# Calculate hydraulic motor for a Flywheel

• Hans Heyde
In summary,The flywheel will spin at maximum speed, regardless of the torque received by the flywheel. You will need to determine the dimensions of the spinning disk, the moment of inertia, the power required to overcome friction and the numbers for air resistance and bearing friction. The purpose of the machine is to allow the flywheel to spin at maximum speed. Think about safety before building this machine.
Hans Heyde
Gentlemen:

I got stuck in this problem and I really need your help:

I have an hydraulic line of 23Mpa ( 3.300 psi) 10 gallon/min

I built a flywheel weight 58,000 grams with the following Inertial properties Principal moments I1= 2.5 , and I2= 2.3 and I3= 632170437 grams mm3

Flywheel will turn around I1.

I have V belts connecting the flywheel to an Hydraulic motor:

Flywheel have a nice shaft with taper bearings and it is well dynamically balanced. The pulleys. between Hydraulic Motor and flywheel are not fabricated yet, waiting for your answers and can be built in any diameter.

I would like to make this flywheel spin at maximum rpm, regardless of torque received by flywheel.

Question: what are the necessary data that I will need to order the hydraulic motor?

Best regards and thanks for your time.

Hans

1. When a flywheel exceeds its maximum speed, it breaks up into pieces. What that speed is depends on the material the flywheel is made of.
2. The power needed to turn a fly wheel is determined (a) by how fast you must accelerate it, (b) the power needed to overcome friction in bearings and the air surrounding the flywheel. If you neglect acceleration and friction, then zero power is needed (no motor needed to allow the flywheel to keep spinning at constant speed, just like no motor is needed to keep Earth spinning once revolution per day.). So in real life, you must specify the acceleration and the friction forces. Friction is very hard to estimate, you probably need to build the flywheel and run experiments to measure friction.

If you really want maximum speed for the flywheel, you probably should first determine what that maximum speed is. As anorlunda indicates, the true maximum speed is just short of that which causes the flywheel to disintegrate. If that is known, then I suggest that you back off from that speed by a healthy margin of safety and set that as your design goal.

Then again as anorlunda has said, you must determine the bearing losses and friction. These will govern the power required to run at design speed. V-belts may not be the best way to transmit power if the speed is extremely high as they too are subject to strength limitations.

Hi
anorlunda said:

1. When a flywheel exceeds its maximum speed, it breaks up into pieces. What that speed is depends on the material the flywheel is made of.
2. The power needed to turn a fly wheel is determined (a) by how fast you must accelerate it, (b) the power needed to overcome friction in bearings and the air surrounding the flywheel. If you neglect acceleration and friction, then zero power is needed (no motor needed to allow the flywheel to keep spinning at constant speed, just like no motor is needed to keep Earth spinning once revolution per day.). So in real life, you must specify the acceleration and the friction forces. Friction is very hard to estimate, you probably need to build the flywheel and run experiments to measure friction.

Hi Anorlunda.

Flywheel is made of Steel plates welded together.

I will have a brake system to avoid spinning too high and breakup in pieces.

Also, my flywheel shape has many open plates that will find air resistance and reduce speed.

Bearings are very good and friction is very low.

What I will need is to achieve maximum speed in the shortest time.

Then I will stop it with a brake system they will impose a torque against the free

I have to spin it with an hydraulic motor, that will also stops de rotation when the oil flow stops.

My problem is, therefore, find out what will be the characteristics of this motor that will spin it very fast at a maximum rotation. Note that we can supply oil at maximum 3300psi and 10 gal/min, and I will like to use the full power of it.

Best regards Hans

What is max speed? How fast must you accelerate?

It would take infinite power to accelerate in zero time, so you have to choose the time and then we can calculate the power.

The dimensions of the spinning disk are also needed. We need to know the moment of inertia.

The numbers for air resistance and bearing friction are also needed, not just words high or low.

The more specific you can be with your question, the better the quality of the answer.

What are your plans for safety? If a flywheel breaks, it could kill everyone standing nearby.

Think also about vibration. If everything is not carefully balanced, vibrations can destroy everything. Do you know how to balance spinning things?

What is the purpose of this machine? Can you draw us a diagram?

Hi Russ & Anorlunda
My machine is to cut tree branches.
See attached photo.
The hydraulic motor is not shown.
The fly wheel has steel blades attached to a turning "steel cave".
This structure is turning by an hydraulic motor and pulleys and belts.
The hydraulic motor maximum speed is 750 rpm, torque is 19.5 Nm power is 12.5 W.
My idea is to have pulleys that will turn the "Flywheel" at around 2.000 rpm.
I already tested this speed on the real flywheel and there is no vibration ( it is well balanced).
My idea is to make the flywheel turn up to maximum speed of the gear motor, and the to feed it the tree branches that will cut them in little pieces (chips).
Each revolution will cut a small part ( chip) of the tree branch, and will reduce it speed.
If the branch is too strong ( stronger wood or bigger diameter) the flywheel will reduce the speed.
When the "machine operator" finds that the speed is too slow, he will deduce the velocity that he is feeding the branch .
Outside diameter of the flywheel is 300 mm and its weight is 58 kilos ( 580 N).
Well, I believe it may work: what do you think?
Thanks a lot for all your help.
Hans

#### Attachments

• Flywheel.jpg
30.6 KB · Views: 440
Commercial wood chippers are on the market. you might want to look at one of them.

berkeman and russ_watters
Hi Dr D
Yes, I already checked those, but they do not match what I need.
This is a unique application...a new one...similar but not equal to the existing models.
I decided to make my own to match what i Need
Thanks a lot for your information.
Regards
Hans

When building a machine that has the same function as commercially available machines, it is good practice to take a look at similar machines, then design around their weaknesses. A commercially available chipper with about the same power as your 12.5 Kw hydraulic motor is: https://www.drpower.com/power-equipment/chippers/wood-chippers/self-feeding-wood-chipper-16-5.axd. If the chipping head has enough inertia, it can be direct driven by the engine.

Larger chippers automatically vary the feed rate to get maximum chipping speed. One of these will chip an entire tree in a few seconds: http://www.morbark.com/equipment/3036-whole-tree-chipper/#1365620863249-5-4.

MTA: Dr D beat me to it... In what way is your design better than the commercially available chippers?

berkeman and russ_watters
I'm still seriously concerned with safety. As those blades hit the wood, they will enentually break sending sharp,pieces of metal flying. Suppose there is a nail in the wood you're cutting. Then the remaining wheel will be seriously unbalanced. It might throw off more blades. Your machine needs heavy duty shielding to contain any flying bits.The slower the RPM, the safer. Why do you think you need such high speeds?

Here is a wood chipper that sounds close to,your description. Rotating disc 434 kg, 4 knives, 250 hp engine, no data on RPM.

berkeman

Hans Heyde said:
Hi Russ & Anorlunda
My machine is to cut tree branches.
See attached photo.
The hydraulic motor is not shown.
The fly wheel has steel blades attached to a turning "steel cave".
This structure is turning by an hydraulic motor and pulleys and belts.
The hydraulic motor maximum speed is 750 rpm, torque is 19.5 Nm power is 12.5 W.
My idea is to have pulleys that will turn the "Flywheel" at around 2.000 rpm.
I already tested this speed on the real flywheel and there is no vibration ( it is well balanced).
My idea is to make the flywheel turn up to maximum speed of the gear motor, and the to feed it the tree branches that will cut them in little pieces (chips).
Each revolution will cut a small part ( chip) of the tree branch, and will reduce it speed.
If the branch is too strong ( stronger wood or bigger diameter) the flywheel will reduce the speed.
When the "machine operator" finds that the speed is too slow, he will deduce the velocity that he is feeding the branch .
Outside diameter of the flywheel is 300 mm and its weight is 58 kilos ( 580 N).
Well, I believe it may work: what do you think?
Thanks a lot for all your help.
Hans
@Hans Heyde -- What you are working on is potentially pretty dangerous, especfially with your limited background and experience. Basically if you need to ask for design help on an Internet forum, you probably shouldn't be undertaking the dangerous project.

So this thread will remain locked, and I have a couple quick pieces of advice for you. First, on projects like this, it is best to find or hire an experienced professional who has the skills to help you design the project with all applicable safety measures. Second, please look into the liability insurance ramifications of building and fielding such a project. Even it it is for private use, you are opening yourself up to lawsuits by anyone injured by the device, and if you plan to use it professionally or sell it, that opens up a much larger liability world (please consult a liability lawyer for that). Please stay safe.

## 1. How do you calculate the required hydraulic motor size for a specific flywheel?

To calculate the required hydraulic motor size for a flywheel, you will need to know the weight of the flywheel, the desired rotational speed, and the required torque. These values can be used in the formula: Motor Size (in HP) = (Flywheel Weight x Rotational Speed)/5252. This will give you the minimum motor size required for your flywheel.

## 2. What factors should be considered when selecting a hydraulic motor for a flywheel?

When selecting a hydraulic motor for a flywheel, you should consider the weight and size of the flywheel, the required rotational speed, the available hydraulic pressure and flow rate, and the type of application the flywheel will be used for. It is also important to choose a motor with enough power and torque to properly drive the flywheel.

## 3. How does the rotational speed of the flywheel affect the required hydraulic motor size?

The higher the rotational speed of the flywheel, the larger the required hydraulic motor size will be. This is because the motor needs to provide enough power and torque to maintain the desired speed and overcome any resistance or load from the flywheel.

## 4. Can the hydraulic motor size be adjusted for different flywheel weights?

Yes, the hydraulic motor size can be adjusted for different flywheel weights. The formula for calculating motor size takes into account the weight of the flywheel, so a heavier flywheel will require a larger motor size to maintain the desired rotational speed.

## 5. Are there any safety considerations when calculating the required hydraulic motor size for a flywheel?

Yes, safety should always be a top priority when working with hydraulic motors and flywheels. It is important to choose a motor that can handle the load and stress of driving a flywheel. Additionally, proper installation and maintenance should be followed to ensure safe and efficient operation of the motor and flywheel system.

• Mechanics
Replies
7
Views
1K
• Mechanical Engineering
Replies
6
Views
4K
• DIY Projects
Replies
6
Views
3K
• General Engineering
Replies
58
Views
5K
• Mechanical Engineering
Replies
1
Views
2K