Crawler Brainz

OK, got the Brainz installed.  The processor I used on this one is a PIC18F1788.  Its mission is speed control, and telemetry.  I need to be able to send it commands, and receive data from its sensor.  The speed control function is Pulse Width Modulation.  The PIC has a Capture, and Compare Module in it.  With the Capture, and Control Module you can setup a Pulse Width Modulation scheme to vary the Voltage that the motor gets.  Then to tell the Modulator what to do there is a potentiometer analog input.  This lets you send voltage information to the PIC, which it uses to vary the Duty Cycle of the Modulator, in turn changing the Voltage to the Motor, and changing the speed of The Crawler.

Crawler Drivetrain

Here is a closer shot of The Crawler's drive train.  I'm already looking at a motor with more power, LOL!  The trouble with toy motor is they are toy motors.  I need to move toward industrial grade, but that is usually a trade off with weight (bigger motor), and power (bigger battery), so I need to find the right one (Balance).  I'm going to move the power switch, install a potentiometer, and mount the PIC18F1788 Microcontroller board today.  Might even get it wired...

The Crawler

I spent a little more time working on The Crawler this weekend.  I managed, despite my effort at precision, to get the two shafts out of parallel.  The primary driven shaft is pretty straight, but the secondary shaft was out of parallel.  This means I needed to move one of the bearing mounting points to bring the secondary shaft into parallel with the primary shaft.  To do this I cut one of the frame rails, slotted the mounting holes in the top sheet metal, and then shortened the frame rail by 0.050 inches.  The modification is barely noticeable.

Also I found a battery holder that I can tuck under the frame rail that was modified.  This gets the battery off the top of The Crawler so there is more space for the microcontroller board, and test equipment.  Another thing that needed to be modified was the motor shaft.  It has a notch in the 1/4" output shaft, and the Pulley is round in its bore.  So a made a 0.060 inch thick piece from a 1/4" shaft to fill in the notch in the motor drive shaft.  This holds the pulley more squarely on the motor drive shaft, and helps alleviate periodic strain on the drive system.  The pulley is still kind of eccentric, and causes periodic strain on the drive system.  Its something I need to fix next.

Crawler Test Platform

I build a lot of test equipment.  This time I got a request to build a test platform which is mechanized, and moves very slowly.  I've built a few mechanized test platforms, but this is the first one that has synchronous all wheel drive.  Take a look...

The really slow motion is provided by a Worm Gear Motor, which you could think of as a clock motor.  It provides the spinning force which can be less than one revolution per minute.  The Worm Gear Motor that is on the Crawler now is 64 RPM.  I bought a couple more Worm Gear Motors also, 14 RPM, and 24 RPM.  I'm still working on the drive mechanism, and the goal is 0.1 Miles per Hour.  The overall speed has a lot of factors like the weight of the platform, and test equipment, friction through the drive train, the Voltage applied to the Worm Gear Motor, and even the friction of the tires on the surface.  With all of these factors I want the end speed to be 0.1 MPH, or 8.8 feet per minute.

1.5 inch Aluminum angle bracket, and a 5" x 10" piece of 0.625" Aluminum make the frame on the Crawler.  My starting point on this project was a robot platform with tank treads.  The treads were the first idea to get thrown out because they were hard plastic, and would do nothing but slide on a hard surface.  Then the frame of the robot platform was pretty irregular, hard to route the belts, so it got replaced with the Aluminum pieces.  This way all the mechanization is under the Crawler, and we have a large surface area for the test equipment on top.

I used Synchronous Gear Pulleys for the power transfer from the Worm Gear Motor to the wheels.  The Synchronous Gear Pulleys have teeth in them like a gear.  The Gear Belts have matching teeth which make this drive train Synchronous, meaning all four corners move at the same rate.  There is one belt that couples the Worm Gear Motor to the first drive shaft, and a second belt which couples the first drive shaft to the second drive shaft.  The length of the belt is determined by the distance between the shafts, and the outside diameter of the gear pulleys.  Two times the distance between shafts plus the outer circumference of one of the gear pulleys.  In this case the distance between shafts is 5.9 inches, and the pulley outside diameter is 1 inch, so a 15" Gear Belt was the one.

Now that I have built a Synchronous Four Wheel Drive I'll need to apply this to some other things.  For this Crawler Test Platform 0.1 MPH is the goal, but I can see the next one being a little more powerful.  The next step in this process involves Speed Control.  The one factor I have control of we can use to vary the speed of the Crawler is the Voltage applied to the Worm Gear Motor.  This motor can go from 6 to 15 Volts, and move the platform.  Previously I had blogged about using a PIC to do Speed Control using Pulse Width Modulation of a DC Motor.  That same control system will get used here to do speed control on the Crawler.  I'm also looking at using the PIC to get wireless communications to, and telemetry back from the Crawler.  The device we are testing sends data back to a piece of test software running on a computer.  So the crawling part of the Crawler is done, now I need to get to work on the brains...  Brainz!

Seized O2 Sensor

The engine light is on, got to get it fixed before we can get the Truk inspected.  My OBDII Code Reader is giving code 1155.  The manual for the Code Reader says that the "Rear Main O2 Sensor Signal Faulty".  OK, what does that really mean?  There are three Oxygen Sensors on the Truk (V6).  One is right up front between the motor, and the radiator, on the exhaust manifold.  The second, under the car, between the motor, an the firewall, on the exhaust manifold.  The third is downstream behind the Catalytic Converter.  So the Code Reader Manual says rear, so I figure the one on the back of the motor is the one that needs to be changed.  I was able to change it, although it was difficult to get to, on my back, under the Truk.  But it didn't clear the Check Engine Light.  I started searching for better definitions for the ODBII Codes.

My best tool for working on cars now is the interwebs.  So, I found out that code 1155 is the Oxygen Sensor on the Second Bank of the motor, which is the front bank, and code 1135 is the Oxygen Sensor on the rear bank.  So, I changed the wrong sensor.  The plan at this point was to replace the front Oxygen Sensor with the one I removed from the rear.  This is where I had a kink in my plans.  The front Oxygen Sensor was seized in the exhaust manifold.

The rear Oxygen Sensor was tough to break loose, but easy to turn after that, finger tight.  The front Oxygen Sensor broke loose, then was totally stuck.  There are a number of specialized tools for Oxygen Sensors that are all 7/8 inch.  First its the wrong size, the nut on the Oxygen Sensor is 22mm.  Plus open ended wrenches are not going to work in a seized bolt situation because they stretch when you put a lot of torque on them.  So the specialized Oxygen Sensor Wrenches are out, and the open ended combination wrench was out.  They only rounded off the corners of the nut.

In order to remove the Oxygen Sensor I literally had to break it off.  I used my Blacksmith Hammer, and an Iron Bar to break off the stem of the Oxygen Sensor.  Its a metal tube with a ceramic interior, so you'll crack the ceramic by hitting it, and de-swage the metal tube from the nut part of the sensor in the exhaust manifold.  With the stem removed you can then use a regular 22mm, 6 point, 1/2 inch drive socket, and a heavy duty driver to force the remaining part of the Oxygen Sensor out of its hole.  I also had the Blacksmith Hammer to move the socket driver.  This sensor did not want to come out, and it took some threads with it.  The Oxygen Sensor was literally welded to the treads of the Exhaust Manifold.  After getting the old sensor removed then I had to deal with the damaged threads.  There is a tool called a Thread Chaser which is a specialized Tap which will clean up the damaged threads.  Its in the Tool picture above, on the right with the Anti-Seize Compound.  You could also use thread cutting oil for tapping the threads.  So I ran the Tap in, and out a few times, then the new sensor went in easy, and sealed, the threads are saved, Yay!  The Check Engine light went off the second time I drove the Truk.  That was a good project for a rainy weekend...

Renew Old Pencil Erasers

I'm old school, and still draw with pencils.  Something that irks me about pencil erasers is they become oxidized, and hard, don't work no more...  Through some experimentation I found that this oxidized layer is maybe 50 mils thick, and once it is removed the eraser is supple again, and can be use effectively on paper once again.  The process is to uniformly scrum off the oxidization with a moderate grit sand paper, and the eraser is happy again.  I have hundreds of old pencils that are useful again...

Renew NiCad Batteries

Don't toss those weak NiCad batteries...  OK, we have all experienced the NiCad Battery memory effect.  That cordless drill or saw begins to loose its vigor, doesn't last as long, and this can be maddening when you have a job to do.  My Ryobi 14.4 Volt cordless drill would drive 3 inch screws all day long when it was new.  But after a while it starts getting weaker, doesn't last as long.  A while later the thing is useless, and you have to buy new batteries, or at least the manufacturer wants you to...

What is happening to your NiCad batteries is there are microscopic shorts that form between the electrodes in the battery, and the short out parts of the battery.  This is a drawback of the Nickel Cadmium battery architecture.  These microscopic shorts form, and it creates the "memory effect" where the battery looses capacity over time, and is eventually worthless.  There are a lot of people that have worked around this problem with various techniques.  There are various ways to use high current pulses to annihilate the dendrites that short out the electrodes in the battery.  What I found through research is that you can use the battery's charger itself to do this for you.

This case is the Ryobi 14.4 Volt series, a strong battery, and device when its new, but when the dendrites grow in the battery it quickly becomes worthless.  When the battery get internally shorted out the green, and yellow lights on the charger come on together, and this indicates that the battery needs to be replaced.  You can find many people on the internet (You Tube) that have figured this out, and developed a work around to annihilate the dendrites.  Basically they use the inrush current of plugging the charger into the AC Voltage to generate high current pulses to the battery.

Plug the battery into the battery charger, then you will see the green, and yellow light come on simultaneously, indicating a not chargeable state.  At this point unplug, and replug the charger from the AC outlet, allowing the inrush current from the AC to generate higher than normal current pulses that hit the battery, annihilating those damn annoying dendrites.  The basic NiCad charging circuit could be redesigned with a pulsed high current technique that would make the dendrites, and the memory effect history.  I am putting this theoretical technique to the test now...

 The next morning I developed this into a process.  I'm lining up the batteries, and run all of them through the process several times.  When one gets the green light I'll pull it off, and put the next one in line on the charger.  Then cycle the AC power 10 times.  I think the process is working because they are charging longer, and getting stronger.  There was one battery that was dead dead, nuthin', and now its running the drill at full power.  The real test will come when the Sun comes up, and I can start using the power tools...