StenSat Robotic Arm

2

Legal Stuff

● Stensat Group LLC assumes no responsibility and/or liability for the use of the kit and documentation.

● There is a 90 day warranty for the Sten-Bot kit against component defects. Damage caused by the user or owner is not covered.

– Warranty does not cover such things as over tightening nuts on standoffs to the point of breaking off the standoff threads, breaking wires off the motors, causing shorts to damage components, powering the motor driver backwards, plugging the power input into an AC outlet, applying more than 12 volts to the power input, dropping the kit, kicking the kit, throwing the kit in fits of rage, unforseen damage caused by the user/owner or any other method of destruction.

● If you do cause damage, we can sell you replacement parts or you can get most replacement parts from online hardware distributors.

● If you need to contact us, go to www.stensat.org and click on contact us.

3

Tools Needed

● Type of battery to use

– 9V alkaline battery, Duracell or Energizer. Other brands may not put out enough current. Ni-MH or Lithium 9V batteries will also work and can be recharged.

● Tools needed

– Small phillips screw driver, #1 size

– Phillips jeweler or precision screw driver for the really smalls screws

– ¼ inch nut driver or small pliers

4

Introduction

● This robotic arm kit is a complete kit with controls, a computer and actuators which are the servo motors that make the robotic arm move.

● The picture to the right shows the controls, the processor and the actuators.

Servo

Servo

ServoControls

Computer

5

Operating Block Diagram

● This is a diagram that shows are everything interacts.

● The potentiometers send a voltage based on the control knob position to the computer.

● The computer translates the voltage from the potentiometers to a signal that the servos use to move to a desired position.

ComputerComputer

Servos

Potentiometers

6

How a Potentiometer Works

● The potentiometer is a resistor device with a wiper that can contact any part of the resistor. The wiper will have a different resistance based on where it is making contact.

● Contact X is connected to the negative side of a power source which is zero volts. Contact Z is connected to the positive side of a power source.

● Contact Y, which connects to the wiper, will have a voltage in between the negative and positive side of the power source.

● The closer the wiper is to X, the closer to zero volts. The closer the wiper is to Y the more positive the voltage.

ResistiveStrip

Wiper

X Y Z

7

What is a Servo

● A servo is a geared motor with feedback used to control the position of the shaft of the motor.

● The servo consists of a motor that drives a bunch of gears to reduce the speed of the output spline or shaft. A potentiometer or variable resistor is connected to the output shaft and turns with the shaft. As it turns clockwise or counter clockwise, the resistance of the potentiometer changes. The resistance value indicates the angle of the shaft.

8

What is a Servo

● The potentiometer feeds a voltage signal based on the position of the shaft. A reference signal feeds a voltage signal for the desired position.

● The error detection circuit compares the two voltages and generates a voltage to power the DC motor in the desired direction until the position signal equals the reference signal.

● When the position signals equals the reference signal, the DC motor stops turning and the shaft is at the right angle.

DCMotor

MotorDrive

Power

Reference Signal

Position Signal

Error Detection CircuitMotor Driver Circuit

Output ShaftGears to reduceshaft speed

Potentiometer

9

What is a Servo

● The processor board uses pulses to control the position of the servo. The servo has an electronic circuit convert the pulse width to a position voltage.

● The processor board sends a pulse 50 to 60 times a second. The width of the pulse determines the position of the shaft which can range from 0 to 180 degrees.

● Neutral position is 90 degrees. The pulse width is 1.5 milliseconds (ms).

● 0 degree position is specified with a pulse width of 1 ms.

● 180 degree position is specified with a pulse width of 2 ms.

● The wave form below show what the signal looks like.

00

900

1800

1ms 1.5ms 2ms

10

Parts List

● Bag A

– 4 - 1.5 inch standoffs

– 4 - Nuts, 4-40 size

– 4 - ¼ inch 4-40 screws

● Bag B

– 4 – ½ inch 4-40 screws

– 8 – 4-40 Kep Nuts

11

Parts List

● Bag C

– 4 - ¼ inch 4-40 screws

– 2 – 4-40 nuts

– 2 - right angle brackets

12

Parts List

● Bag D

– 6 1/4 inch 4-40 screws

● Bag E

– 3 3/8 inch 4-40 screws

– 3 Lock nuts

● Bag F

– 4 ½ inch 6-32 screws

– 4 rubber boots

13

Parts List

Base

AzimuthPlate

ElevationBracket

ArmSegmentHook

Linkage

Second Segment

Servo Plate

14

Parts List

Processor Board

3 Servos3 Potentiometers 3 Knobs

15

Servo Parts

● A servo is a geared motor that is used to rotate to specific angles. It is used in model airplanes to control the rudder, flaps and aeriolons.

● The servos come with parts. Most will be used.

Pointy wood screws

Different Servo Horns

Screw toSecure Horn to Servo Shaft

Servo

ServoShaft

16

Definition of Components

● Screw – A cylindrical device with a raised helical thread running around it used to join things together.

– Sizes

● 4-40 means it is a #4 size screw with threads that wrap around 40 times per inch length.

● #4 size is .112 inches diameter● #6 is .138 inches diameter● #8 is .164 inches diameter

– Length is how long the threaded part of screw is.

– The screw pictured at the right is a machine screw.

– Screws with a pointy end are wood screws

or sheet metal screws.Threaded part

Head

17

Definition of Components

● Nut – A device that mates to a screw to secure things together. The sizing is specified the same way, ie 4-40 or 6-32.

● Kep nut is a nut with an integrated lock washer.

● A nylon lock nut is a nut with a piece of nylon material inserted to keep the nut from spinning freely. It is used to join things together but let them move against each other.

Nylon Lock Nut

Kep Nut

18

Definition of Components

● Right angle bracket – A device that allows two things to be attached at right angles to each other.

● Standoff – A device that allows things to be attached to each other at a distance. Allows stacking. One end can be threaded like a screw and the other hollowed and threaded to be like a nut. They are made in different lengths.

Standoff Right Angle Bracket

19

Prepare the Parts

● All of the plastic parts have a sheet of paper sticking to both sides.

● Peel off the paper from both sides of all the parts shown below. The paper protects the plastic from being scratched.

20

Base Assembly

● Locate the base. It is the large rectangular plate.

● There are many holes and slots in the plate.

● The holes in the four corners are for screws to be used as stands.

● The three holes along the bottom are for the control knobs.

● Other holes are for mounting the processor and the robotic arm.

● Slots are used for routing wires.

Stand Stand

Stand StandPotentimeters

RoboticArm Mount

ProcessorMount

RouteWiresThroughHere

21

Base Assembly

● Locate the ¼ inch screws, nuts and standoffs as shown in the picture from bag A.

● These parts will be used to hold up the base of the robot arm and allow the arm to turn from side to side.

22

Base Assembly

● Insert the four ¼ inch screws from the back side through the holes as shown.

● Screw in the four standoffs and finger tighten.

¼ InchScrews

Standoffs

23

Base Assembly

● Locate the ½ inch 6-32 screws from bag F.

● Install the screws from the top side in the four corners and the slide the rubber boots over the screws from the bottom.

½ inchScrew

½ inchScrew

½ inchScrew

½ inchScrew

24

Base Assembly

● Use the screws and nuts from bag B.

● In the middle of the base, insert four of the screws from the bottom side and secure with nuts.

Insert ScrewsFrom Behind

Insert ScrewsFrom Behind

25

Base Assembly

● Place the processor board onto the four screws as shown.

● Make sure the power switch is on the left.

● Secure the processor board with four kep nuts.

Secure with Kep Nuts.

26

The Controls

● The picture below shows which potentiometer controls what part of the robotic arm.

Elbow Arm Base

27

The Controls

● The robotic arm is controlled by three potentiometers. The potentiometers are used as a variable voltage divider.

● The potentiometer has an alignment pin. This forces the potentiometer to be oriented in a specific position on the base. The base has an alignment pin notch where the potentiometer is to be installed.

AlignmentPin

Nut

Washer

WiperConnection

EndConnection

EndConnection

28

The Controls

● Install the three potentiometers as shown. Each one has an alignment pin to the right. Make sure it is inserted in the square hole next to the round hole where the potentiometers are inserted.

● The potentiometers are inserted from below.

AlignmentPin

29

The Controls

● Secure them with the included washer and nut. Hand tighten.

Washer isInstalled FirstThen the Nut

30

Controls

● Locate the three knobs.

● Turn each potentiometer clockwise all the way.

● Install the knobs by pressing them onto the potentiometer shafts with the orientation as shown.

31

The Controlers

● The picture is of the processor board.

● The left highlighted side has six three-pin connectors. These are for connecting the servo motors.

● The right highlighted side has six connections. These are for connecting the potentiometers to control the servos.

ServoConnections

PotentiometerConnections

32

Controls

● On the end of the wires are connectors that get inserted into the pins.

● Take the center wire and connect it to the pin marked 0.

● Take one of the side pins and connect it to the pin marked GND.

● Take the last pin and connect it to the pin marked 5V.

33

Controls

● Route the wires of the center potentiometer through the slot on the right.

● Take the center wire and connect it to the pin marked 1.

● Take one of the side pins and connect it to the pin marked GND. Notice the different location.

● Take the last pin and connect it to the pin marked 5V.

34

Controls

● Route the wires of the left potentiometer through the slot on the right.

● Take the center wire and connect it to the pin marked 2.

● Take one of the side pins and connect it to the pin marked GND. Notice the different location.

● Take the last pin and connect it to the pin marked 5V. Notice the different location.

35

Azimuth Assembly

● Locate a servo like the one shown to the right.

● Locate the servo plate like the one shown.

● Place the plate on top of the servo as shown.

Put on Topof Servo

ServoUnderneath

Plate

36

Azimuth Assembly

● Use two of the small screws from bag D and insert them as shown from the top into the servo.

● You need to push and turn the screw clockwise to secure the servo.

Secure with screws

Bottom View

37

Azimuth Assembly

● Place the servo and plate on top of the standoffs on the base.

● Secure with the four nuts that were shown in the Base assembly.

InsertNuts

InsertNuts

Processor board and potentiometers not shownfor clarity.

38

The Controls

● Connect the base servo to the processor board.

● First, connect the base servo to the column of pins marked D3.

● Make sure the brown wire is against the edge of the circuit board. Connecting in reverse will damage the servo.

OrangeRed

Brown

39

The Controls

● Connect the battery to the processor board and turn it on. You will most likely hear the servo move.

● Turn the base control knob to the far left. The servo shaft should rotate counter clockwise. If not, swap the wires for 5V and GND shown in page 32.

● The idea is to position the servo horn so when the rest of the arm is assembled, the arm will be in the proper orientation.

● Turn off the processor board and continue assembly.

OrangeRed

Brown

40

Azimuth Assembly

● Locate the azimuth plate like the one shown and the parts from bag C.

● Install the right angle brackets on to the azimuth plate and secure with the supplied screws and nuts.

● Use the larger hole on the right angle bracket to secure to the azimuth plate. It's the holes in the bracket that the screws can freely enter.

ThreadedHole

LargerHole

4-40 Nuts

4-40 ¼ inchScrews

ThreadedHole

41

Azimuth Assembly

● Use the servo horn from the servo package like the one below.

● Place it on the opposite side of the plate as the right angle connectors. Make sure the larger cylinder on the horn is facing away from the plate.

Servo HornTop Side

Servo HornBottom Side

Bottom sideof ServoHorn

Servo HornOppositeSide of Brackets

42

Azimuth Assembly

● Secure with the two small pointy screws from the servo.

● The holes on the servo horn will not line up quite right.

Insert pointyscrews fromtop side intoservo horn.

Servo horn holeswill not be centered.

43

Azimuth Assembly

● Mount the azimuth plate with the servo horn onto the servo. as shown.

● Secure the horn with the screw that came in the servo package. (not the pointy one)

Use Servo Horn Screw

44

Arm Assembly

● Take another servo and the bracket as shown.

● Mount the bracket on top of the servo as shown.

● Use two screws from bag D and insert from the top and screw into the servo.

● Do not overtighten as the bracket may crack.

Insert Screws

45

Arm Assembly

● Attach the servo and bracket assembly to the base mount.

● Secure the

● Use two short #4 screws and screw in from behind the bracket into the metal right angle bracket on the base.

Insert short screws from

the back side

ShortScrews

46

The Controls

● Connect the second servo that raises the arm segment to the pins marked D5.

● Again, make sure the colors of the wire in the correct order.

● The order is shown below.

OrangeRed

Brown

47

The Controls

● Turn the processor board on and turn the center knob to the right all the way. The second servo will raise and lower the arm. The shaft should rotate clockwise.

● The servo is being positioned so when the arm is installed, it will be installed pointing upward.

● Turn off the processor board and continue assembly.

OrangeRed

Brown

48

Arm Assembly

● Locate the second servo and get the servo horn that is shown.

● Locate the arm segment as shown.

● Position the servo horn under the arm segment as shown in the upper right.

Align servo horn holes to holes in arm.They will not be exactly centered.

Servo Horn

Spline Hole to Mounton Servo

Note Orientation ofServo Horn

Back Side

49

Arm Assembly

● From the top side, use the two pointy screws and screw from the arm segment into the servo horn. Use the holes that line up with the arm holes.

Insert pointy screwsfrom this side into

servo horn

50

Arm Assembly

● Install the third servo onto the arm segment as shown. Pay attention to the orientation.

● Secure the servo with two screws from bag D. Do not overtighten.

Insert Screws

Pay attention to orientationof the Servo. The shaft is toward the edge.

51

Arm Assembly

● Locate the second segment with the three holes. Locate bag E.

● Attach it to the arm segment using a 4-40 3/8 inch screw and a lock nut as shown. Pay attention to which side the second segment is relative to the arm segment.

● Tighten the screw and nut using a screw driver and nut driver. Keep screwing until it gets a little tight then unscrew by a ¼ turn to loosen it so the second segment moves freely.

● Do not over tighten as you can break the plastic material.

Second Segment placedon this side Use Nylon Lock Nut

52

Arm Assembly

● Attach the hook to the end of the segment as shown.

● Secure with a 3/8 inch 4-40 screw and lock nut.

● Keep the screw and nut loose like the previous step so the hook can freely move.

Nylon Lock Nut

4-40 3/8 Inch Screw

SecondSegmenton LeftSide ofArmSegment

53

Arm Assembly

● Locate the horn shown to the right from one of the servo packages.

● Install the horn onto the servo.

● It will be adjusted later.Servo Horn

54

Arm Assembly

● Connect the linkage to the second segment with a 3/8 inch 4-40 screw and lock nut. Do not tighten the lock nut. Let the linkage move freely.

● Using the last pointy screw, insert the screw through the linkage into the second to last hole on the servo horn.

● Screw the pointy screw into the servo horn just enough so it just starts coming out of the other side. Do not tighten the screw. It needs to be very loose.

Servo horn3/8 inch 4-40 Screw

and Lock Nut

Insert PointyScrew Here

55

Arm Assembly

● Insert the arm assembly onto the arm servo as shown.

ServoScrew

56

Arm Assembly

● Secure the arm on the servo with the screw that came in the servo package. (not the pointy one)

InsertServoScrewHere

57

The Controls

● Connect the third servo that controls the linkage position to the pins marked D6. The servo is highlighted in the picture to the right.

Elbow Servo

OrangeRed

Brown

58

Making Adjustments

● Turn on the processor board and turn the left knob all the way to the left. The elbow servo shaft should rotate counter clockwise.

● Pull the servo horn off and twist it so the arm is extended as much as possible.

● Insert the horn back onto the shaft and secure it with the servo screw.

Elbow segmentmoves up

Take horn offand rotate

59

Operating the Arm

● Plug in a 9 volt battery.

● Turn the power switch on the left to the ON position.

● The servos briefly twitch and then move into position based on the potentiometer positions.

● The left knob controls the elbow segment position.

● The center knob control the arm position.

● The right knob turns the arm left and right.

Left Knob

CenterKnob

Right Knob

ElbowSegment

ArmSegment

60

Operating the Arm

● Turn the right knob and observe the robotic arm turn. If the robot arm turns the opposite of what is expected, then swap the 5V and GND wires.

● Do the same for the other servos. Refer to pages 33 and 34 for the wiring diagram.

Swap thetwo Wires