Sunday, January 19, 2014

Speed Sensor for a Live Steam Train

My fingers hurt too much after the last session last weekend to type up a post.  I used a pin vice to drill a hole by hand in the aluminum motor mount and tapped it with a 6-32 for a place to mount the speed sensor.  I got smart for the second hole.  I wound some embroidery thread around the pin vice and pulled it like a rip cord to activate the drill.  It took close to 25 to 30 time to complete the job.

First step is to wind up the thread.  A handheld drill with an almost dead battery worked wonders to assist.
Next is to set the drill in place.  I used my right hand to steady the back end and apply some pressure.  Too much and it will bind up, too little and no chips will be made.  The left hand pulled out the thread as steady as I could.  Most of the time all I got were small chips, out of the hundreds of 3 foot pulls about 3 or 4 total gave me a nice spiral.  If a spiral did start I would have to turn the drill by hand to break it off before starting the next pull with the thread.

The next step was tapping the hole.  For the outer hole I used a small monkey wrench to drive the tap, but that tool was too big for the hole closer to the motor.  A square notch was cut into the end of a scrap of steel to allow me to make quarter turns of the tap, the back end to the tap steadied with my finger.  Every half turn I spun the tap backwards as far as I could to break the chip.


I used the bench grinder and a lot of fitting to make a plate that contoured around the axle and motor.
Then the sensor for a Bell Dashboard 300 bike computer was zip tied into place.  A small magnet is placed on the wheel, it will be epoxied into place soon.  I am also waiting to set the plates mountings screws tight until after I add some Loctite.

 The computer was on clearance at Target, normal price was $16 I paid $8.  It is set for the wheels actual size, so distance and speed will be actual not scale.  It also has an odometer, max speed, average speed, current trip odometer and some other less useful features, such as estimated calories burned.  I will mount the computer next to the driver, maybe disguised as a lunchpail or something useful for him.

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