This is a new experimental bug that is now operational. It was designed to try out some ideas that could make a very compact instrument with acceptable performance. It has worked quite well on the air and has proved out some new concepts.
Most of the pictures on this page have plenty of resolution - right click on each image to see things up close. Click here for a video of the bug in action.
The NanoBug uses a number of design elements that have been worked out for previous instruments, and it has some new features as well.
As happens with most construction projects, I had trouble waiting to hear how it would sound. This explains the lash-up (successful) at the left, which led to the finished instrument at the right. What follows are some of the stages of assembly.
The Lever Assembly
Since all bugs use an oscillating mechanical element in one form or another, this is an important part of the design. It is also the reason that most bugs are rather long, since the length of the pendulum is one of the things that determines the speed of the key. And because the pendulum usually extends out in front of the actuating lever(s), this adds to the length of the mechanism. To shorten the length of the NanoBug, the pendulum was folded back into the actuating lever itself. The sequence below shows how this was done.
All of the parts are shown at the upper left. The pendulum will be pivoted on ball bearings that run on the same shaft used to pivot the actuating lever, which also runs in identical ball bearings. The lever consists of an aluminum block to which the fingerpieces are attached, along with the electrical contacts. The block also supports the upper and lower elements of the lever and contains a magnet in its underside for centering the lever. The beginning of this assembly is shown in the top center. At the top left the pendulum and bearing stack are shown assembled. Fastened below the pendulum is its "signal" magnet, which will be actuate a magnetic reed switch. A "follower" magnet at the end of the lever will be attracted to the "driver" magnet carried on the red-topped screw that is threaded through the upper element of the lever. At the lower left, the pendulum is shown in place, with the top element of the lever removed. A top view of the assembled lever is in the lower center, with the pendulum swung out (the position shown is far in excess of the actual operation for illustration). The side view is at the lower right. The extension of the bearing shaft will fit into a hole in the base of the key.
As with previous magnetic designs, when the fingerpiece is moved, the pendulum, under the attraction of the driver magnet, will follow the motion. When the lever hits its stop (in the assembled key), the pendulum will overshoot and then oscillate around the point of maximal magnetic attraction. This motion, through the action of the signal magnet, will alternately close and open a magnetic reed switch to generate the string of dots. Dashes will be made manually by a set of conventional comments.
The Base and Support Structures
While the lever and its internal pendulum are the mechanical heart of the key, support and contacts, etc. must be provided by the base. The amount of brass in the base was maximized (within the size constraints) to provide adequate stability during use.
At the upper left are the base, feet, contact and support pillars, and top plate, with their upper surfaces shown. The top center shows the undersides, with the wiring channels in the base. The oblong hole in the top plate provides clearance for the driver magnet, whose position (in or out) determines the speed of the key. At the top right, most of the contact and support uprights are in position. The binding posts will mount to either end of the front foot. The lower left shows the lever assembly ready to mount- the extension of the bearing shaft will be inserted into the hole at the front of the base, and the upper end of the shaft will be supported by the top plate after the final assembly. At the lower center, the mechanical elements are all in position, ready for the top plate. The final assembly is at the lower right.
Further Construction Details
The centering magnet for the driving lever is shown at the upper left. It is borne on a brass screw and extends up through the base, where it interacts with a magnet on the underside of the lever. This attraction sets the centering tendency of the lever - the proper adjustment involves a trade-off between minimal paddle effort and the tendency of the paddle to overshoot and cause false contact closures. The centering tension is adjusted from below the key.
The wiring is contained in channels milled into the base (upper right). The rear foot has been removed to show the connections to the dot and dash contacts. The hex nut and screw combination just behind the front foot are for locking the radial and horizontal position of the reed switch assembly. This is shown at the lower left - the position of the signal magnet below the switch tube is adjustable through an access hole in the top of the key. The center adjusting knob (lower right) sets the resting position of the pendulum, while the dash contact adjustment is near the rear of the key. Its dot counterpart, which also sets the duration of individual dots, is on the other side of the key.
The "Proof of the Pudding"
There were several design goals. Some were the mechanical arrangements apparent in the pictures above, and some were related to trying to make the key as small as possible while producing good performance.
These pictures show that the "smallness" goal has been approached. It is a bit smaller than the MicroBug and TinyBug, shown at the lower right. While it is about one-fifth the size and weight of a Vibroplex Original, its operating force is correspondingly less, it does stay put on the operating table.
But, how does it sound? Here is a video of the key in action, so you can be the judge. It has been used on the air for several days and has proven to hold its adjustments well and to be pretty error-free in character generation. It does have trouble spelling some words, but it is learning to avoid using them.
While the key covers a respectable range of speeds as constructed, the use of an outboard weight (left) can extend the lower part of the range. The gain is not as much as might be expected, since the internal pendulum is purposely made rather massive, and external mass (unless it is on a long extension) does not affect the rate very much.
At the right is the key in action in my "open air picnic table" hamshack. Its size makes it handy for portable QRP operation. On the air the key has proved to be stable and precise, although it is sensitive to the slope of the table on which it is sitting.
The Final Analysis
As an experiment, this key was successful in that it proved out some design ideas that may find their way into future keys. As a key, it does have some drawbacks. They include the following -
Because both the lever and the pendulum pivot at the same point, there is no mechanical advantage anywhere in the system. While this reduced the length of the key, it also resulted in rather large paddle travel in the "dot" direction.
Having a horizontal pendulum that pivots on ball bearings at one end makes the key rather sensitive to the levelness of the surface on which it is sitting. This arrangement also means that at lower speeds (where the magnetic forces are lower), the operation is more sensitive to imperfections and friction in the bearings.
This key could be made even shorter by changing the dimensions of critical parts. However, while building this key, a new approach has presented itself to me, and that design (if it works) will be NanoBug II. Watch for updates here.