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A $1 Gear Motor

Tom Gray                Apr. 28, 2002
 

Pics are here.......Apr. 25, 2002
 Tom...... I suspect that this is not an easy project for the beginner; altho it requires no special tools or equipment, it does require care and precision. You might be able to add pics as you do yours.  I will take pics...... 

 I think you might try again with a pager motor.  You can widen the hole that the adjustment shaft goes thru to accept the body of the pager motor (make a tight fit), cut off the adjustment shaft and drill a tiny hole in it for the pager motor shaft.  The problem will be aligning that pager motor.  It must be dead centre in the alignment gear and  absolutely perpendicular to the back cover when you glue it down, as with any angle or off-centre alignment it will shake itself loose in seconds.  And altho I don't have equipment to check, I think the pager motors run faster at a given voltage than the cassette motors. 

 I am so pleased with the clock gearbox that I want to try it in a head (I haven't made a head yet.  I've revised my plans many times.  I started with a beautiful base and toy motor/gear combo, but abandoned it when I realized it takes 300 mA to run.  Maybe with an H-Bridge?) 

 Even tho the clock gearbox runs well, it draws about 75 mA at 3.0V and I need to add more inverters to drive it, will breadboard that tonite.  What do you think, is 180 RPM too fast for the head response? Will it overshoot badly?  When I clamp the drive shaft in the vice and run it with 3V batteries, it doesn't seem to spin all that fast, but I'm too ignorant to know.  Might also be able to use a friction drive to a larger wheel, the mechanics should be interesting as the head would swing in an arc instead of swivelling.  Just have to try it tonite... 

 Tom

A ONE-DOLLAR GEAR MOTOR
CLOCK HACK GEARBOX

Andy Pang experimented with a pager motor (7200 rpm) to drive a hacked clock gearset, but found that the tiny nylon gears self-destruct within a few minutes. There are a couple of reasons: first, the gears themselves are flimsy; second, there is a lot of 'slop' in the bearings, which results in vibration and wear at high speeds. 

This mod uses a cassette-motor and only the sturdiest of the gears in a clock body . The case of the clock I used said TIA NGUAN  M5188-X.  The gear teeth count 16:48 and 8:32 for a reduction of 12:1, giving a final shaft rotation of about 180 rpm at 3.0V. This is still a little high but there is sufficient torque for rollers and you may find some friction-drive applications. 

BTW, altho my prototype worked straight away (I lucked out) be prepared to kill a couple of clocks before you get this right. At a buck or two Cdn a piece, it won't break you, and you'll have a few nice parts to use afterwards. If you can find them, get the rectangular clocks that have a push-button night light.  Of the different clocks I've demolished,  they have the best clock boards, the sturdiest gears, and the most useful parts. 

1) PREPARATION AND DISASSEMBLY

a) Study the back of the clock. As you hold the clock with the battery compartment towards you, the adjustment on the left sets the alarm, and the one on the right sets the clock. You are going to throw away the adjustment gear on the left and keep the one on the right. 

b) Remove the two adjustment knobs. Remove the clock from its case. Save the case and any switches or lights that are in it. Remove all the hands from the front of the clock. 

c) Carefully remove the back cover by prying the two end and two side catches apart with a small screwdriver. Open carefully or—SPROING!-- you will have little gears flying about. 

d) Remove the top layer of gears. Set them aside for disposal or use in other projects. 

e) Remove the motor coil and its little gear; set aside as above. 

f) Holding the clock with the battery container towards you, carefully remove the adjustment gear on the left and set aside as above. Remove the adjustment gear on the right and KEEP it for this mod. 

g) Carefully remove the gear retainer (the plastic cover over the lower level of gears). Study the arrangement of the gears before you remove them. Take care not to lose any of the gears underneath, you need them. Remove gears, the metal parts that form the alarm switch and the battery contacts, the remaining gears and the cam plate, until you come to the bottom gear, which is snapped into the hole in the faceplate. Leave this one in. Chuck the metal bits and the cam plate into your junk bin or trash 'em. 

h) Remove the clock IC and set it aside for future use, it's a great little board. 

2) GEAR MODIFICATIONS

a) Find the black central shaft (it was originally the minute hand). Slip the shaft into your Dremel and carefully file away all the teeth on the pinion at the top. Take care not to file too deeply—just enough to remove the teeth right down to the root. You must remove all traces of the gear teeth. No dremel? Well, patient use of the Armstrong mill (hand file) will do. 

b) Find the white gear that was the hour hand driver. Study the shaft that went through the hole in the faceplate. It is swaged (has a thin part and a thicker part). Carefully saw or cut this shaft just below the swaging. You will cut off the thinner part at the end. Clean the shaft inside and out. This is a good time to saw off the battery holder, which can be used in other projects. 

c) Slip the cut-down hour gear over the minute shaft. The black shaft should stick through about 5 mm. Slip them both thru the snap-in gear and check that you have a reasonable shaft length. If you want a bit more shaft length, remove the black minute hand and you can cut the two remaining shafts flush to the face of the clock. Then clean and reassemble and check for free movement. 

3) MOTOR MOUNT

a) The cassette motor will mount on the outside of the back cover with its shaft going thru the adjustment hole on the right. Here is where you have to be creative. And careful. You need to attach that adjustment gear to your motor shaft so that it is on STRAIGHT and is the right DEPTH to mesh with the idler gear. I used a motor with a long shaft, so I was able to just cut the pinion off the gear shaft, drill the hole all the way through the pinion, and mount it onto the motor shaft. But if you have one of those cassette motors with the stub shaft, 5 mm or less, you will have to carefully measure to cut the gear shaft at the right place. Then, ever so carefully, drill a hole in the end of the gear shaft so it will slip over the motor shaft. It's wide enough, and if you go slowly and carefully by hand, you can do it. 

b) Before you fasten the motor down, grab your multimeter and find the current consumption when the motor runs free.  Use whatever batteries you have on hand.   Note this figure for later.  No meter?  Listen carefully to how the motor sounds when it runs with no load. 

c) I drilled holes thru the back cover and screwed the motor down with appropriate spacers (I always keep the little screws that held the motor down by screwing them back into the motor they came from). Of course, you can always grab the hot glue gun and just get it done. BEFORE you glue check that the motor/gear shaft combo is straight and at right angles and that when you pop the back on, all the gears will mesh properly. 

d) Whether you have drilled or glued, stop at this point  and measure the current consumption.  If it is higher, or if the motor sounds like it is running more slowly than before, then the motor shaft is rubbing where it goes thru the back cover.  Check the motor alignment, spacing, etc. again.  If you can't find any other cure, remove the motor and drill the hole thru the cover a little bigger (altho the motor I used fit well, this step may be necessary for some installations). 

4) REASSEMBLY AND TESTING

a) Reassemble the bottom layer of gears. You will have first a snap-in gear that has stayed in place throughout; then the hour and minute gears; then the idler gear. Snap on the gear retainer—that black plastic plate you removed in step 7. Flip the clock over and you should be able to grab the protruding minute shaft and spin the gears. All smooth? 

b) Snap the back cover on, being sure that the drive gear on the motor shaft slips into place. Start with 1.5 or 3 V and make sure everything runs okay. This is a test run; the black shaft may not turn.  If there is a grinding, whining, or  clacking noise, STOP IMMEDIATELY.  The clacking means you may not have removed all of the gear teeth from the minute gear in step 9, or there may be bits of plastic in the gears.  An old toothbrush may be useful for cleaning the gears.  Whining or grinding noises mean misalignment in the gears; your motor shaft/drive shaft assembly may be crooked or off-centre, or another gear is mispositioned.  Correct as necessary and check again for smooth operation. 

5) FINAL ASSEMBLY

a) When all runs smoothly, disassemble down to the snap-in gear. 

b) Use CA or 5 min epoxy to glue the black minute shaft inside the hour gear. Check that the shaft is straight (there is a LOT of play between these two, and you'll notice that the black shaft is thicker on top and thinner where it comes out the face. If you are not careful here, you can build in a lot of wobble and whine. 

c) While this is setting, find some petroleum jelly (aka Vaseline). When you reassemble the gears, coat everything with a liberal layer of jelly. Put the jelly on the ends of the shafts where they fit into sockets rather than into the sockets themselves. Yes, this adds some friction, but it will smooth and quiet the operation of the gears at high speeds and reduce wear. 

d) Reassemble and test. Carefully wipe the output shaft with a tissue and a little rubbing alcohol to remove any petroleum jelly. 

The prototype has run at 6V for 10 minutes and at 5V for several hours with no noticeable wear.  While the free-running cassette motor draws about 22 to 23 mA in the prototype,  the gear drive with no load draws 25 mA at 5V. 
 

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