I’ll be installing a custom counterweight for my new garage door – it requires some clever engineering to make it work since a residential garage door doesn’t have a fixed weight: its track bends right above the door opening, and the part that is in the horizontal raceway provides no vertical load to the counterweight. So, as the door opens, it gets lighter and lighter.
The solution I chose is to segment the counterweight: as it descends, the segments get caught on retainers so that the effective weight of the counterweight decreases the closer to the floor it is. Each segment weighs just 3 lbs, making installation easy, and there’s plenty of them so the operation will be smooth. A silicone washer will absorb the shock of the segments coming into contact with the perches and with the counterweight stack.
Another solution I considered was a linkage (4-bar or two of them in series) to scale the load – not a problem with designing it; but manufacturing it would be too much effort for me.
Another workable solution would be a cam that could even be manufactured out of wood, but I didn’t care enough to set things up to actually do that.
Since the counterweight will be made of a stack of custom cast cement blocks, with attachment points for skate bearings as raceway rollers, it will have a small footprint and will be confined to an enclosure.
I’m designing the system with a factor of safety of 5 after redundancy is lost, and the weight reduction system makes it inherently safe on the counterweight end of things: by the time the counterweight hits the bottom of the enclosure (a.k.a. the floor), it will weigh about a pound (from the point of view of the door) and that will be only the retainer plate for the cement blocks, as all the blocks will be resting on their padded perches throughout the travel range.
I have figured a 3D printed last-resort brake for the garage door, so if both redundant cables snap on either side, the door will be immobilized by the sacrificial brake parts.
The cables are going to be a redundant pair for each side of the door, with separate attachments to both the door and the counterweight stack, so that no single point of failure will affect both cables at the same time. The cables will be routed in a PVC pipe for confinement in case one snaps. The idlers for the cables are 11in diameter cast iron parts with suitable grooves that I found at a junkyard – I installed four ball bearings at each end of the cast shaft sleeve, and the shaft will be supported on both ends. This provides a decent bend radius for the oversized cable – twice as large as the minimum from the cable spec sheet. It also will look quite steampunk I think.
I expect the counterweight system to be maintenance free and to easily outlast the house. I hate the garage door springs with a passion – I have dealt enough with them to just lose all respect for whoever came up with the idea, for the execution is so poor.
I’ll also install my own opener – a junkyard worm gearbox I found in perfect condition, and a standard electric motor – both oversized for the job. A simple and reliable cable tension “sensor” will provide overload and safety protection – a really simple system that will disconnect power to the motor and short the windings for electrodynamic braking should the cable get too taut or gets pulled too hard.. No electronics: just a spring loaded rocker with a roller, and two adjustable cams on the rocker to trigger a set of micro switches (again, redundant). The motor has soft start. The opto sensor “eye” will be a standard industrial Omron part that should last forever in the conditions I will be using it in.
So, all in all a counterweight system is perfectly feasible if you want to make one yourself; but perhaps most people wouldn’t pay the cost if it was a commercial product. It would cost way more than a spring does. Unsightliness-wise, it will be neatly tucked in the space between each door and the side wall. Nobody will even notice it’s there if they won’t be told first :)
I’ll probably update this answer once I get some pictures whenever I find time to install this thing.
Update: installation is happening as I write this.