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OTish Adding a swing crane to a vehicle hoist?

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  • OTish Adding a swing crane to a vehicle hoist?

    So I finished my ceiling drywall extravaganza that some of you may have seen in another thread.

    Anyhow I have a rotary 10K# overhead two post A-symmetrical lift. I have been thinking of adding a crane to the one post that would be able to swing 180 degrees. The idea for the crane is that I could use it for pulling motors on cars, holding up heavy parts in engine bays, etc. The idea in my head is for the crane to be able to swing like I said and also have the 'head' of the crane slide in and out (toward and away from the hoist post). I would be looking at the same weight that a cherry picker would handle (up to 1ton).

    My concern about the deal is if it is safe to have the weight on the end of the crane swung around to the outside of the post? Obviously a vehicle hoist is designed to have the weight between the posts. But what I am thinking is if the post is designed to have 5000# to the inside of the post it should be alright to have up to 2000# on the opposite side of the post.

    What are your guys thoughts? Anyone ever seen anything like this?

    It would be nice to have an engine crane without the 'feet' of the cherry picker under the vehicle and whatnot.


    This is the hoist, the crane would be going on the left post.

    Andy

  • #2
    I think the crane would impose bending forces on the post far in excess of its design especially with a two poster . The pressings are probably up to the job but wont have a lot in hand .
    Would you not be better rigging a small overhead gantry and drop the vehicle out from under the engine. You might have to consider how the balance of the vehicle would change as you take the lump out.

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    • #3
      Sorry I ment the crane would be on the right post in the pic.


      The problem with an overhead is the space the beam would take up. Right now I lift cars right up to the ceiling of the shop so there is no room for a beam of any kind to be up there. With the lift it is easier to drop the motors out the bottom of vehicles which the cherry picker also doesn't work for. No problem balancing vehicles while pulling heavy chunks out of them, I have plenty of practice with it, understand what I am doing, and take into consideration what I will be doing when positioning the lift arms under the vehicle the first time.

      More than I can say for the local ford dealership that dropped my first truck off their lift after disconnecting the rear end from the truck.
      Andy

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      • #4
        I agree wholeheartedly with john about the lift possible bending. It only takes dropping one vehicle off a lift to make you appreciate them 1000x more-never done it but had to help fix the situation after. Is there a reason you would want to pull an engine from a vehicle on a lift? How would you control it or do other work necessary from the top with it up there? The only time I have ever done anything similar is when removing the entire front end from a unibody vehicle for work, but in doing that the vehicle is lifted off of the engine/trans/front suspension which stays on the ground. I believe pulling an engine with the vehicle up would likely be dangerous should the engine hang up on anything and/or move suddenly as happens quite often as it could knock the vehicle off the lift. If you want safety and comfort when pulling engines - use a pit or grease rack and a regular engine hoist.

        Just my $0.02
        Last edited by justanengineer; 01-08-2011, 02:43 PM.
        "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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        • #5
          The crane would be helpful for letting the engine down after unbolting it from the car. It also would come in handy for heavy items such as complete diesel intakes that can weight 75-100 pounds. They could be lowered onto the engine with ease and precision instead of muscling them up into the engine bay and guessing where it is going when dropping it onto the engine. Could be used for lifting heads on and off motors, holding up all steel bumpers, x-members, etc. Just simply anything heavy that needs to be held in place perfectly for bolting.

          I feel pits are the most dangerous thing ever for any shop. Not only for the owner walking around the shop day in and day out but for anyone that walks into a shop expectantly not knowing there is a gaping hole in the middle of the shop.

          I use a rack with wheels to drop motors/transmissions onto now but it doesn't work as good for aligning the assembly back up going back into a vehicle. Always some corner or the whole assembly needs to be lifted to line up to mounts and with the engine under the car it is impossible to get a cherry picker over the motor.



          From what I read the rotary posts are single piece formed 1/4" steel. Pretty much identical to the posts I see used for shop cranes however they are open on one side which I understand make the post weaker than a complete post.

          How about reinforcing the one post to take the forces of the crane? Like say adding a H beam from the floor to the top of the lift. Possibly adding in an extension of the floor plate and a couple or few more anchor bolts into the cement.
          Andy

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          • #6
            If you dropped a car with its engine hanging, the weight distribution of the vehicle would change instantly. I can see the vehicle dropping trunk downwards.

            Are the two posts connected at the top ? If they were, you could at least share the bending out moment of the crane post with the other post.

            The moment about the base that each post is expected to take is half the weight of the car at a lever arm of about two feet. If you start hanging further out than that, and in the wrong direction too, I see trouble.

            And it would be much better to take some of the moment off the post at the top, than try to get the concrete to take it. This is because the lever arm (again) is ten feet long if you take it at the top, but only a couple of feet if you fabricate an extra bracket at ground level.
            Richard - SW London, UK, EU.

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            • #7
              Yes the posts are connected at the tops with eachother. The arms are unequal lengths because the lift is an A-semmetrical lift. the front arms around about 3 feet long fully extended and the rear arms are about 5-6 feet fully extended.

              The total length the crane would be estimated 6 feet. Obviously I would use judgement of what weight I would be lifting with the crane and how far out to go with the head of the crane.



              The arms all the way in:


              I'll see if I can find a pic with the arms fully extended. Dropping motors, rear ends, transmissions, etc. while a vehicle is on the lift is nothing new to me. No worries on vehicle balance safety there.
              Andy

              Comment


              • #8
                VPT,

                How about using a chain hoist and trolley rolling on an I-beam that is supported crossways on arms projecting forward from the top of each post? The loads on the posts would be in line with the original design parameter. It would just be like a slightly front-heavy car - no additional twisting or side loads.

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                • #9
                  I ran a quick calculation on the idea. Assume a six foot long swing arm with 400 lbs on the end. It will produce a torque at the other end of 2700 foot lbs.

                  Put in an overhead stay to the 3 foot point cuts the torque moment but then produces an end thrust of around 300 lbs. The stay will have to be able to support at least a ton for safety margin. All this assumes the swing arm is plenty strong which adds another hundred lbs to the load.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Your lift looks to be about the same as mine, except mine is a symertrical. If you keep the crane attached below where the upper lighter weight section of the verticle post is I can not see a problem.
                    Most of the cars and trucks that have to have thier engines removed from below are not that heavy and neither are their driveline components.
                    Sounds like a good idea to me.

                    THANX RICH

                    People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!
                    People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!!!

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                    • #11
                      Torque of 2700 pounds at the single point of where the crane met the post right? If the actual top mounting point of the crane was higher than wherethe crane arm met the post the force should be reduced is it not?

                      So right now say I have a 9000# truck on the hoist and the rear arms are extended all the way out to their 5-6' point and are taking their 1/4 of the weight of the truck which would be 2250# 6 feet out from the post, what is the torque value at the post then?

                      Besides the possibility of the post twisting under load I find it hard to believe that the post can't take the load. A load that it is already suporting in the vehicle threw the arms of the lift.
                      Andy

                      Comment


                      • #12
                        Originally posted by v860rich
                        Your lift looks to be about the same as mine, except mine is a symertrical. If you keep the crane attached below where the upper lighter weight section of the verticle post is I can not see a problem.
                        Most of the cars and trucks that have to have thier engines removed from below are not that heavy and neither are their driveline components.
                        Sounds like a good idea to me.

                        THANX RICH

                        People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!

                        Yes I would definitely keep the crane on the lower portion of the lift. That upper portion seems like it doesn't do much more than support the equalization (correct terminology?) cables.
                        Andy

                        Comment


                        • #13
                          Torque of 2700 pounds at the single point of where the crane met the post right? If the actual top mounting point of the crane was higher than wherethe crane arm met the post the force should be reduced is it not?

                          So right now say I have a 9000# truck on the hoist and the rear arms are extended all the way out to their 5-6' point and are taking their 1/4 of the weight of the truck which would be 2250# 6 feet out from the post, what is the torque value at the post then?
                          The 2700 foot lbs is produced when you have an arm supported only at one end with a load at the other. It is trying to twist the arm around the support point downward. Naturally it is impossible to mount the arm to an infinitely small point so the load will be distributed over some distance depending on how you build it. It the swing arm were attached to a healthy swivel pin with bearing supports spaced one foot apart on the post then the torque trying to bend the post would be 2700 lbs pushing in on the bottom bearing and 2700 lbs pulling out on the top bearing. If you make the bearings 2 feet apart the the numbers are reduced by half as long as the support point for the arm is centred between the bearings.

                          For your second question, the load is balanced. The only torque value on the posts is produced by the deflection of the horizontal members. I can't calculate that without knowing the material, the section shape, the section dimensions and thickness.

                          The lift posts fall into the category known as slender columns. When weight is applied to a slender column the resonant frequency of the column falls. That is the oscillation period of the column when it is disturbed laterally. It is equivalent to a reduction in stiffness. The greater the load the lower the resonant frequency and the lower the effective stiffness. At any particular value of load there will be some value of lateral force that will cause the column to bend enough that it will pass a point where the load changes to compression on one side and tension on the other side instead of being compression on the entire section.

                          That point marks a transition from essentially linear behaviour to extremely non linear changes in the internal strains on the material. It is a point of instability. Once the beam goes even slightly past that point the strains almost instantly change enough to cause failure and the beam buckles. The values at which this happens for any particular material and section are nearly impossible to calculate accurately so empirically derived values are used that have been determined by experiment.

                          Safety margins are estimated by using rules of thumb for any particular design and testing carried out to make sure that the design rules are valid. The maximum load capacity of the hoist is based solely on the weight being carried on the hoist as intended. That produces far lower torque moments than would hanging a hoist off the side of one of the supports.

                          Without doing a full analysis of the entire assembly it is impossible to predict what the result would be. There is a very distinct chance that it would cause the hoist to buckle as the torque loads imposed are more likely to cause buckling than a simple lateral force.

                          I would not trust that hoist to handle an engine hanging on the end of a six foot arm. My personal experienced based gut feel is that it would fail or be dangerously close to failure. If it does fail you will have no more than a tenth of a second warning. It will fail almost instantly. All it might take is a nice jerk from the engine shifting on it's chain or something similar to momentarily double the instantaneous load. Gravity will do the rest.
                          Last edited by Evan; 01-09-2011, 12:22 AM.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            VPT,

                            As this is a 2 post car lift, the posts are designed to take a significant bending load. It's not a 4 post, where the vehicle's on a sort of pallet, and the columns are in pure compression. You're right when you say the individual posts are designed to support an assymetric load of 5,000lbs each (plus a hefty safety factor).

                            If you build a swing crane onto one post (and spread the load in a similar manner to the existing sliders), then as you start to lift the engine, the load on the car supports decreases. It'll put more load on one post than the other, but I don't think that car weighs 5 tons, so you're unlikely to be anywhere near the lift's capacity.

                            The back supports are so far back that there's no realistic chance of the car falling off boot (trunk) first - even without an engine & gearbox, the CG must still be between the front & back support points.

                            The only thing I'd watch for is the fact that the slider will be supporting a load in front of the post (rather than between them as at present). This will mean the slider will try to rotate and spread the sides of the post. A couple of hefty steel clamps around the slider & post might not be a bad idea.

                            Once the engine has been lifted, don't be tempted to swing it forwards and outwards - lift it, drop the car, pull it out backwards and drop the engine straight down.

                            Ian
                            All of the gear, no idea...

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                            • #15
                              Once the engine has been lifted, don't be tempted to swing it forwards and outwards - lift it, drop the car, pull it out backwards and drop the engine straight down.
                              How do you plan on preventing that from happening? You cannot count on the operator to simply know that shouldn't be done. Any number of scenarios could arise where it may happen regardless of previous instructions. Perhaps a helpful friend swings it out while VPT is looking for some tool.

                              That sort of restriction on use is never an acceptable way to provide safety. The system must be able to operate with sufficient safety margin in all configurations in which it may be reasonably used. Not swinging a load on a swinging crane does not meet that criteria.

                              This is not a situation where "common sense" or eyeball judgement is adequate to make an accurate estimate of the capability of the existing structure to handle the load. Since somebodies life may depend on it you need to be certain. Obviously, by the limitation you impose, you are not.
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