Maxon presentation sizing drive systems with low power dc motors 02-2014

Introduction
drive seminar

maxon seminar:
Drive systems with
low power DC motors
 Typical performance and its significance
 Selection of drive components
 Use in dynamic drive systems
© 2014 maxon motor ag, Sachseln, Switzerland

Learning objectives
The participants …

 get an overview on the parts of a Servo Drive System and
the interaction between them.

 learn to read the data sheets of DC motors, EC motors,
gearheads.

 know the main properties and application ranges of DC

and EC motors and be able to select the correct system.

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1

© 2014, maxon motor ag

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1

Introduction
drive seminar

Agenda Electromate Seminar
09.30 – 10.15

Motor selection: What is it all about?
– Application and situation analysis
– Extracting key load parameters

10.15 – 10.45

Properties of brushed and brushless DC motors
– Design variants
– Commutation systems: brushed, brushless

10.45 – 11.00

Coffee break

11.00 – 11.30

Motor data sheets
– Characteristic motor lines
– Operation ranges

11.30 – 12.15

Motor selection example

12.15 – 13.00

Lunch

13.00 – 13.30

Motor selection example continued

13.30 – 14.30

Introduction to ESCON and EPOS Systems

Media
 maxon Formulae Handbook
– epaper.maxonmotor.ch/formulaehandbook

 maxon catalogue
– epaper.maxonmotor.ch/en/

 Presentation hand-outs
 www.maxonmotor.com
– Service & Downloads
– Service Desk (FAQ)
– maxon academy

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Overview of the selection steps
drive seminar

Selection of
drive components
 Systematics of the drive selection
 Situation analysis, boundary conditions
 How is the integration into the environment?
 Preselection

 Determining the load requirements
 Result: key data for load characterization

Systematic selection process
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

Page

step 5+6
step 7
motor type sensor
winding
controller

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drive seminar

Step 1: Gain an overview
 analyze

 recognize dependencies

problem

mechanics
power

operating mode

motion profile

control concept

 checklist

operating points

control accuracy

boundary conditions

Drive system as a black box
environment
electrical power
task

 current
 voltage

 temperature, atmosphere
 impacts, vibration
…

boundary conditions
 dimensions
 service life
…

 set values
 commands

emissions

mechanical power
quality, accuracy
 resolution
 mech. play






electro magnetic
heat
noise
…

 force, torque
 velocity, speed

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2

drive seminar

Operating mode
 What is a working cycle?
 How often is it repeated? Which breaks?
 continuous operation
 cyclic operation
 intermittent
 Short-time operation

Operating modes
 continuous (S1)

load

time

 short term (S2)
 working cycles
 intermittent (S3)

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drive seminar

Control concept
 What kind of communication?
– communication with
higher level host system

– set value range

– inputs and outputs

 Controlled variable
– torque, current
– speed, velocity
– position

feedback
sensor

 Controlled range, accuracy?
– position resolution
– speed stability

Controller: Heart of the drive system

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drive seminar

Sensors in feedback systems
Power

Motion
Controller
Closed loop
system for speed
or position

Commands,
Set values
Control parameter

Feedback, sensor

Position
∆𝑝𝑜𝑠 Speed,
Direction
∆𝑡

Encoder
 Hall sensors
Resolver

Speed, Direction

DC Tacho
 IxR

Task and control accuracy
 The accuracy of control is the combined result
of all components in a drive system!
– resolution, precision
signal
amplification
command

controller

mechanical play
motor

gearhead,
drive

load

control loop
sensor

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5


phase shifts
time shifts

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5

drive seminar

Accuracy of drive systems
 position accuracy
–
–
–
–

absolute, relative, repeatability
overshoot allowed?
mechanical play in couplings, gearheads, …
encoder resolution and accuracy (linearity)
r

 speed accuracy
–
–
–
–

Corrected in what time frame?
t
min. speed nmin by encoder resolution
max. speed nmax by limiting frequency of the encoder
Speed ripple by current and / or torque ripple

 electronic components
– resolution of A/D-converters, frequency voltage converter
– bandwidth, temperature influences

Time and frequency aspects

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drive seminar

Power flow
power
supply

Losses

controller

gearhead,
drive

motor

Pmech = v * F
Pmech = ω * M

sensor

Pel = U * I

load

 energy is not stored: Power flow

– Power: a „constant“ reference value of the drive system

 Power consists of 2 components:

– voltage and current
– velocity and force or speed and torque
– One components can only increase at the expense of the other.

Transformation of power
 transformation of power  efficiency η describes losses
– electrical to electrical:
η = 90 – 95%

η = 90%

– electrical to mechanical:
optimum
η = 80 - 90%

– mechanical to mechanical:
ball screw spindle
η = 80 - 90%

η = 90%
per stage

trapezoidal spindle 40%

worm gear < 40%

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drive seminar

Mechanical drive concept
 Drive design: linear – rotation
 Drive elements and coupling with load
 relative position of motor and load
– e.g. bridge a distance with a belt

Motors up to 500W
n

DC behavior
(shunt)

DC motors
M
I

BLDC motors
linear motors

f

stepper motors

 Stator
winding
 magnetic
rotor

synchronous motors
start

M

asynchronous motors

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drive seminar

Particular boundary conditions
 dimensions
 service life

– specific depending on load cycle, ambient conditions and application
– given as service hours or numbers of working cycles
– limited by the weakest component

 temperature, atmosphere

– can influence the achievable power and service life

 noise, vibration

– specific depending on load cycle, mounting
and ambient conditions, application
– influences on service life

Interfaces: Connections
 electrical connections
– cable type, cable length, colours
– plug
– strain relief

 mechanical interface
– mounting type, mounting pilot, threads, number and location of bolt
holes
– output shaft: length, diameter, flats
– drive elements, pinions, couplings
– tolerances

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drive seminar

Definition of the load requirements
 motion profile and

 forces and torques

operation points

v(t), F(t)

 mass inertia and

n(t), M(t)

 Key values

acceleration

Operating points
 Pair of
– torque and speed
– force and velocity

 standard representation: (x,y) = (M,n) or (F,v)
speed n
velocity v
deceleration

acceleration

torque M
force F

dwell

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drive seminar

Operating point and motion profile
n
1

2

3

4

1
t

n

extreme
operating point

2
3

4






1

M

(M1,n1)

acceleration

friction and acceleration

(M2,n2)

const. speed

friction only

(M3,n3)

deceleration

friction helps during deceleration

(M4,n4)

dwell

depending on friction

Key load data for characterization
 maximum load
 average effective load (RMS)
MRMS 



1
2
2
t1M1  t 2M2  t 3M3  ...
2
t tot

Fmax / Mmax

F/M



FRMS / MRMS
Δtmax
Δttot

 maximum velocity or speed

vmax / nmax

 duration of the maximum load
 duration of a load cycle

Δtmax
Δttot

 required position resolution
 required speed accuracy

t

Δs
Δn

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drive seminar

Example: Conveyor belt for samples
 pulley diameter
 maximum mass on belt
 coefficient of friction on




100 mm
3 kg

support
friction force (empty belt)
feed velocity
supply voltage

approx. 0.3
approx. 40 N
0.5 m/s
24 V

Step 1: Situation Analysis
What information is missing?

 operating mode
 current
 task of the drive / setpoints
 maximum length / diameter
 service life
 movement quality
 emissions
 environmental conditions
 control concept

Page

 pulley diameter
support

100 mm
3 kg
approx. 0.3

 friction force (empty belt) approx. 40N
 feed velocity
0.5 m/s
 supply voltage
24 V

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drive seminar

Step 2: Load requirements

 acceleration value
 motion profiles
 Mass (rollers, conveyor belt)
 Forces / torques
 …….

 pulley diameter
support

100 mm
3 kg
approx. 0.3

 friction force (empty belt) approx. 40N
 feed velocity
0.5 m/s
 supply voltage
24 V

speed

nL =

30
30 vL 30 0.5
 



 100 min 1
d


 0.05
2

feed force

FL =   m  g  FR  0.3  3  10  40  9  40  50N

torque

ML =

power

PL = vL  FL  0.5  49  25 W

acceleration

Fa = m 

d
0.1
 FL 
 49  2.5Nm
2
2

vL
0.5
 3 
 1.5N
t
1

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drive seminar

Example conveyor belt: Key values
Looking for a drive that can accomplish the following:

 maximum speed
 average torque
 maximum torque
 duration of Mmax

nmax

100 rpm

Meff

approx. 2.5 Nm

Mmax approx. 2.7 Nm
1s

n
100 rpm

2.5

Page

2.7 Nm

14


M

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14

maxon DC and EC motors
drive seminar

3. Low power motors
 DC motors
 EC motors
 Structure, properties, options

© 2012, maxon motor ag, Sachseln, Switzerland
Top

DC motor designs
conventional, slotted
e.g. Dunkermotor

coreless

e.g. maxon
DC motors - overview

Top

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drive seminar

Conventional DC motor
el. connections

winding

brush system

iron core

commutator permanent magnet
(external)

flange

housing
(magn. return)


Top

Coreless maxon DC motor (RE 35)
self supporting
winding
commutator
plate

press ring
shaft

ball bearing

brushes
el. connections

flange
housing
(magnetic return)
ball bearing

commutator

permanent magnet
(in the centre)

press ring

Top

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drive seminar

What makes maxon motors special?
 no cogging
– no soft magnetic teeth to interact with the permanent magnet
– smooth motor running even at low speed
– less vibrations and audible noise
– any rotor position can easily be controlled
– no nonlinearities in the control behavior

 compact design
– more efficient design of the magnetic circuit
– compact magnet, high power density

– small rotor mass inertia
– high dynamics

Top

What makes maxon motors special?
 no iron core - no iron losses
– constantly impressed magnetization
– high efficiency, up to over 90%
– low no-load current, typically < 50 mA

 no saturation effects in the iron core
– Even at the highest currents the produced torque
is proportional to the motor current.
– stronger magnets = stronger motors

 low inductance
– less brush fire, longer service life
– less electromagnetic emissions
– easier to suppress interferences: capacitor between connections,
ferrite core at motor cable

Top

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drive seminar

maxon DC motor families
 DCX motor range
– configurable system
– high performance motor with NdFeB magnet
– high torques and speeds

 10 - 35mm

 RE motor range

 6 - 65mm

– high performance motor with NdFeB magnet

 A-max motor range
– attractive price-performance ratio
– DC motor with AlNiCo magnet

 12 - 32mm

 RE-max motor range

 13 - 29mm

– performance between RE and A-max
DC motors - variants

Top

DC commutation systems
Graphite
 graphite brush with 50%





copper
copper reduces the contact
and brush resistance
copper commutator
graphite serves as lubricant
spring system (schematic)

Precious metal
 bronze brush body with plated silver contact area
 silver alloy commutator
 smallest contact and brush resistance (50 mW)
 CLL for high service life
DC motors – commutation

Top

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drive seminar

DC commutation: Characteristics
Graphite
+ well suited for high currents and

Precious metal
+ well suited for smallest currents

+

+

+

peak currents
well suited for start-stop and
reversing operation
larger motors (>approx. 10 W)

 higher friction, higher no-load





current
not suited for small currents
higher audible noise
higher electromagnetic emissions
higher costs

+
+
+
+
+

and voltages
well suited for continuous
operation
smaller motors
very low friction
low audible noise
low electromagnetic interference
cost effective

 not suited for high current and


peak currents
not suited for start-stop operation

DC motors – commutation

Top

EC motors
 electronic commutation
– with Hall sensors
– sensorless
– sinusoidal commutation
2/4-pole EC motor
internal rotor

Multipole EC flat motor
external rotor
Multipole ECi motor
internal rotor
EC motors - overview

Top

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drive seminar

Brushless DC motor
 names: EC motor, BLDC motor
 motor behavior similar to DC motor
– design similar to synchronous motor (3 phase stator winding,
rotating magnet)
– the powering of the 3 phases according to rotor position

 main advantages: higher life, higher speeds
 slotless windings: no magnetic detent, less vibrations
 becomes more attractive
– costs and size of electronics
– strength of magnets
EC motors - overview

Top

maxon EC motor families
features in common

EC motors - variants

Top

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drive seminar

maxon EC motor families

 maxon EC motor

– high speeds and torques

 EC-max

– good value for money
– not optimized for performance: relatively high torque
– speeds up to 12’000 min-1

 EC-4pole

– optimized for performance: high torque

 EC flat motor

– very good value for money
– relatively large amount of torque


Top

maxon EC motor
PCB with
Hall sensors

preloaded
ball bearings

magn. return:
laminated iron stack

control
magnet

housing

el. connections winding
and Hall sensors

3 phase knitted
maxon winding

balancing rings
rotor
(permanent magnet)


Top

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drive seminar

Electronic commutations systems

 common goal: applying the current to get the maximum torque
 perpendicular magnetic field orientation of
- rotor (permanent magnet)
- and stator (winding)
 knowledge of rotor position with respect to winding
commutation
type

block
sensorless

DECS

sine

rotor position
feedback

Hall sensors
ESCON

encoder (+ HS)
EPOS2

maxon
controller
families

ESCON

EPOS2
EPOS3
EtherCAT

EC motors – electronic commutation

Top

Block commutation
rotor position from Hall
sensor signals
north



control magnet

south

Hall sensor

1
0
0
0°

EC-max and EC flat:
Power magnet is probed directly

1
1
0

0
1
0

0
1
1

0
0
1

1
0
1

1
0
0

60° 120° 180° 240° 300° 360°
rotation angle 


Top

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drive seminar

Block commutation
commutation
electronics

+

power stage
(MOSFET)

EC motor
(magnet, winding, sensor)

commutation
logics

Phase 1

HS1

Phase 3

HS3
HS2

Phase 2

–
rotor position feedback

Top

DC and EC motor: Comparison
EC motor
+ long life, high speeds

DC motor

+ simple operation and

 preloaded ball bearings

control, even without
electronics

+ no electronic parts in the
motor

 brush commutation system

+ no brush fire

 iron losses in the



 more cables
 more expensive

limits motor life

 max. speed limited by

magnetic return
needs electronics to run

 electronic parts in the

commutation system

motor (Hall Sensor)

Comparison DC and EC

Top

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drive seminar

DC and EC motor: Comparison
maxon motor family

RE (DC)

EC

EC-max

(20 … 100 Watt)

EC-4pole

EC-flat

EC-i

50 000 min-1

10 W/cm3

25 000 min-1

5 W/cm3

2 mNm/cm3

10 ms

1 mNm/cm3

5 ms

max. speed

power density

torque density

mech. time

(min-1)

(W/cm3)

(mNm/cm3)

const. (ms)

Comparison DC and EC

Top

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maxon Motor Data and Operating Ranges
drive seminar

Motor data and
operating ranges of
maxon DC motors
 Motor behaviour: speed-torque line, current
 Motor data and operating ranges

© 2012, maxon motor ag, Sachseln, Switzerland
Top

DC motor as an energy converter
 electrical in mechanical energy
Pel  U  I

– speed constant
– torque constant
– speed-torque line

Pmech 


30

nM

PJ  R  I2

 applies to DC and EC motors
– "EC" = "brushless DC" (BLDC)

Overview

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drive seminar

Characteristic motor data
describe the motor design and general behaviour
 independent of actual voltage or current

 strongly winding dependent values (electromechanical)
10

Terminal resistance (phase to phase) R

11

Terminal inductance (phase to phase) L

12

Torque constant kM

13

Ω

Speed constant kn

mH
mNm / A
rpm / V

 almost independent of winding (mechanical)
14

Speed / torque gradient Dn/DM

15

Mechanical time constant tm

16

Rotor mass inertia JMot

rpm / mNm
ms
gcm2

Characteristics

Different windings

R

 low resistance winding
 thick wire, few turns
 low rated voltage
 high rated and starting

 high resistance winding
 thin wire, many turns
 high rated voltage
 low rated and starting

 high specific speed
 low specific torque (mNm/A)

 low specific speed (min-1/V)
 high specific torque (mNm/A)

currents

currents

(min-1/V)

Characteristics

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drive seminar

Electromechanical constants
 Torque constant kM

– produced torque is proportional to motor current
– unit:

mNm / A

 Speed constant kn

– law of induction: changing flux in a conductor loop
– mostly used for calculating no-load speeds n0
– unit:

min-1 / V

M  kM  I

n  k n  Uind
n0  k n  U

 Correlation
– kM and kn are inverse, but in different units
– expressed in the units from catalog:

kM  kn 

30'000 mNm min 1

A
V

Characteristics

Motor as an electrical circuit
U
+

I

_
R

L

EMF: induced voltage Uind
(winding) resistance R

EMF

winding inductance L
• voltage losses over L can be
neglected in DC motors

applied motor voltage U:
U  L  I  R  I  EMF  R  I  Uind
t

 30'000 R 
 M
n  kn  U  

2
 
kM 


Dn
n  kn  U 
M
DM

Uind  U  R  I

n
M
 UR
kn
kM
Characteristics

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drive seminar

Speed-torque line
speed n

n  kn  U 

Dn
M
DM

U > UN

n0
n0  k n  U
Dn

U = UN

DM

MH
IA

torque M
current I

Characteristics

Speed-torque gradient
by how much is the speed reduced Dn,
if the output motor torque is enhanced by DM?

Dn 30'000
n

R  i
2
DM   k M
MiH

speed n

strong motor:

M1, n1

n0

Dn

• flat speed-torque line, small Dn/DM
• not sensitive to load changes
• e.g. strong magnet, bigger motor

M2, n2

DM
weak motor:

• steep speed-torque line, high Dn/DM
• sensitive to load changes
• e.g. weak magnet, smaller motor

MH

torque M

Characteristics

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drive seminar

Winding series
n

numerous winding variants adjust

at U constant

 electrical input power (voltage,
current of power supply)

thick wire

 mechanical output power
(speed, torque)

thin wire

M
speed-torque gradient
 basically constant for the winding series
 constant filling factor: a constant amount of copper fills the air gap
Characteristics

Values at nominal voltage
describe the special working points:

 at rated voltage UN
 at rated current IN

 No-load operating point
n

– resulting no-load speed n0
– resulting no-load current I0

 rated working point
– resulting rated speed nN
– resulting rated torque MN

 Motor at stall
– resulting stall torque MH
– resulting starting current IA

M

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drive seminar

Thermal motor data

plastic
plate

describe the motor heating and thermal limits

 depend strongly on mounting conditions
 standard mounting:

horizontal
mounting

 heating and cooling

– thermal resistance housing-ambient Rth2
– thermal resistance winding-housing Rth1
– thermal time constant of winding tthW

free convection
at 25 °C ambient
temperature

– thermal time constant of motor tthS

 temperature limits
– ambient temperature range
– max. winding temperature Tmax
Specifications

Mechanical motor data

describe maximum speed and the properties of bearings

 max. permissible speed
– limited by bearing life considerations (EC)
– limited by relative speed between collector and
brushes (DC)

 axial and radial play
– suppressed by a preload

 axial and radial bearing load
F5

– dynamic: in operation
– static: at stall
axial press fit force
(shaft supported)

l

Fd

d

Specifications

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drive seminar

maxon standard tolerances
 Sources

– winding resistance
– magnetic properties
– friction and losses

n

±7%
±8%

 Results

1.1
1.0
0.9

– general tolerance level
– tolerance in no-load current
– tolerance in no-load speed
 weaker magnet =>
 stronger magnet =>

0.86

1.0

1.16

5 to 10 %
± 50 %
± 10 %
enhanced n0
reduced n0

M


Influence of temperature
temperature coefficients
Cu

AlNiCo

- 0.02 % per K

Ferrite

- 0.2

% per K

NdFeB

temperature

+ 0.39 % per K

- 0.1

% per K

resistance

magnetic properties

R: + 19.5 %

kn + 5 % (no-load speed)

 example: RE motor
DT = + 50K

kM - 5 % (more current!)
stall torque MH : - 22 %

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drive seminar

Motor limits: operation ranges
Speed
n

nmax

continuous
operation

- higher ambient temperature
- heat accumulation

short term
operation

torque M
current I

MN
IN

- lower ambient temperature
- good heat dissipation

Operating Range

Short-term operation overload
 motor may be overloaded for a short time and repeatedly
– limit: max. permissible winding temperature
– depends on thermal time constant of winding tW and amount
of overload

overload
duration
5tW
4tW
3tW
2tW

continous
operation

1tW

thermally
prohibitted
short term
operation

permissible
short term
operation

torque M
load

MN

2MN

3MN

4MN

Operating Range

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Examples for motor and drive selection
drive seminar

Examples for motor and
drive selection
 Continuous operation
 Cyclic operation
 maxon selection program

Systematic selection process
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

Page

step 5+6
step 7
motor type sensor
winding
controller

1


Page

1

drive seminar

Step 5: Motor selection conveyor belt
 selecting the motor type
 selection of the winding
 planetary Gearhead GP 32 A
– reduction

51:1

 Motor requirements (key values)
– Speed

5100 min-1

– average torque

70 mNm

– maximum torque

about 75 mNm, 1s

Selection criteria motor type
Commutation
(Service life)

Sensor

Shaft

Bearing
(Service life)

Electrical
connection

Ambient
condition

Page

2


Page

2

drive seminar

Motor type selection
 Combination with

maxon Modular System
+ motor




A-max 32

RE-max 29

(continuous torque)
max. torque
max. permissible
speed

RE 35, 90W

A-max 26

 Nominal torque

RE 30, 60W

RE 25, 20W

n

+ motor

RE 25, 10W

selected gearhead

EC 32, 80W

MRMS  MN
continuous
operation

nmax

short term
operation

deceleration

acceleration

MN

M

Motor type selection
according
maxon
modular
system

motor type

MN suited?

RE 25

< 30 mNm

too weak

A-max 26

< 18 mNm

too weak

RE-max 29

< 30 mNm

too weak

RE 30

ca. 80 mNm

RE 35

100 mNm

strong

EC 32

< 45 mNm

too weak

A-max 32

< 45 mNm

too weak

EC 32 flat

< 10 mNm

too weak

Page

3


good

Page

3

drive seminar

Step 6: Winding selection
 Goal: Reach the required speed at maximum possible motor
voltage under maximum load

 for a given motor size (motor type) this means: sufficiently high
speed constant

n0,theor
nmot

n
Mmot
M

n0,theor  nmot 

speed n

n
k n  k n,theor  0,theor
Umot

nmot, Mmot

speed-torque line high enough
for the required load speed

speed-torque line
too low for the
required load speed

torque M

Mmot

n

n
Mmot  5100  9  70  5700 min 1
M
n
5700
rpm
k n  k n,theor  0,theor 
 270
Umot
21
V

n0,theor  nmot 

[rpm]

5700
5100

 select motor 310007:
– speed constant

kn = 369 min-1/V

 needed current
– with torque constant kM

Imax 
70 mNm

M



Page

Mmax
 I0
kM

70
 0.15  2.8 A
25.9

4


Page

4

Feedback and Motion Control
maxon drive seminar

Feedback and
Motion Control
 Feedback systems
– Specifically: Encoder

 Properties of controllers
– control value
– performance, motor type
– communication, signal processing

Motion Control System Overview
Power Supply

CAN

Motion Controller
I/O

Supervisor / Master
(PLC / PC)
v(t), F(t)

Motor
Gearhead

Encoder

Load

Page

1


Page

1

maxon drive seminar

Sensors in feedback systems
Power

Motion
Controller
Closed loop
system for speed
or position

Commands,
Set values

Control parameter
Position
∆𝑝𝑜𝑠
∆𝑡

Speed,
Direction

Speed, Direction

Feedback, sensor
Encoder
 Hall sensors
Resolver
DC Tacho
 IxR

Drive component: Controller

Page

2


Page

2

maxon drive seminar

mmc product families
controller
family

EPOS

ESCON
current control

control loops

speed control
position control

system
architecture

commanded by
master system

setup
feedback
sensors

commanded by digital
and analog inputs

graphical user interface (Studios)
needed feedback:
• EC: encoder and Hall
sensor
• DC: encoder

possible feedback:
• encoder
• Hall sensor (EC)
• DC tacho (DC)

Configuration – EPOS/ESCON Studio
Communication
 Bus types
 Baud rates
 …
Motor type
 DC
 BLDC
 Commutation

Feedback type
 Encoder (resolution)
 Hall sensor
 DC Tacho

Configuration
Graphical User
Interface
(GUI)

Inputs / Outputs
 Stop
 Direction
 Enable - disable

Operation mode
 Current control
 Speed control
 Position control

 Ready
 Speed comparator
 ….

Page

3


Page

3

Selection example – step by step
Drive seminar

Selection of
drive components
 The systematics of the
drive selection on a
practical application
example


Page

1


Page

1

Drive seminar

Step 1: Situation Analysis
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

step 5+6
step 7
motor type sensor
winding
controller

 operating mode, motion profile
– acceleration
– inertias (rollers, belt)

 current power supply
 control concept, variable
– set value
– movement quality

Given:
 pulley diameter
support
 friction force (empty belt)
 feed velocity
 supply voltage

 maximum length / diameter
 service life
 environmental conditions
– emissions

Page

2


100 mm
15 kg
approx. 0.2
approx. 30 N
0.5 m/s
24 V

Page

2

Drive seminar

Step 2: Load Requirements
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

step 5+6
step 7
motor type sensor
winding
controller

Conveyor belt: load data
 Maximum load speed

𝑣 𝐿 = 0.5

𝑚
𝑠

 feed force
𝐹𝐿 = 𝐹 𝑅 +

 acceleration

𝜇

∙ 𝑚 ∙ 𝑔 = 30 + 0.2 ∙ 15 ∙ 9.8 ≅ 60𝑁

𝐹𝑎 = 𝑚 ∙

∆𝑣 𝐿
0.5
= 15 ∙
= 15𝑁
∆𝑡
0.5

 power
𝑃 𝐿 = 𝑣 𝐿 ∙ 𝐹 𝐿 = 0.5 ∙ 60 = 30𝑊

Page

3


Page

3

Drive seminar

Conveyor belt: Key values load

 maximum velocity
 average force
 maximum force
 duration of Fmax

vmax

= 0.5 m/s

Feff

= approx. 60 N

Fmax

= approx. 80 N

Δtmax = 0.5 s

v
0.5 m/s

60 N 80 N

F

Step 3: Drive
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

Page

step 5+6
step 7
motor type sensor
winding
controller

4


Page

4

Drive seminar

Conveyor belt: load data gear
 maximum speed
 average torque
 maximum torque

𝑛 𝐺 = 30 ∙ 𝜔 = 30 ∙
𝜋
𝜋

𝑣𝐿
𝑑
2

= 30 ∙
𝜋

0.5
≅ 100𝑟𝑝𝑚
0.05

𝑑
0.1
∙ 𝐹𝐿 =
∙ 60 = 3.0𝑁𝑚
2
2
𝑑
0.1
= ∙ 𝐹 𝑚𝑎𝑥 =
∙ 80 = 4.0𝑁𝑚
2
2

𝑀 𝐺,𝑒𝑓𝑓 =
𝑀 𝐺,𝑚𝑎𝑥

Example conveyor belt: Key values

 maximum speed
 average torque
 maximum torque

nG,max = 100 rpm
MG,eff

= approx. 3.0 Nm

MG,max = approx. 4.0 Nm
Δtmax

= 0.5 s

3.0

4.0 Nm

Page

5

n
100 rpm


M

Page

5

Drive seminar

Step 4: Gearhead selection
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

step 5+6
step 7
motor type sensor
winding
controller

Step 4: Gearhead selection

 maximum speed
 average torque
 maximum torque

nG,max = 100 rpm
MG,eff

= approx. 3.0 Nm

MG,max = approx. 4.0 Nm
Δtmax

= 0.5 s

?
Page

6


Page

6

Drive seminar

Limits gear selection
torque
MN > MG,eff

output
speed n

Reduction out of input and
output speeds:
𝑖<

nmax,L

𝑛 𝑚𝑎𝑥,𝑖𝑛
𝑛 𝑚𝑎𝑥,𝐿
nmax,in

continuous
operation

nmax,L

short term
operation

MN

Mmax

output
torque M

Selection Guide maxon Gear
3 Nm

Page

7


Page

7

Drive seminar

Conveyor belt: Gearhead selection
 planetary gearhead
– continuous torque
– max. input speed
– max. reduction
– selected reduction
– efficiency ηG

GP 32 C
3 Nm (at least 2 stages)
8000 rpm

𝑛 𝑚𝑎𝑥,𝑖𝑛 8000
=
= 80: 1
𝑛 𝑚𝑎𝑥,𝐿
100

𝑖<
79:1
70 %

 requirements motor (key values)
– speed

𝑛

– torque

𝑀 𝑚𝑜𝑡 =

𝑚𝑜𝑡

= 𝑛 𝐺 ∙ 𝑖 = 100 ∙ 79 = 7900 𝑟𝑝𝑚
𝑀𝐺
3.0
=
= 54 𝑚𝑁𝑚
𝑖 ∙ 𝜂 𝐺 79 ∙ 70%

Conveyor belt: Key values motor
Looking for a motor that can accomplish the following:

 maximum speed
 average torque
 maximum torque

nmax

= 7900 rpm

Meff

= 54 mNm

Mmax = 72 mNm
Δtmax = 0.5 s

n
7900 rpm

54

72 mNm

Page

8


M

Page

8

Drive seminar

Step 5+6: Selection motortyp & winding
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

step 5+6
step 7
motor type sensor
winding
controller

Step 5: Motor type selection
Motor type according
to modular system
RE 25
RE 30

Nominal torque
MN > 54 mNm

RE 35
A-max 26
A-max 32
RE-max 29
EC 32
EC-max 22, 25W

max. permissible speed > 7900 rpm
continuous
operation

short term
operation

EC-max 30, 40W
EC-4pole 22
EC flat 32
EC-i 40

MN

Page

9


M

Page

9

Drive seminar

Further selection criteria motor type
Commutation
(Service life)

Sensor

Shaft

Bearing
(Service life)

Electrical
connection

Ambient
condition

Conveyor belt motor type
Motor type according Nominal
to modular system
torque MN

suitability

RE 25

< 30 mNm

Too weak, with brushes

RE 30

ca. 90 mNm

OK, but with brushes

RE 35

ca. 100 mNm

strong, but with brushes

A-max 26

< 18 mNm

too weak, with brushes

A-max 32

< 45 mNm

too weak, with brushes, nmax= 6000 rpm

RE-max 29

< 30 mNm

too weak, with brushes

EC 32

< 45 mNm

too weak

EC-max 22, 25W

< 23 mNm

too weak

EC-max 30, 40W

< 34 mNm

too weak, (60W version => 63 mNm)

EC-4pole 22

< 64 mNm

OK, only 120W version, builds long

EC flat 32

< 23 mNm

too weak

EC-i 40

< 70 mNm

OK

Page

10


Page

10

Drive seminar

Step 6: Winding selection
 Goal: Reach the required speed at maximum possible motor voltage
under maximum load

 for a given motor size (motor type) this means: sufficiently high speed
constant

∆𝑛
∙ 𝑀 𝑚𝑎𝑥
∆𝑀
𝑛0,𝑡ℎ𝑒𝑜𝑟
𝑘 𝑛 > 𝑘 𝑛,𝑡ℎ𝑒𝑜𝑟 =
𝑈 𝑚𝑜𝑡

speed n

𝑛0,𝑡ℎ𝑒𝑜𝑟 = 𝑛

n0,theor
nmot, Mmot
nmot

𝑚𝑜𝑡

+

speed-torque line high enough
for the required load speed

speed-torque line
too low for the
required load speed

torque M

Mmot

n

∆𝑛
∙ 𝑀 𝑚𝑎𝑥 = 7900 + 17 ∙ 72 ≅ 9100
∆𝑀
𝑛0,𝑡ℎ𝑒𝑜𝑟 9100
𝑚𝑖𝑛−1
𝑘 𝑛 > 𝑘 𝑛,𝑡ℎ𝑒𝑜𝑟 =
=
= 415
𝑈 𝑚𝑜𝑡
22
𝑉

𝑛0,𝑡ℎ𝑒𝑜𝑟 = 𝑛

[rpm]

9100

𝑚𝑜𝑡

+

7900

 select motor

311537:

– speed constant kn = 497 rpm/V

 needed current
– with torque constant kM

𝐼 𝑚𝑎𝑥 =
72 mNm

M

=

Page

𝑀 𝑚𝑎𝑥
+ 𝐼0
𝑘𝑀

72
+ 0.166 = 3.9 A
19.2

11


Page

11

Drive seminar

Step 7: Sensor and controller
Step 1
overview
situation

power
communication
ambient
condition

step 2
load

step 3
drive

step 4
gearhead

Page

step 5+6
step 7
motor type sensor
winding
controller

12


Page

12

Maxon presentation sizing drive systems with low power dc motors 02-2014

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