Making My Bed

NOTE: This is a currently active project. This page will be recieving updates and alterations as the project progresses over the next few months. Probably check back every few weeks if you are interested. There was a big progress delay late in the year as work swamped me, but I am back into it again as of December!

So I went looking at recliner beds.... Not bad. However having seen the mechanisms involved I am confident I can do better*. For a start, weld up a nice solid stainless steel frame. And put in space for under-bed storage.

The storage trunks will be custom at 1x2x4 of my preferred units of measurement. They will have recessed bearing-rollers on the bottom to easily slide in and out on guide-rails integrated into the bed frame.

The other advantage of building the bed myself is that if I ever need a second one, I can guarantee availability of a perfect match.

* Emphasis here is on better, not cheaper! The costs of this project (not counting false-starts and re-designs!) are coming in at about twice that of buying an adjustable bed off-the-shelf (just the bed, not the matress: more on that below!). But mine will be considerably more durable and have the exact features I need (eg: integrated standardised storage, supplimentary-equipment attachment points, 48V electrics, microcontroller I can (re)program to suit myself).

Main Plan

Above is revision (about) eight. I have moved from four side-load storage bays to two end-load. The front bay was sacrificed as it becomes inaccessable once a bedside table is installed. The end bay was sacrificed to keep the entire frame as short as the bed tray in fully-retracted state. The remaining two bays were rotated 90° since end-access is easier in my preferred room layout. One useful side-effect of turning the storage bays was that the width of the frame now comes very close to the standard width for a single mattress without artificial padding.

My weird units

I invented my own unit of measurement. I call them hydrogen-units for want of a rolls-better-off-the-toungue alternative. They use a numeric base-8 (octal) multiple/division of the 'hydrogen line' wavelength.

1 h-unit is 21.10611405413cm (211mm being sufficiently accurate for most of my purposes) and is my chosen base unit of length. 1/8 of a h-unit is also close enough to 1 inch for casual use.

I have always found the metre too unwieldy for a lot of day-to-day use and the centimetre too fiddly. The decimetre is far more human-scale friendly, but not in common use. While the non-uniform 3-12-60-8-16-based divisions spread all over the place were not great, the actual scales in the imperial system (feet, inches) seem to be much more human-centric to me. (The metre, I believe, was origionally based of a crude estimate of the polar circumfrence of the Earth, rather than any units of measurement in daily use by actual people).

There are a number of these 'natural' units about based on various things that can be accurately and consistently measured by scientific means. I have played with a few and the Hydrogen-line length seems the most human-scale-friendly one (though a rather useless one for simplifying any actual physics equations - but no worse than the metre in that regard!). Interesting aside: The 'Hydrogen-length' was also used as a human-scale unit of measurement on the Pioneer space probe plaque.


I tend to use a base 8 counting system in my personal life. I like numbers that easily and cleanly convert to binary! Binary itself is far too fiddly for day-to-day use by humans. Base-16 (hexadecimal) is popular for easily representing binary in human-readable form, but is a bit large and unweildy for doing actual calculations with. Nicely, a signed base-8 integer also fits very neatly into 16 and 64 bits which are common data-widths on computers.


Why? If you have to ask, you wouldn't understand anyway. :-P


Alpha-level Sanity-check

Just a quick check to make sure my counter-lever struts work as expected. They do.:

Function-test in Lego


I have the advantage of at-work access to some good manufacturing equipment:

Metal-cutting saw

Above: Metal-cutting band-saw. Still slow, but semi-automated.


Above: Milling machine. Cutting slots for things like wheels and pivots to fit into the steel framework.

MIG-welder Alien camera probe.

Above: I've been welding mild steel since I was 12 years old, but this is my first time with stainless steel.

The workshop technician set up the voltage, amperage and feed speed for me, then it was not much different.

Long-sleeved shirt to avoid flash burn (welding makes a lot of UV light and you can 'sunburn' in less than a minute if you are close).

The big flexible pipe hanging from top-of-shot is the fume extractor, not a War of the Worlds alien probe taking an interest!


Build Stage 1: All Your Base...

The bed's base is a stainless steel frame with 2 bays for holding storage trunks. Here is the parts/cutting diagram:

Metal-cutting plan for base.

Here are the parts for the base cut out (except the 40x80mm channel, which I have yet to order in):

All the angle and flats cut.

Rather than purchase 6m of 100x6mm flat when I only need 85cm, I made the whole centre box-guide-rail T-section from 3 pieces of 50x6mm flat I already had. Spot-welded together from beneath via slots cut in the horizontals:

Centre guide-rail construction.

And welding has begun:

Bottom of Base-section welded together.

Welding of the base section largely done (tab to attach linear actuator to pending completion and fitting of recline mechanism):

Base-section welded together.

The glide rails were a bit tricky as the metal warped slightly during weld and had to be forced back into place. Note the extra horizontal struts acrous the 'open' ends of the structure too to keep things better in place. In an ideal world these wouldn't be needed, but this is my world :-)


Build Stage 2: The Reclining Years...

The bed's recline mechanism is a set of stainless steel struts and levers operated by two linear motors. Here is the parts/cutting diagram:

Metal-cutting plan and other parts for recline-mechanism.


The actuators themselves are 48V units with potentiometer positional feedback. I also had the mounting holes rotated 90° by the manufacturer so they can lie 'flat' between the matress tray and the frame.

Looking forward, cars and solar DC seem to be heading for predominantly 48V systems: 12V just can't provide enough power for all the modern gizmos in today's car (at least not without rediculously fat power cables). Higher voltage means lower current for the same power (meaning better efficiency without heavier, more expensive cabling). Also above 50V you are supposed to have an electrician's licence and although, as a non-commercial, plugged-in device I could (legally) still work at mains voltages, I don't like working above 50V anyway. (Note: 48V - and even 9V - can still be dangerous if the current is high. Just not as dangerous.) I expect to normalise a lot of my personal equipment (ie: everything except major appliances) to 48V going forward. The bed will be one of the power-distribution hubs for this low-voltage stuff. I also found some 48V to 5V USB power converters online recently, to cover the Very-Low-Power range devices.


Build Stage 3: Matress Platform...

The bed's matress platform is made of 19mm form-ply with stainless steel hinges and brackets to attach to the glide rails and linear actuators. Here are the parts:

Parts for matress platform.

I was origonally going to make a set of mesh trays from 25mm angle and 3mm woven stainless steel mesh, however: 1) it would have ended up costing over $1200 in metal and a LOT of time (for a part that is pretty-much always covered) and 2) I probably couldn't have made it rigid enough not to flex and warp.

And for the benefit of the hardware store (which, at $1 per cut, has much better cutting equipment than I can access), the cutting diagram from a 2400x1200mm sheet of 19mm black laminex form-ply:

Cutting plan for matress platform.

Also, since I travel on foot, I can actually transport pre-cut pieces on a hand trolley. Transporting an uncut peice would require I borrow or rent a suitable vehicle.

The "1st/2nd cut" annotations are to account for the shop's cutting equipment not being able to handle over 1.5m lengths - most of the people there are experienced enough to work it out for themselves, but sometimes they have the trainee on!


Here is the assembled matress tray:

Top View of Centre guide-rail.

I slotted and embedded the hinges because I could! :-P


Build Stage 4: Electrics...

The linear motors will be controlled by an arduino microcontroller and some push buttons on a wired hand pad. Also a USB device so that I might one day even voice-control it via my computer!

48V+ DC solid-state-relays are hard to get and expensive, so I am making my own motor-control circuit with appropriate Power FETs (Field-Effect Transistors in switching-mode).

Example circuit pulled off the internet.

I will be adapting the above H-bridge circuit for each motor, using MOS-FETs in place of the BC548 transistors (which are good little general-purpose transistors but not suitable for the wattage I am pushing!) and adjusting other components to suit. I will put up my own circut here (along with a fuller description of what it does) once I have it worked out, assembled and tested.


Buy Stage 5: Matress...

The mattress will be an off-the-shelf 'long-single' - I don't have the ability (or the need) to be making my own mattress! As expensive as the bed project is, the matress will still make up around 2/3 of the cost (don't be cheap on matresses -- your back will thank you!)


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