# DIY Heavy Bag Base Calculation: How Much Weight Do You Need to Prevent Toppling?

• I
• Kickboxer
In summary, the heavy bag requires a cylindrical base that is 10-11" in height and 30" in diameter, with a 3/4" thick base underneath it. It can be filled with up to 150lbs, and the base must be capable of withstanding a 650lbs kick. The base must also have a secondary base and stand that slips onto it, and the bag must be allowed to move in order to prevent it from tipping over.
Kickboxer

I'm building a freestanding heavy bag. Since I live in an apartment I can't hang my bag, so I've decided to build a base to slip my bag onto. I have the materials but not the knowledge. Can someone please help me figure out what the base needs to weigh to keep the bag from toppling over?

Thank you!

The bag is cylindrical; height is 6' and diameter is 16". It can be filled up to 150lbs.

The base is cylindrical as well; height is 10-11" and diameter is 30".

I'll be adding a 3/4" thick base underneath the base to help with balancing. I'm thinking a diameter of 45" should be enough.

I will also create a secondary base and stand that will be placed inside of the base for the purpose of slipping the bag onto.

The average generated force of my kick is about 650lbs.

Kickboxer said:

From the mass center of the bag, you draw a vector representing the gravitational force.

When you kick the bag, you add a horizontal force vector.

Now, add these two vectors. When the direction of the resulting vector crosses the edge of the base, the bag will tilt.

Hesch said:
From the mass center of the bag, you draw a vector representing the gravitational force.

When you kick the bag, you add a horizontal force vector.

Now, add these two vectors. When the direction of the resulting vector crosses the edge of the base, the bag will tilt.
This is nonsense. Force and displacement are two different quantities. You cannot add them.

He was talking about a horizontal force vector and not a displacement.

Does the bag have any freedom to move when you kick it (such as a stiff spring for a support)? If not, it may be hard to keep it from tilting up off the ground when you kick it. But it is basically just a torque calculation:
The weight of the bag, support and base times the radius of the base equals the torque it can handle. And the torque you supply is the force of the kick times the height above the ground you hit it.

Kickboxer
For a static or slowly changing torque, things are simple and one can do a force balance as @russ_watters suggests -- force of kick times height compared to weight of bag times offset of center-of-gravity from support rim. But a kick is the opposite of a slowly changing torque. Rotational impulse would seem to be the better measure of kick intensity.

Rotational impulse gives you rotational velocity by conservation of angular momentum. Rotational velocity gives you rotational energy. Rotational energy tells you how high the bag can lift as it rotates up into the air about the rim of its support. The balance point when the center of gravity passes over the rim tells you how far the bag can tip and, accordingly, how high it can lift before tipping over. Set up the equations and solve.

If we assume that oscillation (a series of kicks in rhythm with the back and forth motion of the bag) is not an issue, that general approach should solve the problem.

jbriggs444 said:
For a static or slowly changing torque, things are simple and one can do a force balance as @russ_watters suggests -- force of kick times height compared to weight of bag times offset of center-of-gravity from support rim. But a kick is the opposite of a slowly changing torque. Rotational impulse would seem to be the better measure of kick intensity.
So yeah, different assumptions and goals lead to different paths. With impulse, the bag has to be allowed to move. Is it? As I said, absent a spring base and if we assume lifting is unacceptable, the static analysis works.

If lifting and motion are allowed, then impulse and momentum (energy?) is definitely better. But IMO if motion is allowed, the design needs a spring, which is common for commercial products like this:

Because I don't think it is a good idea to design this in such a way as to allow the base to lift off the ground.

jbriggs444
Wow, thank you very much for the responses!

I'll have to get on some calculations this weekend.

I have been thinking of adding some kind of absorption mechanism. Maybe making the base bendable and attaching 8 heavy duty springs, equally spaced, around the bottom base connecting to the weighted base.

I'll do some more research this Sunday and do an update.

Kickboxer said:
I have been thinking of adding some kind of absorption mechanism. Maybe making the base bendable and attaching 8 heavy duty springs, equally spaced, around the bottom base connecting to the weighted base.

I'll do some more research this Sunday and do an update.
I'm sure you can find a sporting goods store to go kick around some ideas (see what I did there? ).

## 1. How do I calculate the mean?

The mean is calculated by adding up all of the numbers in a set and then dividing the sum by the total number of values in the set.

## 2. What is the difference between a median and a mode?

The median is the value that falls in the middle of a set of numbers when they are arranged in order. The mode is the number that occurs most frequently in a set of data.

## 3. How do I find the standard deviation?

The standard deviation is a measure of how spread out the data is from the mean. It is calculated by taking the square root of the variance, which is found by subtracting each value from the mean, squaring the difference, adding them all together, and dividing by the total number of values.

## 4. Can I use a calculator for my calculations?

Yes, you can use a calculator to help with your calculations. However, it is important to understand the formulas and concepts behind the calculations in order to ensure accuracy and understand the results.

## 5. What should I do if I am stuck on a calculation?

If you are stuck on a calculation, try breaking it down into smaller steps and double-checking your work. You can also ask a colleague or consult a textbook or online resource for assistance. Don't be afraid to ask for help if you need it.

• Other Physics Topics
Replies
1
Views
3K
• Mechanical Engineering
Replies
20
Views
2K
• Calculus and Beyond Homework Help
Replies
2
Views
6K
• Other Physics Topics
Replies
4
Views
9K
• Introductory Physics Homework Help
Replies
1
Views
1K
• Sci-Fi Writing and World Building
Replies
9
Views
2K
• Mechanics
Replies
2
Views
2K
• DIY Projects
Replies
2
Views
5K
• Mechanical Engineering
Replies
24
Views
7K
• Calculus and Beyond Homework Help
Replies
2
Views
3K