Saturday, August 24, 2019

Power-Up


I paid $3 for this drill at the local garage sale. The battery was dead (as you can expect from several years old NiCd battery) but the motor was OK.  I decided to fix it with an external power supply. The battery output was 14.4 V. It is hard to find any supply with such a voltage, but 12 V sources are ubiquitous.   Inside e-waste bin at my job I found one with 6 A current output. That should be enough to power the drill, right? So I removed the battery from the unit, dissembled terminals from it, attached barrel jack to terminals, and assembled unit back. Now time to test. Alas, the result of the test was not exactly   I expected.  Indeed drill worked, but only if I pull the trigger slowly. Make it fast and behavior of drill becomes strange. Its chack starts to rotate and then immediately stops. On the clip below you can see it with the voltmeter showing voltage applied to the drill.
This clip shows that voltage drops to zero unless I squeeze the trigger slow enough. Is there an explanation for such an effect? Could it be fixed?
I believe I have answers to both these questions. Two things influence the drill start. First, there is an inrush current, which is the maximal instantaneous input current drawn by an electric motor when it first turned on. While under normal load this drill needs 3-4 A of electrical current, at the moment of start it may draw twice or even thrice more. So for some time (till motor reaches stable rotation), current may exceed  6A for which supply is rated. And now the second thing comes into the picture:  power supply is sophisticated enough to protect itself from the overload. As a result of that protection, it shuts itself down. As soon trigger is released, voltage is restored. 
But why does it work if the trigger is pulled slowly? Modern drill trigger is a variable speed device. It not just switch but power regulator. If it is engaged partially only partial voltage is applied to the motor, so inrush current is not that big. While rotor speed increases created by the rotation back EMF (electromagnetic force) limits the current through the motor winding.
Here is the remedy to the fast start problem: limit electrical current at the initial stage. To test this statement I tried resistor with 0.3 Ohm resistance and 10 Watt power rate. Indeed fast start effect is gone but  I did not like how it worked. Under the normal load, when current reaches 3 A, more than one volt dropped on the resistor and less than eleven volts applied to the drill.  And the resistor becomes hot.
So It tried another approach: inductor.  Inductor possesses big resistance to variable current but small resistance to direct current. Means, during start when current jumps from zero, the inductance will limit current but it will have no effect during stable rotation. Here is Toroid Inductor I bought on Amazon (several pieces for $2 all).  You can see it next to a penny  (for size comparison).

This inductor is rated for 100 micro Henry of inductance and 6 A of current. Current is OK, sure,  but what about inductance? The test shows it works as needed: drill could be turned on fast enough and no voltage drops when the drill is up to the speed.


Some more details regarding this project and how I build it you can find on Instructables site .

Saturday, May 25, 2019

Lock & Unlock

This post again about Ford Taurus 2006 (as of today ~171000 miles). While officially it is still mine, my son mostly drives it nowadays. On one of his trips (either Berkeley or maybe Oakland), there was an unsuccessful attempt to burglarize the parked car. Nothing was stolen but the car door lock was irreparably broken.  At the photo below you can see it.

So there was the need to replace this lock. On eBay, I have found a lock service package which suites our car. That package allows assembling the lock so existing car key will fit. Assembling the lock and replacing the old lock with the new one was relatively an easy task but as usual with some caveats. On the photo below, you can see the kit and all the tools needed for the job.


Apart from the kit, there was a need in the next set:
  • Vernier Caliper (to measure existing key for recreating lock steps codes). Given the fact that steps differences are more than 1 mm, a good ruler may work as well.
  • The hook custom made out of inexpensive awl.
  • Philipps screwdriver.
  • Ratchet with 7mm socket and extender.
Assembling the lock and fitting the key was straightforward. I just need to follow enclosed instruction.
The package is universal: not all packed elements were needed, but instruction gives enough details to understand what to use and what not to for your model. 
Next step was replacing the old lock with the new one. First  I have found this video. As all videos from 1aauto.com it is excellent and all that you need to remove and install back Ford Taurus door panel. 

 

But, alas, that video tells nothing about lock replacement. So I have found another one:



While it is not well polished as the first,  it contains some very valuable tips. Based on that video I may describe next steps to replace the door look (assuming door panel already removed):

1. Unscrew with 7mm sockets two bolts holding the door handle. That will make handle loose but not enough to take out the lock.
2. The door handle has a metal rod attached. The bottom end of this rod is secured with plastic clip to the door wall. On the snapshot below (I made it out of the second video)  you can see that clip (left bottom part of the picture) opened up. To open it up I used the metal hook, which I showed early. 

After that, I moved the handle out far enough to get access to the lock.

3. Then there was the need to remove e-clip from the back of the lock cylinder and take out lock lever.
4. The last step was to move to the left metal clip, which secures lock on the door. The snapshot below ( from the second video: many thanks to its creator) shows exactly where it is.


The new lock installation is straightforward:
  1. Putting new lock into the place.
  2. Securing it with the metal clip.
  3. Putting the lock lever back to the lock cylinder.
  4. Securing lever on the cylinder with e-clip (either from the kit or old one).
  5.  Screwing back two bolts into the door handle.
  6. Putting the bottom end of the rod into the plastic clip and closing the clip.
  7. Installing the back door panel.

Job is done! 


Saturday, April 27, 2019

Steel and Plywood

I found this HDD rack in an e-waste bin. It supposed to be sent away and eventually destroyed. What was its destination? To be melted in the furnace? Or to end its days in the garbage collector?
I feel sorry for this well-made steel guy and wanted to prolong its life.  Can I find some use in it?
Wide opening (probably served for better air ventilation) on one of the sidewall reminded me of an open human mouth. So here came an idea: make office supply organizer and give it some humanoid like look. Below you can see the result.

This was an easy project.  In addition to the rack, I needed several pieces of plywood, a few screws, some glue: nothing special to buy. Overall it cost me nothing. But it serves its new purpose well.
  • It has two compartments to hold pens or pencils.
  • It has a panel to accommodate several push-pins.
  • Its rim can be used for keeping paper clips. 
  • It has a compartment for small items like SD card, thumb drive, or staplers.
  • There is even hook to hold penknife.
Given the fact that the project is very simple, I hesitated to publish it. But eventually, I submitted it to "Trash to Treasure" Instructables contest. To my surprise, it was "featured" by one of the site editors. It happened to be my tenth "featured" Instructables project.  Now I am the proud winner of site silver medal (10+ featured projects). Where is the medal? Actually, the medal is virtual and only site visitors can see it. Anyway, Hooray! 


Sunday, January 20, 2019

Through the Soratama Glass

There will be not much text in this post (mostly pictures). I recently acquired new toy: Soratama glass lens attachment. While it is relatively inexpensive (~$50), it provides a way to take non-standard pictures. I found it is even more interesting than a fisheye lens.   Here are some samples from the first session, which I  shot in our front yard:

Metal Butterfly 


 

Red Pot


 
The Rooster

The usage of this photo gear is simple.  First I needed to put the "soratama" in front of my digital camera macro lens. The distance between the lens and the glass ball should be big enough to allow the camera to focus on the ball. Soratama arrived with 20mm extension tube, I had attached it (by scotch) to the old Takumar hood which has approximately the same diameter (72 mm). Hood I had put on Pentax DA 35mm limited macro lens with help of 49mm-58mm step-up ring. Below is the picture of the whole setup:

  • Pentax K-01 mirrorless digital camera.
  • Pentax DA 35mm Limited Macro lens.
  • Polaroid 49-58mm step up ring. 
  • Old Takumar hood for telelenses (58mm mount size).
  • Soratama 72 mm with 72mm x 20 mm extensions tube.

Shooting itself was confusing at first: the image on the  LCD screen was seen upside down.  But eventually, it was not that hard to get used to.  I shot in raw and processed images (upside-down rotation,  exposure tweaking, some cropping) with Adobe Photoshop Elements 2018.