# Selecting the correct vibration motor

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#### mark sheldon

##### New Member
Hi all, I am building this cct to reduce the vibration in a 2.4Ghz radio controlled helicopter. I will be using a vibration motor instead of a basic one. I have a couple of questions I hope you guys could help with. 1. What vibration motor would be the best to use to achieve my aim and 2. The breadboard I am using is quite small, is there a min/max voltage/current to certain sized breadboard? Thank you in advance for any expert input.

#### gophert

##### Well-Known Member
Hi all, I am building this cct to reduce the vibration in a 2.4Ghz radio controlled helicopter. I will be using a vibration motor instead of a basic one. I have a couple of questions I hope you guys could help with. 1. What vibration motor would be the best to use to achieve my aim and 2. The breadboard I am using is quite small, is there a min/max voltage/current to certain sized breadboard? Thank you in advance for any expert input.

Vibration control is a very difficult task and especially difficult with counter balancing rotating mass.

Do you know the exact mass that is off-center and by how much (distance from center of shaft to center of mass).
The momentum of the counterbalance must match the momentum of the off-cheer mass causing the vibration.

How do yo plan to match the motor speed to the vibration?

What is "cct"?

#### dknguyen

##### Well-Known Member
cct = circuit in shorthand

#### JonSea

##### Well-Known Member
Big or small, an eccentric mass on a motor is not going to cancel vibration from another source.

With an eccentric motor, by varying the speed, you vary both the frequency AND amplitude. You have no way to match the speed to the frequency while at the same time controlling the vibration level.

You need to independently control frequency, amplitude and phase to cancel out a random vibration.

If you are trying to cancel out 1x rotor vibration AND rotor speed is exactly fixed, your idea still will not work because you have no way to vary the force of a vibration motor while maintaining constant speed.

Sorry, your idea is a bust. No matter how you ask the question.

#### Pommie

##### Well-Known Member
I think this is the third time I've said this.

If you have a known out of balance mass then balance it.

Mike.

#### unclejed613

##### Well-Known Member
the best way to tame the vibration you describe, is to fix it at it's source. find out where the imbalance is and correct it. doing that will solve two issues, the vibration itself, and anything that might eventually fail as a result of the vibration. even if you did find some way to counterbalance the body of the chopper, you would still have the out-of-balance condition in the rotor, and the rotor would fail (actually since the counterbalance is working against the offset of the rotor, it might make the rotor fail even quicker).

#### mark sheldon

##### New Member
the best way to tame the vibration you describe, is to fix it at it's source. find out where the imbalance is and correct it. doing that will solve two issues, the vibration itself, and anything that might eventually fail as a result of the vibration. even if you did find some way to counterbalance the body of the chopper, you would still have the out-of-balance condition in the rotor, and the rotor would fail (actually since the counterbalance is working against the offset of the rotor, it might make the rotor fail even quicker).
Because a radio controlled helicopter doesn't tend to produce too much vibration (unless components are damaged) I will input vibration by adding tape to one of the blades to input some vibration. The aim is to prove that I can use a shaker to oppose the vibration caused by the helicopter.

#### unclejed613

##### Well-Known Member
inertial sensors driving linear motors will probably be a better avenue to follow. in other words, you sample sensors that detect motion in all 3 axes, and use them to drive linear motors to counteract the wobble. using a rotating counterweight is much more difficult to synchronize because you are introducing motion in two axes, and there may be some undesirable resonance modes. with a rotating counterweight, you also have no control of how much force is applied to counterbalance the airframe. you have to match the rotation of the vibrator rotor to the speed of the propellers, but you also have to be able to control the magnitude of the counterbalancing, which because the counterweight is a fixed mass, can't be done. with 3 axis linear motors, you can change the force exerted by changing the slug's speeds. think of the linear actuators in the form of solenoids with permanent magnet cores. one for pitch, one for yaw, and one for roll.

#### JonSea

##### Well-Known Member
Because a radio controlled helicopter doesn't tend to produce too much vibration (unless components are damaged) I will input vibration by adding tape to one of the blades to input some vibration. The aim is to prove that I can use a shaker to oppose the vibration caused by the helicopter.
If you are trying to prove a shaker can counteract vibration, a motor is going to be an ineffective test. But I believe even a shaker is a flawed theory. Of course, I don't know much about the subject, having only been involved with vibration analysis and problem solving for about 35 years.

#### mark sheldon

##### New Member
If you are trying to prove a shaker can counteract vibration, a motor is going to be an ineffective test. But I believe even a shaker is a flawed theory. Of course, I don't know much about the subject, having only been involved with vibration analysis and problem solving for about 35 years.
What alternative would you suggest then using your 35 years experience!

#### JonSea

##### Well-Known Member
From my perspective, you have a splution looking for a problem.

What vibration source are you trying to address? Your posts I have read haven't been too clear about that. "Whatever the biggest problem is" isn't a realistic answer, because the source of the vibration determines where and in what direction you have to apply force to counteract the vibration.

I'm pretty skeptical of the entire idea of active vibration cancellation of mechanical deficiencies. Let's presume the biggest source of vibration is rotor imbalance that appears as 1x vibration in the radial direction (which is not a certainty as imbalance on an overhung rotor may be predominate in the axial direction). You would need to apply a rotating force opposite to the imbalance. Your could theoretically do this with 2 shakers located 90° apart.

Assume you have solved the problem of applying a rotating force exactly out of phase with the vibration. The force of imbalance is acting at 0°. You apply an opposite force at 180°. Your feet might feel less vibration on the deck. But what about the all important rotor bearings? Because of your "fix", the bearings are being subjected to twice the force!

#### mark sheldon

##### New Member
From my perspective, you have a splution looking for a problem.

What vibration source are you trying to address? Your posts I have read haven't been too clear about that. "Whatever the biggest problem is" isn't a realistic answer, because the source of the vibration determines where and in what direction you have to apply force to counteract the vibration.

I'm pretty skeptical of the entire idea of active vibration cancellation of mechanical deficiencies. Let's presume the biggest source of vibration is rotor imbalance that appears as 1x vibration in the radial direction (which is not a certainty as imbalance on an overhung rotor may be predominate in the axial direction). You would need to apply a rotating force opposite to the imbalance. Your could theoretically do this with 2 shakers located 90° apart.

Assume you have solved the problem of applying a rotating force exactly out of phase with the vibration. The force of imbalance is acting at 0°. You apply an opposite force at 180°. Your feet might feel less vibration on the deck. But what about the all important rotor bearings? Because of your "fix", the bearings are being subjected to twice the force!
Having only ever done this sort of thing in a full sized Lynx Mk3 & 8 I can tell you it is pretty impossible to get a perfect 100% track and balance it is just a matter of getting the figures as close to a pass as possible. I appreciate the other vibrations throughout the helicopter but just by cantering on the 1R vert vibration as long as I can visually produce a reduction in the vibration I intend to in force onto the blade using tape then my theory/concept will be a success

#### JonSea

##### Well-Known Member
.....then my theory/concept will be a success.....
For some value of success and ignoring that you've doubled the force on a bearing designed to run near its limits.

#### dknguyen

##### Well-Known Member
Is there a school project or competition going on or something? Why are there so many posts about something like this in the last few months?

#### JonSea

##### Well-Known Member
Is there a school project or competition going on or something? Why are there so many posts about something like this in the last few months?

Mark doesn't like the answers he's been getting so he re-words the question and asks again.....

#### mark sheldon

##### New Member
Mark doesn't like the answers he's been getting so he re-words the question and asks again.....
Nothing to do with that, I’m asking questions in the hope people can help. Unfortunately JonSea people like you are more interested in needlessly bragging about your 35 years experience (that no one asked for or cares about) than giving constructive help. Maybe it helps fuel your self importance?

#### unclejed613

##### Well-Known Member
Assume you have solved the problem of applying a rotating force exactly out of phase with the vibration. The force of imbalance is acting at 0°. You apply an opposite force at 180°. Your feet might feel less vibration on the deck. But what about the all important rotor bearings? Because of your "fix", the bearings are being subjected to twice the force!
my thought exactly, the two opposing forces have to cancel somewhere, which means there is a point where they are doubled. the stresses are not going to be distributed, but will be concentrated at a single point of failure. that point of failure will be near the source of the original imbalanced motion. if i'm not mistaken, real helicopters are built with special care taken to balance the masses of the rotors. there are very few times these masses would become unbalanced (like maybe in combat?). if you are in a situation where you lose a chunk of rotor, you have other problems to deal with than vibration, and it's likely that whatever caused you to lose a chunk of rotor has done other damage to the airframe. the last thing you want to do at this point is to double the stress on the rotor shaft and bearings, the main concern is getting down safely, preferably in a safe location.

to use a counter-rotating mass to cancel the vibration in such a situation, you need to know BEFOREHAND what the missing mass from the rotor will be, and most pilots don't have a crystal ball that will tell them how much rotor blade is going to get shot off.

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#### JonSea

##### Well-Known Member
Nothing to do with that, I’m asking questions in the hope people can help. Unfortunately JonSea people like you are more interested in needlessly bragging about your 35 years experience (that no one asked for or cares about) than giving constructive help. Maybe it helps fuel your self importance?
Actually, Mr. Sheldon, I have attempted to share with you some of what I have learned over the years. Part of that included how to use counter-rotating excentric masses to generate a directional force. I mentioned my experience, because everybody seems to be "an expert" in vibration analysis. I wouldn't call what I said bragging.

I have also attempted to explain why you can't control frequency and amplitude simultaneously with a motor driving an eccentric mass (as have others) and the need to do so, but that's fallen on deaf ears.

I'm sorry my real-world knowledge suggests a number of problems with your theory. You might want to step back and honestly evaluate the merit of my comments.

#### gophert

##### Well-Known Member
Nothing to do with that, I’m asking questions in the hope people can help. Unfortunately JonSea people like you are more interested in needlessly bragging about your 35 years experience (that no one asked for or cares about) than giving constructive help. Maybe it helps fuel your self importance?
Mark,

Imagine that you find the source of the vibration and are able to calculate the necessary weight to put on your counterbalancer shaft. Now you need to get your motor exactly in the same axis as your rotor (ideally). Unfortunately, you will not be able to place it above the copter so below is the only option. Placing the counterbalancer well below the source of the vibration will, even if perfectly synchronized, will produce a new mode of vibration.

Now, I am a firm believer that people learn better different methods. And not all learners understand to the same degree with each lesson. Therefore, I strongly encourage you to try something because the best lessons and the deepest understanding is from making mistakes and iterative re-design of failed attempts. Solid understanding does not come from reading about other people's mistakes. Go solder some wire, batteries and motors together. But, don't expect a lot of others to help you design control systems for the motors - anyone who can explain that will quickly discourage you from learning so you'll have to figure out a control system, too.