Question: What do you call a forklift ram, three-phase motor and pump, a small shed and some latching relays?
Answer: A home-baked elevator.
Above: The entrance door opened showing the sliding cage door and Kevin's various knick-knacks.
Above: Inside the elevator looking to the left we can see the hydraulic ram and lifting chains.
Above: All hidden nicely behind an access door.
Prologue: In mid-2011, an elderly man approached me at work with a schematic provided to him by an 'electrician'. Sadly for him, the circuit he built from the diagram did not operate. The schematic in question proved to have an elementary error. After working out the error together he left the store and returned the next day satisfied with some marginal progress in his project.
The project in question was a hydraulic elevator. With the backbone being a forklift ram, a three-phase motor powered the hydraulic pump which would raise the elevator through the shaft. A single phase powered release valve allowed the elevator to lower. When the valve is actuated, the elevator's downward pressure pushes the fluid back to the reservoir. In this way, the resistance of the fluid passing through the valve provides the necessary pressure to slowly lower the elevator cab through the shaft. in other words, the descent is powered only by gravity and regulated by the viscosity of the hydraulic fluid.
Above: The pump assembly showing the motor, (the protruding cylinder on the upper left of the assembly) the release valve (right of the motor) and the large reservoir. The pump itself is a fully immersed pump and as such is hidden inside the reservoir.
Kevin had spent 15 years in hydraulics and has experience in construction. He was comfortable casting a hydraulic ram into his basement slab and wiring in three-phase mains for the lifting pump. But when it came to DC circuitry he was completely at a loss. You see, Kevin had to convert the control systems of this elevator to 12V DC in order to receive certification on the unit. No certifying authority would even look at the elevator system while the cab had mains power lurking behind the control buttons.
Seeing his dilemma, I offered assistance. After describing to me as best he could the system, I completely ruled out a microcontroller driven system. I put together a prototype controller board along with wiring connection diagram. The prototype consisted of two latching relays which would control the three phase pump assembly to raise the lift, and a release solenoid to lower the lift. Reaching the limits of the shaft would actuate industrial micro-switches to reset the state of the latching relays.
I visited Kevin in early December 2011 to help him out with wiring my control board into his network of 12v DC switches, buttons, led's, microswitches and electromagnetic door strikes. I arrived at Kevin's at 9:30AM. I was driving back home at around 10:30PM. The day was spent first comprehending the system; Going up is powered by a three phase motor and hydraulic pump. Going down however is a single phase hydraulic solenoid that opens to allow fluid to return to reservoir – the cab just coasts down slowly as the fluid is pushed back to reservoir. The following hours were installing my control board, chasing cables, simulating rides based off the state of the relays, faults, power outages, and general, potentially property damaging mishaps like pressing the up button when you're already at the top of the shaft. Tinkering with various wiring harnesses, getting the top and bottom exterior doors to lock and unlock at appropriate times.
Above: The first prototype of the elevator controller. The blue terminals down the bottom are all the inputs from the control switches and user buttons. The top two pairs of blue headers are the outputs for up and down. With only two storeys in the house, the whole board is electrically very simple.
Kevin already had the lift “working” off two industrial switches. One for the 3-phase ‘up’ and one for the single phase ‘down’. These switches were mounted on some compressed fibreboard and connected to very long leads. The purpose of this was so the control board could ride inside the cab, with the leads trailing out of the cab, down the shaft and into the pump room. Though crude and unsafe, this setup was necessary to put the relay control board through its paces. We would have to manually move the cab around with this switchboard while the state of the relays in the control box simulated what would be actually happening if my controller board was really in control.
While my board performed well during testing, there was no way a controller could be built, to address every issue that could arise, based off just a description of the system given to me on my half hour lunchbreak a week prior.
It was mid-January 2012 when I was finally able to visit Kevin again. This visit went much smoother. A five hour session of swapping out the MARK I and replacing it with the far superior MARK II. This of course was accompanied by miscellaneous debugging, but nothing close to the order of confusion encountered during the first visit.
I had brought with me two more new pieces of gear which promised to make the operation of the elevator more reliable and safer in a fault condition. These were an industrial 12VDC switchmode, (to replace the crappy plug-pack that we had implemented for the construction phase) and a wireless relay receiver which is actually intended for car modifications. Thanks to it's rock-steady RF protocol it is perfect for this project. The receiver's duty was to be wired into a master reset terminal on the control board. If the remote button was pressed, the relay would close its contacts and initate a hard reset of the control board - forcing each latching relay back to its neutral position. The range of the remotes for this unit are nothing short of exceptional. As a test we connected the unit to power and I just started walking down the street, pressing the button. As it was raining, I only had the motivation to get about 60 metres from the house. Kevin stood at the door the whole time with thumbs up to show that the relay was still receiving even at that distance and through several feet of concrete blocks.
I had intended to build MARKII as a completely compatible unit that would be a straight swap out with the original. Unfortunately, during planning, I drew the circuit diagram with the up and down circuits swapped because it was simpler to put onto paper that way. One thing lead to another and MARKII ended up following suit.
After swapping the first control board out for the second, I drew up a long list of test scenarios that would really put the board through its paces. Things we usually take for granted in a control system like exclusive operations - If the elevator is on the ground floor and I press the down/call-down button, will it try to lower... further? Silly, rediculous things like that. Basically every button combination for every state of the elevators being; At ground floor, at top floor, travelling up and travelling down.
With the controller passing the tests with flying colours, there was only one milestone left. The point of no return - handing full automatic control of the system over to the board. With this rather intimidating prospect looming, and the sun drooping below the horizon, we closed up the switchboard and called it a day. I promised to be over again to finish the job.
I made my final house call to Kevin's in late January 2012. This was to be the day. Kevins manual switchboard was removed, the leads were shortened and routed to the control box and into their respective terminals which until now had been unpopulated.
Above: The high voltage side of the control system. To the right, a 12VDC relay (below power outlet) which switches the mains which in turn energises the 3-phase contacts. In the middle of the shot, the spiral bound cable leads to the relay that switches the mains for the release valve located on the pump assembly.
Above: If you haven't noticed until now - The switchboard is housed inside an old barfridge. The clear front panel makes everything remarkably pretty, I think.
We stepped into the elevator cab, slid the cage door shut and pressed the up button. We heard the positive *THUNK* as the three-phase contacts drew in and the cab lifted off its bed and began its ascent. With nervous grins I opened the access side door while Kevin covered the E-Stop button. We watched the walls of the shaft moving past and saw the limit and redundant stop switches. Kevin was ready to press the E-Stop if the cab overshot the floor level. With our hearts in our mouths we watched the stop bar approached the limit switch. Then the bar was catching the switch lever. And the cab stopped. As planned! The electronic door strike embedded into the door frame unlocked and allowed our safe access out to the kitchen where we promptly shared a celebratory drink.
Below is a video of the whole thing coming together. Kevin is a bit awkward about being filmed, and I'm a bit awkward at filming. A wondrous combination but then again, the focus is on the elevator!
If you're wondering why Kevin has to press a button on the remote, it's because we had tinkered with the system a little and had forgot to master reset the control board.
Home Made Hydraulic Elevator from michael r on Vimeo.
Epilogue: So why not use a microcontroller?
I came into the project quite near its completion. Kevin had the elevator shaft as a feature when the house was being built. He had already installed the hydraulic ram, the elevator cab and close to all the buttons and switches. This also meant that cabling was already installed and I had to work with what was there. What was there happened to be 3-phase cabling for a 2kW motor running adjacent to the sensing lines such as those from buttons and limiting or reset switches. Induced voltage into these lines got as high as 3VRMS. Ideally, every line of every switch, button and light would have returned to the switchboard and could be controlled digitally by whatever microcontroller would be most convenient. In this way, all changes to the system could have just been controlled in code, not with hardware.
Why hydraulic?
1. Factor of safety: Commercial domestic elevators max out at 300kg or 660 pounds. Get three agerage sized men in that cab (myself, my father, kevin) and you fast approach this safe limit. The hydraulic ram is specced for carrying >at least 1000kg< on the edge of two metre tines. Thats heavier than the maximum number of people who could even fit in the thing!
2. When you stop pumping, the cab stops moving. Kevin mentioned that someone else in the neighbourhood had a cable elevator professionally installed. Three months later and the thing will not level properly, and if left at a single floor the cable flex means that the cab delevels further. With hydraulics - if you aren't pumping, or allowing fluid to escape; That cab is going nowhere. Ever. Hydraulics does have a much more limited range when compared to cable driven 'vators. However, the house is only two storeys and the cab only requires about 3.5 metres of travel. Back to the professionally installed job - What's worse is that the installers are nowhere to be found and apparently cannot be contacted to rectify the de-levelling problem. Having built the whole thing practically by himself, Kevin can make adjustments to switch positions or replace relays if any maintenance is ever requried. And as can be seen in the last few images of the page, my card has been taped into the switchbox - So I guess I'm in it for life!