Re: NXT Synchro Drive

On Dec 7, 2006, at 7:03 AM, Chris Phillips wrote:

> In lugnet.robotics, Rich Thompson wrote:
>> I have been playing with the turntable from the NXT kit to try and
>> build a synchro drive train. It got a bit complicated but it works. I
>> posted a video at my blog:
>>
>> <http://www.robotthoughts.com/index.php/lego/archives/2006/12/06/ 
>> lego-mindstorms-nxt-synchro-drive/>
>>
>> or just:
>>
>> <http://www.robotthoughts.com/>
>>
>> Have Fun!
>
> This looks pretty cool, and I can well respect any attempt to  
> design a cool
> device out of LEGO, but I wonder how necessary something like this  
> is with the
> NXT?
>
> It seems to me that the new servo motors with their integrated  
> rotation sensors
> are incredibly accurate for navigation, especially since the  
> firmware is capable
> of precisely matching the speed of the motors.  The design of the  
> servo motors
> (as depicted in the NXT booklet) has the rotation sensor geared  
> almost directly
> off the motor shaft at the head of the internal reduction  
> geartrain, so it has
> extremely high accuracy.  The documentation claims it has a  
> resolution of one
> degree of output shaft rotation!
>
> The demo robot, built from the Open Me First set of parts and run  
> with the Demo
> program that comes pre-loaded on the NXT, is an amazing  
> demonstration of this
> capability.  This robot moves straight forward a few feet, then  
> turns 180
> degrees, returns to its original location, and then turns 180  
> degrees again.  On
> a level surface, I have found that it is capable of returning to  
> its original
> location within a few millimeters!
>
> Navigation by odometry was something I had long tried to accomplish  
> using
> <http://www.drvegetable.com/pic_franken02.html the RCX and a pair  
> of Rotation
> Sensors> without ever coming close.  With odometry so greatly  
> improved on the
> NXT, is a synchro drive platform really necessary?
>
> Just wondering...
>

You are touching on the exact reason I am playing with the synchro  
drive platform. Previously, to maintain "sync" between the rotation  
of different wheels I had to use locked gearing or a chain. you can  
see examples here:

http://www.robotthoughts.com/index.php/lego/archives/2000/07/20/astro- 
droid-synchro-drive/

and here:

http://www.robotthoughts.com/index.php/lego/archives/2000/07/20/ 
synchro-drive-with-360-degree-bumper/

By working with NXT motors, I hope to not have that design requirement.

As to why this platform, I like the zero degree turn radius and the  
design is fun to watch when the full synchro drive is in motion. See  
the videos in the robots above. Once you understand the synchro  
drive, it really opens up some of the robotic possibilities of the  
turntable.

Have Fun!

Rich