Kicker power restrictions

Hello everyone,

As we started to plan our next robot for the Soccer Open League, we came up with some inconsistencies with the rules about the kicker. On the one hand, the power of the kicker is restricted but on the other hand, the rules want us to shoot vertically (as a technical challenge). In our opinion, the restrictions for the kicker in Open League should be adjusted. Some alternatives would be:

  1. Bigger/another ramp
    E.g. the ramp is as high as the border of the field with an angle of for example 20 degrees to the ground and when testing the kicker-power with a ramp, the ball isn’t allowed to go over the ramp.

  2. No restriction at all
    No restriction would motivate the teams to deal with the physics of a solenoid and support the dynamic gameplay. In case the ball leaves the field, it is a foul and treated like an out of bounce. The golf ball won’t be damaged, and the playing robots should resist this kind of strength.

  3. Two different measuring
    One ramp for the two-dimensional kick and a height restriction for the vertical kick.

  4. Another measuring
    E.g. measuring the speed of the ball after the kick with a photoelectric barrier

We would be very glad if you would think about our proposals and would be happy for any feedback.

If we allow for more powerful kickers, how do we ensure that no one is going to get injured by the golf ball? For the technical challenge, safety measures can be put into place but those same measures may not be practical for competition play.

It would be great to see some calculations/tests on what would be the practical upper limit of a robot kicker with a golf ball and how much of a safety concern it would be if played with the current field setup.

Thanks for starting this thread - definitely something worth discussing!

I understand your Point @Mike , that without any power regulations Teams would build to powerful Kickers and i hope not, hurt themselves or other participates.

On the other side, the RCJ-Team wants us to build a vertical Kicker, but with the current regulation, a vertical Kicker would be completely useless. So no Team would spend his time, to build such a kicker.
Rules must be changed, so that it would be useful to teams to spend their time on such a difficult technic.

I hope the RCJ-Team will think about this, and hopefully change the rules.


On the other side, the RCJ-Team wants us to build a vertical Kicker, but with the current regulation, a vertical Kicker would be completely useless. So no Team would spend his time, to build such a kicker.
Rules must be changed, so that it would be useful to teams to spend their time on such a difficult technic.

I wasn’t on the TC when the technical challenge was written and don’t speak for the entire committee here. I think the point of having such a challenge is to encourage teams to test out what can be done with the golf ball in the hopes that a vertical kicker could be integrated into future seasons (see 9.3.2).

I agree that it would be difficult to integrate a vertical kicker into a legal 2022 robot and it would serve no use with the current rules. On the other hand, it is very difficult to verify significant rule changes like the vertical kick without the help of teams trying it out first. Perhaps we need to allow for some technical challenges to be completed on non-competitive robots/simple chassis if these challenges are to be included in next season’s rules.

Thanks for replying.

We understand your points and the highest goal should still be a fair game with no injuries, but we could look at the Small Size League-Rules, because there are no restrictions for the kicker power and still no team has caused a change of this. No injuries in this league were caused by the robots, neither the kicker, although the referees are walking on and close to the field without a barricade during the game. We think that next year the kicker restriction should be changed as a test so that we all can see the impact of an useable vertical kicker.
Team Faabs

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Hey @Elias and @TeamFaabs_GER,

Well, I was there when this part of the rules was written – in fact, I am afraid I might have even written this particular version :slight_smile:

@Mike is right though – the idea of making the vertical kicking part of the rules was to encourage teams to experiment with building robots that would be capable of doing that. We did not really expect any team to make use of it in games, the aim was mostly to see if it was even technically feasible, so that the rules could perhaps change accordingly in the future. As this discussion shows, we haven’t really managed to communicate that clearly which is something that we should be able to fix in the next version of the rules.

All in all, thanks for highlighting it!

Unfortunately, I do not think we can easily compare RCJ Soccer to Small Size League.

For one, the robots in Small Size League are remotely controlled from a single “server”, which makes it much easier for the referees to interact with the game – the robots normally do not move when the referee does something at the field, which is currently very different from RCJ Soccer.

Secondly, the field is being monitored by a high-precision camera at all times and so enforcement of rules is slightly simpler than in RCJ Soccer where this is left for humans to do (it does have its advantages though :slight_smile: ). In this regard, I would like to point out that there actually is a limit on ball speed instead of kicking speed in Small Size League but doing something similar is currently unfeasable in RCJ Soccer.

A robot must not accelerate the ball faster than 6.5 meters per second in 3D space.
Rules of the RoboCup Small Size League

Finally, the field is simply much larger in Small Size League and so vertical kicking is a little less problematic health-wise than in RCJ Soccer.

Still, I am convinced that after receiving feedback like this the rules will be altered so that things like vertical kicks are possible within the bounds of the rules, not just “for demonstration”, so that they can become part of the standard gameplay.

Hope this gave you a bit more background on the whole debate – if there is any specific point I might have missed, please do not hesitate to reach out!

Hi there,
I absolutely agree with TeamFaabs.
It is quite a challenge to build an 18cm robot anyway - which is good!
It is quite a challenge to see the small golf ball, so the robot must become less high to see
the golf ball when it is near the robot - which is also good!
Both leads to not only smaller and lighter but also to slower robots that need to have more tactics.
If you stick to the very slow 1m/s rule for the ball and want a strong chipper there is simply no space to build both into the much smaller “inner space” of the “first level” of robot.
So either teams can try to build one(!) stronger device or just skip the technical challange with a chipper. And if we have a chipping device build in, why not use it?
I do like the suggestions of TeamFaabs.
I also agree with Marek that no restrictions at all could be too much.
But face it: the walls around the field are set to 22cm by rule.
If we restrict the speed of the ball to never go higher than the walls we can use simple physics:

2 m/s is 4 times the power we are allowed to use now. That seems to bee inside the limits without the need of an “insane-mode”.
It also would ensure that the ball will not fly over the walls. That reduces the risk of injuries.

And than the technical challange…
as any athlete knows, the best way to throw a ball is with an angle of 45 degrees.

So even if we double the allowed max speed of the ball, we are still far to slow to chip as wanted in the technical challenge draft rules.

I cannot think of any team building a chipper powerful enough to do the technical challenge in this very restricted space.

So what about a „step in the new direction“ by doubling the allowed speed to 2 m/s measure with a new 20cm high ramp and a technical challenge to chip the ball from one of the neutral spots near the goal into the penalty area. This is at least 22cm distance. This can be done without exceeding the allowed maximum power (2m/s speed).

And than we should allow this chipping during normal gameplay, so there is no need to have two devices.

The only problem I see is that the robots itself must me prepared to get hit by a flying golf-ball that could hit the optical equipment that is necessary to see the ball.

After writing all this I could imagine another scenario.

We increase the speed of the kicker/chipper accelerated golf-ball to the 2 m/s, measured with a 20cm ramp.

And than we have the technical challenge to chip a ball trough a window.

If we have a kickoff point 10cm away from the window an have a window that starts at a hight of 2cm and ends a a high of 10cm we can assure that it is a real chipping without encouraging the teams to have a 45 degree angle an so we could restrict the chipping hight to lets say 8cm to protect the robots sensitive area.

This technical challenge chipping window is easy to build and a real innovation without producing to many other problems.

What do you think about it?

Let me ask a pointed question: Is there any point in chipping unless you lob the ball up and over an opposing robot? If I was in a team I would consider shooting the ball at the other bot in a slightly higher place a waste of time.

I think that is a big ask for teams - building something mechanically complicated that serves no tournament purpose on short notice is hard. But I would argue having a discussion going and teams thinking about the options is already a great result of having it mentioned in the rules.

The ramp only works if the ball reaches its highest point while on the ramp - otherwise on the ramp/not on the ramp tells you nothing about the amount of kinetic energy. If anything we’d probably need the optical

I have a couple thoughts:

  • usable kicker needs to be able to go above a robot
    • this makes handles a concern, if I was a team my handle would become a big cylinder so nobody kicks over me
    • this makes the occasional ball going out of the field a (safety) concern
  • Even non-chip-kick can get a ball over wall height, I have done it with my hand, the golf ball gets an upward speed from the ramp-wall-setup if you bounce it of the wall hard-ish - although it at least bounces back into the field
  • If I’m right about having to kick over other bots not to be pointless we need a safe way to allow high kicks
    • I remember from the little ball sports I did that straight at you is worst: High speed meets short reaction time. So I’d argue for >45° if not >60° chip-kick angle at least: makes the ball spend a bit of time at the top of the parabola for people to react before it hits them
    • At max. ~2.5m horizontal distance for a kick horizontal speeds teams want to have limit themselves due to minimum flight times if bots must to kick “more up than forward”
    • Do we need to put plexiglass roofs on goals or do we score goals for kicking really really well and making it in up there?
  • 48V is the globally valid max. voltage before high voltage safety applies (automotive industry uses this)

Having seen the games in Bangkok I changed my mind in kicker/chipper concerns and I absolutely agree with David.
I think a slightly higher kicker power would be a good way to improve tactics over pure robot speed.
But chipping needs far more kicking power and causes more trouble than benefit on this small field, as David pointed out you need the power to chip over 18cm high to overcome the other robot and on this small field it would need a chipping angle of far more than 45 degrees. And I actually do not want to see golfballs flying around hitting cameras and people. This would only lead to a new restrictions in the following years rules.
So I suggest to limit the power to kick/chip to something measurable.


Kicking power restrictions adapt to more power:
lightweight is fine
open: increase the kicking power and have a new measure:
Kick in one corner of the field - the golf-ball must not touch the opposite corner of the field.
This is easy to measure and depends on the field itself. So a “slow” carpet allows slightly higher power than a “fast” and “flat” carpet. So teams have to adopt the power on every location, what they do anyway.

This is from following post 2022 World Championship is over by @stiebel

We tested this today with an selfbuild solenoid with an 4S Lipo Battery Pack. It would have to be less powerful than a shoot with the ramp. So in my opinion, this wouldn´t change anything.

Hi everybody,

we came up with an idea we’d like your help with: We are considering (description is in the current draft, see here for PDF making the kicker test an on-field test where the robot gets placed on the back wall of one goal, kicks towards the other goal and permit what ever kicker power it takes for the ball to go to the opposite goal, bounce off the back and return to where the penalty area that the kick came from starts (or, if that seems like too much the ball may just be allowed to return to the center line or maybe would have to stop inside the opposite penalty area after bouncing from the back of that goal.

What do you think?

  • Go with the new idea
  • Keep the old rules
  • Make small changes to the new idea (post changes below)
  • Do something very different (post ideas below)
  • I have an idea for LWL (post idea below)

0 voters

If any of you can turn up your kicker device to have enough power to go to the maximum allowed power by the new rule and film the result so everyone can get an idea what ball speeds to expect. If you can then turn the power down so the ball only comes back to the center line and turn it down even more so the ball remains inside the penalty area after bouncing back that would be great to see as well.

This change is just for Open League (Golf Ball) as with in Lightweight League we need to handle the expensive infrared balls with care. If you have any ideas how to measure a higher (but not too high) amount of kicker power without building a giant hard to handle ramp please suggest them below.

Best Regards

We tested this today with an selfbuild solenoid with an 4S Lipo Battery Pack. It would have to be less powerful than a shoot with the ramp. So in my opinion, this wouldn´t change anything.

Thanks for this test!
So we need to think about another testing device…

in lightweight the ball is large an heavy. We saw lots of teams not even manage to kick the ball to maximum allowed height of the testing device. So in my opinion we could stick to the old rules in LWL

Open: a “bouncing rule” heavily depends on the ball !
We dropped balls to the floor and saw re-bouncing results form 30% height to 80% height depending on the ball. So if we use a “bouncing rule” we need to have a worldwide accessible golf ball for training.

What about a ramp, but not in front of the robot but to be placed in the opponents goal.
This would have to have a plain and wide ramp side, but you could provide the pcb files for such a ramp and every team could get their ramps build by pcb-board manufactures for less then 10$ each.
Using a thinner material (like 1mm instead of 1.6) and a less steep angle this could be a good possibility in my opinion.

Greeting Roland

Thinking about it, forget what I just wrote.
The kicking device must be adjustable anyway.
So it doesn’t matter if the ball bounces in a different way at home.
As long as every robot gets tested with the same ball at the tournament, Davids method is fine.


That is indeed a lot of variability and would require to have large power reserves in case the ball was less bouncy which would not necessarily be a problem but it would also change gameplay significantly depending on what ball is used.

In conjunction with the field enlargement the part of the rear side ramp that gets removed to place the goal could be cut down to fit inside the goal and serve this purpose. The question would then become if that is enough kicker power to make the kick more widely used.

That is where any teams that could provide a video of what a kick that distance looks like would be super valuable.

It would be consistent within a tournament but some degree of consistency between tournaments is also desirable, if some balls bounce twice as hard as others we should probably take that into account.

The 2023 rules (final version out now now contain the aforementioned kick-bounce-return measurement scheme. We will have to see how it plays out in practice and maybe tune how far the ball is allowed to bounce back for 2024 if it’s either a bit too much or too little.

Best Regards