Nexus bot assembly manual

NexusBot
Assembly and Control Manual
Taiwan Coding
Education Association
v0.1

Content
1. Servo indexes of NexusBot (page 7)
2. Download MakeCode extension (page 14)
3. Assemble NexusBot (page 24)
4. Calibrate servos (page 65)
5. NexusBot basic control (page 78)
6. Convert into 2WD car (page 85)

Nexus:bit expansion board
This doc does not contain Nexus:bit user manual.
Download user manual http://bit.ly/2JmvvBZ
Power switch
USB charging port

Warning!
• Children need to be assisted /supervised by
adults during whole time.
• Operate the robot/car on flat surface with low
resistance. Be aware of your safety in the
surroundings.
• Charge the battery regularly with micro USB
cable.

Package Contents
• NexusBot robot body parts and wheels
– Body: 2 parts
– Arms and hands: 3 parts x 2
– Legs and feet: 2 parts x 2
– 2WD wheels x 2
• BBC micro:bit x1
• Nexus:bit expansion board and joystick x1
• HC-SR04P ultrasonic module x1
• SG90 mini servo (orange-red-brown cables) x8
• DC motors in SG90 body (red-black cables) x2
• M3 screws x4
• Micro USB cable x1
• Screwdriver x1

SG90 mini servo motor
• Servos are special motors which can rotate to
a specific degree (0~180o) at a time on
command.
• Servos are connected with 3 cables (orange-
red-brown); not the same as DC motors
connected with only 2 cables (red-black).

SG90 mini servo
Orange- - signal
Red - power
Brown - ground
To 0 degreesTo 180 degrees
cone screws
small flat
screws

Servo indexes
• To make sure your robot can be configured
correctly as in our manual, the indexes (order)
of servos should be arranged as next page:

Servo indexes
1. left leg
2. right leg
3. left foot
4. Right foot
5. left arm
6. right arm
7. left hand
8. right hand

Servo pins
S: signal
+: power
-: ground
8 7 6 5 4 3 2 1 servo indexes
1. left leg
2. right leg
3. left foot
4. Right foot
5. left arm
6. right arm
7. left hand
8. right hand

Servo calibration
• There are two steps in servo calibration:
– Hardware calibration
– Software calibration
• Hardware calibration: use code to turn servos to
90 or other degrees, and try to install servos as
straight as possible. (It’s normal that servos may
not be able to line up perfectly.)
• Then we use software calibration to fine tune
servos.
• We will elaborate details in the following section.

Download extension
• Open the MakeCode editor, go to Advance ->
Extension… and enter “nexusbit”, “nexusbot”
or “TCEA” in the search box. Click the
extension to import it.
– MakeCode editor: https://makecode.microbit.org/

Change the language if you
need to

Enter nexusbit and import
It might take a while depending on Internet status.
You can also copy/paste the this link to search:
https://github.com/alankrantas/pxt-Nexusbit

Flash code to micro:bit
• Connect the micro:bit to your computer via
micro USB cable, and it would appear as a USB
device (name MICROBIT). Drag and release
the .hex file you just downloaded into the USB
device.
• Remove USB cable after flashing and make
sure Nexus:bit is powered off as well.
– Or use Web USB for direct download:
https://makecode.microbit.org/device/usb/webusb

• The code we just downloaded would turn all
servos on the robot to the default degrees.
(You’ll have to install micro:bit onto Nexus:bit.)
• We will use this code for hardware calibration
in the next section.

Types of screws
M3 (3mm)
screw
(need at least 2)
Servo
cone
screw
(need 8)
Servo small
flat screw
(need 4)

Install leg servos (cone screws)
forward (the side with semi circles)

If your screwdriver is not magnetize, you can try
this method:

Install arm servos (cone screws)
front

Servo indexes
front
1. left leg
2. right leg
5. left arm
6. right arm

Servo Pins
6 5 2 1 servo indexes
Double check if servo indexes are correctly connect
to pins and properly installed.
S: signal
+: power
-: ground

Connect servos to Nexus:bit
front
1
2
5
6

Calibrate first 4 servos
• Power up your Nexus:bit; micro:bit would turn
these 4 servos to default (90 degrees) and lock
in. Now install arm and leg parts and try to
make them as straight as possible, while
keeping Nexus:bit power on.
– See section 3 if you haven’t flash the calibration code.
– It’s ok if the parts cannot be installed straight or lined up;
You can fix that by software calibration later.

Install leg parts
front
For the legs, the side with bigger openings is facing back.

Install leg parts (small flat
screws)
front

Install arm parts
For the arms, the side with larger holes is facing back.
front

Install arm parts front
It is recommended to keep the front end lower than the back end.

Place feet servos
Thread servo cables through leg parts
front

Place feet servos
Then thread cables into the body
front

Connect feet servos
3 left foot
4 right foot
Turn on Nexus:bit to do hardware calibration.
(Remember to install your micro:bit first!)
front

Servo Pins
4 3 伺服馬達編號
S: signal
+: power
-: ground

Install feet parts
front
For the feet, the side with the hole is facing back.
Install servos as straight as possible with cable underside.

Install feet parts
1. Push foot/servo into leg part and lift up the front end

Install feet parts
2. Push front end forward until it “click” into the leg

Install feet parts
3. Push the back end firmly into the leg
(if the side of servo shift up, use your screwdriver to press it down)

Install hand servos
This might take some efforts to click it into position.
Tip: Tilt the servo slightly when you press it.

Connect hand servos
Likewise, turn on Nexus:bit to do hardware calibration
front
7 left hand
8 right hand

Servo pins
8 7 servo indexes
7. left hand
8. right hand
S: signal
+: power
-: ground

Install hand parts
front
Servo head to the back. Connect servo head first,
then the front end.

Install hand parts
Make the hands’ default position close to body
(but not too tight)
front

Install Nexus:bit
Put Nexus:bit into upper body part
front

Install Nexus:bit (M3 screws)
You can screw all 4 corners or just 2 diagonal corners
front

HC-SR04P ultrasonic module
Vcc (power, 3.3~5V)
Trig (sonar trigger)
Echo (sonar echo)
Gnd (ground)

Install HC-SR04P
Vcc->5V
Trig->P5
Echo->P11
Gnd->G
The 4 slots in the middle

Wrap servo cables
Turn the upper body part several times to wrap cables.
Stuff the cables to the back of robot so they don’t get into the way of micro:bit.

Assembly completed
Combine two body parts and make sure the cables
of hand servos go through body side openings
cable through here

Add anti-slip mats (optional)
You can paste high-resistance materials (like sandpapers)
under feet to improve walking stability.

Use calibration block
Adjust default degrees of each servos
(plus or minus from default position)
Make all servos of robot turn to default
after calibration

The “preset stance”
• When you use the block without any
adjustment (all parameter to 0), the robot
should stand roughly straight with its hands
close to the body:

The “preset stance”
It is ok if legs and feet are not completely straight

Default degrees of arms and
hands
• Servos can only turn 180 degrees. In order to
maximize arm/hand movements, arm/hand
servos are set close to their min or max
positions.
– The calibration block would automatically add or
subtract 90 degrees for arm/hand servos.

Calibration direction
Left leg: outward-, inward+
Right leg: outward+, inward-
Left foot: down+, up-
Right foot: down-, up+
Left arm: high-, low+
Right arm: high+, low-
Left hand: high+, low-
Right hand: high-, low+
Example:
Left leg -10
(Default position 90 – 10 = 80
degrees; turn outward 10 degrees)
Left leg default: 90
Right leg default: 90
Left foot default: 90
Right foot default: 90
Left arm default: 180
Right arm default: 0
Left hand default: 0
Right hand default: 180

Feet movement
Right foot up Left foot down

Legs movement
Left leg outward
Right leg inward

Arms movement
Arm low Arm level Arm high
Actual movable degrees may be different depending on
servo models/specs

Hand movement
Hand low Hand out Hand high
Actual movable degrees may be different depending on
servo models/specs

Calibration tips
• It’s better if you can keep adjustments within
15 degrees. The extension would stop servos
turning to where it can’t, but if they are not
installed straight enough in the first place,
movable degrees would be limited (for
example, the hands cannot lift high enough).
– To reduce adjustment degrees, adjust servos’
installation positions.
• Each robot has different adjustment
parameters. Save the code for your future use.

Calibration example
Be noted that these parameters
probably would not work for
Your robot.

Basic movements
• The extension has implemented 8 walking movements, which
utilize “servo graduate turning” to smooth the performance.
These movements only use the 4 legs/feet servos, so they are
applicable on robots without hands.
• The block would only do 1 cycle (for example, move each foot
once when walking forward), so you have to use loops to
create continuous movements.

Basic actions
The extension implemented 40 actions, which allow users to control various joints
of the robot. They would simply turn to position (no graduate turning), all positions
are pre-defined. However these are enough to be combined into gestures or dance
moves.

Action combination example
This is a 3-part action sequence

Tips on combining actions
• Servos would turn as soon as it receive signals;
however they would need a short time to
finish the turn. If you switch to next action too
quickly, servos may not be able to complete
the move.
• It is recommended to set delay between 100-
1000 ms between actions, so that actions can
be performed properly.

Other blocks
Robot stands still
(all servos to default position, adjusted or not)
If sound level is loud enough to trigger the onboard mic
(the mic block would stop detecting while you are using
movement or action blocks)
If the ultrasonic module detects objects in front of the
Robot (10 cm away)
Speed of servo graduate turning
(1-10, only effect walking movements)

Advanced servo control
• You can use blocks in the Nexus:bit toolbox for
more precise servo-degree controls with more
variety. See TCEA’s Nexus:bit manual for
details.

• The body of NexusBot can be converted into a
2WD car by installing 2 DC motors and wheels.
• You’ll need DC motors in SG90 body (included
in the package) or continuous rotation servos.
In this manual we use the DC motor version.

DC motors in SG90 body
It looks exactly the same as SG90 servos, but with
only 2 cables and would run whenever you connect it to DC power

Dismantle robot
• You’ll need to dismantle arm/hand and
leg/foot parts of the robot and remove all
servos.
• It is recommended to pry hand/foot servos
out with a flathead screwdriver.
• Put away screws properly in a box – don’t lose
them.

Install DC motors
Install them at arm joints with cone screws

DC motor pins
A1/A2 = right motor; A1 to red wire，A2 to black wire
B1/B2 = left motor; B2 to black wire，B1 to red wire

Connect DC motors
front
front
Be noted of the reversed left and right direction on Nexus:bit

Install wheels (small flat screws)
The same ones you used to install arm/leg parts

Car control
• Direction: forward, backward, left, right, stop
• Speed: 0-100 (100 = full speed)

Car calibration
• Due to minor speed difference of each DC
motors, your car may not be able to run
completely straight forward.
• You can use Nexus:bit blocks to fine tune the
motor speeds. Check out TCEA’s Nexus:bit
user manual.
http://bit.ly/2JmvvBZ

About us
Taiwan Coding Education Association
• Headquarter
– Address: 4F., No. 143, Sec. 1, Chongqing S. Rd.,
Zhongzheng Dist., Taipei City 100, Taiwan (R.O.C.)
– Tel: 00-886-2-2316-7734
– Email: service@beyond-coding.org.tw
– Official website: http://www.beyond-coding.org.tw
– Facebook: Taiwan Coding Education Association

THE END
Thank you so much for purchasing and using our product!

Nexus bot assembly manual

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