Kinetostatic Motor Torque and Speed dialog-box

Use this dialog-box to:

select a Servomotor
select a Gearbox
plot the Servomotor Torque and Speed curve; find the Maximum and RMS Torque values
plot the Gearbox Torque and Speed curve; find the Maximum and RMS Torque values
find the Servomotor Duty Cycle as a percentage of the machine cycle
upload your own database of Servomotors and Gearboxes.

You must use Display Forces to see the Motor Symbol at a Pin-Joint in the graphic-area.

Note: The options for a Slide-Joint will become available in a later release.

To Open the Kinetostatic Torque and Speed dialog-box


1.Make sure Calculate Forces and Display Forces Vectors are Toggled In
See Force Toolbar
2.Makes sure you have Configured the Power Source correctly for the kinematic-chain
3.Click the Motor Symbol element in the graphic-area. The Pin-Joint element shows in the Selection
4.Right-Click the Pin-Joint element, and click Edit element in the contextual-menu.

Motor-MessagesNote: The first time you use this dialog in a session, MechDesigner loads the database of Motors and Gearboxes. Please wait to open.

The Kinematic Torque and Speed dialog-box opens.

tog_minusSelect a Motor and Gearbox

Select a Motor Manufacturer and a Motor Part Number:

1.Click a Motor Manufacturer

The Motor selection box is at the top and left of the dialog

2.Click a Motor Part Number

This is immediately to the right of the Motor selection box

To help you make a selection, we show Rated Torque and Rated Speed with each Motor in the selection boxes

There are more parameters for the Motor in the Database.

Select a Gearbox Manufacture and Gearbox Part Number:

1.Click a Gearbox Manufacturer

The Gearbox selection box is to the top and right of the dialog

2.Click a Gearbox Part Number

This is immediately to the right of the Gearbox selection box

To help you make a selection, we show Gear Ratio and Rated Torque with each Gearbox in the selection-box.

There are more parameters for the Gearbox in the Database.

Note: You should make sure the parameters are correct with the most recent hardware available from your hardware supplier.

tog_minusAbout the Torque vs Speed and the Duty-Cycle Analysis Curves

X and Y Axes

X-axis : Speed [RPM] (RPM: revolutions per minute)
Y-axis: Torque [N.m]

The Torque and Speed show: ± Torque and ± Speed;  the four quadrants.

Torque and Speed Graph Scales

Clear the Show Limit Lines check box:
The Torque and Speed Graphs will auto-scale to the maximum and minimum as required from the Motor, even if the motor cannot deliver the Torque or Speed.
Select the Show Limit Lines check box:
The Torque and Speed Graphs will scale to the capacity of the Motor.

Curve Plot Points

We plot a point on the graph for each machine step.
The number-of-points is set in the Machine Settings dialog-box

Curve Point colours

The graph points have a colour code. The colour-code shows whether the Motor and Gearbox have the capacity to drive the mechanism at the required speed.
oGreen to indicate the Motor has the Speed and Torque have the capacity in all respects.
oAmber/Orange to indicate the Motor and Gearbox do not have the Continuous Torque or Speed capacity
oRed to indicate the Motor and Gearbox cannot provide the Torque or Speed, or both.

Duty-Cycle Percentages

There are three Duty Cycle Plots

Power Duty Cycle
Torque Duty Cycle
Speed Duty Cycle

Each Duty Cycle Plot shows the distribution of the Power, Torque and Speed of the Motor for a complete Machine Cycle.

If you select 'Show Limit Line' check box, then you can see if the motor must perform beyond its rated or maximum capacity.

If you want more detail for each chart, then increase the 'Bin Count'. You may also need to increase the number-of-steps in the Machine Settings dialog.

Kinetostatic Torque and Speed dialog box

There are two tabs.

tog_minusTorque vs Speed tab

Kineto-Static Toque Speed Graph
Click to Expand & Collpase

tog_minusDuty Cycle Analysis tab

Kineto-Static Duty-Cycles
Click to Expand & Collpase

More information on Motor Torque and Speed

tog_minusWhy the motor torque is different to the mechanism torque

Why is the Motor Torque different to the Torque given at the Pin-Joint when you Display Forces with the Display Force Vectors tool?

The Torque we show in the graphic-area when we 'Display Force Vectors' is the torque to move only the mechanism.

It does not include the Torque to move the motor and gearbox. It is necessary to add the Torque to accelerate the motor and the gearbox to Torque in the graphic-area.

Clearly, the Torque to move motor depends on the ....inertia of the motor and gearbox as well as the gearbox ratio.

The higher the gear ratio, the less Torque the motor 'sees'. But the motor must run faster and accelerate more. This influences the overall power, as well as system efficiency.

tog_minusMore on Torque vs Speed Curves

The performance characteristics of a brushless servo motor (motor/drive combination) are described by a torque/speed operating envelope.

As shown below, the coloured areas of the curve identify the Exceeded Duty, Continuous Duty and Intermittent Duty zones of the system.

Exceeded Duty

To move the mechanical system, the gearbox and itself, the servomotor must exceeds its maximum speed or the maximum torque, or both.

Continuous Duty Zone

The continuous duty zone is bordered by the maximum continuous stall torque up to the intersection with the intermittent duty line. The continuous torque line is set by either the motor’s maximum rated temperature, or the drive's rated continuous current output, whichever is less.

The system maximum continuous or 'voltage line' is set by the voltage rating of the drives, the line voltage supplied, and the motor winding.

The system can operate on a continuous basis anywhere within this area, assuming the ambient temperature is 40°C or less.

Intermittent Duty Zone

The intermittent duty zone is bordered by the peak stall torque line and the system voltage line. The peak torque line is set by either the drives’ peak current rating, which the drive can give for a limited time, or the maximum rated peak current for the motor, whichever is less. Higher torque levels may be achievable at higher power levels.

Typical Torque / Speed Duty Capability of a Brushless Servomotor.

Typical Torque / Speed Duty Capability of a Brushless Servomotor.

Peak Torque: (ԎPS ) The Peak Torque the Motor and Gearbox at Stall Speed

Continuous Stall Torque: (ԎCS ). The Continuous Torque the Motor and Gearbox can give Continuously at Stall Speed.

Maximum Speed: (ωMAX ) Maximum possible speed of the Motor and Gearbox. Not attainable when the voltage is limited by the drive.

Knee Speed: (ωK ) The Speed at 'knee' in peak envelope that is the intersection of the Peak Torque with the Voltage Torque/Speed Limit Line.

Motor Providers also give a Rated Power - this is dependent on the Drive.

Continuous Rated Torque:(ԎCR ). The Continuous Torque at the Speed of the Rated Power.

Rated Speed: (ωR ) The Rated Speed or Speed at Rated Power. The motor can operate at this speed with the supply voltage.

tog_minusHow we calculate the Motor Torque and Motor Speed

The Reflected Inertia at the Motor shaft usually continuously changes in a machine cycle.

With Constant Inertia Mechanical Systems it is easy to calculate Torque.

With mechanisms, the Torque is dependent on reflected inertia that is a function of Acceleration, Velocity, and Position.

PSMotion has developed algorithms to calculate these, which give a true indication of the reflected inertia at a motor shaft for even the most complex mechanisms.

The equations below, are calculated at every instant in a machine cycle.

Typically, you aim to make the Reflected Load Inertia = (Motor + Gearbox) Inertia.

However, when the Load Inertia is not constant, it is more difficult to select the Motor and Gearbox.


ωm = N × ωL

αm = N . αL


Tm = - αm (JG + JM) + sign(TVD)

TL = (TMD  ∕  N )  ∕  η

TT = Tm +  TL

N    = Gear Ratio

ωm = Motor Angular Velocity

ωL  = Load Angular Velocity

TT   = Total Torque

Tm  = Motor Torque

TL  = Load referred to Motor Shaft

TVD = Viscous 'Drag' Torque. It is always opposite to the direction of motion

TMD = Torque derived by MechDesigner at Motor Shaft ( f{PL , ωL, αL } )

JG   = Inertia of Gearbox

JM   = Inertia of Motor

αm  = Motor Acceleration

αL = Load Acceleration

η    = Gearbox Efficiency

About the Database

The Database

Click Image to Exapand Collapse
Database for Drives, Motors, Gearboxes...

You must now edit the database with the Edit Database tool

There are Six tabs


Ts = Stall Torque [Nm]

Tr = Rated Torque [Nm]

Tp = Peak Torque [Nm]

Wr = Rated Speed [RPM]

Jm = Motor Inertia [^2]

Ke = Voltage Constant [Vrms  ∕  1000RPM]

Kt = Torque Constant [Nm ∕ Amp]

R = Winding Resistance (Phase to Phase) [ohms]

L = Inductance (Phase to Phase) [mH]

Vmax = Maximum Voltage [V]

Frame Sizes
Gear Heads
Ball Screws

tog_minus        How to Import your own data into the database.

Step 1: Make a Copy of the Old Database

It is best to ZIP and make a copy of the Database Folder.

This folder is: C:\ProgramData\PSMotion\DBase\

Step 2: Suppliers

1.In this dialog, Click the Suppliers tab
2.Click the 'tog_plus-red' , at the top
3.Enter with your keyboard a new:
Index number
Components (for example: Motors)

Step 3: Units

1.Click the Units tab

Check that the unit you will be using in your database is in the list of Units.

If not, you can add a new Unit to the list.

2.Click the 'tog_plus-red' , at the top
3.Enter with you keyboard
Index number
Make the Quantity the same as another, unless you have a new 'Quantity'.
Make sure the UnitString is text, and does not not have any spaces. For Example:
N . m = no ;
N.m = yes.
You must add the ratio to convert 'your' new unit to SI (System International) units.
Make this number as accurate as you need.


Step 4: Prepare the CSV file.

The CSV file must include the text:

'Units' in Cell A31s-red
'Fields' in Cell A4

Row 3 must include the Units identical in text to the units in the Units Units tab - see Step 3

Row 4 must have the Fields Identical to the Column Header in the tab to which you will append your new data.

An example CSV File, the image shows:

Units 'N.m'.
This unit must be the same as in the Units tab in the database.
Field 'Ts'
This must the same as the Header 'Ts' in the Drives tab in the database.

If you do not have the particular data, for a Part, for example, Ke, then add zeros ('0') to the column in the CSV File.

Step 5: Click the tab in the database in to which you want to import the CSV data

Step 6: Import the CSV File

The data in your CSV file will append to the data in the database.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd