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# Inertia matching question

## Inertia matching question

(OP)
I need a little help understanding the logic of the statement below.

#### Quote:

The secret to the extra boost of inertia is its special inertia flywheel, which adds from three to 10 times the inertia of a standard servo motor. This flywheel replaces the more expensive gearbox traditionally added to the motor for applications where the customer has a high load-to-rotor inertia mismatch. Now, on applications where customers would normally add a gearhead, they can simply use a motor, saving money and eliminating the speed constraints normally associated with a gearhead.

### RE: Inertia matching question

I'm not a motion control expert but if you need to have more motor inertia (to match the load inertia) you could do it in serveral ways:

1) Use a gearbox as an "inertia translator" for the load.  For a speed reduction gearbox, the reflected inertia is equal to the gear ratio squared times the load inertia (plus some added inertia from the gears).

2) Use a flywheel to add inertia to the motor.

### RE: Inertia matching question

It would be best to know the whole context of that statement.  It looks like marketing propaganda to me.

The real question should be do the inertias have to be matched? If not then why add inertia to the motor?

Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com

### RE: Inertia matching question

(OP)

#### Quote:

It looks like marketing propaganda to me.

#### Quote:

The real question should be do the inertias have to be matched?
I agree. .

#### Quote (Nick Repanich):

Inertia ratio is an indicator of possible stability problems. It is not the cause of the problem.

### RE: Inertia matching question

this is BS.
Adding gear box is one thing, motor interia is another.
For fast servo - never do this (add interia).

For spinning with one dirrection and with one speed - yes , adding interia makes system smoother.
It also  minimizes torque ripple cause by commutation in 6-step drives.
Stability - now can play with poles and zeros inside DSP driving this motor.

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