Controlling two chain hoist at once

[skienblack]

For a final project in my rigging class we are designing and installing a motrorized lighting position in our theatre. Currently our apron lighting position is dead hung over the stage and only accessable via genie or ladder. Our TD/teacher has offered us the opportunity to motorize it as the final project to our rigging, hydralics and pnumatics class. Obviously anything we do will be okayed by him before we implement it.

Currently we are in the design stages of our system. We are planning on using two chain hoists to raise and lower the truss. What we haven't been able to find out online is how we can easiliest and cheapest control two motors at once, because they need to be in sync as each is carrying one end of the truss. We have an old electric motor controller and panel left over from a motorized lighting bridge which existed before my time. It has an emergency stop, up/down and lockout key. Is there anyway to wire the control cables for the motors into this? Any input would help so we can have a complete and thought out system to present.

 

[Footer]

You will need some type of encoder to keep them even. Chain hoists never run at exactly the same speed.

Sent from my Galaxy Nexus using Tapatalk

 

[rochem]

For a final project in my rigging class we are designing and installing a motrorized lighting position in our theatre. Currently our apron lighting position is dead hung over the stage and only accessable via genie or ladder. Our TD/teacher has offered us the opportunity to motorize it as the final project to our rigging, hydralics and pnumatics class. Obviously anything we do will be okayed by him before we implement it.

Currently we are in the design stages of our system. We are planning on using two chain hoists to raise and lower the truss. What we haven't been able to find out online is how we can easiliest and cheapest control two motors at once, because they need to be in sync as each is carrying one end of the truss. We have an old electric motor controller and panel left over from a motorized lighting bridge which existed before my time. It has an emergency stop, up/down and lockout key. Is there anyway to wire the control cables for the motors into this? Any input would help so we can have a complete and thought out system to present.

Footer is right. If you're looking for a solution that will travel completely in sync without you needing to fudge it, chain hoists are not the way to go. Due to the way they're built, you will almost never find two chain hoists that run at precisely the same speed, and even two hoists that have been leveled out at working trim could easily become dangerously uneven once they reach out trim. Really, the only way to have the position stay completely level is to use a line shaft hoist such as this where every line is raised and lowered from the same motor. Even individual drum hoists such as this can't really stay consistent 100% of the time, because that's not what they're designed for.

In answer to your second question, no, there's no way to wire your hoists into that remote. The only way to make chain hoists a viable option when used on the same piece is to have individual control over each hoist, which you would not with that remote. Your best bet is to look into something like Motion Labs' 4-channel hoist controller, which fits nicely into a small rack, and you can buy it with a 4-channel remote as well. I don't believe I've ever seen any 2-channel remotes and distros, but I'm sure they could build you one if you really didn't want the extra two channels. As you take the truss to trim height, you'll need to be monitoring the height of each side and compensating for it. The traditional way to do this is to put a person on each side of the truss with a measuring tape, and adjust to make them the same. A more expensive but easier solution would be to put a load cell between the hoist and the truss, then you can monitor the force that each motor is taking and compensate accordingly.

 

[mstaylor]

Do you actually have a truss or an electric? If it is truly a truss then you can do as planned and use two hoists. The best way to control is with a controller as mentioned, but you could use two pickles. It isn't going to run exactly anyway so pickles shouldn't hurt you that bad, it just means you need long extensions to get it to the ground. I have two 1/4 tons that I use for a rag truss that has extensions so I can stand in the middle and run both myself.

 

[skienblack]

...even two hoists that have been leveled out at working trim could easily become dangerously uneven once they reach out trim. Really, the only way to have the position stay completely level is to use a line shaft hoist such as this where every line is raised and lowered from the same motor. Even individual drum hoists such as this can't really stay consistent 100% of the time, because that's not what they're designed for.

Ok. For educational purposes only at this point would it be possible to incorporate a limiter into the system, or adjust the internal one so the hoist automatically stops at the out trim? We are using this for a fixed position so our trim will always be the same.

Do you actually have a truss or an electric? If it is truly a truss then you can do as planned and use two hoists. The best way to control is with a controller as mentioned, but you could use two pickles. It isn't going to run exactly anyway so pickles shouldn't hurt you that bad, it just means you need long extensions to get it to the ground. I have two 1/4 tons that I use for a rag truss that has extensions so I can stand in the middle and run both myself.

Currently it is two sets of pipes which compose a dead hung electric. We have a few boxes wired to the celing and 4 soca runs to it. Our plan is to replace the pipes with truss so we can achieve this with two pick points. The two pickle idea is looking more appealing.

 

[mstaylor]

Ok. For educational purposes only at this point would it be possible to incorporate a limiter into the system, or adjust the internal one so the hoist automatically stops at the out trim? We are using this for a fixed position so our trim will always be the same.



Currently it is two sets of pipes which compose a dead hung electric. We have a few boxes wired to the celing and 4 soca runs to it. Our plan is to replace the pipes with truss so we can achieve this with two pick points. The two pickle idea is looking more appealing.

Yes, you can set your limits to whatever travel you wish. There are two ways to do it, set it on the ground and guess or wait to you get it to trim and leveled, then set the limits. Hopefully your instructor knows how to set limits.

 

[skienblack]

Yes, you can set your limits to whatever travel you wish. There are two ways to do it, set it on the ground and guess or wait to you get it to trim and leveled, then set the limits. Hopefully your instructor knows how to set limits.

Does this not at-least mostly solve the issue that they wont be in sync? If the limits are set to the same trim height will they always return to that height within an inch?

 

[mstaylor]

Depends if you are taking the truss off the hoists or just bringing it down to change instruments. The problem is everytime you remove the spansets they may not reset exactly the same. It's not a huge problem but it could make a small difference. All that said, setting the limits will get you pretty close most of the time.

 

[skienblack]

Depends if you are taking the truss off the hoists or just bringing it down to change instruments. The problem is everytime you remove the spansets they may not reset exactly the same. It's not a huge problem but it could make a small difference. All that said, setting the limits will get you pretty close most of the time.

This will all be permanently rigged so the spansets and stuff will not come off. Our goal is to have it only get lowered to about 4' above the deck to protect the instruments from getting smashed into the floor.

 

[mstaylor]

Sounds like you have your solution then. All you have to decide is whether to spring for the controller or just use pickles. The downside to the pickle idea is what to do with the cable after it reaches trim. I generally pull them with a lift, but I have a lift6, not everybody has that option. The other thing is to run the extensions the way of soco and deal with them backstage.

 

[soundman]

Do you plan on going motor up or motor down?
Motor up will make cabling easier but motor down will make annual servicing easier.

I would not count on limit switches to level a truss, those micro switches are not very precise having about 2 links of play in them. Might be fine for a wash focus but could be an issue if it had to be tighter. There are three types of thread pitch you can get on the limit wheel shaft so depending on how much travel you need you might be able to get a finer threaded shaft giving you a more actuate stop.

Building a motor controller is not difficult. Your average CM ET style motor uses 7 wires. Phases (x)(y)(z) and (ground) and three control lines (up)(common)(down). Motion labs does make a very nice product but if you are electronically inclined building a basic one is doable. For a permanent instal phase detection and reversing are not as critical.

How ever you choose to control the motors I would suggest looking into using chain slides [chain runners] to manage the cables required by the position. If you have the trim height it is possible to make a very reliable system.

 

[skienblack]

Do you plan on going motor up or motor down?
Building a motor controller is not difficult. Your average CM ET style motor uses 7 wires. Phases (x)(y)(z) and (ground) and three control lines (up)(common)(down). Motion labs does make a very nice product but if you are electronically inclined building a basic one is doable. For a permanent instal phase detection and reversing are not as critical.

We would go motor up. Above the false ceiling of the lighting position is a small crawl way which we currently use to run extra cables or whatever to the position.

As for building the motor controller.... We used to have a counterweight assisted lighting bridge which was removed some time ago though the controller for it and the relays still exist on the US side of our proscenium. Our hope was to be able to wire the chain motors into this and use it since it already has a lockout function as well at the other functions of a pickle as well as the power ran to it. If we were able to use it could we build in an external limiter to each motor? Would this help with the ability to restore the position to the exact same trim height? My concern is that this position is often filled with our instruments for US front light so I would hate to have to worry about it getting returned to the exact position.

Another option is we just don't lower it once we have focused. Currently we use Genie lifts or ladders to access the position so even just having the ability to have it on the ground for hang and troubleshooting would already be a massive benefit.

 

[skienblack]

Attached is a mockup of our space and the potential new system. This should help give you a better idea of what we are proposing.

 

[MPowers]

If you are buying new, a motorized clew winch is probably cheaper than two chain hoists. They have built in limits and sync is not an issue. Thern, JR Clancy and iWeiss all have models available for off the shelf installation. Yes you need to figure out locations for loft and head blocks as well as a mounting position for the winch itself. controls can be permanently wired to one or more locations with key switches, E-stops etc.

 

[soundman]

As for building the motor controller.... We used to have a counterweight assisted lighting bridge which was removed some time ago though the controller for it and the relays still exist on the US side of our proscenium. Our hope was to be able to wire the chain motors into this and use it since it already has a lockout function as well at the other functions of a pickle as well as the power ran to it. If we were able to use it could we build in an external limiter to each motor? Would this help with the ability to restore the position to the exact same trim height?

Without seeing the controller I can't say how it will work. With install gear (and even some rental) there is little common ground. Alot of it can be built for one off situation stuff. Unless you get bonus points for reinventing the wheel for setting trim heights I would suggest sticking with tape measures.

 

[Wood4321]

Ok had a long reply typed out and the Internet must have eaten it.
Here is the summary version,
Chain hoists should not be used for permanent install unless you allow for annual inspection.
The need to be able to be taken down, and have a physical inspection as well as a load test.

I also would not suggest building your own controller, while they are easy to build, they are also easy to mess up.
And messing up a chain hoist controller could leave you with a hoist running with no easy way to stop it.

I would go with mpowers suggestion, that system could be inspected easily along with the rest of your rigging system.

 

[djyojoe]

Find yourself a local electrician and explain to them what you have and would like to accomplish. Pretty simple task to achieve for most. But can be hard to explain over the internet with a good chance of messing something up. Your internal limit switches of the chain hoist wont move on there own. So once they are set for your min & max height, it will always go back to the same spot just as good as a garage door opener would.

 

[josh88]

Find yourself a local electrician and explain to them what you have and would like to accomplish. Pretty simple task to achieve for most. But can be hard to explain over the internet with a good chance of messing something up. Your internal limit switches of the chain hoist wont move on there own. So once they are set for your min & max height, it will always go back to the same spot just as good as a garage door opener would.

Sounds like something he probably can't hire out to an electrician though since I would assume they are supposed to do it themselves as part of the rigging course he's taking.

 

[rochem]

As someone else already pointed out, using the limit switches is a bad idea. Limit switches will drift over time (they're one of the big things you need to look at in your annual inspection), and when exactly they trigger the hoist to stop can vary between operations. The mechanics inside are just a plastic plate that gets set to a certain point on a spinning shaft, and when the plate depresses a button, the hoist stops. So obviously, when that plate finally depresses the button is very variable and unreliable. While Michael's suggestion seems to be the best, I don't think there's anything inherently wrong with using chain hoists if you already have those. Since you're a school, you'll presumably be able to take down your hoists every summer for yearly inspection and maintenance. And it's not difficult to properly trim a truss supported by two chain hoists - it's done every single day in hundreds of venues, and it's hardly beyond the technical capabilities of a college rigging student.

 

[djyojoe]

Well if you are taking a rigging class than it should be geared towards proper rigging of the chain hoist and truss ... You're not on tour where it's a plug and play setup. Leave the wiring to the electrician to wire the chain hoist for a permanent install. Also if your at a school. I'm sure you can find an electrical tech class of some sort and have them handle the wiring schematics and list what additional parts are needed to what you currently have and hand it over to you to finish up the install. Then the electrical class can get some benefit of learning some control work.

Out of my 20 or so years, I've never experienced limit switches on a quality chain hoist drifting overtime. Plastic actuator or not. I have used many chain hoists on touring & permanent installs without any issues. The chain hoist isn't much different of a Commercial Lift Master Door Opener. Those get more cycles in a day than a chain hoist would on an entire tour without drifting. If you think it will drift. Than put a little dab of Locktite onto the shaft where the limit actuator will sit, set it and leave it, recheck it a year later. If you're giving it a yearly maintenance, it will be readjusted then. If your still not satisfied, than have you electrical shop class help design and implement external limit switches to be installed. They can get really fancy and install a laser or two to be used as limit switches. Endless possibility if you have the money, or until the insurance company and lawyers get involved after personal injury. You will be finding the money then.