Speed control for a pulse motor

For my next clock I want to make some innovation in the driving system. My idea is to design and build a simple DC motor with wood, some permanent magnets and a coil. My expectation is to make something of very low power consumption to be ablate to run the clock on batteries .

A simple DC motor is what is called a pulse motor. A disc with magnets is forced to rotate when the magnets are facing an electromagnet  and the electromagnet is activated at the right time to create a magnetic force that can either attract or repel the magnets. The timing to switch on  the magnet is given by a reed switch or any other sensor like another coil. For this prototype I used a reed switch and the coil form a damaged contactor that was changed in the central air conditioner of my house. This kind of motor normally run at high speed and there is no speed control except by adjusting the voltage of the battery. The problem is that as the battery loses power the speed will slower.

For a clock drive we need a constant speed, so I had to add some kind of speed regulation. In the case I made my design based one that was part of all the steam engines that is the centrifugal governor or speed regulator. 

This tiny motor runs at 750 RPM when the voltage is above 5 volts and will keep the speed from 5 volts to 24 vols. That is the maximum voltage I can use in the coil before burning it

The video below shows the prototype running and explains the principle. This one runs with 4 AAA batteries.

Now I need to work in a nice and robust design to be used as a real wooden clock driver. The final design will use a pickup coil and transistor to drive the main coil. It will also use four 1/2” Neodymium magnets and a regulator design very similar the the picture below

My Toucan wooden clock is ready!

I finished the clock and now is part of the decoration of my living room. She is a beauty

I think that what made me more happy was the comments from Clayton Boyer after I send him the pictures and the video of the clock finished:

 

“…

Aloha Carlos, you do not know how much joy it brings me to know that I have helped make another builder so happy.  

My whole mission from the very beginning has been to spread to other woodworkers that joy that building these wonderful mechanism has brought to me.  

Your Toucan turned out wonderfully.  Thanks so much for the video link, and the nice email.  

I am SO Happy to read that you are a "very happy guy."

Aloha.  Clayton

…”

This is the video I post in YouTube

 

I had to make the dial 6 times as I damaged it in many ways while learning and making mistakes. It is not easy to work the wood in large pieces and multiple milling jobs. Anyway I am very happy with the results.

This is a video of the machine milling the last dial:

 

The other part required a little bit of home engineering was to build a small machine to wind the coil for the electromagnet that drives the pendulum:

Now I am planning my next project for my CNC!

Building the “Toucan” wooden clock Part 6

After staining and finish of  the gears I put all together to see what issues come out but fortunately the only problem was in the Escape wheel, I had to sand all the teeth as they were too slippery. Here is a video of the test. I hope the mechanism  is smooth enough for the electric coil to kept it making “tic tack”

For the coil I used a screw and to pieces of round PC boards that I bought in Radio Shack to complete the reel. I used a heat shrink to cover the screw before winding
I made a small winding machine using a toy dc motor with gearbox and 2 AA batteries. A lithe bit of wood, a piece of 1” rod and two screws  helped to complete this provisional machine



I ordered a stepper motor to add a rotary axis to my CNC. For the next coil I will use my CNC as a winding machine to make a perfect coil! as I will advance I a coordinated way.

Building the “Toucan” wooden clock Part 5

Testing Gears

 

 

 

The nice thing of cutting the gears with the CNC is the precision: Everything fitted perfectly and no rework at all. I made a mistake opening the holes in the frame: the one for holding the arbor of the escape wheel was too big so I inserted a brass tube and fixed the arbor to the wheel. I had to cut a longer arbor and add a stopper in the back of the frame. I asked Clayton about this and he explained that he does not like bushings but I think that this one will not harm the final result…

Tomorrow I will add some finishing to the wheels and I will start to work on the pendulum and the electrical part. I am also milling a new dial but with a small modification in the thickness of the Roman numbers.

Building the “Toucan” wooden clock Part 4

Work is advancing and now I am working in the “beauty” aspects  

The base and the frame are finished and they have now a really nice color combination. As you can see the dial is on its way although I will probably  make a new one as a couple of Roman numbers are a little bit broken . This  happened during sanding.

Now I am preparing the wheels for stain and finishing.

I don’t know if I will be able to make this clock to give the right time, it looks that the pendulum adjustment will be very tricky, but it will be a really beautiful clock

Building the “Toucan” wooden clock Part 3

Finished with all the small parts and arbors. I made a preassembly to check that everything fits. Although it looks very good I am not happy with several things:

I cut the pinion supports and the wood spacers using a manual saw and even I used a cutting guide in many of the parts the main faces are not parallel

This means that either I work the parts with sand paper or a make all the parts in the CNC milling a flat 1/4” piece of wood. Tomorrow is another day and I will see…

Building the “Toucan” wooden clock Part 2

I have worked on and off during the last few days as my home was full of visitors for Thanksgiving

All the main parts (frame, base, wheels, pinions and dial) of the clock are already cut. The most difficult one was canon pinion as I had to mill it in both sides and the .0625” end mill bit was not long enough to mill all the part. Milling the rest of the parts was quite easy but anyway it is time consuming because it is necessary a slow feed rate and very high speed at the spindle to obtain good results without damaging the wood

 

 

I had to cut the frame in two parts because the piece was too big for my machine I hope I can hide the joint with wood putty and stain!

Now I have to work in a lot of very small parts that are all the spacers, pinion supports, and arbors and then mill the parts for the pendulum.