Close encounters of the swarf kind (new rotary dump drive)

[Bob]

It has been pretty quiet, so I'm reaching deep for something to post.

I've been working on a new, quiet drive for David's A&O operating Whiting Rotaside rotary dump. It has required a lot of planning, because I'm not a mechanical engineer, nor have I ever played one on TV.

Anyway, I think I have a workable design to make a quiet stepper drive to replace the original noisy gear motor, and add synchronized sound from a prototype Whiting Rotaside.

Fortunately, a German company makes a "Silent Step Stick" driver board that runs the motor smoothly without the need for any cheese to accompany a whine.

This doesn't look like much, but it is the result of a lot of planning. Wish me luck! This is a NEMA17 stepper motor mounted on a pivoting platform (diving board) to provide downward tension on a G22 timing belt. Since I'm behind in my work, so I've enlisted some help, recruited at the recent Denver Train Show.

Reminder: click on thumbnail images to enlarge them.

[RickBacon]

You know Bob, the true mark of a professional is an integrated laser!  Don't forget the laser!

Where did you get the sound recording of the prototype rotary? 

[Bob]

At one time I was going to use a laser for a home-made home sensor, but that wasn't going to be sufficiently precise. I found an optical interrupter that has a 0.1mm aperture and a 0.01mm switching uncertainty. I plan to use it as an "almost home" sensor. When the cycle starts, measure the time it takes from start to a break of the sensor beam. Then on the way back down, after the beam breaks for the last time, and then opens again, continue running down for the previously measured time. When necessary, home position can be adjusted using hidden up and down pushbuttons. The main reason adjustment will be necessary is that wood moves with humidity and temperature.

I found a single Youtube video of a Whiting Rotaside in operation. The sound could be a lot better, with some wind noise in the microphone, but that's all I could find.The stepper motor cycle will be synchronized with the audio track.

Yesterday the rotary was removed from the layout and dismantled on the work bench. We decided to add ball bearings on the drive shaft because there will now be a strong side-force on the shaft to keep the belt in tension.

[Bob]

Actually, Rick, upon further reflection (pun intended) there is currently a VL6180X LIDAR sensor in the design. The plan is to use it as a car-fouling sensor, so that the dump cycle can't start if the next hopper is too close and might hit the drum as it rotates. The goal is to avoid what happens when a CSX locomotive is erroneously coupled to the non-rotary coupler end of a modern hopper and the dump cycle begins... I have a photo of that somewhere.

Anyway, that counts as a laser. An ordinary red laser would work as well as a beam-break, but then there would be visible coherent laser light splattered on the side of the next hopper instead of an invisible IR LIDAR laser beam.

[RickBacon]

All hale the laser!

I managed to find a real-life, all American, old fashion mercury switch yesterday, just have to figure out what to make with it!

[Bob]

The drive mechanism is pretty much finished. Here it sits on the table of my Sherline mill.

It is a 6:1 double belt reduction drive to get more torque from the motor. Belt tension comes from gravity as the motor is mounted on a pivoting plate. Tension is adjusted by sliding a shim block under said plate. Both shafts run on ball bearings.

The controller uses a Trinamic TMC2209 "Silent Step Stick" driver. During operation it is completely silent without any of the typical stepper motor whine.





Next step—head to the mothership to test fit it in the rotary.

[Bob]

Back to the mothership. The drive is sitting loose inside the rotary cabinet. I intended for it to be a tiny bit short and that was indeed the case. A bit of styrene shim brought it to the proper height. We can shim it up, but we can't shim it down.



The controller board is temporarily taped in place. From left to right are a DFPlayer MP3 player, PJRC Teensy 4.0 ARM processor, and the TMC2209 driver (with heat sink.)

After a little bit of wood trimming we got the drive hooked up to the rotary barrel.
 


After adjusting some of the torque settings we were successfully mock dumping hopper cars. This is one of the heaviest.



I'm glad to report that "sensorless homing" works great. At initial power-up, the processor turns the barrel towards home for a little while but at very reduced motor current (i.e. torque.) The stepper acts as a clutch as it skips steps. This process is completely silent.

The pushbutton, illuminated red in the photo, is the sole operator control and will be mounted on the layout fascia.

After the operator presses the button when it is illuminated green, it switches to red and the MP3 player starts a sound track of an actual Whiting Rotaside going through a full dump cycle.

Remember that picture thumbnails can be enlarged by mouse clicking on them.

The last photo shows a top view of the drive before installing the barrel.

[Bob]

Here's a link to a video showing first operation of the new drive on David's work bench. The video sound quality is degraded because the speaker had not yet been installed in an enclosure.

Link to Smugmug video

[david]

The smoothness of the operation as it starts, then gently, completely returns is a sight to behold. And the sound adds so much to the action. Truely amazing. Thanks so much Bob, from all of us who call the A&O our favorite play place.

Now to finally finish the surrounding structure.

Pictures at 10.

David

[Bob]

Rut roh! There is a new pushbutton on the fascia in Glenn Forge. It is now green but when an AC cord underneath the rotary was first plugged in it briefly went from dark to blue before turning green.



Following the cable on the back of the pushbutton I discovered that the other end went inside here to a white 6-pin connector hiding in the left bay shadows.



Later on Saturday afternoon, this disturbing video was recorded by a concerned citizen. Oh, the humanity! What did those lumps of coal ever do to deserve this? Carbon Rights Now!

Link to disturbing video

And yes, Rick, if you look at the far right side of the rotary, there is a bare circuit board standing vertically. It is mounted to a white block of styrene plastic. On the PC board is a LIDAR (laser) module to detect cars that are fouling when the operator did not pull back the switcher and cars far enough to avoid creating a problem. So we do need a laser!

Should an operator manage somehow to create a problem, when the button is red, a quick press cuts motor power. Once the <ahem> problem is resolved, press it again and the barrel returns to home with very low torque, as it auto homes.

[Bob]

There is a new instruction card posted on the fascia. One pushbutton does it all.



We enjoy hosting guests who are not familiar with the layout. Occasionally an unfamiliar operator would unintentionally hoist a coupler or even the idler car in the air.

So now we have a LIDAR sensor (laser for Rick Bacon) that senses when a car is too close to the rotary. When that occurs, the pushbutton turns blue.

The rotation was increased by 10% to more fully evacuate the coal in a hopper after this video was shot. David re-spiked the rails and all is ready for the O Scale National Convention in Denver 2023.

If you come to visit during the convention, a host will explain the flying pig logo...