Why Dynamic Balancing?
Dynamic balancing is a way of balancing machines by rotating parts quickly and measuring the imbalance using electronic equipment. The imbalance can then be corrected by adding or subtracting weight from the rotating parts until the vibration is reduced.
All machines have some form of residual vibration. Excessive vibration in rotating machinery can cause unacceptable levels of noise and more importantly, substantially reduce the life of components. Hence, the ideal would be to remove all causes of vibration and run the unit totally "smooth". Unfortunately, in practice the ideal cannot be achieved and whatever one does, some inherent cause of vibration or unbalance will remain.
The best you can do is to reduce this unbalance to a level that will not adversely affect the bearing life and will reduce noise levels to an acceptable level. The process of reducing the out-of-balance forces that cause vibration in rotating machinery is called "Balancing". The unbalance is caused by an effective displacement of residual mass from the centre of rotation.
The process of "Balancing" is the removal or addition of weight to the device such that this effective mass centre approaches the true axis.
The simplest form of "Static" balance involves placing the unit on low friction bearings and allowing it to rotate and "settle" with the "heaviest" point falling to the bottom. Material is then removed from this point (or added at the top point) and the unit gently rotated until, when stopped the new "heavy" point again falls to the bottom. This process is then repeated until no obvious "heavy" point seems to exist. Unfortunately this doesn't always work that well.
Going one step further, the unit can be mounted on a purpose built "Balancing Machine" which has its bearings or housing connected to sensors which detect the "heavy" point in relation to a datum on the unit whilst it is being rotated. This increases the sensitivity and hence the accuracy of the balance. If one considers correction at a single position along the plane of rotation, then the balance is said to be "Single-Plane."
Most RC modelling and drone applications such as ducted fans, propellers and wheels fall within the single plane category with the exception of gas turbines which require a two plane balancing solution.
Benefits of Balancing
- Reduce and eliminate vibration levels.
- Increase motor life.
- Increase performance.
- Reduced noise.
There are many reasons why a component may need to be balanced:
- Dirt build-up (typically on fans)
- Erosion (impellers)
- Corrosion of internal parts
- Casting imperfections, voids and inclusions
- Mismatched lengths of keys and keyways
- Mechanical and thermal distortion
- Shifting mass due to loose parts and poor tapered hub fits
- Previous unsuccessful balancing attempts
- Improper assembly of parts