Robot Arm Team:

Objective: Design and prototype one (or possibly two) robot arm(s) that can accomplish the game's tasks. Choose the best one in terms of functionality, efficiency, etc.
Deliverable(s): A prototype robot arm(s) that can hook up to motors/servos to test its functionality
Deadline: Friday, 9/14

Team Members:
Head: Farita Tasnim
Brandon King
Jinny van Doorn

Tasks Accomplished
Goals for Next Meeting
Friday, 9/7
  • became cognizant of specific measurements of parts to pick up (habitation module, T-structure, solar panel, balls, bottles)
  • brainstormed robot arm ideas
  • keep brainstorming the arm(s)
  • look at available materials in kit of parts
  • choose at least one, max three plausible plans
  • work out the specifics and the details of the plans (engineering drawings, possibly CAD?)
  • begin prototyping (if time permits!)
Saturday, 9/8
  • confirmed strategy for robot arm (designed to be on top of the robot; has 3 parts and 3 joints; has one claw [made of plexiglass], and two arm segments [one made of PVC pipe and one made of two wood pieces] ... more details to come
  • built the base of the robot arm (with lazy susan, motor, and model first arm segment)
  • tested the weight capacity of the motor with a comparable weight to prototype/real arm (the small motor works!)
  • see below for extra calculation
  • continue prototyping arm
  • test weight for both motors
  • possibly see dual servo action can support wrist-like movement of claw
Tuesday, 9/11
  • backtracked a little bit and had to (for the fourth time?) detach the robot arm from the base
  • conceded to the inherent learning process embedded in the engineering process
  • in place of the lazy susan, we are using a geared motor for BOTH joints in the arm in order to gain mechanical advantage and be more precise (thank you mentor Mr. King for help on that!)
  • began working on the geared motor for the first arm segment
  • established plan and prototype dimensions for claw and second segment, as well
  • finish the first arm segment
  • continue working on the second arm segment and the claw
  • test and work out issues
Wednesday, 9/12
  • finished first arm segment (18")! (geared the motor, and in fact, had to add an extra free spinning pinion to tighten the belt)
  • made 2 claw prototypes with cardboard
  • brainstormed more ideas for the claw
  • lock a nut in place for the first arm segment
  • work on the second arm segment and its motor placement
  • continue work on claw
Thursday, 9/13
  • added velcro for super increased friction for the first arm segment's attachment to the rack of the belt and pulley system on the motor
  • made basic measurements for the second arm segment (16") and its attachment to the first arm segment
  • new assignment: we need to make a rack and pinion from the available metal pieces given for the belt and pulley system for motor on the second arm segment
  • continued prototyping for claw ideas
  • CAD the rack/pinion system needed
  • send to the CNC machine to get the rack and pinion made
  • cut the PVC for the second arm to the correct length
  • consider lighter alternatives for the second arm segment
  • if no lighter alternatives come to mind, use the PVC (cut to the correct length and attach to the end of the first arm segment)
  • if the rack and pinion have been made, motorize the second arm segment, and, if not, wait until Sunday for that.
  • build claw prototypes with wood/lexan/other material
Friday, 9/14
  • mounted second arm segment onto the first arm segment
  • continued work on the claw
  • CAD rack/pinion needs to be done!
  • motorize second arm segment
  • continue working on the claw
Tuesday, 9/18
  • secured the second arm segment onto the first arm segment in a more secure manner that also has less friction!
  • continued claw prototyping
  • made significant progress on CADing the rack/pinion system for motorizing the second arm segment!
  • developed great strategy for arm-servo action
  • Finish CAD model and send over to CNC to cut aluminum piece into rack/pinion
  • attach claw to second arm segment! and motorize
Wednesday, 9/19
  • discovered a strategy for implementing a claw with a wrist that has 4 degrees of freedom! The whole arm will have 6 degrees of freedom, and the whole robot will have 7! Cool!
  • made a cardboard model of part of the claw system
  • continued working on the claw prototype
  • still waiting on belt-pulley system model to be CAD'd and CNC'd
  • finish making cardboard prototype,
  • test the prototype
  • build the prototype out of wood!
  • continue work on claw
  • finish CAD/CNC for rack and pinion for belt-pulley system
  • motorize second arm segment!
Thursday, 9/20
  • strategized optimal mechanical placement and workings of claw system
  • did some motor torque, force, and radius calculations (need to document these for engineering notebook)
  • continued working on claw prototype
  • attach group of 3 servos to hinge
  • motorize (servo-ize?) the hinge claw with the brake cable
  • document design calculations!
  • document engineering designs
Friday, 9/21
  • finished claw prototype for now (needs some changes)
  • practiced some game action with the half working version of the robot arm (discovered shortfallings and potential problems)
  • fix issues with claw prototype (align group or three servos along same axis as fourth servos to reduce tension on fourth servo)
  • gear up the motor for the second arm segment
  • perhaps, start programming automated motions for the robot to go through to complete tasks and score points
Saturday, 9/22
  • fixed issues with claw prototype
  • made motor mounts
  • geared up the motor for the second arm segment
  • saw some claw action (issue with motor on elbow joint: friction tape is not strong and dissolves to goo) with program
  • made lots of progress!
  • remake the gears for the elbow joint with rubber tread and regulation wood
  • test the arm again
  • think about chassis placement more deeply and start building chassis, hopefully
Tuesday, 9/25
  • remade gear system with rubber
  • tested new gear system: it works great, but would be EVEN stronger if the wood for the small gear was thicker (see right)
  • cut out some circles for the sprocket and pole team: need to attach rubber to them
  • replace the small gear of the gear system with a thicker, but same radius, piece of wood. this will help it to grab on easier to the other gear piece
  • test this again-it should work better
  • attach rubber to the wheels for the sprocket ipt
  • optimize robot arm system as much as possible
  • begin to incorporate with chassis
  • Find a place to mount the cardboard basket that carries the balls/bottle
Wednesday, 9/26
  • pretty much finished the arm/claw in its entirety
  • tested the final basic arm design (all parts work)
  • discussed chassis and arm placement
  • begin optimizing arm in terms of weight, balance, length and material (make sure everything on it is regulation material! use robot arm drawings)
  • place the arm on a chassis (Mr. Kennedy's probably) temporarily, for testing
  • begin rebuilding Mr. Kennedy's chassis
Thursday, 9/27
  • discussed much about robot arm placement on chassis
  • no change in robot arm lengths needed for optimization
  • determined measurements for base of arm
  • began designing/rebuilding Mr. Kennedy's chassis
  • attached a rotary potentiometer to the elbow motor
  • replace pieces of the arm with regulation wood!!! (first thing to do before you forget)
  • cut base of arm to size
Friday, 9/28
  • replaced arm pieces with regulation wood
  • fixed arm elbow joint spur wheel (still needs tensioning and twist)
  • put arm back together
  • discussed very specific methods of arm optimization
  • create aluminum mount for spur gear on first motor
  • replace arm base with regulation wood and put arm and motor on base
  • re-gear first arm segment motor with an adjustable wood base for tension-er
  • add twist to second arm segment
  • add compressing tension to rubber wheel gear system of elbow joint
  • attach bungee cord to counteract the force of the gravity on the arm
  • apply heat shrink to potentiometer/axle joint
  • replace motor wires with red/black competition wires
  • attach arm to chassis with 4 angle brackets
  • attach pieces to claw to hold solar panels/T-structure
  • add friction tape/inner tube rubber to claw for grip
Saturday, 9/29
  • created aluminum mount for spur gear on first motor
  • replaced arm base with regulation wood and put arm and motor on base
  • re-geared first arm segment motor with an adjustable aluminum base for tension-er
  • added twist to second arm segment
  • replaced pinion of elbow joint to a much smoother piece cut with the drill press
  • added compressing tension to rubber wheel gear system of elbow joint
  • attached bungee cord to counteract the force of the gravity on the arm
  • replaced motor wires with red/black competition wires
  • attached arm to chassis
  • going to mall day tomorrow!!!!
  • fine tune arm after performance at mall day
  • balance weight on first motor
  • attach and apply heat shrink to potentiometer at elbow joint
  • attach pieces to claw to hold solar panels/T-structure
  • add friction tape/inner tube rubber to claw for grip
Sunday, 9/30 MALL DAY
see for the details

Torque Calculation for BEST Robot Arm = Limitation on Chassis 9/8

The robot arm has three segments (according to the current prototype design) and should be mounted on top of the robot.

The segment attached to the robot remains in the same horizontal plane the whole time, and has full 360-deg rotation on that plane via a lazy susan and a small motor (this 360 degrees will definitely be limited somewhat due to the pole being in the way). Weight testing confirmed that the small motor can support the approximate weight of the arm. Ideally, we would place the base of the robot arm so that it is on the same y-axis as the pole is on the 3D plane. If we move the base left or right, our robot becomes biased (plays much more efficiently) towards the right or left side of the game field.

The middle segment, which is to be made with PVC and which can be rotated roughly 360-deg in the same vertical plane the whole time, however, poses some issue because the small motor has a stall torque of 9.49 lb*in. Since torque = force * distance when the force is being exerted in the same rotational field as the motor, I set up an equation to reveal the maximum distance the middle segment of the arm can be: Tmax = Fmax * Dmax. The maximum force is the weight of the heaviest object (the 0.6875 lb habitational module). Thus, the max Distance = 13.8 in. To be safe, I would go with 13 in. Since the farthest to grap is the green fuel bottle at 33.1875 inches, the segment of the robot arm attached to the robot has to be 20.5 or 21 inches. This poses an issue as far as placement on the robot. However, this would mean that when the robot arm is folded on its joint between the first and middle segments, it would still constitute 21 inches of the robot length. The robot could still fit into the 2-ft cube, yes, but the chassis that can be hanging outside of the arm would have to be sqrt(3(24)^2) [using diagonal of cube] - 21 or -20.5 = 20.56 in or 21.06 in cube, except it would have to be placed in an oblique plane. This assumes the robot fits inside the 2-ft cube from one diagonal to another. This just complicates things as far as robot chassis fit, shape, size, and placement on pole. The Chassis Team, when it forms, should consider this.

By the way, the last segment is a claw. This would be perpendicular to the middle segment on the horizontal axis, so it does not project out from the 13 in. of the middle segment.

Plausible Solution to Above Obstacle 9/11

We are gearing the motor, so this adds mechanical advantage to the motor/robot arm. Furthermore, we are shortening r to 15 or 16 inches.

Solution Worked 9/12

Hooray, the solution worked!