Technical Section - Overview
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Constructing the Chassis Read and understand all the instructions before you start construction - You can print extra copies of these instructions to help you. Most of the problems experienced by teams constructing Rampaging Chariots are because the team has not read the instructions. A basic robot design is described and we recommend you construct this first. Once you have a working robot you can test it and formulate ideas (within the rules) that will improve upon the standard design and thereby gain a possible advantage over your opponents. You can then, if you wish, make a replacement chassis and transfer the working and tested components into it.
What Your Finished (Unpainted) Rampaging Chariot Should Look Like
Chassis Base The more accurately you lay out the pattern on the base and cut to it, the easier it will be to assemble the robot later. 1.
Hint: Clearly identify the pieces to be cut out to avoid cutting the wrong line.
2. Drill six clearance holes 3.5 mm diameter in the base for the screws at the positions of the black crosses. Countersink these holes on the bottom.
3. Place the two motor drive board PCBs (printed circuit boards) onto the chassis base 13mm from the edge. With a pencil mark the positions of the PCB retaining screws through the four corner holes. 4. Drill eight holes 2.5 mm diameter through the base. 5. Cut a scrap piece of 12mm MDF to a size of 32 x 32mm. Drill two 3.5mm dia holes through the block in opposite corners and countersink the hole to make the screw head flush with the surface. Drill a 1.5mm hole in the centre for the aerial wire.
Note: This aerial housing will be fitted later. Chassis Sides
6. Mark out the positions of the five screw holes in each of the two sides (Black crosses) and drill clearance holes 3.5 mm diameter through the sides and countersink the holes on the outside of each side. 7. Mark out the positions of the two 4mm bolt holes in each of the two sides (Blue crosses) and drill clearance holes 4mm diameter through the sides and countersink the holes on the outside of each side. 8. Mark the positions of the centre of the balancing wheels (Shown in red). Centre punch the position of the holes and drill a 5mm diameter pilot hole and then a 10mm diameter hole for the coach bolts. Note: The balancing wheels are bolted directly to the side of the chassis in the front left and rear right positions. Hint: Recheck you have marked the correct positions before drilling. The critical dimension is 44.5 mm above the bottom of the chassis. 9. Cut off the front bottom corner of each side as shown. Note: This is to allow the Rampaging Chariot to mount a ramp without grounding. Chassis Front and Back No screw holes are required in the front or the back.
Holes for Rear Safety Lights 10. Drill two 5mm diameter holes completely through the rear of the chassis for the Red LED (Light Emitting Diode) Safety Lights. Counterbore from the inside with a 7mm drill to a depth of 5mm. Countersink the outside to increase the angle of view of the LED. Hint: Wrap some masking tape round the 7mm drill bit 5mm from the end to tell you when you have reached the correct depth from the inside.
11. Drill a 3.5 mm diameter hole through the back in the position shown for the Tug-of-War rope attachment eye. Assembling the Chassis Hint: We recommend that you initially assemble the base and sides of the chassis with screws and glue the joints later. 12. Grip the chassis front in a wood vice with one long edge about 5mm above the bench top. Place on the chassis base (upside down) and insert three 3.5 x 30mm wood screws in the holes. Line up the base and front exactly and when absolutely happy, tap each screw lightly with a hammer sufficient to make a small indentation in the edge of the MDF. Lift off the base and drill 2.5mm pilot holes into the edge of the chassis front to a depth of about 18mm. Screw the two pieces together.
13. Repeat this procedure for the chassis rear ensuring you have it the correct way round. 14. Fit one side onto the chassis the correct way round and using the technique above, screw in place using five 3.5 x 30mm wood screws. Fit the other side in the same way. Hint: Remember to drill pilot holes 2.5 mm diameter to stop the MDF splitting 15. When you are happy with the fit, remove the front, back and sides, glue the joints (we use a PVA adhesive from B&Q) and reassemble using the screws to hold the joints together. Chassis Protection and Strengthening Front of Football Guides 16. To protect the ends of the football guides, cut the two 12mm aluminium channels to a length of 90 mm. Drill two holes 3mm dia through one side near the top and bottom and one hole 3mm dia through the other side in the centre. Countersink these screw holes. 17. Fit the aluminium channels over the ends of the MDF and use a rubber mallet (or hammer with a scrap piece of wood) to make sure they are fully seated and in the correct position. Screw in place using three 3 x 12mm screws.
18. To protect the MDF rear corners and to strengthen the chassis, cut two 35mm x 35mm aluminium angle plates to a length of 100mm and fit each of these to the rear corners of your robot with six 3 x 12mm screws. Countersink the holes in the aluminium on the outside of the angle. Hint: Think about the best positions for these screws: They should not be too near the ends of the MDF or they will pull out under stress. They must also miss the existing screws fixing the chassis together.
19. To strengthen the chassis in the centre cut two 35mm x 35mm aluminium angle plates to a length of 45mm and fit these to the centre of each side of your robot with four 3 x 12mm screws. Countersink the holes in the aluminium on the outside of the angle. Hint: Drill the holes in the aluminium protection plates in places where the screws will not be too near the edge of the MDF sides and will also miss the existing screw fixing the chassis together. Front Corners 20. To strengthen the chassis and football guides, cut two 35mm x 35mm aluminium angle plates to a length of 100mm and fit each of these to the front corners of your chariot with six 3 x 12mm screws. Hint: Again think about the best position for these screws. Like the rear protection plates they should be well away from the ends of the MDF and miss the existing screws. In addition, during a football match, the protruding football guides will be hit in three directions:
21. Hint: If you wish, you can cut off surplus thread on the inside and put a spot of Loctite® ScrewLok glue on the nuts to prevent them vibrating loose. 22. Cut off the corners of the aluminium where the chassis corners have already been removed. Painting 23. Paint the inside and outside of the chassis with a white undercoat paint before installing the motors. 24. Redraw the two drill centrelines across the base 88mm from the inside of the front MDF and 88mm from the inside of the back MDF. Check that there is a distance of 200mm between these two centrelines. Dismantling the Drills Hint: Test that the cordless electric drill rotates clockwise and anticlockwise before you start to dismantle it. There should be sufficient charge in the batteries to do this, but if not, charge the batteries brief for a short while and confirm they work BEFORE you start to dismantle them. The two drills require exactly the same modifications so you may wish two team members to do the following sequence of actions simultaneously. 25. Remove the drill handle by unscrewing and removing the bolt with the lever arm. Expand open the attachment ring and slide the handle off over the chuck. Hint: Put all the pieces you remove in a container or plastic bag and keep them safe. Never throw any parts away until you have a fully working robot. 26. Turn the Torque selector ring fully clockwise as viewed from the front (chuck) for maximum torque (Twisting Power). The drill symbol will then be in line with the small arrow on the top of the drill. Removing the Chuck The drill chuck is attached to the drill shaft by a normal thread. To stop it coming loose when you operate the drill in reverse it also has a special screw in the centre of the chuck that has a reverse thread (or left hand thread). Which ever way the drill is rotating, one method of attachment is always trying to tighten up the chuck. 27. Remove the chuck by opening its jaws to the maximum size and unscrewing the screw in the centre of the jaws. This screw has a left hand thread and is removed by twisting in a clockwise direction viewed from the front. Then unscrew the chuck from the drill by twisting the whole chuck in a normal counter-clockwise direction viewed from the front. Hint: If the chuck refuses to budge and the motor turns instead, check you are twisting in the correct direction. If more twist is needed, fit a fully charged battery, select forward or reverse as appropriate and operate the trigger just enough so that the motor tries to turn in the direction to oppose your twist. This should loosen the screw or chuck immediately. 28. 29. Unscrew the two (one) brass screws in the end of the round battery connector and pull off this brass connector. Note: Some drills only have one brass screw.
30. Confirm the torque selector is turned fully clockwise (drill symbol at the top in line with the arrow) and place the drill on a clean table or bench as there is a good chance some loose parts may drop out. Turn the casing so that the Nutool logo is underneath. 31. Unscrew the ten self tapping screws and very carefully lift off the top half of the black plastic casing starting at the handle, then the rear and finally the front. Note: Try not to remove the torque selector as it will now be loose. If it does fall off the front of the drill, replace it to protect the mechanism, noting that the correct orientation is with the little drill symbol at the top of the drill. DO NOT DISMANTLE THE TORQUE SELECTOR or you will have ball bearings running all over the floor and no one will know how to reassemble it! Hint: Note how all the parts fit in the lower half of the drill casing. During reassembly of the motor and battery connector you will have photographs to assist. 32. Note Keep the nuts and washer safe for reassembly. 33. Remove the Reverse Selector and the magnetic plate. 34. Lift up the motor, gearbox and torque selector as a single unit. Note: The gearbox in front of the metal motor has a plastic tab that locates into a slot in the lower half of the black plastic drill casing. 35. Remove the motor assembly and the other parts from the casing and place them on the bench. Hint: When storing and working with the motor be careful that no metal filings or screws are allowed to enter the ventilation holes attracted by the magnets inside. Never put the motor in the same bag as metal screws or nuts. 36.
37. Take the top drill casing (The one with the ten screw holes) and mark exactly where you are to cut off the plastic handles (see photo). Carefully remove the central section with a hacksaw. Note: The lower cut is above the upper screw hole and parallel with the bottom of the drill.
38. Place the cut off motor casing onto the mating part of the lower drill casing and continue the hacksaw cut though the lower casing. In the same way place the cut off battery connector casing onto its lower mating half and continue the cut though the lower casing. Remove the burrs from the cut faces using a file or knife to make it look good. Reassembling the Battery Connector 39. Take the bottom half of the battery connector cover and the central spring connector. Slide on the washer, squeeze the spring and insert the two washers into the sockets in the plastic case as shown. Insert the brass eye tab on the end of the black negative wire into the recess and insert the brass nut above it as shown
40. Hint: If the two halves don’t fit together easily, separate them and check that the parts are seated correctly and the wires are not obstructing the screw housings. 41. Refit the brass connector to the bottom of the handle and tighten the brass screw(s) to hold it in place. Warning: Do not fit the connector onto a battery until you have fitted the crimp terminals or the leads may short. 42. Crimp a red and blue female terminal to the appropriate colour wires emerging from the top of the connector using a special crimping tool or a pair of pliers and a lot of squeeze. Hint: Ensure the wire is fully inserted and the part of the terminal you crimp is within 5mm of the spade or you will just be squeezing plastic!
43. In the same way, crimp a red and blue male spade terminal to the appropriate coloured wires connected to the motor. 44. Repeat for the other drill. Drive Wheels There is a huge twisting load between the two drive wheels and their shaft/axle when you try to reverse direction at high speed. It is therefore important to fix the aluminium axle firmly to the drill shaft and the wheel firmly to the axle. If either comes even partially loose the drill will turn without the wheel and you will have difficulty steering the chariot. The wheel axle is manufactured and fitted to the wheel for you by the Rampaging Chariots Guild. We also pre drill the wheel and axle to take a 4 x 25mm pan head bolt.
45. Temporally insert the 4 x 25mm pan head bolt into the wheel and axle. This bolt will cut its own thread in the lower part (3.5mm hole) of the nylon hub and this will stop the screw vibrating loose. Note: The purpose of inserting the screw at this stage is to maintain the alignment between wheel and screw hole whilst you fit the wheel to the drill. 46. Screw the wheel and axle onto the drill (Normal right hand thread). Ensure the wheel is screwed fully on by giving it a sharp twisting jerk. Hint: If you wish, you could apply a small amount of Loctite® glue to both the drill thread and the chuck bolt thread before fitting the wheel and bolt for the last time. 47. Remove the 4mm bolt (which was originally inserted to keep alignment of the wheel and axle hole) and insert the 4mm left hand thread chuck bolt. Fully tighten this bolt by twisting anticlockwise. 48. Recheck both the wheel and chuck bolt are both tight and insert the 4 x25mm wheel bolt. 49. Repeat with the other motor and wheel. Fitting the Motor Assembly The two drive wheels are the left rear wheel and the front right wheel. 50. Temporarily tape the 50mm x 50mm piece of 6mm thick MDF to the inside of the chassis in line with the motor shaft. This is to ensure the correct positioning of the motor and wheel.
Plastic Casing 51. Fit the motor plastic casings with the position of the handle (cut off earlier) facing towards the centre of the chassis. Hint: Make sure the bottom half of the plastic casing is the half without the six black self tapping screws that join the two halves together. 52. Drill four 3mm holes in the lower half of the plastic casing in the positions shown below.
53. Hint: The rear of the torque selector fits just inside the plastic casing and the protruding plastic tab under the gearbox locates into a socket in the lower plastic casing to stop the motor rotating. When lined up, the motor and gearbox should drop vertically into the plastic case with no forcing required. 54. Fit the motor and wheel into the chassis checking the following:
When you are absolutely happy it is in the correct position drill through the rear screw hole and completely through the chassis. Hint: Depending on how accurately you drilled the rear hole through the plastic casing, you should be able to see the pencil centreline for the drill under this screw hole.
Position of Motor and Wheel 55. Remove the motor, gearbox and wheel from the bottom half of the plastic casing. Remove the MDF spacer from the side of the chassis. 56. Place the lower casing in the chassis and locate it in the correct position by inserting a 3mm x 20mm bolt through the rear screw hole. 57. Line up the drill casing so that its centre line is exactly across the chassis and drill through the three other fixing holes. Hint: Depending on how accurately you drilled the front hole through the plastic casing, you should be able to see the pencil centreline for the drill under this screw hole. Additional Shaping Unfortunately the drills and batteries provided for the 2007 chariot are larger than the originals and this requires some additional shaping of the plastic drill casings. 58. Without the drill motor in place, hold the upper and lower casings together with two or three screws. Cut a curved section from the case round the blue plastic piece. Do not remove the internal plastic spacer holding the casing screw. Hint: You can remove the plastic with a coping saw and half round file. The curve radius should ideally be the same as the narrow end of the battery. See picture with instruction 67 below. 59. Hint: You can file this hole, or even cut a thin slice of the back of the casing. If you make a neat job of this your friends may think that the drill motor is driving the balancing wheel out of its back end!
The balancing wheels are bolted directly to the side of the chassis in the front left and rear right positions. 60. Each balancing wheel should be 2.5mm higher than the drive wheels so that the robot rocks on the drive wheels and keeps these wheels in contact with the ground.
61. Insert the clear plastic axle tube into the wheel. 62.
Insert the coach bolt through the MDF from outside and fit a nut on the inside until the bolt protrudes about 10mm. Fit a washer followed by the wheel with its plastic axle. Continue to insert the coach bolt whilst tightening the nut. This will draw the square shank of the coach bolt into the MDF. Tighten the nut very tight to hold the axle bolt firmly to the chassis. Fit another washer and then the self locking nut with the nylon insert. Tighten the nylon nut until the wheel just stops rotating. Then loosen this nut by quarter of a turn to allow the balancing wheel to rotate freely.
Hint: The Chariot should rock on the drive wheels such that there is a 4mm to 6mm gap under one balancing wheel whilst the other is touching the ground. If necessary you can adjust the height of the balancing wheels by elongating the 10mm fixing holes in the sides of the chassis with a round file. Fitting the Casings and Motors 63. Test fit the two motor casings and ensure that there is good clearance round the coach bolts. Check that the two batteries will fit between the drill casings with their narrow end located in the casing cut outs. Enlarge the holes and cut outs if necessary, but do not remove the internal plastic spacer holding the casing screw. 64. Counterbore the four fixing hole exits on the bottom of the chassis with a 6mm drill to a depth of the thickness of a nut to allow you to fit the nuts easily. 65. Bolt the lower casing to the MDF chassis using four 3mm x 20mm pan head bolts (Nuts on the under side of chassis). Hint: Watch the casing for distortion as you tighten the bolts and stop tightening if this occurs. 66. Refit the motor and wheel and route the wires out through the hole that originally housed the magnet. 67. Screw the top half of the plastic motor casing in place using the six black self tapping screws. Hint: If the cover does not fit easily, recheck the location of the motor assembly. Is the tab correctly located in the black plastic casing?
68. Cut two strips of Velcro loops 100mm long, peel off the backing paper and press onto the under side of each battery. Place two strips of Velcro hooks 100mm long on top of the loops. Peel off the backing paper and press each battery firmly onto the chassis in the correct location. Allow the Velcro glue to harden for two minutes before lifting off the batteries. Leave a gap of 32mm between the batteries for the receiver and aerial block. Hint: The section on Improving your Robot describes an additional method of securing your batteries for robust football competitions.
Rear Safety Lights
69. 70. Push the wires firmly into the top of the red plug using a small thin screwdriver. The negative wire with the black stripe is on the left side as shown in the photo above. Hint: Tin the ends of the wires with solder before you push them into the plug, but don’t use too much solder. Hint: Get someone to hold the red plug firmly on a bench with pliers whilst you push down the wires. 71. Insert the LEDs into the 5mm holes at the back of the robot and when they are flush with the outside bend the leads downwards against the MDF and tape them to the inside of the back of the chassis.
Tug of War Eye 72. Screw the towing eye into the rear of the robot. Radio Receiver and Aerial 73. Cut a piece of Velcro to fit the bottom of the receiver and attach it to the chassis in the position shown. Note: Velcro makes it easy to remove the receiver to change the frequency crystal. 74. Take the small MDF aerial block you made earlier and screw it to the base of the chassis in the position shown to hold the aerial.
75. Insert the aerial and piano wire through the red 3.2mm heatshrink. Hint: First attach the aerial to the piano wire with a small piece of adhesive tape whilst you insert it. 76. Bend over the end of the metal aerial support piano wire to avoid it sticking in your eye. 77.
Fit the piano wire into the hole in the MDF aerial block. Hint: Grip the piano wire with a pair of pliers to push it into the hole. Finishing 78. Paint the Chassis and personalise your Rampaging Chariot. 79. Think of ways of improving your Rampaging Chariot such as adding a superstructure. Hints are given in the section on Improving your Robot
Next The next section is on the construction of the motor controller boards |
