Hang a heavy bag from suspension trainer (TRX) ceiling mount?

[skribs]

I have a TRX suspension trainer (pictured below) which is attached to my ceiling using the TRX X mount. It's anchored on a joist. It holds my weight (185 lb.) just fine. I'm thinking about getting a heavy bag that I can hang onto the yellow extension strap. I see some ceiling mount products that are on a single joist, or even a single eye bolt. Other folks recommend mounts that spread across multiple joists.

The TRX mount is rated for around 350 pounds, and the bags I'm looking at are 70-100 pounds, but when I've done some research I've seen words like "live load" which suggest the forces of a swinging heavy bag are different than the force of a resting heavy bag, and I'm not enough of a physicist or engineer to know how much I need.

Would I be fine using this? Or would I really be better off with a product that spans multiple joists? I am also planning on getting a BOB and that may be enough for me.

 

[Dirty Dog]

Static load is the bag just hanging there. Dynamic load is the bag moving.
Force=Mass x Acceleration and if Force is less than the rating of the mount, you should be OK. Of course, you need to know not only what the TRX mount can hold, but also what the joist can hold (don't ignore the weight it's already holding).

 

[skribs]

Static load is the bag just hanging there. Dynamic load is the bag moving.
Force=Mass x Acceleration and if Force is less than the rating of the mount, you should be OK. Of course, you need to know not only what the TRX mount can hold, but also what the joist can hold (don't ignore the weight it's already holding).

Unfortunately, I don't know what the acceleration is, or how its affected by being lateral movement, or for example the sudden acceleration if the strap gets any slack and the bag drops and jerks.

Edit-to-add: I appreciate the answer, but now I'm just left with more questions.

 

[Dirty Dog]

Unfortunately, I don't know what the acceleration is, or how its affected by being lateral movement, or for example the sudden acceleration if the strap gets any slack and the bag drops and jerks.

Edit-to-add: I appreciate the answer, but now I'm just left with more questions.

Calculations would always be worst case. So slack in the strap is easy. Acceleration under 1G is 32 feet per second per second. Measure from the top of the bag to the ceiling. That is your maximum drop distance. Calculate from there.

You also need to consider how long deceleration takes.

Let's assume a mass of 75lbs, drop height of 12" and a rapid deceleration, say 0.001 seconds.

An object dropping 12" will land at a velocity of 32 f/s. So the force required to stop is is 32/0.001 or
F=(.75/32)32000 = 750.

So a 75lb bag dropping 12" with a quick stop can generate 750lbs of force.

If your strap has a spring, it might stop in 0.005 seconds.
So 32/0.005 = 6400. Thus F=(.75/32)6400 = 150lbs

Physics is fun.

 

[skribs]

Calculations would always be worst case. So slack in the strap is easy. Acceleration under 1G is 32 feet per second per second. Measure from the top of the bag to the ceiling. That is your maximum drop distance. Calculate from there.

You also need to consider how long deceleration takes.

Let's assume a mass of 75lbs, drop height of 12" and a rapid deceleration, say 0.001 seconds.

An object dropping 12" will land at a velocity of 32 f/s. So the force required to stop is is 32/0.001 or
F=(.75/32)32000 = 750.

So a 75lb bag dropping 12" with a quick stop can generate 750lbs of force.

If your strap has a spring, it might stop in 0.005 seconds.
So 32/0.005 = 6400. Thus F=(.75/32)6400 = 150lbs

Physics is fun.

It will take less than 1 second to drop 12", so it will be at a slower velocity. Ran it through a calculator and it's 8 ft/s after a 12 inch drop.

 

[Dirty Dog]

It will take less than 1 second to drop 12", so it will be at a slower velocity. Ran it through a calculator and it's 8 ft/s after a 12 inch drop.

Using simple numbers for a simple example is pretty common...

But now that you've got it all figured out, do some maths and let us know how your bag is going to do.

 

[JowGaWolf]

Lol way too much work to be hanging a bag.

 

[Dirty Dog]

Lol way too much work to be hanging a bag.

Personally, in a residence, I'd get a free standing hanger and be done with it.

 

[JowGaWolf]

Personally, in a residence, I'd get a free standing hanger and be done with it.

I'm always amazed how the math formulas come out in Martial talk. Some serious stuff.

 

[Oily Dragon]

I have a TRX suspension trainer (pictured below) which is attached to my ceiling using the TRX X mount. It's anchored on a joist. It holds my weight (185 lb.) just fine. I'm thinking about getting a heavy bag that I can hang onto the yellow extension strap. I see some ceiling mount products that are on a single joist, or even a single eye bolt. Other folks recommend mounts that spread across multiple joists.

The TRX mount is rated for around 350 pounds, and the bags I'm looking at are 70-100 pounds, but when I've done some research I've seen words like "live load" which suggest the forces of a swinging heavy bag are different than the force of a resting heavy bag, and I'm not enough of a physicist or engineer to know how much I need.

Would I be fine using this? Or would I really be better off with a product that spans multiple joists? I am also planning on getting a BOB and that may be enough for me.

View attachment 30272

Good for you, putting it somewhere you can actually move around it.

I can tell just by your room placement you're well trained with one. Nothing bothers me more than seeing a bag in a corner, or near something fragile. Some people always want to put the bag in the worst possible places, and I think they also tend to be the people worst at bagwork, imho.

Wish I could help with the math stuff, but I am dumb.

 

[HighKick]

I have a TRX suspension trainer (pictured below) which is attached to my ceiling using the TRX X mount. It's anchored on a joist. It holds my weight (185 lb.) just fine. I'm thinking about getting a heavy bag that I can hang onto the yellow extension strap. I see some ceiling mount products that are on a single joist, or even a single eye bolt. Other folks recommend mounts that spread across multiple joists.

The TRX mount is rated for around 350 pounds, and the bags I'm looking at are 70-100 pounds, but when I've done some research I've seen words like "live load" which suggest the forces of a swinging heavy bag are different than the force of a resting heavy bag, and I'm not enough of a physicist or engineer to know how much I need.

Would I be fine using this? Or would I really be better off with a product that spans multiple joists? I am also planning on getting a BOB and that may be enough for me.

View attachment 30272

Engineer here.
Is that a sheetrock ceiling? Is the mount attached to a single joist or truss? If so, what I have seen before and what to be worried about is the mounting member moving, damaging the sheetrock. The swinging load of the moment arm created by the mounting strap and the weighted bag will cause a single joist to move. Just a little movement will damage the sheetrock around the nails/screws that are attaching it to the joist. The same can be said for the bouncing of the bag, but it will be distributed in a ripple effect to a larger area.
If you have access to the joist above the ceiling, bridge several of the joist (ideally to all the vertical inner walls) and make a framed unit.
The strapping would allow for some cushion, but you can also add a heavy spring to mount from to protect the mounting surfaces.
Nice looking workout room.

 

[JowGaWolf]

Engineer here.
Is that a sheetrock ceiling? Is the mount attached to a single joist or truss? If so, what I have seen before and what to be worried about is the mounting member moving, damaging the sheetrock. The swinging load of the moment arm created by the mounting strap and the weighted bag will cause a single joist to move. Just a little movement will damage the sheetrock around the nails/screws that are attaching it to the joist. The same can be said for the bouncing of the bag, but it will be distributed in a ripple effect to a larger area.
If you have access to the joist above the ceiling, bridge several of the joist (ideally to all the vertical inner walls) and make a framed unit.
The strapping would allow for some cushion, but you can also add a heavy spring to mount from to protect the mounting surfaces.
Nice looking workout room.

Good points. Something to think about.