Automating the Bedroom Window
Master Doc.
(Draft in progress; please contribute)
Goal:
Fully or partially automate the raise/lower of the bedroom read window that's positioned behind the bed. If only partially lowered, consider adding a thicker strip to the top of the window to serve as a sort of railing.
Challenges:
- Window is approximately 80 kg
- Window has an arclength (overall length) of 6 meters which potentially leads to large overhang moments
- Blending 3D contour of Seapod shell with 2D contour of window.
- Sealing from the elements and not compromising R value
- Hiding components allowing access
- Automating affordably, ideally with off-the-shelf products
Concepts:
- Gilles' working concept as of 2-13-21 (follow link)
- Using a linear actuator - see below
- hybrid concept
Using a linear actuator:
This is an attempt to use a linear actuator (self-contained unit) to solve the problem. While these can be expensive, the tradeoff will potentially be in time spent engineering, proving, and troubleshooting a custom solution. Therefore, this can also be thought of as an "easy-button" to solve the problem, which is not inherently an easy problem.
Considerations:
Drive type:
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- Ball-screws vs. lead screws
- Ball screws ~90% efficient - > can backdrive
- lead screws ~ 40% efficient - > usually can't backdrive do to inefficiencies
- Ball screws are more precise and expensive
- lead screws sometimes use a plastic carriage rather than a steel
- Belt drive seems more oriented towards horizontal applications, whereas ours is vertical
- Ball screw is most likely the most appropriate for our application
- Ball-screws vs. lead screws
Lubrication:
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- Screw drives and linear bearings usually require periodic lubrication
- Lubricate using grease rather than oil for vertical applications
- Some ball screws will advertise that they are maintenance and lubrication free (internally lubricated)
- These products have a finite lifespan. Once the internal lubrication runs out, the product may fail.
- Depending on our intended # of cycles and lifetime, such a product may still be appropriate.
- Some lead screws advertise lubrication free
- plastic on metal
- Likely not suitable for our heavy-lift application
Linear guides:
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- will help align the window pane and resist the overhanging moment loads (which are really heavy)
- therefore, these must be robust due to the high pitch and yaw moments (392 Nm)
- For instance, a counterweight or screw-drive system on its own would be unable to counterbalance these moments, so we need robust guide rails to do so.
Travel life:
-
- Travel life seems to be an important factor:
- Assumptions for travel life. Raised/lowered once per day, everyday for 100 years
- 605 mm of travel (1300 mm per open/close)
- 48 KM traveled in 100 years worst case - on the very low side for these sorts of applications
Electronic Brake:
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- Some systems allow electronic emergency brakes. These are electric open (24 V) - spring close
- In other words, these are energized during actuation of the window, and normally stay closed
- This can alleviate the need for a counterweight and/or other safety systems
Linear actuator and motor calculations:
https://docs.google.com/spreadsheets/d/17lEcmTDpThAO0ecSoPah9yGxuAAONtuhxkV19Jpn0XI/edit?usp=sharing
Selecting a linear actuator:
https://www.lintechmotion.com/products2.cfm?ModelNo=170&t=Group6
Selecting a motor and gearbox (see calculation page):
https://www.amazon.com/Gyheung-Extruder-Stepper-Planetary-Gearbox/dp/B08LH19VBG/ref=sr_1_6?dchild=1&keywords=gearbox+5%3A1&qid=1614476207&s=hi&sr=1-6
Costing (TENTATIVE - big ticket items only - hold off ordering anything):
| Component | Make | Model | Price | Qty | Ext. Price |
| Linear actuator | Lintech Motion | 1741224 | $3,319 | 2 | $6,638 |
| 24 V Motor | Newark | DB59S0124035-A | $108.52 | 2 | $217 |
| Gearbox | Gyheung | B08LH19VBG | $50 | 2 | $100 |
| Approx. Total System Cost | $7-$8k |
Other notable systems:
https://www.igus.com/info/page-19897
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- Could offer interesting options for counterweighting
- This model is unable to resist heavy loads (plastic on aluminum)
- Still unsure if a toothed belt drive is appropriate for vertical applications
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https://www.youtube.com/watch?v=lQWBI0gnhpI
On another note, I noticed the mechanics that control the slide-out function of an RV slide-out. Its a combination of linear guides, pulleys, cables, motor, chain-drive, and mechanical advantage, albeit in a 'horizontal application' . These mechanics are cheaply available online, and may serve some purpose to us on this window or another.
