2019NexusBot Assembly Manual http://bit.ly/2KZ4025 Taiwan Coding Education Association http://www.beyond-coding.org.tw/ NexusBot https://www.beyond-coding.org.tw/component/sppagebuilder/?view=page&id=91

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

2. Taiwan Coding Education
Association
• Taipei headquarter
– Business hours:
• Mon/Tue/Thu/Fri 9:00-21:00
• Wed/Sat/Sun 9:00-18:00
– 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

3. Content
1. Servo indexes of NexusBot (page 8)
2. Download MakeCode extension (page 15)
3. Assemble NexusBot (page 25)
4. Calibrate servos (page 66)
5. NexusBot basic control (page 79)
6. Convert into 2WD car (page 86)

4. NexusBot

5. Nexus:bit expansion board
This doc does not contain Nexus:bit user manual.
See TCEA’s Nexus:bit user manual for details.
Power switch
USB charging port

6. Materials
• NexusBot robot body parts and wheels
• BBC micro:bit/micro USB cable x1
• Nexus:bit expansion board x1
• 18650 rechargeable lithium battery(2600 mAh) x1
• HC-SR04P ultrasonic module x1
• SG90 mini servo (orange-red-brown cables) x8
• DC motors in SG90 body (red-black cables) x2
• SG90 cone screws x4, small flat screws x2
• M3 screws x4
• Screwdriver x1

7. Caution!
• Younger children or children with no robot-
assembling experiences should be assisted
/supervised by parents.
• Operate the completed robot/car on flat
surface with low resistance. Be aware of your
safety in the surroundings.
• Recharge the robot/car after usage for some
time.

8. SERVO INDEXES OF NEXUSBOT
1

9. SG90 mini servo
• Servos are special motors which can be turned
to a specific degree (0~180) at a time on
command.
• They have 3 cables; not the same as DC
motors with only 2 cables which would run as
soon as you connect it to power.

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

11. 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:

12. 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

13. 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

14. 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.

15. DOWNLOAD MAKECODE
EXTENSION
2

16. 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/

17. Open new project in MakeCode

18. Change the language if you
need to

19. Select Advanced -> Extension

20. 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

21. Drag the calibration block

22. Download code

23. 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

24. • 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.

25. ASSEMBLE NEXUSBOT
3

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

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

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

29. Install leg servos
front

30. Install arm servos
front

31. Install arm servos (cone screws)
front

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

33. 對應伺服馬達腳位
6 5 2 1 servo indexes
Double check if servo indexes are correctly connect
to pins and properly installed.
S: signal
+: power
-: ground

34. Connect servos to Nexus:bit
front
1
2
5
6

35. 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;
we can fix that by software calibration later.

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

37. Install leg parts (small flat
screws)
front

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

39. Install arm parts front
However it is recommended to keep the front end
lower than the back end.

40. Install arm parts
front

41. Place feet servos
Thread servo cables through leg parts
front

42. Place feet servos
Then thread cables into the body
front

43. 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

44. 對應伺服馬達腳位
4 3 伺服馬達編號
S: signal
+: power
-: ground
Double check if servo indexes are correctly connect
to pins and properly installed.

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

46. Install feet parts
front

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

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

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

50. Feet installation complete!

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

52. Install hand servos

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

54. Servo pins
S 橘線
+ 紅線
- 褐線
8 7 servo indexes
插上馬達線時請留意是否接對腳位、編號是否正確
7. left hand
8. right hand

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

56. Install hand parts

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

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

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

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

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

62. Install HC-SR04P

63. 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.

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

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

66. CALIBRATE SERVOS
4

67. Connect micro:bit to computer

68. 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

69. 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:

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

71. 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.

72. 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

73. Feet movement
Right foot up Left foot down

74. Legs movement
Left leg outward
Right leg inward

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

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

77. 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.

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

79. NEXUSBOT BASIC CONTROL
5

80. 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.

81. 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.

82. Action combination example
This is a 3-part action sequence

83. Tips on combining actions
• Servos would turn as soon as it receive singals;
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.

84. 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)

85. 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.

86. CONVERT INTO 2WD CAR
6

87. • 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 or
continuous rotation servos. In the manual we
use the DC motor version.

88. 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

89. 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.

90. Install DC motors
Install them at arm joints with cone screws

91. 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

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

93. Connect DC motors
B2 A1
B1 A2

94. Assemble body

95. Install wheels

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

97. Assembly completed

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

99. 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.

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