The Vexmen of Brandywine Robotics

Blog Post

How Will You Score In A 30″ Goal?

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[heading]How will you reach the tall goal this year?[/heading]
This year, Gateway has a new tough obstacle – 30″ goals. If you can not get the game pieces in here, your opponent can score at will. So how do you start at 18″ and grow to be over 30″?

There are a few ways and the friends (and KTOR’s nemesis) at AURA robotics in New Zealand have put this slideshow together. The gear looking green circles are gears, the pink diamonds are joints where the lift bends, the yellow is to show where you will have your basket or claw or conveyor belt, and the gray is the base and tower parts of the robot on wheels. So now that you can read the pictures, let’s go over them.

Swing LiftThe first slide is a swing lift. This will move an entire basket up to a higher position the radius of the arm. You could get to about 30″ for the base of your swing lift platform so it can get pretty high. The basket is pretty stable but somewhat tough to move. You could try a big gear in the corner of the arm to the tower post or you could push from below using a slide and motor (or two). Not having made one of these I imagine it might be slow to get up and down and hard to control anywhere in between the up and down positions. The edge of the swung platform is in an arc too which is another disadvantage.

Simple ArmThe second slide shows a simple arm. This will take your arm and lift it along the pivot. You might barely get to 30″ with this but there’s not a lot of room for a contraption to grab the balls and cylinders. You may want to use this in conjunction with one of the other lifts or the arm is really a conveyor belt as shown in one of the videos below.
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So this leads us to some other more complex types.

The third slide is really complex. It’s a six bar linkage and we’ll discuss that one later.
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Scissor LiftNext one gives a basic idea of a scissor lift. The Chinese teams at worlds that beat us all used these types of lifts quite effectively. The X squeezes together and the height goes higher. A two level scissor lift with two X’s should get to 30″ high. The downside to scissor lifts are a few. They can be shaky or heavy and make them underpowered. Aluminum may be needed here to reduce weight. The Chinese teams used rubber bands from the furthest points to help squeeze the two ends together giving the lift motor a break. Sliders are needed on the top and bottom to help guide the scissor. This can get caught if not on track and aligned or bent loose over lots of wear.

Scissor lifts from roundup:
Scissor 1. Lots of aluminum on this one.

Scissor 2. Notice the rubber bands

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Linear SlidersThe fifth type is a linear slide. Here only one lift is used. The math does not work on this one. You start at 18″ and the slide only moves about 10″. So the top may be near 30″ but the bottom is not. Unless that linear slide has a conveyor belt on it, the objects have to get from the bottom to the top. So this may be OK for a conveyor belt but not many other kinds of robots attempting to go the full 30″. However, if you put another kind of lift on the end, you could get to 30″. This is how the KTOR college team did it last year. They used a linear slide on the tower and then a four bar linkage for the arm to get to 30″ off the ground.
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Multi-SliderThe sixth slide shows a multi-slider. The multi slider uses a bunch of sliders to go much higher. Considerations needed for this is the compound slider movement. It has a chain or a rope having multiple sliders work together to lift you up real high. The downside is they are a bit complex to make, somewhat heavy, and susceptible to tipping over. See how the lift is a lot of mass up high and on one side of the robot? Just one bump or a jerky drive movement could tip this robot over. So you may want to have the lift in the center rather than the edge as shown here. The chain also needs to have mechanical stops to keep the slides from going right off the tracks.
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4-bar LinkageThe last slide shows a four bar linkage. Quite a few teams used this last year in round up. This is a pretty good lift but it takes a bit of force to raise to the top. The advantage this has over the simple arm is the front yellow box stays parallel to the wall. To help a four bar linkage raise up and control it on the way down, rubber bands or surgical tubing can be used to act as a spring. Without it, the motor has to lift the weight of a claw or basket times the length of the arm.
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6-bar LinkageOK, back to the six bar linkage. It’s a four bar linkage on steroids like the multi slider is compared to the one slider. This seems to be popular early on in the early matches. This adds a multiplier effect of the four bar linkage. The extra set of bars fold up in the bottom position and then when extended, they can reach pretty high. Disadvantages to this lift is it uses a lot of metal so it can be heavy. Aluminum seems to be the metal of choice on these making it expensive.
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So think hard and choose well on your design!

Tipping over robots playing gateway:
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Hawaiian Robots using a six bar lift, one with a simple arm, and two with multi-sliders
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Chinese robots using a six bar lifts, and one with a simple arm/conveyor (with one no show yet red still won)
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