Ever since I was a kid I have been fascinated with mechanized automation – yes, I watched all the Jetson cartoons eager to some day build my own automated world.
This childhood passion never left me, to my wife's chagrin, I automate everything possible.
So it was no surprise when I built my Media Room I was keen to automate the glass doors on my TuneCloset. This Instructable tells you how I did it!
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Step 1: Overview - If at First You Don't Succeed...
When I built my Media Room I had glass doors custom made. When the doors were being built I had two holes drilled at the top edge to support a bracket where I could eventually install connecting arms to motorize the doors.
I made curved connecting arms that extended behind the doors into the mechanical room above my TuneCloset rack then started designing mechanicals. It took me two attempts to develop the right solution. The first attempt had some shortcomings; the doors had a jerky movement during travel, the mechanism wasn't silent or robust and eventually broke. I used this failed attempt as training for the next and ultimately, final design.
The new design is SOLID! I spent a lot of time planning and designing the current solution and am very happy with the outcome. It has been operational for two years now.
Come, let me show you the behind-the-scenes magic…
Step 2: The Design Challenge
I used the following criteria as I worked through the entire design phase:
- Motorize two glass doors to perform mechanical OPEN and CLOSE operations with a single 12 volt DC motor.
- Initiate OPEN and CLOSE functions using simple dry contacts or a serial RS232 Interface.
- Doors must travel smoothly and quietly.
- Ensure that the doors operate in perfect unison, i.e. they initiate movement at the same time, cease movement at the same time and meet fully aligned in the closed position at precisely the same time.
Step 3: The Design
I did my concept designs in a basic CAD package, the concept is as follows:
Figure 1 illustrates the mechanics of the glass doors installed into the TuneCloset access doorway and the connecting rods attached to the doors.
As the glass doors swing open, the tails of the connecting rods sweep a radius of about 10” / 254mm from the hinge of the glass door as shown in Fig 2.
I’m sure there are several potential drive solutions for this type of operation, however, I decided to build a Cam Arm (my name for an Arm that pivots at one end and causes movement across a varied radius of a traveller riding a slotted guide, not unlike a Camshaft except operating in partial rotation) as illustrated in Fig 3. The Cam Arm is designed with a drive sprocket that meshes with a 0.4" / 10mm wide x 0.2" / 5.08mm Pitch Stepper Motor Rubber Timing Belt.
Fig 4 shows the Cam Arms in the door open position. Note the different orbits taken by the tail of the connecting arm vs the Cam Arm, hence the reason for the slotted guides.
Also worth mentioning, is the twist in the timing belt; this is necessary to have the two Cam Arms rotate in opposite directions from a single drive source.
I chose to use a 12 volt automotive electric motor for this task because it offered a powerful worm gear drive and operates at a very slow rotational speed, had suitable mounts for installation and it conveniently had a 12 tooth gear affixed to the drive shaft. All I had to do was design and print a larger (50 tooth) gear fastened to the hub of the main Cam Arm, shown in Fig 5.
Step 4: 3D Parts Design - Main Cam Arm
Once I had settled on the final concept I modeled the operation in 3D using Blender (illustrated in the embedded video and GIF).
I then jumped onto Autodesk 123D Design to create parts that needed to be 3D printed (files attached).
The Main Cam Arm assembly shown in Fig 6 is comprised of the main Cam Arm, 50 tooth gear, upper and lower mounting brackets c/w pockets for ‘roller blade’ bearings and the Dog used as a traveler guide. The bearings and 5/16” / 8mm shaft are attached during assembly.
Note that it is not possible (with my 3D printer) to print the Cam Arm and Gear as one assembly so I created and printed them as separate parts. This turned out to be beneficial as it allowed me to do a complete integration right down to motor, and limit switch testing before fastening the gear and the Cam Arm together.
Step 5: 3D Parts Design - Auxiliary Cam Arm
The auxiliary Cam Arm shown in Fig 7 for the opposite door control is comprised of the Cam Arm (almost identical to the first except lacks the top collar which aligns with the gear during assembly) as well as the upper and lower mounting brackets c/w pockets for ‘roller blade’ bearings and the Dog used as a traveler guide.
Step 6: 3D Parts Design - Limit Switch Brackets
Fig 8 shows the two limit switch brackets. These are designed to accommodate industry standard micro limit switches. These brackets include slotted screw holes for incremental switch tolerance adjustments and integrated pockets for 6-32 nuts to allow alignment adjustments without the need for a nut wrench.
Step 7: 3D Parts Design - Timing Belt Splice Clip
I had to cut the timing belt to fit it to the right length, so I designed this handy belt splice clip. You simply position both ends of the belt into the clip and place two ty-raps around the clip at the provided recesses.
Step 8: Assembly
The attached pictures show the various parts, assemblies and installation.
For a detailed view of how it all went together, be sure to watch the embedded video.
Step 9: Glass Door Connecting Rods
The connecting rods are comprised of ¼” / 6.35mm round metal rod curved on a 5 ½” / 140mm radius for 90 degrees then straight for the remaining 8 ½” / 216mm.
The tails were drilled and tapped to an 8-32 screw thread.
The Traveler Dog, shown in photo holds a small bearing in place that rides in the slot of the Cam Arm.
I got the bearing at a local model shop: 0.25" / 6.35mm ID x 0.375" / 9.5mm OD x 0.125" / 3.18mm long.
The Traveler Dog assembly is held in place with an 8-32 ready rod that screws into the bottom of the Dog, passed through the slot on the Cam Arm then a flat washer and nut are installed loosely. The ready rod then screws into the threaded ends of the connecting rod.
This description is rather tricky to visualize put the photos with image notes should really help.
Step 10: Idler Tension Wheels
In order to properly time the precise point of door closure I had to be able to alter the effective distance between the two Cam Arm drive sprockets. Since they were permanently fixed by secure mounts I decided to accomplish the task by adding two idler wheels, each with adjustable tension. These idlers could then be fine tuned to change the pitch of each cam arm until they both came to rest at the 'Door Closed' position.
You can see the two idler tension pulleys in the attached photos. They are simply a small pulley wheel mounted on a piece of aluminum tubing with a small angle bracket as a pivot point. Then a long threaded screw with a retaining nut provides the adjustable tension on the belt that runs on the pulleys.
Step 11: Installation
The attached photos illustrate how the integrated pieces function in the design, image notes are included for clarity.
Step 12: The Electronics
My home is equipped with an RTI Home Automation system which provided the ability to operate this door from a custom touch-screen handheld remote and an in-wall touch screen. The motor control and interface described below can be applied to almost any trigger source or home automation controller including Arduino, Raspberry Pi, etc.
I used an HVW DMC-8 dual DC motor controller (it was in my collection of left over robot parts from years gone by). The advantage of using this module is it provides very precise speed control including ramp up and ramp down. This appealed to me because it's hard to get smooth quiet mechanical operations without ramping. The DMC-8 can work with dry contact input however I elected to use the RS-232 input and send serial commands from my Home Automation system. The attached DMC-8 manual describes the command structure for serial operation.
I used the N.O. contacts on each of the two limit switches which delivered door status to the automation controller which in turn issued 'STOP' commands at 'Door Open' and 'Door Closed' detection.
Step 13: Conclusion
Finishing this design and integration was a tremendous accomplishment for me. It had been about 3 years from the time the glass doors were installed to when I finally got this design built and working. It smoldered in the back of my mind for some time, it just took the right idea to create the drive to get it done.
I truly enjoyed this experience, it taught me a lot about mechanics, gear making, levers and timing.
I hope you enjoyed the tour too! Thank you for taking the time to come along for the ride. If you have something you want to automate, make it happen, there are a lot of great ideas and examples at Instructables.
If you found my Instructable helpful I'd love to hear your comments and see your Automation projects.
Kent at the FrontierShed.
Step 14: Materials
Most of the parts I used were either salvaged or created on my 3D printer (files attached) so the shopping list is quite limited.
¾” / 19mm aluminum angle stock, two pieces 11 ¾” / 298.5mm each
Two ¼” / 6.35mm wire rope clamps (clamps at Amazon)
Two ¼” / 6.35mm metal rods x 17” / 431.8mm long
Two 8-32 ready rod x 1.5” / 38mm long c/w two nuts and two flat washers
Timing belt (5.08mm / 0.2” / 5mm pitch x 0.4” / 10mm wide x 53” / 1351.28 mm length) (timing belt at Amazon)
5/16” / 8mm metal shaft x 3.1” / 79mm long
5/16” / 8mm bolt x 2.5” / 64mm long c/w nut and flat washer
Four roller blade bearings (bearings at Amazon)
Two miniature bearings 0.25" / 6.35mm ID x 0.375" / 9.5mm OD x 0.125" / 3.18mm long (sourced at local model shop)
DMC-8 DC Motor controller (or equiv) (DMC-8 at Palm Ind)
Two limit switches (limit switches at Amazon)
Electric window motor from automobile (sorry no part number reference on it anywhere)
JB Weld epoxy
Two small tie-wraps
If you’re like me you will probably have sufficient screws and nuts to assemble the bits or run to Home Depot to get the hardware that fits your build.
Step 15: Tools
3D Printer (you can order 3D printed parts on-line as an alternative)
Basic hand tools; screwdrivers, drill, drill bits, adjustable wrench