Weapons are an important part of any robot in order to win a fight on gamaged caused. Without offensive weapons, the robot becomes another "brick with a spike" which make for boring fights. We are going to have two weapons, the lifting flap and the axe:
The Lifting Flap
This works on a lead screw from an old car jack, it consists of a lead screw with a big cubic nut on it and a ball joint at one end. We are going to remove the ball joint and have both ends turned down to remove the thread. It will lay horizontally at the front of the robot supported on bearing blocks. The end furthest away from the front of the robot will be chain driven by a motorbike starter motor, which spins in both directions with a 3:1 gear reduction. This should give lift from full down to full up in under four seconds.
Well, that was the plan. We went out and bought two motorbike starter motors from an Auto Jumble, one is 700W and the other is 800W. We thought that these would be great, powerful, compact, light….but when we got home and span them up, unlike Spin Doctor's motor these, like most starter motors only spin in one direction. Then we realised that we can still use them, you have two motors, one to lift the flap up and one to bring it down. Although with chain drive the motors would have to face in opposite directions, in order to spin the lead screw in different directions.
The way to over come this problem is to use gears, because when one gear turns another, each of the gears turns in opposite directions. This allows us to have both motors alongside the lead screw.
Although both motors are spinning in the same direction, they rotate the large gear in opposite directions. The motors obviously won't be both on at the same time. Although 700W does sound a lot just to lower a flap, having motors with the same gears makes things easier and if it was powerful enough, we could fit blades along the edges of the flap and the chassis to have a big pair of scissors!
Below is the results of another brain-storming session. These scribblings are great at the time, but the next day who knows what they could be?
The Axe
The axe will work on a cam system, like on a car wiper mechanism to give fast and repeated beatings.
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The small cam is driven by the motor. |
The large cam is driven by the linking arm and the shaft it rotates on is fixed to the axe handle. |
It will be powered by a small car starter motor, like that from a Metro. We want our axe to rotate through 180 degrees, you can't do this with a standard mechanism because the linkage arm would have to pass over the centre of the second cam causing it to jam.
The answer to this problem is to have the large cam rotating through only 90 degrees and to have a 2:1 gear increase to give the desired 180 degrees.
The drive motor will have a fly-wheel to keep the speed even and there will be rubber end stops which the axe shaft will hit at the end of each stroke, this should reduce stress on the linkages and bounce the axe helping it to change direction.
We were going to use an ordinary pick axe head, but have now decided to make our own head as the pick head is far to heavy to move and change direction quickly. The head is going to be a weighted block with a blade on either side, the blades will be either home made or from a pair of garden shears, if they are strong enough. There will also be a counter weight on the other end of the axe shaft. You may be thinking that if the blade hits something (a robot would be good) then the motor would stall and the axe would remain still. We think that we have found a solution to this which would enable the motor to continue the cycle despite the axe not moving, this would allow the motor to reach the part of the cycle where it can pull the axe back for another strike. I don't want to reveal this just yet, in case it does actually work!
