DIY

Oskar the food processor

Submitted by Ed_B on Mon, 07/25/2011 - 07:11

A while back someone gave me a little food-processor type thing called a Sunbeam Oskar. It had barely been used, but it didn't want to run. The blade turned very slowly, and the motor made the kind of strained hum that usually preceeds a release of magic blue smoke. The problem seemed mechanical.

As I was initially looking Oskar over, I tried to turn the blade assembly by hand. It was very hard. It didn't take long to find out that the drive shaft was sticking on the axle. After pulling the drive shaft out (which should have been easy but wasn't) I could see, feel, and smell a material called packing grease on the axle.

 

Oskar needs grease. Unilube All Purpose Grease, specifically.

The slinger ring keeps food out of the motor.

The brush wear on the commutator is very slight. It's still very coppery colored. The grey band of graphite will get darker (black) with use. The windings are clean and their color shows that the motor has never been hot. The motor looks basically new.

 

Getting the screws out was a bit awkward.

A big surgical clamp was the right tool to hold the screws.
Ready to lift out the mechanism.
The axle has a slot to hold the ears of the spring clip. I've got the clip halfway off.
In pieces.
The amber colored spots on the axle are packing grease residue. The drive shaft has been packed with fresh grease.

Driveshaft, meet axle.

The retaining clip back in place.

To grease the motor pinion and the drive shaft gear, put on a few blobs then turn the shaft a few times to even it out. When the motor runs the first time, much of this grease will be flung off the gears and onto the inside of the case. This is messy but harmless. A heavier grease would cling better, but there would still likely be some flingage. This does not show from the outside, and it doesn't matter.

Yes, it's supposed to look this way. Really.

The image doesn't capture the noise.

Now where's my Mr. Coffee?

The motor is a "universal" type, also called a "series" motor. These motors are known for very high starting torque and very high speed which is sensitive to the size of the load. This type of motor is also used in drills, vacuum cleaners, and elevated railway trains.

Oskar's motor shaft is machined into the shape of a helical pinion gear. The pinion mates with a molded plastic gear that is part of the drive shaft that holds the blade assembly. This componant is molded nylon or Delrin or something similar. The drive shaft is hollow. It turns on a stationary steel axle that is fastened to the frame. The drive shaft is held onto the axle by a retaining clip made of spring steel. (In most machines, the part with the hole is a bearing that is stationary, and the axle is the part that turns. Oskar is diffrent this way.)

A freshly machined steel surface can start to rust visibly an hour after coming off the lathe or mill. In manufacturing, a material called packing grease is applied to freshly machined precision steel parts to protect them from rusting. Any kind of grease will do for that purpose, but packing grease can be applied in a thin layer, almost a film. It clings well and won't wipe off easily. Oskar's axle was coated with packing grease when it was made. Packing grease is usually removed from from machine parts before final assembly. It's replaced with a lubricant or paint. One thing packing grease will not do well is lubricate moving parts, especially after it's a few months old. In fact it becomes quite hard.

I'm sure that on the whole, Sunbeam Corp. make fine products. But on the day Oskar was assembled, some person in charge of how things would be done on the assembly line had this inner dialog: "Hmmm. Assembly drawing says to grease the shaft. Well, these axle thingies seem to already have grease on 'em, so that part is done already!"  The result was that the driveshafts were assembled with something more resembling glue than grease.

Some plastic gears and bearings can run against metal gears and axles without lubrication. High speeds and heavy loads work against running ordinary plastic gears "dry". After greasing the axle and the gears with a cheap, general purpose grease, Oskar was frighteningly eager to chop things up. I used some old coffee beans as a test. Oskar munched them to medium-drip in a minute or so.

There is a powerful trend in design to make the spaces we occupy and the things in those spaces intelligent and resopnsive. The 1990's joke abbout the he intenet connected toaster isn't funny anymore. There are now good easons for a toaster to access data and produce information that exists in the cloud. For the toaster example, assume I like "medium toast". Different breads toast at different rates and with different depths browning depending on the intensity of the heat source, and the toasting time.

Fix ur clock

Submitted by Ed_B on Wed, 03/30/2011 - 21:17

 

Project Cabrini Green uses about 132 light boxes that are run on a timer. Their operation starts at 7:00pm and ends at 1:00am. While the light boxes are active, they go on and off at controlled time intervals that range between two and ten minutes. The light box timer circit is made from an ATmega168P microcontroller. This has turned out to be a not-simple thing to do. Accounts of some of the difficulties in getting the microcontroller to work correctly are given in other entries in this blog. Testing a clock takes time. To serve as a datalogger to test the behavior of the microcontroller's timing and pattern generating, I set up tests that compared the microcontroller clock to a real clock. Since I was going to be looking at the clock fairly often, I thought that it should be a pleasent experience. To that end, I decided to fix up one of my favorite clocks and use it as a time standard.

Here is my Telechron "Cathedral" clock. It was made in about 1930. It's motor is worn out. It makes noise and runs slow. I want to use it to monitor time on a microcontroller experiment. To make things better, I will oil the motor. The clock motor and gears are in a small sealed housing. To get oil into the motor I will have to drill a hole in the gearcase.

To oil the motor, I had to remove the machanism from its case. The case is made of cast phenolic, a very early synthetic plastic.

After removing the screws, I'm able to lift the mechanism out of the case. The face moves around freely. It is not attached to the rest of the clock at this point. If the hands were not attached, the face would fall off. If you tip the mechanism forward, the face will fall against the hands and scratch the surprisingly delicate paint.

The motor and gear assembly is constructed inside an almost completely sealed solid brass shell. To get lubricant into the motor, I had to drill a tiny hole into the side of the motor for oil and another hole for a vent. I used a small drill running at high speed. When the drill breaks through, it carries cuttings into the gear housing. Brass cuttings from a small drill are a fine dust. A gentle touch kept the amount of metal dust entering the motor to a minimum, and apparently no harmful amount went into the gears. The lubricant is silicone based, so it shouldn't dry out like the original oil did, after the short span of 80 years.

The clock will tell you if its power has been interrupted. A small metal flag behind the clock face is painted half red and half white. It is moved by the shaft by my fingertip. Attached to the shaft is a small, oblong steel weight. When the weight is hanging in its "relaxed" position, it is horizontal. The picture shows the weight in the relaxed position.

When the weight is "relaxed", the flag shows red.

When the motor is powered, a small magnetic field appears at the gap in the frame. The frame carries the magnetic flux from the magnet coil (not visible) to the back of the gearcase. The weight is too heavy for the field to move it from its relaxed position. If the flag is showing red, and if the power is on, you can rotate the knob on the back of the motor so the weight stands on end and the flag shows white. The magnetic field from the motor will keep the wight standing on end when you let your finger off the knob. If the power fails, the weight will fall, and the flag will show red again.

The flag shows white only when the power has been uninterrupted.


Reassembling the clock involves some sort of trick for aligning the face, the mecahnism, and the case. Registration between the face and the case is accomplished by a lining up a notch on the faceplate with a registration bump on the case. The glass goes between the two. The process is difficult because the mecahnism goes behind those pieces and obscures the view of the notch and the bump.

The people at Telechron obviosly had some collection of tools and techniques for getting the alignment right between the bump and the notch, but unfortinately for the paint on this clock face, I dont know what they were. By the time I got everything put back together, I'd made some very unappealing sctatches on the dial.

The clock pieces prior to reassembly.

Here's the Telechron cathedral clock in use as a time standard. Two microcontrollers are running test programs that include printing to the reciept printers when an event occurs. From time to time I check the tapes to be sure the events have been firing off as they should. I also note how far off the AVR clock has drifted from the real time. In effect, this is semi-automatic data logging. It tells me exactly what I need to know, and I get hard copy as a souveneir.

 

"Radio Hat" - Wearable Electronics from 1949

Submitted by Ed_B on Sat, 11/20/2010 - 14:25

Making /Hacking/DIY, 1949 style. This image was found at  http://www.swtpc.com/mholley/RadioElectronics/Jun1949/RE_Jun1949.htm The image is in the public domain. Yes, it really is a working vacuum tube radio. All the parts are fuctional.

Yes, it really is a vacuum tube radio.

tinkering makes a comeback WSJ article

Submitted by mbenitez on Fri, 11/13/2009 - 16:01

 

tinkering makes a comeback WSJ article

 online.wsj.com/article/SB125798004542744219.html

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