MarkTeachers Pet ... Robotics Challenge

http://www.element14.com/community/roadTests/1417

Putting it Together

Let me say the instructions for this kit are incredible, and comprehensive.

It should be easy to follow and get right without head scratching ....

I was hoping this would be a simple matter of "follow the instructions found at https://www.parallax.com/downloads/board-education-shield-arduino-product-guide

However this isn't the case.

I thought I'd detail some of the changes that I found in my kitset.

There are no revisions or dates on the outer packaging, however the kit of parts inside is labelled 572-28132 Rev D.

Extra hardware.

I found 11 nyloc nuts and nowhere can I see what they were for.

     source      https://en.wikipedia.org/wiki/Nyloc_nut

I still had the required amount of nuts, so these are extras.

There are three countersunk nylon screws, and I know two are used to mount the 4 cell battery holder.

     source       M3X12 NYLON COUNTERSUNK SLOT SCREWS | Premier Farnell CPC UK

What the other one is for is a mystery.

I seem to have an extra nylon washer.

source      M3 Nylon Washers - UNBRANDED - M3 NYLON WASHERS | CPC UK

Two are used for the 'feelers' but I haven't found what the other is for.

I did find this image on the Parallax website, which shows exactly what I got ... including the extra parts

               source       https://www.parallax.com/product/570-35000

Servo Mounting

The instruction states you need to decide what way to fit the servos

However the image below shows the chassis cutouts for the servo and crucially there is a small notch at both ends of the opening.

I suspect that the previous servos had a single notch and the chassis also had only one notch.

Since these servos have a double notch, you can mount them either way around.

BUT

Because the servo output shaft is approx 20mm closer to one end, the BOE wheelbase will be longer.

The net result is it will have a longer tail, which will tend to add friction on tight turns .....

If you intend to add items to the front and increase the weight forward of the wheels, then rotating the servos so the wheelbase s longer might be an advantage.

I don't like screws and nuts without any retainer, since they will come loose and get lost, so I used 8 of the nyloc nuts for holding the servos onto the chassis.

It is a bit tricky holding the lower ones and you need to do it before the battery holder is fitted.

The advantage is you'll never have to do it again.

Battery Holder

When mounting the 5 cell battery, it suggests using flathead phillips screws, but there were none in the pack.

The standard pan head version are low profile, but not quite enough to allow the two outer batteries to lie properly in the holder.

The hole isn't countersunk to accept the nylon screws, and this might be a modification I make later.

The battery holder lies against the underside of the chassis, but it relies on the spring pressure to overcome gravity trying to make the batteries fall out.

I suspect I'll be adding a support to stop the batteries falling out.

I also didn't like how close the battery holder came to the end of the chassis, with the possibility of a short, so I added a strip of mylar (the clear stuff you get when pages are bound).

It may never short, but if the magic smoke does escape, things tend to stop working, so a small amount of insurance will be worth it ... even if it's just for peace of mind.

Sensor Mounting

The Sensor has a single mounting hole, and I simply used one of the spacers to hold it to the chassis.

It doesn't include a plug so I need to do some digging around to find a means of connecting it.

Since I'm away, it will need to wait until I return.

The next blog will deal with setting it up and calibration.

Mark