Rolloff Roof Page

Winer Observatory Sonoita Facility Rolloff Roof Details

For each of the photos below, click on the photo for a larger version of the image.

Crane Rail Detail

The roof is supported on six double-flanged 8-inch hardened steel wheels that roll on crane rail weighing 25 pounds per yard. The rail is held down to the inverted U-channel on top of the wall by hook bolts that go through holes in the rail. The rail and channel are painted black to increase their thermal emissivity, to help them get rid of heat accumulated during the day more rapidly. In this way, they come to the same temperature as the air and cut down on air currents that damage the seeing. For those contemplating a large roll-off roof, we recommend that you DO NOT use this approach, but instead, use casters on an I-beam to support the weight of the roof, guide the roof in lateral motion, and to hold the roof down in high winds.

Roof Drive System

The rolloff roof consists of a steel structure made with 4"x4" square tubing and 2"x2" cross bracing. The roof is decked with 26 gauge steel and the walls are covered with 29 gauge steel. Two #80 (1-inch pitch) nickel-plated steel chains running near each wall of the building move the roof. The chains are moved by the motor and drive shafts shown here. It takes about 4 minutes to open or close the roof. The Boston Gear worm gear is non-backdriveable, making sure the weight of the roof will not move the motor when power is removed from the motor. Winer acknowledges the very generous donation by Boston Gear of over $6000 of equipment, including the motor, worm drive, U-joints, pillow blocks, chain, sprockets, and three ACE-I motor inverters.

Roof Motor Detail

The roof is driven by a 2 HP 3-phase motor attached to the Boston Gear worm gear gearbox. The 60:1 worm gear gearbox drives two driveshafts, each with U-joints on each end. The far end of each driveshaft near the walls of the building drive a sprocket on a shaft suspended between two pillow blocks. 110 feet of #80 (1-inch pitch) chain under about 1000 pounds of tension loops over each sprocket on the drive end, and a similar idler sprocket at the opposite (north) end of the shop.

Closeup of a Universal Joint

The takeoff shaft of the gearbox is not at exactly the same height as the shafts holding the sprockets. This requires the use of universal joints (U-joints) at each end of the driveshafts between the gearbox and the sprockets. Shown here is a closeup of a U-joint between the gearbox and the east driveshaft.

North Chain Idler

The view towards the north shows the chain that moves the roof and the idler assembly and the end of travel. The "shark's fin" or "sail" at the end of the track is a wheel stop that serves as a last resort to stop the roof if the limit switches fail (see photos below). Chain and sprockets are used to keep the forces on each side of the roof equal and to prevent slippage of the drive system.

Southwest Wheel Stop

This is the wheel stop on the south end of the west rail. If the wheel were to engage the stop, the ACE-I controller is programmed to stop the motor and declare an anomalous condition. If this happens at the north end, it prevents the roof from "going over the edge" and off the track, but it does leave the roof open and the telescopes at the mercy of the elements.

Roof Control System

The system that controls the roof motor consists of the "gray box" at top, that permits either manual or computer control, the black ACE-I inverter to the lower right, that converts 230 volts AC single phase current (typical of most house current) to 230 volts AC 3-phase current for the 3-phase motor, and the 2-HP magnetic motor contactor in the tan box at the lower left, that acts as a "fail-safe" measure. If the normal limit switches fail to stop the roof, the "fail-safe" limit switches activate the contactor to remove power from the motor, independently of the gray box or the ACE-I inverter.

Gray Roof Control Box

The gray box in the photo at left is the main control "brain" of the Winer rolloff roof. Due to the extremes of temperature and severe lightning typical at our site, instead of using integrated circuit logic, we designed custom relay logic using 24 4-pole, double-throw relays. Eight of these relays are activated by limit switches (two in each direction for the south "wall" garage door, and two in each direction for the roof) and the other 16 implement logic to move the roof, but not before the garage door is up. The front panel controls override the computer when the key switch is in the "Man" (manual) position, otherwise they have no effect. The corrugated flexible plastic conduits contain various cables, mostly wires from the limit switches. LED's on the front panel indicate when the limit switches are activated, and are "echoed" in the control room on an annunciator panel.

Roof Motor Drive Electronics

The black box on the right is the ACE-I motor inverter donated by Boston Gear. It converts 230 VAC single phase current to 230 VAC 3-phase current. It contains a microcontroller and can be programmed to ramp the motor up and down in several ways, and to run the motor at several different selectable speeds. One can select a speed from the front panel as well, or program the unit to be operated by remote pushbuttons or relays, as it is here. It is amazingly versatile, rugged, and reliable. The tan box on the left contains a magnetic motor starter (relay) that is normally closed (activated). If the roof hits a "panic" limit switch upon failure of the normal limit switches, the relay opens, removing power immediately from the motor.

South Wall (Garage Door) Limit Switches

The south wall of the observatory is formed by a garage door that must be raised before moving the roof, otherwise the telescopes will be damaged. To tell the roof control logic in the "gray box" whether the garage door is up or down, there are limit switches at each end of travel of the door. For safety, there are two, of different types (mechanical switch and non-contacting), and the logic is wired such that the roof does not move unless both "door UP" switches are closed (activated). If a switch fails, the roof doesn't move, even if the door goes up OK. The black Igus "energy chain" that carries limit switch signals and electric power to the moving roof is seen at the bottom and to the left.

Rolloff Roof Limit Switches

The pairs of limit switches for controlling the rolloff roof are mounted together on the wall separating the shop and observatory. The pair that stop the roof when opening are on the right, while the closing pair are on the left (the non-contacting switch of that pair is mostly hidden).

Roof "Panic" Limit Switches

If the normal limit switches on the east side (shown above) fail to operate properly to stop the roof, the roof will continue to move until it operates one of these "panic" switches (which one depends on the direction of motion; the one on the left if the roof is opening, the one on the right if the roof is closing). When either one of these switches is activated, it interrupts the current to the coil of the magnetic motor starter relay, which snaps open, interrupting any current from the ACE-I inverter to the motor. The roof immediately stops.

Roof Tie-Down Chains -- Top

When the weather forecast includes winds over 40 mph, we stay closed and we chain down the roof. Engineering calculations show that, given the area of the roof, the 9-ton roof levitates at a wind speed somewhere around 60-65 mph. The actual speed, given the shape of the roof, is probably somewhat higher, but we are not going to take any chances. If the roof blew off the rails, we would have to remove the siding and cut the roof frame with a torch into pieces, then lift them with a $700/day crane back into place, then weld everything up again and replace the siding, so it would be very expensive to put the roof back on the rails. Instead, we flip the chains you see in this photo over the steel frame into the matching bolt holder seen below.

Roof Tie-Down Chains -- Bottom

The chains bolted to the roof tie-downs shown above bolt to the observatory walls at bosses welded to the inverted U-channel that is held down by J-hooks embedded in the grout in the walls of the observatory.

Last modified: January 1, 2008.

	Crane Rail Detail The roof is supported on six double-flanged 8-inch hardened steel wheels that roll on crane rail weighing 25 pounds per yard. The rail is held down to the inverted U-channel on top of the wall by hook bolts that go through holes in the rail. The rail and channel are painted black to increase their thermal emissivity, to help them get rid of heat accumulated during the day more rapidly. In this way, they come to the same temperature as the air and cut down on air currents that damage the seeing. For those contemplating a large roll-off roof, we recommend that you DO NOT use this approach, but instead, use casters on an I-beam to support the weight of the roof, guide the roof in lateral motion, and to hold the roof down in high winds.
	Roof Drive System The rolloff roof consists of a steel structure made with 4"x4" square tubing and 2"x2" cross bracing. The roof is decked with 26 gauge steel and the walls are covered with 29 gauge steel. Two #80 (1-inch pitch) nickel-plated steel chains running near each wall of the building move the roof. The chains are moved by the motor and drive shafts shown here. It takes about 4 minutes to open or close the roof. The Boston Gear worm gear is non-backdriveable, making sure the weight of the roof will not move the motor when power is removed from the motor. Winer acknowledges the very generous donation by Boston Gear of over $6000 of equipment, including the motor, worm drive, U-joints, pillow blocks, chain, sprockets, and three ACE-I motor inverters.
	Roof Motor Detail The roof is driven by a 2 HP 3-phase motor attached to the Boston Gear worm gear gearbox. The 60:1 worm gear gearbox drives two driveshafts, each with U-joints on each end. The far end of each driveshaft near the walls of the building drive a sprocket on a shaft suspended between two pillow blocks. 110 feet of #80 (1-inch pitch) chain under about 1000 pounds of tension loops over each sprocket on the drive end, and a similar idler sprocket at the opposite (north) end of the shop.
	Closeup of a Universal Joint The takeoff shaft of the gearbox is not at exactly the same height as the shafts holding the sprockets. This requires the use of universal joints (U-joints) at each end of the driveshafts between the gearbox and the sprockets. Shown here is a closeup of a U-joint between the gearbox and the east driveshaft.
	North Chain Idler The view towards the north shows the chain that moves the roof and the idler assembly and the end of travel. The "shark's fin" or "sail" at the end of the track is a wheel stop that serves as a last resort to stop the roof if the limit switches fail (see photos below). Chain and sprockets are used to keep the forces on each side of the roof equal and to prevent slippage of the drive system.
	Southwest Wheel Stop This is the wheel stop on the south end of the west rail. If the wheel were to engage the stop, the ACE-I controller is programmed to stop the motor and declare an anomalous condition. If this happens at the north end, it prevents the roof from "going over the edge" and off the track, but it does leave the roof open and the telescopes at the mercy of the elements.
	Roof Control System The system that controls the roof motor consists of the "gray box" at top, that permits either manual or computer control, the black ACE-I inverter to the lower right, that converts 230 volts AC single phase current (typical of most house current) to 230 volts AC 3-phase current for the 3-phase motor, and the 2-HP magnetic motor contactor in the tan box at the lower left, that acts as a "fail-safe" measure. If the normal limit switches fail to stop the roof, the "fail-safe" limit switches activate the contactor to remove power from the motor, independently of the gray box or the ACE-I inverter.
	Gray Roof Control Box The gray box in the photo at left is the main control "brain" of the Winer rolloff roof. Due to the extremes of temperature and severe lightning typical at our site, instead of using integrated circuit logic, we designed custom relay logic using 24 4-pole, double-throw relays. Eight of these relays are activated by limit switches (two in each direction for the south "wall" garage door, and two in each direction for the roof) and the other 16 implement logic to move the roof, but not before the garage door is up. The front panel controls override the computer when the key switch is in the "Man" (manual) position, otherwise they have no effect. The corrugated flexible plastic conduits contain various cables, mostly wires from the limit switches. LED's on the front panel indicate when the limit switches are activated, and are "echoed" in the control room on an annunciator panel.
	Roof Motor Drive Electronics The black box on the right is the ACE-I motor inverter donated by Boston Gear. It converts 230 VAC single phase current to 230 VAC 3-phase current. It contains a microcontroller and can be programmed to ramp the motor up and down in several ways, and to run the motor at several different selectable speeds. One can select a speed from the front panel as well, or program the unit to be operated by remote pushbuttons or relays, as it is here. It is amazingly versatile, rugged, and reliable. The tan box on the left contains a magnetic motor starter (relay) that is normally closed (activated). If the roof hits a "panic" limit switch upon failure of the normal limit switches, the relay opens, removing power immediately from the motor.
	South Wall (Garage Door) Limit Switches The south wall of the observatory is formed by a garage door that must be raised before moving the roof, otherwise the telescopes will be damaged. To tell the roof control logic in the "gray box" whether the garage door is up or down, there are limit switches at each end of travel of the door. For safety, there are two, of different types (mechanical switch and non-contacting), and the logic is wired such that the roof does not move unless both "door UP" switches are closed (activated). If a switch fails, the roof doesn't move, even if the door goes up OK. The black Igus "energy chain" that carries limit switch signals and electric power to the moving roof is seen at the bottom and to the left.
	Rolloff Roof Limit Switches The pairs of limit switches for controlling the rolloff roof are mounted together on the wall separating the shop and observatory. The pair that stop the roof when opening are on the right, while the closing pair are on the left (the non-contacting switch of that pair is mostly hidden).
	Roof "Panic" Limit Switches If the normal limit switches on the east side (shown above) fail to operate properly to stop the roof, the roof will continue to move until it operates one of these "panic" switches (which one depends on the direction of motion; the one on the left if the roof is opening, the one on the right if the roof is closing). When either one of these switches is activated, it interrupts the current to the coil of the magnetic motor starter relay, which snaps open, interrupting any current from the ACE-I inverter to the motor. The roof immediately stops.
	Roof Tie-Down Chains -- Top When the weather forecast includes winds over 40 mph, we stay closed and we chain down the roof. Engineering calculations show that, given the area of the roof, the 9-ton roof levitates at a wind speed somewhere around 60-65 mph. The actual speed, given the shape of the roof, is probably somewhat higher, but we are not going to take any chances. If the roof blew off the rails, we would have to remove the siding and cut the roof frame with a torch into pieces, then lift them with a $700/day crane back into place, then weld everything up again and replace the siding, so it would be very expensive to put the roof back on the rails. Instead, we flip the chains you see in this photo over the steel frame into the matching bolt holder seen below.
	Roof Tie-Down Chains -- Bottom The chains bolted to the roof tie-downs shown above bolt to the observatory walls at bosses welded to the inverted U-channel that is held down by J-hooks embedded in the grout in the walls of the observatory.