Electronic timers have been around for already more than 15 years. The main advantage over mechanical timers is undoubtedly their precision and reliability. In all the years I have used electronic timers, I have never experienced a malfunction due to the electronics. Of course there are week points, but they always turn out to be due to the batteries or the mechanical interface. Personally I used the Bauer and the Koster timer. The latter proved to be very reliable and offers a lot more convenience in use over the mechanical timers. The timers were so-called 1-function, which was all we needed until the bunt came up.

Bunters could take advantage of the precision of the electronic timers, but they had to be multi-function. One of the first multi-function electronic timers was developed in Delft, the Netherlands. It featured a direct driven DC motor. On top of the axis a cone is mounted which holds the levers. The cone has one flattened side. Turning the cone 180° releases one lever. By reversing the current, the cone turns the other way and the next lever is released. The timer has 9 programmable functions and time settings have an accuracy of 0.01 sec. The mechanical interface by this timer is comparable with the way the conventional mechanical bunters were set up. The only advantage remaining is the timing precision. Besides the direct driven motor is not powerful enough and is easily stopped by the force on the levers. So you have to design something that reduces the friction between the levers and the cone, like looping lines, that halves the tension.

The second generation of electronic timers is using a servo. There are several types available. Matt Gewain has developed one. There is the timer sold by M&K and Stamov. Personally I have a timer which was developed in Denmark. I will not go into detail about the individual differences between the timers. Basically these timers have the same functions and possibilities. The difference is in the mechanical interface. Of course you can set up the system with a scroll and mechanical levers, but the big advantage is if you use the servo for direct control of the stabiliser

So far I have used two different set-ups in connection with a servo, which I will describe in detail later in this article.

The basic set-up for an electronic bunter is to have two microswitches connected to the towhook. One switch signals when the hook is in the forward position, the second one detects if the latch is open or closed. Most timers can adapt a quicksilver-switch. Besides that the Danish timer can be connected a radio unit.

I will further describe the features of the Danish timer.

Via a controlbox you can feed parameters to the timer program for the different settings. The program sequence starts when the latch is open and the hook moves backward. You have the possibility for up to 8 different settings plus DT plus glide. The timer recognises different states. Besides that, there are different events that are flagged. All this is quick and easily programmable via the controlbox. When the power is shut down the settings remain saved in the timer itself.

The different states the timer recognises are:

This means that you can have different stabiliser settings for straight tow, circle tow and launch. And when the launch is too flat, you can skip the bunt and jump directly to the glide or have it DT, or…

1. Hook closed and back for a programmable time.
2. Hook open and forward for a programmable time
3. Hook is back upon opening
4. Radio signal

The first event will result in a DT. With the rest of the events you can instruct the timer to go to one of the 8 settings, DT or glide.

My typical set-up is as follows:

Straight tow Depending on the wind, VIT, glide setting or less than glide

Circle tow VIT setting

On open hook Less than glide

Climbing phase Pitch up the nose by giving more than glide setting

Cruising phase Slightly under glide setting

Initial bunt Somewhere in between bunt and cruising phase

Bunt a lot down

Fast glide for a couple of seconds depending on the weather

Glide

DT

The controlbox also serves as a charger. Up to 4 batteries can be charged at the same time. Via a menu you can choose different battery types as well as the charging method

The Danish timer is manufactured by Torleif Jensen.

Sct. Michaelsvej 3

3550 Slangerup

Denmark

Tel. 0045 47381530

Fax 0045 20571202

Mechanical interface

The family Nyhegn designed the first set-up I will describe:

On the servo a plate is mounted which holds two pylons. On the axis of the servo a disc is fixed, with a pin to hold the steering line of the stabiliser. (Fig.1&2). The two pylons can hold a metal blade (Fig.3) each, which can be kicked off as the disc rotates. A line connects blade 1 to a spring. From the spring two lines continue, one to the stabiliser and the other is going via a turningpoint to blade 2. (See Fig.4). When blade 1 is pulled onto its pylon, the glide adjuster is pulled tight onto the fuselage, giving the stabiliser a fixed and secure position for the glide. When now blade 2 is pulled onto its pylon, the spring is extending and allowing the stabiliser to accept more incidence than the glide setting. The line from the disc to the stabiliser is controlling the actual position of the stab. When the bunt comes, the disc is rotating, pulling the stab to a downward position and blade 2 is kicked off its pylon, the spring is retracting and pulling the glide adjuster onto the fuselage. When the DT comes the disc rotates to the other extremity, the line attached to the disc slides off its pin, blade 2 is kicked off and as all the lines are slack now the model can DT.

An advantage of this system is the very simple mechanical setup and the fixed position of the glide setting. (When you have to replace a line or change something, you always have the reference of the glide setting). Second, the movement of the stabiliser behaves linear with the rotation of the servo, which is very nice for trimming. If you move the disc by one degree, you know, you always move the stabiliser by the same amount.

A disadvantage is that this setup seems to be dependent on the force of the rubber bands acting on the stabiliser.

The second set-up I will describe is the one used by Victor Stamov:

A line goes in a loop from the disc of the servo to the wheel of the buntmechanism (fig.7). A hammer is eccentrically attached to the wheel of the buntmechanism. A spring forces the hammer always to the most forward possible position, which is a plate in the stabiliser. An adjustment screw rests on the plate. By turning the disc of the servo in either direction, one of the two lines pulls at the wheel and make it rotate. As a consequence the hammer moves with it and the vertical position of the adjustment screw changes and so does the stabiliser. For DT you turn the wheel until the turningpoint of the hammer passes the notch on the upper side of the mechanism. The hammer is stopped by this notch and forced backwards so that the stabiliser is freed. (fig7).

Advantage of this system is the very easy handling. Close the hook, hang in the stabiliser and ready. Secondly the positive position of the stabiliser against an adjustment screw.

Disadvantages:

The third generation of electronic timers, which become available now, offer the possibility of storing up to five sets of settings (different trimmings for different kind of weather). On top of that, the program itself is upgradable, so that you could download the latest software via internet en put it in your timer.

The latest development I have seen was during the Max Men contest in Lost Hills , last February. Ken Bauer had a model with four servo's in it. The towhook did not move anymore, but only registered the force acting on it. One servo controlled the stabiliser, another one controlled the rudder , the third one could open the latch of the hook , I believe. I forgot what the fourth one was doing.

So you can see what is possible today with electronics and a lot more will be possible in the very near future. Interesting in this respect was the presentation by Chris Edge at the symposium in Lost Hills. His point was: how far do we want this to continue and if we do not want to let it go past a certain point, than now is the time to think about it in order to have some rules ready for when it is needed.

Cenny Breeman