Aerator - Drill Mechanism
The drill mechanism is built as a separate unit before installation in the robots chassis.
The drill unit shares many features of a 3D printer frame with a central lead screw, GT2 belts, pulleys, upper and lower end microswitches and linear bearings.
The drill mechanism uses a gear ratio of 2 to increase the torque output at the drill spikes. The gearing is achieved through the GT2 pulleys. The motor torque is monitored via an amps to reverse the drill action if the drill become stuck in the earth.
STEP A: Printing the parts
STEP B: Assembly
1 - Lower Plate
Push the bearings into the '02 Lower Plate". The bearing fit should be tight, so use a heat gun if required to slightly the heat the bearing area. This should allow the bearings to be pushed into the print more easily.
The Linear bearings also need to be pushed into the '03 Linear Rail Bearing Holder'. Again heat may be required. Fix the linear bearings to the lower plate but do not tighten them up too much and leave some play. This will help the linear rails installed at the end to find a good running position and avoid binding. The linear bearings can then be tightened at the end once the drill mechanism is moving freely.
2. Motor and Tension Plate
Grind a flat spot on the motor axle and install the 8mm GT2 20Z Pulley. Ensure Locktite is used on the set screw. Now fix the motor to the adjustment plate using the M5 studs and nylon locking nut. Ensure the flat side of the adjustment plate is underneath.
3. Drill Spikes
Using some 8mm Chromed rod (same as from a 3D printed linear rod) grind them at the end to a point. This can be done by spinning the rod in a drill while using a disc grinder to form the spikes. PLEASE WEAR Safety glasses and hearing protection when doing any grinding work,
The chromed rods are important to ensure no rusting happens to these spikes.. Be creative and the more pointy the spike the better :)
Once the tip is formed, test fit the GT2 40Z Pulley to the spike. Ensure that a 5mm stick out is on the end of the rod as this will fit into the upper bearing. Grind flats for the pulley set screws and attach using Locktite on the set screws.
4. Test Fit Drill Spikes and Belt.
Push the 8mm drill spikes into the bearings and ensure a smooth spinning motion for each drill spike. The GT2 belt can be loosely fitted to the assembly. The belt needs to be in before attaching the top plate.
5. Attach the Motor
Attach the motor tensioner to the lower plate by using M6 Bolts. Use the lever on the motor tensioner to pull the belt tight. You may need to wait for installation of the top plate before finally fixing the motor tensioner to ensure the drill rods are straight
6. Top Plate Assembly
The top plate also has 3 upper bearings which need to be press fit into the plate. The T8 lead screw nut is fixed into the top of the plate with M3x15mm bolts and nylon nuts.
7. Top Plate to Bottom Plate Assembly
The top and bottom plate are now fit together. Ensure that the 5mm stick out on the spikes fits into the upper bearing. Ensure that a 8mm washer is fitted between the GT2 pulley and the upper bearing to ensure the spike spins smoothly.
The two plates are fixed together with long M3x50mm bolts, washers and nylon bolts,
Once the top plate is in position and the rods are correctly located in the upper bearings the motor tensioner can be used to pull the belt tight. If the belt is loose it will slip and squeal when turning. Tighten the 3xM6 bolts to lock the position of the motor tensioner.
8. Motor Housing
The 30RPM motor is bolted to the motor housing with M3x15 bolts. Ensure the power leads are soldered to the motor with approx 20cm of cable.
8. Frame Assembly
The frame assembly is completed with M3x30mm bolts and nylon locking nuts. The nuts need to be pressed into the slots so they are a tight fit. This stops the nuts spinning when tightening the M3 bolts.
Should the nuts start to spin, use a flat headed screwdriver tip and wedge it between the frame and the bolt. This should give more support while the bolt is being tightened,
The M8 smooth guide rods can now be pushed into the location holes on the lower frame plate.
9. Drill to Frame Assembly.
The flexible coupling is now attached to the 30RPM motor. Grind flats on the 30RPM motor to accept the set screws. Its better to make a flat and a step on the motor shaft to hold the coupling from slipping off the motor. The same is done on the M8 lead screw. Again grinding a flat spot with a step to ensure the coupling cant slip off the lead screw.
The drill mechanism is now slotted over the M8 smooth rods. The linear bearings should still be slightly loose to ensure a free movement of the drill mechanism. if you have an external 12V power source it can help to spin the 30RPM motor to pull the drill mechanism onto the 8mm smooth rods using the lead screw.
There is an access slot under the T8 nut if you wish to tighten the lead screw after fitting the plate over the 8mm smooth rods.
Some "jiggling" is required to get everything to fit together.
10. Top Frame Plate
The top frame plate is now pushed onto the M8 smooth guide rods and secured with M3x30mm bolts into the frame. This should secure the whole assembly.
The microswitch should be soldered with wires and then fitted to the top plate. 2 holes are provided for the correct location. An M3 bolt can be screwed into the top plate to adjust the contact to the microswitch.
Careful!! The microswitch is not connected so there is no automatic stop at top and bottom. You can use a 12V external power supply to turn the motor and check the movement of the drill mechanism. Do not go too high or too low or you risk breaking the drill mechanism.
Once you are happy with the mechanisms movement you can slowly start to tighten the linear bearings position.