ScoCopTer (Feeder) V3

I realised while making the 3rd version of the ScoCopTer that I hadn't given a moments thought to the program and how difficult it will be to store the image in the NXT's memory as for one thing I am a complete amateur when it comes to programming having only dabbled in visual basic, and a little bit of C#. So I decided rather than dive head first into the photocopier I would just slow down a bit and make a Scanner first, program it and practice making the scanner as efficient as possible. Then I will make a plotter and experiment with making more complicated images, maybe print images from a computer in black and white onto the paper. The good thing about the Scanner and the Plotter is that they can both use the same base to move the paper and have the platform for the scanning/pen module to move across. This base module is what this update is about.

As you can see I've had two previous attempts at the ScoCopTer so I have learned some of the fundamental things about the design, and which methods are better than others for feeding the paper etc. I also decided to abide by KISS (Keep it simple, stupid) and as I still very new to the NXT system I am going to use all my Lego pieces with no limitations to give me a sturdy, well designed paper feeding module and I won't have to worry about not having enough pieces because I was only using NXT 2.0 parts.

The whole robot building is a learning process, and I've always dived in without looking closely at what I'm diving into, and it's only when I hit the bottom that I know next time to be a bit more careful and take things a bit more slowly. So from my original plan of a Photocopier/Scanner/Plotter all in one robot built from parts only from the NXT 2.0 set I have stepped back to a Scanner or Plotter using as many pieces as I need. Then when I have completely mastered the Scanner and Plotter I can move onto trying to combine the two to produce a working photocopier. One day I will learn that it's easier to start at the basics and build your way up rather that jump off a plane and hope to land at the top.

So clichés over, onto the Feeding Module (Feeder from now on), on the previous version the beams connecting the two ends of the feeder together was a lot stronger, but I found it awkward with both the motor and NXT at one end which made it look slightly out of proportion and the far end was a lot weaker than the side with the NXT. So I decided on this version I would have the motor at the opposite end to the NXT. Also with the previous version I tried to have the NXT mounted on top of the feeder which I was doing to try and allow the user to see the scanned image more easily, but in practice this was impractical because the NXT got in the way of the paper as it was being fed through, so this time I mounted the NXT on the end.

Here you can see a photo of the whole Feeder V3 before I look more closely at some areas of it;

Here you can see the overall model looks quite good and both ends are quite well balanced in terms of size and it's also very strong, I can pick it up from either end without it bending at all. Now I have allowed myself access to all my pieces I can use the small 'pulley' wheels on top of the main wheels to provide permanent friction on the paper as it's fed through but as the wheels can rotate that paper doesn't crumple or get stuck against it. The angled beam that the paper comes off is also a lot better than the last version as it isn't restricted be beams above it, or the NXT.

The drive for the feeder comes from the motor on the right which is geared from the motor 3:1 which obviously means there is more torque and less speed which is ideal for feeding paper. The motor is attached in a gear train form the motor going 8t:24t:8t:24t (t=teeth) and you can just about see this in the photo to the right.

In the way of the gear train you can see all the bracing that is used to lock the motor end together.

As well as the motor driving the wheels I also needed to attach some sensors so the robot knows when paper has been inserted, and also when the module riding across the top has hit one end so the rotation count could be reset so no error was carried forward. As in the previous version I used the ultrasonic sensor to detect when paper had been inserted and this was fairly simply connected to the middle of the structure, it also provided more support for when the machine was on a flat table and helped stop the middle from sagging. At the end with the NXT I have got a touch sensor which works with a quite simple mechanism to trigger it when either the pen or scanning module touches it. The touch sensor then bounces back into place with the use of an elastic band, and this took a surprisingly large amount of readjusting to get it to bounce back just right.
In this photo you can also clearly see where how I have used two wheels to to hold the paper in place, the top wheel is on a pivot that is held down by an elastic band - you can just about see the peg with the elastic band on the end of the 5 hole beam.

I have written a couple of short programs to test the feeder module and the only problem I have found so far is that the ultrasonic sensor doesn't really notice when the paper is less than 10cm away, it just has some problems keeping the motors going, so I may have to tweak this slightly or come up with a new plan altogether. But for now I'm going to work on the scanner module and hopefully I will have that built and programmed in the next week or so.

S