Opening Page

Timing Equipment Development Charter

The System - Pictures

Operation of the Equipment

Bushnell Laser Range Finder

The Wind Logger

Description of Wind Logger
Weymouth Speed Week is about having a good time, it is also about getting some performance data for the boats and boards to help with future developments. This project fits with the latter objective.

Objectives:
To record wind speed and direction throughout the day for later analysis in conjunction with the boat / board speeds. The Joddy timing system used at Weymouth Speed Week already provides spot windspeeds at the start and finishes of each run, however this is only averaged over a short period of time and does not give direction. Clearly we have to record the course direction to make best use of the data. Ideas for later developments came out of some very useful conversations with Peter Martin.

Hardware:
The hardware consists of the sensors, cup anemometer and compass, and the data logger board. The compass and the windspeed counter are built on a separate PCB, firstly to allow flexibility, and secondly to cram all the electronics and the battery into the waterproof case. The case its self is a 300ml food storage tub from Woolworths at £ 0-99.

The electronics with the lid removed (actually the bottom of the upside down food storage container is removed)

The compass is a pre-assembled module from Precision Navigation http://www.precisionnav.com and is available in the UK through Willow Technologies. It gives the compass heading to around 2 degrees accuracy in ~ 200ms provided it is kept level. A version with a mechanical gimbals is also available but it is probably less robust and thus less suitable for my later developments.

The compass module's green pcb is clearly visible.

Two 16 bit counters are also included, one for wind speed and a spare for later developments. The whole lot is interfaced to a Stamp 2 processor. The Stamp is also connected to a battery backed CMOS RAM (32k x 8), with a clock. The upshot of al this silicon wizardry is that the device can log 8 bit states of the two counters, the compass heading and the time (hh:mm:ss) 4000 times.

The Stamp 2 processor is a manna from heaven to a cyber-challenged individual like myself. It is a simple processor with built in EPROM memory and an RS232 programming port that allows you to write PBASIC (a BASIC like language, ideal for manipulating bits and bytes) programs and run them as soon as the power is switched on. It is manufactured by Parallax inc. www.parallax.com and available in the UK from Milford Instruments www.milinst.com

Mechanics:
All the components, the anemometer, the data logger and the tail plane are mounted on an aluminium channel. This has a vertical bearing assembly in the middle so the whole assembly points into the wind.

I had intended to use an optical sensor on the cup anemometer but I did not complete it in time so I used a magnetic read switch device from Autonic. This had two problems in my application; firstly it is heavy and secondly it has a magnet in it so it must be kept away from the compass. These to problems meant that the overall device was bigger and heavier than I first envisaged. When mounted on top of a wooden pole (18 mm x 18 mm) in a strong wind it made the pole swing about violently!

Calibration:
In order to calibrate the anemometer it is necessary to find a known steady wind speed. This is where the other counter is useful. I will fix the wind logger to a "bow sprit" on my bicycle and connect the spare channel to the front wheel sensor. On a windless day (or still frosty night) I can now calculate the speed with a fair degree of accuracy and check this against the anemometer. Until this is done I will rely on the manufacturer’s figure.

User Experience:

The device is straightforward to use: Simply switch it on and mount it on its pole. It will take reading every 10 second until it runs out of memory space. At the end of the day it is connected up to a PC by the RS232 port and switched on, it now offers the chance to download the results to the PC. When this has been done the memory is cleared, ready for the next set of results.

The RS232 port and on/off switch are visible on the bottom of the module, the battery is behind these.

The prototype was used for real for the first time at Weymouth Speed Week 2000. It performed reliably for the 7 days of competition. Excel let us down when it came to plotting out the results so we were not able to post wind speed results as quickly as we would have liked. The mechanical layout needs improving, it is currently too heavy and has too much inertia. These problems are being addressed.

The results show fairly dramatic changes of wind speed over a short period of time, this initially lead me to think that the device was not working properly. Discussions with Joddy Chapman and a look at some data published else where suggested that this was expected. There is far more structure in the wind than I had ever expected! The changes in direction are probably exaggerated due to the mechanical problems mentioned earlier.

What is good?
In a word, flexibility. The Stamp is easy to programme and the hardware will allow logging results on a .25sec to 5 minute time intervals. Power consumption is modest, a PP3 battery should do for 15 hours logging, it would be possible to programme it and the compass to go to sleep to save power and extend the recording time.

Dirty Linen
The stamp software needs tidying up and additional features adding. Presently the compass takes a single reading every 10 seconds, in order to average out the swinging due to the mechanical deficiencies it would definitely be better to take readings every 0.5 seconds or so and the average.

Further developments
During my early thinking on this project I has a number of discussions with Peter Martin, who suggested that it could also be used as a performance log for a dingy or sailboard. Joddy Chapman has published a number of articles on this subject in the AYRS Journal and else where, but here was an opportunity to get some information about sailboard performance.

A basic sailing boat performance log has to record water speed, apparent wind angle and speed . My logger has a spare counter for water speed. By fixing the compass relative to the boat and using a wind vane with a magnet in it I can measure apparent wind angle. With this data it is possible to get useful information about the craft. I have not yet resolved where to mount it on my sailboard but a bow sprit is my present favourite.

I will keep this up to date as and when I make progress.

Bob Spagnoletti

Amended 08/04/06