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Unread 06-24-2002, 03:19 AM
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Controlling a FIRST robot with a Lego RCX Controller?

Posted by Andy Baker at 05/24/2001 3:17 PM EST


Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.



A local school is having fun with their lego league team here in Kokomo... but they want to drum up more interest and support.

They have made various cool robots from the Mindstorms kit, and they've done alot of presentations, trying to get more students involved. Whenever they present one of their creations, they are having a hard time getting people to take them seriously and look at the robots for more than just toys.

So, the team wants to be a little dramatic and really show the crowd something drastic during a presentation. They want to run their Lego Mindstorms robot, stop it, manually remove the RCX controller, insert the RCX controller into a big robot (a FIRST robot), and then have the big robot operate just like the Lego robot.

The Lego team would like to do this... but we're not sure how. I would imagine that we would need some amplification of the signals from the RCX, and somehow link it to the Innovation FIRST controller. We have not investigated anything yet. Has anyone else done this? If so, do you have any suggestions?

TIA,

Andy B.


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Re: Controlling a FIRST robot with a Lego RCX Controller?

Posted by Eric Reed at 05/24/2001 6:18 PM EST


Coach on team #481, NASA Ames / De Anza High School, from De Anza High School and It could be you!.


In Reply to: Controlling a FIRST robot with a Lego RCX Controller?
Posted by Andy Baker on 05/24/2001 3:17 PM EST:



How about using the BotBall Handyboard instead? It has PWM outputs, plus the advantage of many more inputs/outputs. It can drive any of the lego motors / sensors. My guess is you won't need any kind of signal amplification. I'm not sure you will be able to drive a speed controller with the Mindstorms motor outputs.

Eric Reed
De Anza High School - 481



: A local school is having fun with their lego league team here in Kokomo... but they want to drum up more interest and support.

: They have made various cool robots from the Mindstorms kit, and they've done alot of presentations, trying to get more students involved. Whenever they present one of their creations, they are having a hard time getting people to take them seriously and look at the robots for more than just toys.

: So, the team wants to be a little dramatic and really show the crowd something drastic during a presentation. They want to run their Lego Mindstorms robot, stop it, manually remove the RCX controller, insert the RCX controller into a big robot (a FIRST robot), and then have the big robot operate just like the Lego robot.

: The Lego team would like to do this... but we're not sure how. I would imagine that we would need some amplification of the signals from the RCX, and somehow link it to the Innovation FIRST controller. We have not investigated anything yet. Has anyone else done this? If so, do you have any suggestions?

: TIA,

: Andy B.


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Autonomous vs. remote control...

Posted by Joe Johnson at 05/24/2001 11:22 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Controlling a FIRST robot with a Lego RCX Controller?
Posted by Andy Baker on 05/24/2001 3:17 PM EST:



Andy,

I can easily imaging having the motor outputs set or clear switches that interface to the digital port on the RC. I can also imagine that the RC could then turn on motors via Victors or Spikes.

I think that you could also replace the motors with an resistor and a capacitor or two in order to turn the PWM output from the motor driver of the RCX into a DC voltage that could interface to the analog port on the RC, this would have the advantage of allowing 8 levels to be set per motor channel (assuming you can get the programming all worked out. Actually, you could potentially get 16 levels per motor channel if you could figure out a way to use the reverse directions of the RCX motor driver as well -- a diode or two and another few resistors and capacitors could do the trick I suppose).

The interface would be a bit clumsy but I think it could work. More fundamental to the problem though is that that the RCX is basically intended for controlling autonomous machines while the Innovation First controller is intended for controlling machines remotely.

You have to decide for yourself whether dumbing down the Innovation First system to appear to be controlled by the RCX is worth the bother.

Joe J.



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Re: Controlling a FIRST robot with a Lego RCX Controller?

Posted by Andrew Rudolph at 05/27/2001 11:36 PM EST


Student on team #212, Lightning Robotics, from Michael Krop Senior High School and ???.


In Reply to: Controlling a FIRST robot with a Lego RCX Controller?
Posted by Andy Baker on 05/24/2001 3:17 PM EST:



Well if all you want to do is control the drivetrain it is very simple. Al you need is the following one of the polarity switches lego makes. I dont kow if they can handle the Amps but you could find out. And a micro motor for each one. the polarity switches work like mechnical speed controllers, so you can buy thoes and hook the micromotors into them. the ploarity switches can be found here http://guide.lugnet.com/set/5120
for the interface its really easy all you have to do is use the IR that the RCXs have ive done it a few times when we have made big confusing robots for demos where 1 RCX isnt enough. Also when we made remote controlled robots for games we made up.
Also you might be able to make the out puts into PWM signals by just pulsing it. But im not the master that Domain. But the RCX puts off 9 volts on a full batteries, so you migght be able to get some help from that info. that all for now if i think of somthing you will hear about it.

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Re: Controlling a FIRST robot with a Lego RCX Controller?

Posted by Ian Mackenzie at 05/29/2001 6:40 PM EST


Student on team #188, Woburn Robotics, from Woburn C.I..


In Reply to: Controlling a FIRST robot with a Lego RCX Controller?
Posted by Andy Baker on 05/24/2001 3:17 PM EST:



Just a couple of ideas from my experience with Mindstorms:

First, there are a whole bunch of ways to get the Lego robot to control the Innovation FIRST controller. To keep things easy, for instance, you could have the Lego RCX control motors that were in turn connected to continuous-turn potentiometers hooked to the Innovation FIRST controller (this might have the added dramatic effect of the Lego motors appearing to be 'amplified', if each motor on the RCX controlled one motor on the FIRST robot).

Second, and possibly more important, try NOT to use Spirit.OCX (the Lego software) to control the robot. Unless you must have feedback, I have found it is much, much more efficient to directly access the serial port to send messages to the RCX and then write a message-interpretation program for the RCX in a language such as NQC. It's quite easy, and very fast; for a demonstration earlier this year, another student and I had one IR tower controlling four Lego robots simultaneously with no detectable lag, using this technique.

If you want any more detailed information on directly accessing the IR tower, or using NQC, please tell me (I didn't want to go into all the nitty-gritty if the method isn't suited to what you want to do.)

-Ian Mackenzie


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Re: Controlling a FIRST robot with a Lego RCX Controller?

Posted by Lloyd Burns at 05/30/2001 10:52 AM EST


Engineer on team #188, Woburn Robotics, from Woburn Collegiate and TorDistSchoolBrd, ScotiaBank. OntPwrGen, Enbridge.


In Reply to: Controlling a FIRST robot with a Lego RCX Controller?
Posted by Andy Baker on 05/24/2001 3:17 PM EST:



: A local school is having fun with their lego league team here in Kokomo... but they want to drum up more interest and support.

: They have made various cool robots from the Mindstorms kit, and they've done alot of presentations, trying to get more students involved. Whenever they present one of their creations, they are having a hard time getting people to take them seriously and look at the robots for more than just toys.

: So, the team wants to be a little dramatic and really show the crowd something drastic during a presentation. They want to run their Lego Mindstorms robot, stop it, manually remove the RCX controller, insert the RCX controller into a big robot (a FIRST robot), and then have the big robot operate just like the Lego robot.

: The Lego team would like to do this... but we're not sure how. I would imagine that we would need some amplification of the signals from the RCX, and somehow link it to the Innovation FIRST controller. We have not investigated anything yet. Has anyone else done this? If so, do you have any suggestions?

: TIA,

: Andy B.

I did a search on "lego mindstorms" and found this site which deals with reprogramming the CPU - one reference therein :

"Paul Haas has figured out that the RCX generates a signal which can control a servo. His Hitec HS-300 servo responds to 1
millisecond (ms) pulses by rotating to one extreme and 2 ms pulses by rotating to the other extreme. You can make the RCX
generate pulses like that. It takes 3 resistors to get the voltage right and the wave form shape clean enough. His Servo is only
rated up to 6 volts, so he used 4 AA batteries for it. Now the servo goes to either extreme under the direction of the RCX. "


While this may not be what you had in mind, it does indicate the extent to which some folk will go. In order to drive the servo, he reprogrammed the CPU, and took the outputs off the board itself.

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