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CNC router 'OTOCOUP'
- Cabling and wiring -

Installation diagram

Steppers and auxiliairies connection

Connection to command box

Steppers wiring

Limit switches wiring

Connection to electrical box

Connectors on steppers


General note : What is recommended here is slightly different from what i've installed on my machine, which is in the process to be modified. That will allow to benefit from my experience.

Installation diagram

Even if router spinning is commanded from computer, it is required, for safety reasons, to validate their energising by a manual command. That will also allow a restart after power shortage.

Cabling / wiring drawings are HERE (size 0.9 Mo).

Connexion of steppers and auxiliaries

Connectors Sub-D 9 pins have been chosen, either for command and for power, because they are easy to find and of low cost.
Also, the maximum current is relatively high for small connectors.
Depending it's quality, each pin (male or female) of a Sub-D connector can drive from 1A to 7.5A, so choose carefully your connectors.

Male pins side
Weld side

With the pinout chosen for the bipolar boards, there are two pins per wire.

With the pinout chosen for unipolar boards, there is only one pin per wire, so the current is more limited.

Connection on command box

Connectors are viewed as looking to the connector panel. If you look plugs on cable side, think to cable in 'mirror'.
It doesn't have any importance for steppers because it only changes the rotation direction, but you can have big problems for auxiliaries connectors.

It exist two incompatibles kinds of command box :
 . Boxes with bipolar boards (4 wires/stepper)
 . Boxes with unipolar boards (6 wires/stepper)

It is not possible to plug a bipolar stepper (4 wires)on a unipolar box.
But it is possible to plug unipolar steppers 6 wires on both kind of boxes, but the wirings are not compatible.
8 wires steppers are compatible with all boxes.
So, in order to avoid wrong connections, connectors on both boxes are differents :
 . Female for bipolar boxes
 . Male for unipolar boxes

Connectors for limit switches and external command are always male.

Buttons 'Temperature +' et 'Temperature -', and also plugs needed for a hot wire cutting machine have beeen set in order to have a unique standard for most CNC applications.

Z selection switch (optional) is used to command a rotating divider instead of Z linear axis, without having to replug the divider stepper on Z plug. It's only action is to swap board output to one connector or to the other. (with a quadripolar switch on a 4 wires output).

Z selection switch :
Outputs are here cabled on female 2mm plugs, but principles remains identical for DB-9 plug

Steppers wiring

It exists two manners to wire unipolar steppers (6 wires) to bipolar boards (4 wires).
The mode called 'Half-winding' have been chosen because, even if it does have slightly lower torque, it's behaviour at speed is much better.
You can, at your will, use the other mode, but if it is for an 'Otocoup' machine, i don't recommand it, because that machine needs fast turning steppers.

See also recommendations from a manufacturer (NANOTEC).

Limit switches wiring

It exists two wiring methods for limit switches, which depends from the software you are using or their parameters. We consider that limit switches are closed when we are on the limit, and that they ground signal line.

Option A/ both switches of each axis (X, Y or Z) ar parallelled and the common line is grouded whatever end we are. There are six limit switches.

Option B/ All switches installed on maximum displacement are paralleled, and so is done for minimum displacement switches.
On each axis exists another switch, used to defined a starting position. There are 9 limit switches.

Connector wiring:

In addition to the three input for limit switches, a fourth signal line was added to detect tool depth.
You position the tool over the contact, and slowly go down till contact action. It does allow automatic depth adjustment when changing one tool. (software do that automatically)
Limit switches on the axis are not absolutely required, but a 'tool switch' is highly recommended.

5V voltage present on limit switch connector will be used for laser power supply.
These lasers are useful to define the origin, on the side of a board for example.
Their cost is very low (i've paid mine 4 Euros each)

Electrical box connection

Output of equipment command (router head or cooling fluid pump), can be with a voltage of 5V or 12V. 12V is recommended, which allow, depending the board output power, to command a mechanical relay. Though, i recommend the use of a static relay (thyristors), but care must be taken of their proper cooling.

Some boards do have relays directly installed on it. Generally, these relays are not adapted to switch high power reactive load, as our router motors, because they create high voltage peak when shut down.
So you will polarised these relays in 12V, and will cable them to the DB-9 connector. Also, that will avoid having domestic voltage (110-230V) in the command box.

It is reminded that domestic voltage can KILL, so it is important that you well understand what you are doing when connecting command box to electrical box.
Electrical box will be energised before any connection to the command box. A careful check with a controller that in all service conditions (emergency shutdown on/off, head motor on/off), domestic voltage NEVER appear on the linking connector.
Earthing of both boxes will be checked.
Connector plugging will only be done after these checking.

Note : AU = ESD (Emergency ShutDown)
Electrical box relay do have a dry contact (normally open or normally closed, at your choice) to stop the machine in case of operation of emergency shutdown button. It is very important that this shutdown stop the steps, but left the steppers current supplied, if not the carriage will fall down under it's own weight.
A lot of control boards cut the current when asking the stop. That function must not be used but you must have a mean to stop the step flow. If the board don't have this possibility, one solution is to cut computer power supply.
This is possible by wiring the relay serially with the computer startup button.
Though, on recent computers (les than 6 years), startup button is not an on/off switch but a pushbutton. That can be modified by changing the computer motherboard settings, and by replacing the pushbutton by an on/off button.

It is also possible to cut 110-230V computer supply, but cables must be perfectly isolated from others cables in very low voltage (5 - 12V), and must NOT go through Sub-D 9 connector.

A signal line sending the information of emergency shutdown to the computer have been set. The computer will then stop the cutting after a shutdown. That may allow to not lost a part, but with no guaranty at all, because decceleration of the heavy carriage of Otocoup machine risk to drive to step losses. On smaller machine, that can be OK.

Plug on stepper

Plug will be isolated with thermoretractable sleeve

Set sleeve before welding
Retract with hot air gun
Retract a larger sleeeve over the ensemble
Stepper plug
After plugging


Currents being relatively low (< 5A), small cables with high current density can be used.
We can use, or even exceed 10A/mm2. Heating, on small cables, will be very low and line resistance, while not negligible, will have marginal effect on performances, especially if your board control current.

For bipolar motors 2 x 2A, which are those used on my machine, i recommend the use of cables 4 x 0.22 mm2, shielded. Shielding is required when using chopper boards (based upon PWM). While cables are very long on Otocoup machine (6 m for the longest), these cables are largely sufficient. Before using these cables, i have used successfully flat cable with a lower sectional area. Though, i've abandoned them because of lack of shielding.
You will not forgot to wire the shield on the ground of DB-9 plug, and on the panel to earth the ground (wire the panel, and remove varnish under DB-9 connector fixation nuts, to have good electrical contact - check with controller -)

For external command signals and limit switches, you can use smaller cables than for steppers, but shielded cables are recommended due to the length of the cables. Section area of 0.12 mm2 by wire is sufficient.

Fixation of 4 mm diameter cables on main beam with aluminium bridge
Cable 4 x 0.22 mm2, shielded, supple, diameter 4 mm