltage that wont destroy the Arduino Microcontroller or any of the electronic shields that I'm using.
These are the two circuit boards moved into the new enclosure. Both adapters are individually protected with relays to protect them in the case of a short. Bellow is just a photo of the container once I screwed it shut. The container is an extra-small project box that I got at Radio Shack for just a few dollars.
This photo is of one of my new adapter's leads powering the relay shield that is connected to the arduino. Ideally I would have more of the adapters but I don't really want to go out and just buy a bunch of adapters just to splice up the wires into my robot. I would prefer to acquire a few that people are just throwing away.
Here are my suggestions for what to use for a laptop and router.
Salvius currently uses a Lenovo net book as a server but that is simply because that is what I had available at the time. Obviously you can use any computer you have. You will also need a router. Salvius uses a Netgear Wireless Router but again; you can use any router that you already have.
Next, all you have to do is turn on your router and plug it into your net book with an Ethernet cable. Installing Ubuntu is very easy once you burn it to disk or a flash drive. Just put the disk/flash drive in the computer and then turn the computer on. You should see prompts for an installation. Just follow the prompts and everything will be setup correctly.
When Ubuntu server starts you will see an IP address in the text right after you login. If you enter this IP into the browser of another computer while connected to the wireless router you will be able to connect to your server. You should see a white webpage with some text which will tell you that it is working. If you are more familiar with programming and servers you will easily be able to connect to this server remotely and make any modification that you want to it.
P.S. I will be making a video on how to do this pretty soon so stay tuned!
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| 5V car adapter charger for cell phones |
The setup was very simple. To do this you don't even have to remove the plastic outer case of the charger like I did. Just connect the end of the charger to the positive battery terminal and one of the side connectors to the negative side of the battery. Then just cut and strip the wire on the end of the charger. There is 5V output between the red and black wire (red being positive +, and black being negative -). There is also about one volt between the red and the white wire. I thought this was a bit odd because electronics don't usually use a positive wire as a common line.
I hooked up a potentiometer to my motor controller today. The controller goes to the right wheel motor and has a port for a potentiometer to control the speed of the motor. I wanted to reduce the speed a small amount so that when I am ready to test the robot's drive system the robot doesn't drive away at 50 miles per hour. Every electrical system in the robot is protected by its own fuse in case there was ever a short or something went wrong, that way the fuse would blow rather than shorting out a few hundred dollars worth of electronics.
What I found today while testing the motor was that as soon as I put a load on the motor I would blow the fuse that protects the motor controller. I put in another fuse (10 amp) and used an amp meter to test the no-load amperage which was about 2.5 volts. Then when I applied load to the motor the meter jumped up to about 12 amps and then the fuse blew again.
I looked up the specs for the motor online and I found that with no load the motor should average at about 2.7 which is about what I got but then I saw that the stall current was 133 amps. That is a huge amount and that is why I was blowing a fuse when ever I applied load to the motor. As soon as I apply load to the motor its amperage jumps up to over 30 amps. This is normal but I have did not expect this when I first assembled the circuit. Luckily fuses are easy to replace so I put in a 50 amp fuse and now everything is working fine.
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| The two cable ends labeled positive (+) and negative (-) |
I recently read a post from MAKE magazine's blog about how to correctly splice wires. It just goes to show that there is a correct way to do everything! Since reading the post I have been using this technique to make strong durable splices while working on the robot.
The name of this splice is the "Lineman's splice". This splice has been NASA approved and is designed to hold up to a lot of tension if necessarily. This splice actually produces a section that is stronger than the rest of the wire. If the wire were to break it would do so at another point along its length.
When doing this splice you have to make sure to do a few things to keep the splice within the topmost quality.
The name of this splice is the "Lineman's splice". This splice has been NASA approved and is designed to hold up to a lot of tension if necessarily. This splice actually produces a section that is stronger than the rest of the wire. If the wire were to break it would do so at another point along its length.
When doing this splice you have to make sure to do a few things to keep the splice within the topmost quality.
- The metal portion of each wire should be pre-tinned.
- There should be a minimum of three turns around the end of each wire
- Be sure not to leave any gaps between adjacent wire turns
- Wire turns should not overlap and their ends should be trimmed flush before soldering
- Wire turns should not overlap the insulation on the other wire
Basically all of these standards are designed to prevent any protruding ends that could potentially contact another conductor. They also insure that the connection is strong and thus wont be subject to being brittle. Also a weak connection can create resistance which then results in heat which can potentially damage nearby electronics.
Yesterday I decided to install a mechanism to make the robot's head be able to turn. I made a quick 1 minute video showing the building process and the part working. I tried to keep the part's design as simple as possible. Following the robot's theme of recycled materials I used some parts from an old erector set and one of the motors I had removed from the original remote control car that I had used to start building the robot in the first place.
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