pic: The Hammer



Close up of the hammer, which we use to kick the balls.

The hammer is 20" long with two 1 lb. steel weights on the end. Its powered by an FP through a modified T-Box. No surgical tubing, springs, ratchets, or dog-gears!

Haha that looks great. It’s so simple. How much power can you get from it?

Just don’t put any part of your body in the way…PAIN!!!

Oh yeah i bet. Our kicker = maximum pain too lol

We can boot it 35’ !

I’m kind of suprised at how few teams did something like this.

2337 and 1388 were my favorite hurdlers from '08. After seeing how easy it was to kick a massive trackball over the overpass, kicking the soccer ball with a hammer was sort of a given :rolleyes:

this was my first idea, I’m glad a team I’m going to see made one

I agree on 1388, they were amazing, we copied them for our 08 cal games bot

horrible picture of it, but it was like 99% scrap we had lying around the shop, and possibly one of my favorite robots we made

Sorry for the thread revival, but I have a question.

How did you stop this kicker when it reached the edge of your robot? How did you stop the motor from stalling when it reached this point? I’m working on something similar for IRI (hopefully) and other off seasons, and we were wondering what you used to stop the motor from trying to spin when the kicker reached the end of its trajectory, and whether or not you needed some foam in your frame to prevent your high velocity kicker from ruining it.

I believe a clutch could fix this issue, and mechanical stops. The stop would stop the kicker and the clutch would allow the motor to not stall once this point is reached.

1350 used solid neoprene blocks mounted on nylon blocks for their mechanicals stops and these worked well with our very violent kicker and was one of the few parts of the kicker that didn’t self destruct ever.

At least that is how I would go about this.

There are neoprene rubber blocks to stop it. The motor is used to accelerate the mass to full speed; we stop giving it power before it contacts the frame, so the motor is under no stress.

This is a great concept, but our implementation was not perfect.

The main mistake we made was making it so powerful. We discovered in competition that smacking balls with full power was not an effective way to score, since the balls would always bounce into the air instead of rolling into the goal. As a result, we only swung the hammer at a fraction of its full power, which mean’t it took a while to swing and kick the ball.

I would suggest using a much smaller hammer (12" would prolly do it) with a lower gear ratio. This is similar to what 78 did. This will give you a more compact mechanism, as well as improving the performance.

PM me. I love answering questions :rolleyes:

Haha, the hammer also reminded me of “AHHHH BOOOOOOM!” (what we called our kicker in 2008)

It’s a pretty sweet kicker though! What kind of distance could you get during a competition when you kicked a ball?

2468 ended up with a semi-similar solution, but instead of using Neoprene rubber we used a Jaguar… wait… ignore what I just said. Please do not use Jaguars as impact absorbers!

We put a quadrature encoder on the shaft and used position control mode to kick. The PID constants that worked best for us were a little bit unstable: Basically, aim for a bit before and let it overshoot. Then we used current control mode to rewind the motor and let it “stall” against a back stop. Since it was only 6 amps, no harm done. This let us reset the encoder to a known state - smashing it into a ball caused it to miss a few pulses each time! Rinse and Repeat.

http://i40.tinypic.com/2w2h7ax.jpg

Lovely spot for an encoder on the toughbox nanos…

We dropped the kicker down without powering the motor until we reached our desired position and recorded the encoder value. The logic behind a kick works like this; If the kicker is not pressing the limit switch (at the top of the kickers path or resting position) then it’s continuously powered backwards until it hits the switch. This is so it doesn’t fall down during driving around and give us half kicks. Pressing the limit switch resets the encoder count. Only variable for each kick is the speed of the kick…which allows us to change the distance, obviously. We had to end the kick a little early to stop it from pummeling into the hard stop we made (just a steel bar bolted across the inside of our frame, to protect our vaccum). After the ball is kicked, the motor is reversed slowly for a short period of time and then fully retracted back to the top with a faster speed.

Thanks! We considered doing something like that again, but we didn’t want to use pneumatics, and we needed the large amount of space for our hanger (frankly, almost certainly the largest in the world).

From what I saw at several events (Arizona, Denver) I thought my team (399) was the only one doing a kicker like this, Good to see some people think alike!

The way that ours worked was similar to all above, but doesn’t have a hard limit switch.

The hammer is tied to a CIM powered toughbox, geared down slightly with chain. On the toughbox there is a quadrature encoder going to the controlling jaguar.
When kicking there is no limit switch for stopping the motor (It is powered the whole way down, needless to say we broke several limit switches), only the encoder and the current sensor.

The encoder messes up sometimes when kicking the ball (chain stretch, etc.) so, the current sensor is a backup (saved many a mechanical stop, and properly ends the kick mode, returning to positon control mode (look at Az. regional webcast for vids without the current sensing in (all of them), wouldn’t properly terminate the kick (the deflector’s code would terminate it properly thus the many actuations) thus the weak kicks)

We have two modes for the kicker, SET and KICK!!.

When in SET mode, the jaguar uses PID in Position control mode to control the placement of the hammer (The higher it is set, the more power it can apply to the ball). There is a neodymium magnet in a plastic enclosure on the kicker arm that is used to zero out the encoder pulses. The reed switch that it passes by is connected to the digital sidecar, and on pulling the line low restarts the jag’s position control.

When in KICK!! mode, the jaguar is placed in voltage control mode. full bus voltage is applied to the CIM and is continued until the encoder passes a set value, or the motor stalls. After either condition, the kicker is immediately retracted and returned to SET mode.

The hard stop we made is designed to absorb the excess energy (and there is a LOT of it) and dissipate it through the frame.