Mindsensors.com have done it again, released a product that really helps out people who build bigger than normal Lego models. I have had 1 major issue with the Lego Mindstorms kit and that is because there is no way to extend the cables unless you make your own or buy custom lengths. Both not a a easy thing to do. The original RCX Brick used standard 9v cables which were easy to extend, however with the advancements of the NXT saw it require a lot more wires (6 in fact) between the motors/sensors and the NXT brick.
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 🙂
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.
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.
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).
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 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.
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.