force for lateral movement

[kicknargel]

I know where to go to really get into the math of this, and know there are many factors. But. . .Are there any quick rules-of-thumb for estimating the lateral force required to move a castered wagon of x pounds? (Assuming good quality casters well inside their rated capacity, etc)?

While we're at it, any estimate on how much lateral force a stagehand produces? For the purposes of this bid, they want options on automation and heave-ho style.

Just for grins, I estimate my wagon to be about 35,000 pounds, including the 40 musicians.

Obviously if the project happens I'll fully engineer the system, but for bid purposes a quick estimate would be helpful.

 

[TheaterEd]

I just built a wagon that was around 500 pounds. I felt comfortable moving it on my own while working with it, but for a production I would say 2 minimum. I would think the biggest problems would be getting it moving and stopping it. My guestimate would be you need half the amount of weight to move the object. so for my 500 pound piece I needed at least 250 lbs of person. 35,000 / 2 = 17,500 / 150 (average weight of stage hand?) = 116 stage hands. Call it 125 to round up and be safe?

I don't think this could possible be more of a guesstimate, but it was a fun thought exercise

 

[techieman33]

I remember watching worlds strongest man competitions when I was little and seeing guys move semi's and planes and other heavy stuff. They had an anchored rope to pull on and a harness attached to their body to help though.

 

[BillConnerFASTC]

It will all depend on the wheels and track. Steel on steel - easy peasy. Neoprene on carpet - bring in the 20 mule team.

 

[porkchop]

If your bidding it you should probably do the math. There are pretty simple formula based on the coefficient of friction and the weight of the object. Here's the first page that came up on Google that seemed to explain it well:
Friction and Coefficients of Friction.

As far as how much weight a stagehand can push, I'd start throwing pig iron on a cart and see how that goes.

 

[TheaterEd]

As far as how much weight a stagehand can push, I'd start throwing pig iron on a cart and see how that goes.

And now I have an activity for tomorrows HS tech crew meeting.

 

[FatherMurphy]

Actually, you need to look for coefficients of rolling friction, wheel diameter and the hardness of the tire have big effect on the force needed.

Rolling resistance - Wikipedia, the free encyclopedia

Also, if you start measuring stagehands pushing carts, you need to reverse engineer the rolling friction of the cart to get a true answer for how much force the stagehand is generating. If you can rig up a tow rope that lifts a weight, you'd get a simpler answer quicker. 1/4 of body weight floats to my forebrain as a rule of thumb for what a person can reliably push, but that may or may not be accurate.

By the way, don't forget that you not only need to figure out the force to get it rolling, you also need to figure out the force needed to stop the wagon on it's marks.

 

[BillConnerFASTC]

Need to know target speed also.

 

[MarshallPope]

Just to add to the flurry of impertinent information, we just closed a show where we had a wagon that I'm quickly guesstimating at 500-600 lbs (including 2 people) that was easily pushed on and off by a middle-aged man, in character. And then there was a ~500 lb wagon (again, with 2 people) that was almost impossible to pull across stage by a 20-year-old actor. The choice of casters makes a world of difference!

 

[zmb]

I take it that it won't need to getting moving too fast? Force = mass * acceleration

Something else to consider friction wise is that whoever ends up pushing it isn't wasting effort with shoes sliding back instead of propelling the wagon forwards.

 

[MPowers]

It's a little more complicated than a simple equation, although for that: F = C_{rr} N is your "simple" formula. F is your rolling resistance , C_{rr} is the rolling resistance coefficient and N is the normal.

For an idea of how complicated and a fairly good explanation, take a look at: <http://www.ask.com/wiki/Rolling_resistance>

As others have already noted, it depends a lot on the wheel material, the "road" surface material, to come extent the size of the wheel (but beware of "Coulomb's law" as it does not apply evenly and some cases is inverse to what it should be). Of course you are already aware of the initial force needed to start the unit moving will be many times the amount of force necessary to keep it moving. With a live load of "talent" and the estimated weight you mention, and at any reasonable speed you will move, I doubt that stopping will require any braking force, merely remove the motive force. In fact to prevent too sudden a stop you will probably have to ramp down the push force (unless you are using air casters or some similar esoteric ). If your speed is precise and repeatable enough, your ramp decline is the same, and depending on how accurate your stop position needs to be, simple timing to start the slow down at the right point.

If your client really wants to think about moving that load with human power, it will take a fairly large capacity manual winch and it will move r-e-a-l-l-y slow. Think about the definition of a horsepower, 550 ft lbs per second or to lift 33,000# 1 ft in 1 min. Now that is straight up, not horizontal but it should begin to give you a idea of the force needed to move a load that size. How far does the unit have to travel and in what time frame?

 

[kicknargel]

This is preliminary work to get a ballpark budget so not all those factors are defined. It probably wants to move ~16', over I'd guess ~30 seconds. I can spec casters; thinking 5" polyolefin on masonite deck. Like I said, I was just curious if anyone had a "for a typical stage wagon on a typical stage at a moderate speed, I figure x pounds of pull for y weight of wagon." So I could at least get in the ballpark of needing 5 hp or 50 without spending a day engineering it all. Cause if it's 50 hp, we just won't do it.

 

[MPowers]

There are some other issues here also. About how large is your unit planned to be? 20'x20' for example would average to 82.5# sq/ft. If you have a caster every 4' in each direction that would be 25 casters or 1320# per caster. Can the stage floor handle that kind of loading? What is the stage floor rated for? 150 pounds per square foot? It will take a lot of casters, 66 casters would be 500# per caster, maybe you should be looking at some dual wheel 8"- 10" units, just 'thinkin' .

 

[BillConnerFASTC]

Steel wheels and steel rails. The neoprene on hardboard will substantially increase the force required to move it - not like a small percentage but by a multiplier.

I doubt it will average near 82 psf. Just a deck and wheels is probably not 10psf and people in a room is rarely 50 psf and usually much less. Maybe this is multiple stories or has a swimming pool on it - I don't know - but seems that 35,000 must be much larger than 400 sq ft.

Air casters would be a good option. That's what I used for seat wagons of 98 seats that move to near center court and are flown for storage and those were 25 X 21 and not 10,000 as I recall - maybe not 5000.

 

[MPowers]

The 20'x20' was just a starting point guess on my part. the 82 psf was simply based on the op's 33,000 guess on total weight. I totally agree that it sounds like steel on steel is probably the best bet if he uses wheels. But I don't think, judging from Nick's post, that track are a likely option, thus my thought on air casters.

 

[Van]

Definately with that much weight you are going to want the unit on rails. steel on steel would be best or the moment of inertia will be impossible to overcome.