Long time coming.......................

 It's my age really.

The body parts of the Trundle all got checked against each other yesterday so I took the opportunity to begin documenting the build. I will publish the photos and instructions here as a continuing saga but also put then into a pdf that will be downloadable and printable at a later stage. First then, the cast.

These are the main hardware parts. Main body, template and partially assembled hubs.

The template is for the end plates on the hubs. The continuous rotation servo has to be mounted off centre in order to place the drive shaft in the exact middle of the circular plate. This could have been very complicated if not for AutoCAD and an expert user being available. The template was cut from 6 mm MDF by the laser cutter and, at the same time, a square from around it was also cut to enable the plastic discs to be accurately placed when they were cut.

This is a partly assembled hub unit. The servo has been fitted to show how the offset of the mounting enables the drive shaft to be at the dead centre of the plastic disc. The rim sitting on top of the disc will eventually be chemically welded to the edge of the disc and then they will slip on to the end of the main body tube to form a closed tube with a drive unit at either end. In the picture, the servo has been mounted from the outside of the disc but I am going to try mounting from the inside in order to see how close that brings the wheels to the hub. If they still turn without catching, then that will be my preferred position.

This is how the hubs will fit on the main tube, once they have been chemically welded, they will fit snugly over the end and a small hole will be drilled through the bottom of the hub and tube and a small locking self tapping screw inserted. The wheels will be fitted to each hub and, with the addition of some electronics and a battery, the whole unit will be able to trundle around on the floor. More will be documented when I have the next set of components to hand (They are currently all in the post).

The whole of the body and hub assembly is made from acrylic cut to very precise sizes. The main body tubing is 90 mm outside diameter by 200 mm long, the hub tubes are 100 mm diameter by 20 mm long. Each tube section is 5 mm thick making the hub tube inner exactly the same size as the body outer. To make them fit, all that was needed was to gently sand the inside of the hub until it is a snug fit. The hub discs are 100 mm diameter and the template was cut to 101 mm diameter in order to allow the plastic to sit snugly inside the square outer in order that the laser cutter has a good reference point to start from. In this photo, it is possible to see just how thick the tube is.

Hiccough!!

Well, so much for my memory. I dug out the motors and wheels yesterday evening and discovered that I had totally forgotten how they mounted. So, this morning I brought all the parts into the office and threw myself upon the mercy of colleagues. Lee produced the scale drawing in AutoCAD for me and Mike cut the two end pieces on the laser cutter for me. Individually, this took practically no time at all but I had to run between the two and wait around for them to be available so the ten minutes worth of clever stuff took nearly all of my lunch hour. It was, however, well worth missing as the resulting pieces of plastic are wonderful and fit perfectly to the various other bits. I still need to fit the wheels to the actuators of the servos but, within reason, most of the mechanical work is ready for assembly now. I will certainly be able to begin documenting the Trundle Mk2 this evening.

Happiness is plastic

I now have all my tubing cut and skimmed so I will probably begin marking out this evening in order to get the two wheels mounted up. I also tried out the fitting of the Gertboard yesterday and have come up with a plan to mount everything on the one sheet of plastic. I will measure up sizes etc. and see what can be done.

I gotta Gertboard (2)

or even too - or maybe two.

'Cos I ordered and received two Gertboards as I have two Pis. They are very well made and, judging by the manual, very capable pieces of kit. I have re-thought using a Pi on the mark 2 Trundle as it probably wouldn't work as well as the Arduino will but I really must get a couple of those self contained wheels for the Mark 3 when I get around to building it. If I do, then I will certainly be able to use the Pi to run it.

Serendipity strikes!

Whilst searching for a completely different item, I stumbled on this at Cool Components. It's a 60 mm diameter wheel with the motor, encoder and drive components built in, just connect power and data lines and off you go. At first glance it looks expensive at nearly £20.00 but when you add up the cost of individual parts all built in to this wheel, it begins to look very good value for money. Cool Components have a whole list of new products on their home page and it's worth a visit. In fact, I would suggest visiting all of the traders listed on the left every so often as you never know what you might find. In the meantime, here's a video of this wheel in action.

I gotta Gertboard

I have just ordered the ready made Gertboard from Farnell. It will be of immense use to me when I start using the Pi in real world situations. I may even fit it into the mark 2 Trundle and run my next series of tests on that. The Arduino will still be used in a lot of areas for local control and, of course, the big advantage with the Gertboard is that the same chip as used in the Duemilanove is installed on it. This indicates a very logical communication system.

Another bonus day for the delivery services.

The tubing for the full sized version of the trundle has arrived and is exactly what I hoped for. The only minor problem is that the sizes are just too accurate. The outer tube won't quite fit over the inner one so I will have to skim a very small layer off the outside of the inner tubes in order to make a good fit. In addition, my long awaited book has arrived via Amazon. Getting Started with Raspberry Pi is an american book and after an hour of study promises to be most useful. It finally made Linux on the Pi fall into context for me. Indeed, it has already helped me to a better understanding of Linux in general. A senior colleague has just wandered through and decided to order a complete Raspberry Pi starter set to try out with his students. WooHoo, this could be very useful to  me.
Good news, I have just had a chat with another colleague and we can put the cut tubes in a lathe and take them down to the correct size on the ends.

Sunday was very cold here.

The whole family went to the local park and, whilst the boys played and the girls shivered, I tried out the quadcoptor on a completely empty football field. Even with the complete camcorder strapped on, the little beast went up about 60 feet before I totally lost control and it fluttered to earth. It seems that the battery died after the effort of raising extra weight quite so high. I have higher hopes for when I take it to the indoor flying club and learn how to fly it properly.

The camcorder works very well even though I forgot to switch it on when I sent it up at the park. I have high hopes of it being very useful. (High hopes, geddit?)

WoW!

The little quadcoptor has arrived and is very, very nice. It is proving to be a fairly sharp learning cure but fun trying. I can make it crash in many spectacular ways but, so for, not actually fly in a straight line or even hover that well. The main problems are that I just don't have enough room to get the feel of the controls at home and cats. Yes, cats. We have two active puddy tats who want to chase that bird and torment it. They will sit very close and stare at it for up to ten minutes after a flight attempt . I'm afraid it will hurt them  or that they will kill it. Never mind, Samuel is with us this weekend and I may get the chance to get it into a much larger space.

The next item to arrive should be the tiny camcorder I have just ordered. It's a surveillance device and weighs next to nothing even when fitted into a key fob. Take it out of the key fob and it should sit happily on the quadcoptor without weighing it down too much.

Life just isn't a bowl of cherries sometimes.

The company I ordered the tubing from contacted me early this morning to apologise for having run out of stock of the 90mm outside size tube and to offer me alternatives. As the design I am working on will not allow any other size, I have told them that a wait of a month will be acceptable and any other options would have to be very carefully worked out. We shall see.

I have also now ordered a tiny quadcoptor at a cheap price in order to play with it and come to terms with controlling one. As always, they look simple in the demo video so I shall see just how easy it is in real life. The model was ordered from Wonderland Models and, including a crash kit that also includes a second battery, was less than £45.00. It really is tiny, it easily sits on one hand as you can see, and seems fairly sophisticated so it will be fun if nothing else.

And I've just discovered that Tom Wadsworth, who made this video, not only lives in my home town but also has much the same interests as me. The trouble is, he's a lot younger than I am and seems to be much better at the building and controlling than I am. Dammit!

Check out the rest of his videos, the're worth it!

Trundle reborn?

I have put another supplier on the left, Bableduck Cybernetics. They are a UK based company who have a very nice line in robotic components. My Trundle project requires somewhat larger wheels than is usual for a small robot and I have had a lot of difficulty sourcing them. Then, suddenly, two sources come along at once. The Bableduck ones are much cheaper and will probably work better indoors and the ones I found at Sparkfun Electronics are American based, more than twice the price and far more suited to the outdoor life. Horses for courses, I have a pair of the Bableduck ones to check out. I am also in the throes of ordering the acrylic tubing for the body of the 'bot as I now have a way of cutting them myself. I have cut the smaller tubes with a small disc cutter but it has to go so fast in order to cut that it melts the swarf and that then sticks to the tube and is very difficult to remove. The best method of cutting plastic is with a slow, sharp band saw and I now have access to one. The basic plastic will cost about £60.00 but, cut correctly, will make at least five Trundle chassis so will be worth the outlay.

Clearing the decks.

Over the Christmas, my amazing daughter came to visit and has done a major tidy up of the things stored on the floor of the attic. So, I start 2013 with a much easier space to sort and organise. I still have some major problems with my back and my hip but I hope, from now on, to be able to sort without too much pain and finally clear the space needed to get back to my electronics. The weeks preceding Christmas were spent working on the rest of the house and getting it ready for the family and the days since have involved a lot of sleeping and relaxing to help me get over Christmas and returning to work. Followers of my personal blog will have by now seen that I have set up a countdown to my retirement there. Currently I have just over 400 days before I can relax and spend a lot more time soldering and programming.