robolink® W FAQs – Joint construction kit for robots
Frequently Asked Questions

1) What types of igus® joints are available from stock?

2) What angle settings are possible? Own weights? Torques?

3) How can the joints be combined?

4) What does the term "modular kit system" mean?

5) Why can't articulated arms themselves simply be modified?

6) What cable distances/forces are necessary to move the joints?

7) What does the scope of supply of a joint include?

8) What does the scope of supply of an articulated arm include?

9) What does the scope of supply of a "complete system" include?

10) What angle sensors are used?

11) Can articulated arms also be used in water?

12) What types of drive are possible?

13) How are robolink® articulated arms controlled?

14) What must I do in order to be able to use the open-source software IME (igus® motion editor) of igus®?

15) What materials are used?

16) What grippers can be used?

17) What do joints or "systems" cost?

18) Where can I find more information?

1) What types of igus® joints are available from stock?

At the moment, there are 6 different standard joints

1 – RL-50-PL1: pivot joint
2 – RL-50-TL1: rotating joint
3 – RL-50-001: a 2-axis joint with a pivoting range of +/-90° ("THE classic")
4 – RL-50-002: a 2-axis joint with a pivoting range of +130°/-50° ("asymmetric")
5 – RL-50-003: a 2-axis joint with a pivoting range of +180°/0° ("foldable")
6 – RL-90-BL1: Basic joint with 2 axes, ("bigger and stronger")

In addition, special versions of the joints can be supplied if necessary.

2) What angle settings are possible? Own weights? Torques?

The following list provides information on basic data. This table can also be found in our catalogue.

Order number	Number Cables		Pivot angle		Angle of rotation		Weight	Max. load
	Own drive	Possible lead- through	Standard (with stop dog)	Option (*without stop dog)	Standard (with stop dog)	Option (*without stop dog)	[gr]	Pivoting [Nm]	Rotating [Nm]
1. Pivot joint RL-50-PL1	2	4	180° (±90°)	210° (±105°)	-	-	235	12	-
2. Rotating joint RL-50-TL1	2	8	-	-	340° (±170°)	540° (±270°)	245	-	5
3. 2-axis joint RL-50-001	4	4	180° (±90°)	210° (±105°)	340° (±170°)	540° (±270°)	345	12	5
4. 2-axis joint RL-50-002	4	4	180° (+130°/-50°)	240° (+135°/-105°)	340° (±170°)	540° (±270°)	345	12	5
5. 2-axis joint RL-50-003	4	4	180 ° (+180°/0°)	235° (+180°/-55°)	340° (±170°)	540° (±270°)	400	12	5
6. Basic joint RL-90-BL1	4	8	180° (±90°)	190° (±95°)	180° (±90°)	-	1250	20	10

Catalogue (PDF)

3) How can the joints be combined?

Each individual joint is fitted with draw wires. In each case, they must be taken through the joint underneath. This means that not just any combination of joints is possible. However, it is possible to combine individual joints with 1 to 6 DOFs and implement very different kinematics. We will happily advise you. The following illustration shows some possible combinations, whereby there are innumerable further possibilities if the newer types of joint, i.e. the RL-50-003 and RL-90-BL1, are taken into account!

4) What does the term "modular kit system" mean?

The basic idea of the robolink® modular construction kit is to provide our customers with individual (mechanical) components that can be used to build a robotic system. Depending on the complexity of what is required, articulated arms of varying degrees of complexity can be configured and ordered. igus® makes the arms in accordance with the stipulations of customers and delivers ready-to-connect units. However, it is not possible to simply join individual joints together (i.e. "like LEGO®" bricks").

5) Why can't articulated arms themselves simply be modified?

All joints are operated with draw wires. 2 wires are needed for each degree of freedom (antagonistic principle). If the wires of the upper joint (2) were to be routed through the lower joint (1) without being guided, the movements of the two joints would no longer be independent of each other. In order to achieve this independence, it is necessary that the wire tension of the upper joint (2) is uncoupled from the movements of the lower joint (1). This is done by means of a special Bowden cable system in the opening of the lower joint (see illustration). The wires them move freely next to each other in the connecting tubes between the joints.
If multi-axis articulated arms are ordered from igus, all Bowden cable elements are fitted in advance and the whole system is always delivered ready to connect, i.e. with all the wires and tubes in the desired configuration.

Pneumatic hose (gripper)

Quadruple Bowden cable

Sensor cable - joint 2

4 wires move freely in the tub

Single Bowden cable for rotation

8 wires move freely in the tub

6) What wire distances/forces are necessary in order to move the joints?

The working point of the wires inside the joints is defined by the designated size:
RL-50: Effective diameter 50 mm (rotating and pivoting movement)
RL-90: Effective diameter 90 mm (pivoting movement), or 120 mm (rotating movement)

With wire distance for a RL-50 joint is therefore calculated to be as follows
π x d/4 ≈ 39 mm for an angular movement of 90°
π x d/2 ≈ 79 mm for an angular movement of 180°

The pulling forces of the wires (depending on the torques to be applied) can be up to 600 N.

7) What does the scope of supply of a joint include?

Assembled joint made of plastic (PA 2200), incl. bearing locations (hard-anodised aluminium = Standard)

Dyneema wires

Aluminium rods (Standard = 100 mm included in each case, special lengths upon request)

Angle sensors as option (-WS), 3 m sensor wire, fitted and tested. Wire nipples as connecting material free of charge as agreed on with customer.

8) What does the scope of supply of an articulated arm include?

All joints preassembled in accordance with point 7)

All wires taken through with special Bowden cable segments in accordance with point 5)

Aluminium tubes between the joints, customised according to customer wishes

Mounting plate at the base of the arm

Sensor wires taken through (option -WS), 3 m sensor wire fitted and tested in each case. Wire nipples as connecting material free of charge as agreed on with customer.

9) What does the scope of supply of a "complete system" include?

Articulated arm as described in question 6), but also MIT drive unit consisting of:

igus® stepper motors, number corresponding to the number of axes of the arm

Planetary gearbox for each motor

"Drive wheel" for connection of the wires to the drive

"Tensioning tool" for easy re-tensioning of the drive wheels

Different versions of the housing in which the motors are fitted and on which the arm is mounted are available

with everything completely assembled, pre-tensioned and tested

The following are NOT included:

Gripper (optionally available from igus®, other products also adaptable)

Control components

Motor cables (optionally available from igus®)

10) What angle sensors are used?

In the joints, there are incremental angle sensors (as an option) from Austriamicrosystems (AS5304A). Absolute encoders are technically not possible at the moment. In order to define the zero position, we use a Hall sensor that is located in the middle of the pivoting/rotating range of a joint. This means that each joint must first be "initialised" when the power is switched on. Further information on the wiring of the sensors and the wire assignment in our technical documentation.

The resolution of the encoders is (different in the different joints!):

4,640 signals / 360° in the case of all rotational movements of joint size RL-50
(29 pole pairs x 160 signal / pole pair) ≈ 0.078°

4,960 signals / 360° in the case of all pivoting movements of joint size RL-50
(31 pole pairs x 160 signals / pole pair) ≈ 0.073°

9,920 signals / 360° in the case of all movements of joint size RL-90 ("Base")
(62 pole pairs x 160 signals / pole pair) ≈ 0.036

Sensor unit for 2 DOFs (RL-50-001/002 and 003)

Hall sensor for rotating motion

Encoder for rotating movement

Encoder for pivoting movement

Hall sensor for rotating motion

Standard sensors:
Magnetic incremental angle sensors. The sensors have a resolution of ~0.07° per axis. All sensor units are ready to install for the respective joints Each with 3 m sensor cable (6 leads for each DOF)

11) Can articulated arms also be used in water?

Yes, the components basically consist of plastic (PA2200), anodised aluminium, stainless steel (screws), Dyneema wires (PE), brass wire nipples. Moulded sensors can be ordered (-SE = sealed encoder).

12) What types of drive are possible?

Very different drives can be used to move the wires. Possible are e.g. hand-operated drives ("levers"), pneumatic components (e.g. pneumatic muscles) or electric motors (BLDC motors, DC motors, servo motors, linear motors, stepper motors). igus® can supply stepper motors with planetary gearboxes as a possible drive concept. The following are available:
- NEMA23 stepper motor (stranded-wire or connector version) with 1:16 planetary gearbox
- NEMA17 stepper motor (stranded-wire or connector version) with 1:35 planetary gearbox

Stepper motor

Planetary gearbox

Tensionable drive wheel

13) How are robolink® articulated arms controlled?

igus® does not develop, build or sell control components. The scope of supply of a robolink® system is limited to either the articulated arm or the articulated arm with "drive unit".
Control components have to be provided or acquired by the customers themselves.

There is free control software from igus® for the robolink® articulated arms with our stepper motors (open source). This software has a simple, intuitive user interface for the entry of angle positions and the storage of simple movements. The software is not suitable for interaction with other systems. A contouring control system (or inverse kinematics) is not included. A particular hardware configuration is necessary for the IME program (igus motion editor). This basically consists of NANOTEC® stepper motor control units (SMCI47-S2) and a ATmega Crumb2560 chip. The ATmega chip will be available from igus® in the course of Spring 2014 (currently CHIP45 on the Internet). The following configuration is therefore necessary:

Hardware configuration: NANOTEC SMCI47-S2 stepper motor control unit, Crumb2560 ATmega memory chip, USB module.

14) What must I do in order to be able to use the IME (igus motion editor) open-source software of igus®?

The software can be downloaded free of charge. The software is in the form of a graphic user interface with which simple movements can be programmed and stored. A contouring control system (or inverse kinematics) is not included.

Current documentation for installation of the IME software (German)

15) What materials are used?

Joints: Polyamide PA 2200 components, stainless steel screws, bearing rings made of hard-anodised aluminium, alternatively iglidur® J or stainless steel.

Connecting tubes: Anodised aluminium, alternatively GRP or CRP

Wires:Dyneema wires, wire end nipples made of brass.

16) What grippers can be used?

"All possible" grippers can be combined with our articulated robot arms. Due to the relatively low load bearing capacity of the system, the grippers should be as light as possible. There is a wide range of lightweight pneumatic grippers on the market, e.g. from the companies SCHUNK, FESTO or e.g. FIPA. If the use of pneumatic components is not desirable, as is often the case, electric grippers are necessary. There are some very light electric grippers on the market e.g. from GIMATIC, SCHUNK or SOMMER (which cost considerably more than simple, pneumatic grippers, however). Since 2013, igus® has been supplying simple plastic grippers, whereby the electric motor is located in the robolink® tube. As an option, gripper jaws can also be individually designed here.

Data sheet for electric gripper, 2-jaw gripper (German/English)

Data sheet for electric gripper, 3-jaw gripper (German/English)

17) What do joints or "systems" cost?

All the prices for individual joints and systems can be found in our catalogue. As a rule-of-thumb, a "complete system" with motors, gearboxes, housings, joints and sensors costs a little more than €1,000.- per axis. In other words, approx. €6,000.- for a 6 DOF system. An articulated arm WITHOUT motors (but with sensors), costs around half of this (i.e. approx. €500.- per axis). Example: