As you may be aware I have been building a Robot called Wheeler out of old parts (old grey and RCX 9V motors etc). I was hoping to have it finished over the Christmas break but had hit a small issue with driving the wheels with the new weight of the body. Anyway what I managed to get up and running is the top half of Wheeer and the controller which is a Android phone (Dell Streak).
Mindsensors RCX Multiplexer
I was utterly impressed with the Mindsensors.com RCX Multiplexer and using Xanders driver suite (check BotBench) how fast I was up and running. I wish there was a way to run the RCX Multiplexer off the NXT power supply but thats a small thing compared to how useful it is. I wish I had 3 more of them so that I could control 16 RCX motors!
Android NXT Remote Control
So to try and work out how to control the NXT via Android, I stumbled across the NXT Remote Control project which is free to download. This uses Lego’s Direct Commands to control the 3 motor ports on the NXT. This means it bypasses your own code and you have no control over it. However, what I managed to do is reduce it down to a very simple program that sends messages to the NXT which you can deal with in your own program. In RobotC, it sends messages that are compatible with the MessageParam command and so you can send a message ID and 2 params to the NXT and deal with them in RobotC anyway you want to.
Code will be available soon once I have tidied it up 🙂
Today I had a little bit of spare time while looking after my son and watching some films, so I decided to try and build a studless (I always build studded) robotic arm using NXT motors (I mostly use PF).
Here is the result.
I have to be honest and admit that I loved building using studless Lego. It does involve building in a different type of way, you could say in a more structured / planned way. However until I have enough of it to build giant robots, I will be sticking with studded Lego which I have tons of!
I still need to spend some more time with the NXT motors as they still feel very alien to use due to their random fitment and shape but I am sure I will master them soon.
Merry Christmas everyone and have a great New Years!
At the weekend I got a chance to do some more work on Wheeler, the Giant wheeled robot. I have decided that this Robot will contain a single Lego NXT with a Mindsensor RCX multiplexer. This will give me access to 3 NXT motors and 4 old style 9v motors.
Wheeler will have quite basic functionally so that I can save enough parts for the Massive T1 and try and keep cost down. I have tons of old 9v stuff so that helps.
The plan is for 2 NXT motors to drive Wheeler, 2 RCX motors to move arms up, 1 RCX motor to control both hands, and 1 RCX motor to turn the head. This leaves 1 NXT motor spare.
Below are some pictures of the current progress.
Before I started!
Now Wheeler has 2 basic arms with connected motors and the neck joint has a motor attached to it.
Top view of the 2 old style 9v Motors. The motors are connected to the turntables via a worm gear that is connected to a 24 teeth cog which then turns the outer cog of the turntable via a 8 tooth cog.
The arm is very simple and light so that the motors can move it with ease. Remember the old 9v motors are not as strong as the Power function ones.
The hand is controlled via a old style 9v micro motor. These are very small, slow turning light motors that have become very rare. I have decided that this type of hand is pretty naff and will be designing a new type that works like a vice.
After Bob, I decided to adapt the KISS approach (Keep it simple stupid)! My objective for the Great Western Lego Show 2011 was to make a Robot that worked, and worked well! It had to move and be able to turn on anti-slip carpet, easy to control and be strong enough to take knocks / drive in to tables without breaking.
George is a fully functional 5 foot 7″ robot. Controlled via a PlayStation 2 controller, he can move about, rotate his upper body, move his arms / shoulders and grab items. His head also rotates, moves up and down and if you get too close, his eyes will roll.
Communications
This time around I decided to scrap having multiple NXT’s and went with the brilliant Mindsensors wireless Playstation 2 controller sensor pack. This allows you to control your NXT via a Playstation 2 controller which has a huge number of buttons / controls on it. Then I linked the NXT to a hiTechnic IR link so that the NXT could send commands to power functions infrared receivers (all 4 channels). This setup gave me a large number of possible functions (11 different motor channels). I used RobotC to program the NXT as I find it an amazing programming language.
Weight
This robot had a large upright body beam. However it did not rise up and down so it did not require any counter balance weight. Also, it was not plated and only carried 1 NXT. This probably cut down a 3rd of the total weight of the robot, even though it was bigger than Bob (5 ft 7” tall).
Drive
The main base of the robot was smaller than the one on the previous robot which would naturally make it move a little easier, especially being lighter. Also the 4 XL motor driving it were geared down via a 8 to 24 tooth gearing. First time around, this just snapped the gears in half. The way to get around this was to use 2 sets of 8 to 24 tooth gears in parallel on the same axle per motor. Also, as a backup, in case the robot did not work on the show carpet, I could swap the 24 tooth gears for 40 tooth gears very easily which would give it even more driving power but at a cost to speed.
On the day
George was a huge success with the members of the public. Most people did not realise it moved and so jumped quite a bit when they realised it did. This was very funny except for the odd small child that got rather scared. People even started taking pictures next to it and a few people felt compelled to try to hug it or shake George’s robotic hand.
Issues
Issues were a minimum really. After transporting George in more pieces than I hoped, I had to do a small tweak to the neck as the gears were slipping. Sadly I only had red technic with me for another one of my models and so it looked a little odd if you saw George from behind.
The main body bearing, as shown below just did not work on the day (well 2 days). I am not sure why it worked at home and then stopped but I could only get it to turn 1 way. Also the footballs kept falling out! I have since swapped them out and made a better version using wheels.
The only other issue which, to be fair, I already knew about, were that the large linear actuators (x3) in each shoulder joint made horrible noises (the built in clutches) and sometimes got jammed. Lego have made improvements to these actuators, but I have not got the newer version yet. I did try using pneumatics for the shoulder but that gives you little control.
The Future
I have already started work on 2 more large robots for next year (while also keeping George). The first will be called Wheeler and is a giant wheeled robot. The start of it can be seen below.
The second robot will be based on Bob (T1) but avoiding all of the downfalls of it. I am looking forward to seeing people’s faces when there are 3 giant robots running around.
One of the robots that really fascinated me that I thought I could build was a T1 from Terminator 3. It was a tracked robot with twin mini-guns (another thing I wanted to build). So I went about building a rather large Lego version for the 2010 Great Western Lego Show which is our club’s (Brickish) largest event.
Weight Due to its weight (well over 20KG) it could only turn on low friction floors. The base of it was nearly a meter square running double tracks each side powered by 4 XL motors (directly linked to sprockets). Going forward was very quick but turning just did not work well. I only actually found this out on the day of the show where I discovered the floor was anti-slip carpet.
Communications.
The robot had very clever communications in my opinion. It used 4 NXT’s (2 slave, 2 master) which communicated via bluetooth. One set of NXT’s had an accelerometer which when moved, would move one of the robots arms so that it would mimic the users moments. The other set of NXT’s also had an accelerometer to control the other arm however it also had a mode button so that you could control the robot’s other functions (moving, body rotation and lift, head movement) via the same accelerometer but in different modes. Each master NXT also had a fire button to fire the Zamor launchers on each arm.
The problem was that the bluetooth communication just was not stable enough and also suffered from lag and loss of data. You would put it in arm movement mode and it would instead move the tracks. There there would be a large amount of lag which meant the robot was always a few seconds behind. In practice, this caused the robot to drive itself in to a table 30 minutes after the show opened causing a partial rebuild in front of many people! Quite embarrassing.
The robot also had a large main body beam (around 4ft long) that had to be counter balanced via many boat/train weights which caused even more weight issues. This main beam actually snapped a few technic beams while it was being built. The main beam could rise up via 5 pneumatic rams. However it required over 30psi to start it off (see below). This caused other issues.
I also completely covered Bob in black plate, which had a habit of falling off and also added more weight.
George is a fully functional 5 foot 7″ robot. Controlled via a PlayStation 2 controller, he can move about, rotate his upper body, move his arms / shoulders and grab items. His head also rotates, moves up and down and if you get too close, his eyes will roll.
