Springs?? (10 lbs. at 22 ft/s)

Does anybody know if there is a kind of spring with enough force to fire 10 lbs. at 22 feet per second? If so, where is the website? Thank You.


  • Renton Coil Spring (where I work)

They specialize in high performance materials and applications, titanium and steel for aerospace, nascar, nhra etc. I doubt you would be able to get anything sub 500$ though as it is a job/specialty shop :confused:

Seems like a garage door spring or something similar could get you in the right ballpark but for that much force and acceleration the systems would be come quite scary and heavy!

Find one of those playground toy springs :slight_smile: You could look into gas springs, but I think generally they will be slower than you are looking for. Maybe with a lever or other way of adjusting speed/force.

I’ll do the calculations for you, but you should be VERY careful about launching a 10lb ball at such a speed. FIRST may deem it a safety hazard.

You want to accelerate 10lbs to 22 ft/s. The potential energy stored in a spring is .5kx^2, where k is the spring constant (basically, the stiffness of the spring) and x is the deformation or extension of the spring.

10lbs traveling at 22 ft/s means a kinetic energy of .5mv^2, or 102 Joules (after conversion to SI units). Thus, you need at least 102 Joules of potential energy from the spring.

There are two ways to do this - either get a higher spring constant, or compress the spring more. So for a given spring constant or compression, you can alter the other factor to yield the potential energy you need.

Now let’s look at McMaster’s website.

All you have to do is find a combination of spring constant (also called rate on some pages) and compression distance that work for you. There are plenty of options there.

I did the math assuming that you wanted to launch the ball at a 45-degree angle in order to maximize the ‘sweet spot’ for shooting, and found that the spring requirements are unreasonable. (From the floor to over the overpass was 221 J not including losses due to the game happening in real-life as opposed to a physics classroom – the spring constants needed were huge.)

The other problem is that you cannot transfer the energy fast enough to launch the ball without running awry of the safety requirements.


emphasis added …

I am curious where you located any specific “safety requirements”, and what the defined limits are?

I wouldn’t advise using a 45 - the force required is nuts and if that device fails it could potentially hurt someone. We thought about a garage door spring as well but those are dangerous - people have gotten cut badly by them.
60 is a little steep but you don’t need to spend so much energy in the horizontal if you fire your device while moving forward. You only need to get the ball up 6.5 + a little, you don’t have to clear the entire overpass.
Someone on here in another thread calculated an estimated 44.7% energy recovery on impact for a trackball. That’s just in estimate - but the ball should in theory bounce off the overpass rails if you get it up there.

Don’t take my words as your 100% valid source - the majority of the time I’m wrong. But in seeing my wrongs I learn.

I honestly think that 22 ft/s is way too fast. They limited AIM high balls to 10m/s which is 32 ft/s. That is for 6 inch poof ball of 3 ounces or so and the game was designed to shoot the ball. We are hurdling the ball. 2/3 of the speed for a ball that is 40 times the mass and about 7x the size. In addition, you cannot even begin to pull that back. The springs that could do that are car springs which are compressed by 500 pounds of force for a light car. The 2 inch cylinders can provide at absolute maximum 189 pounds ( and that’s not for compression!). You’d need 3 2 inch bore cylinders to do so. Even if you pull it back like this… they your not going to have enough air to do so. 189 pounds is at 60 PSI and your psi would significantly drop because the amount of air you would need.

I think we calculated it would take about 80 J to launch the ball over the overpass.

But we also assumed this would be an acceptable means of hurdling–could someone please explain their safety concerns, as specific rules apply?

We are NOT planning on using a metal spring, in case you’re concerned about that…

I think the concept of launching has many people in first worried. The calculations we did about launching a ball came out to be
65-75 degrees is the ideal angle, but you need something about 7.8m/s just to get the ball over the rack when ur 3 meters away from it. Something that fast in Very dangerous in the wrong hands :stuck_out_tongue:

There are no rules expressly mentioned that limit the amount of throwing force or the velocity of a launched ball.

If FIRST plans to add some they better do it quick…cause we’re launching and we’ve already started. :eek:

IMHO part of the intent this year is to have teams design all sorts of mechanisms that do their job safely.

If you want to launch you better have your ducks in a row when an inspector asks you to demonstrate its safety features.

If your mechanism is designed properly, then all of the stored energy will go into the ball. Hopefully the teams trying this will use a smaller force over a longer distance to accelerate the ball, which would mean that there really wouldn’t be any super fast moving parts if it fired while a ball was loaded. The real danger is if it fires without a ball to put all of it’s energy into, but hopefully teams will design safety features that will (mostly) eliminate this problem.

I really don’t see where the danger is if it’s working properly. A ball that was thrown over will hit the ground with about the same speed as a ball that was dropped over. Unless we should all be required to set the ball down on the ground for ultimate safety? :slight_smile:

I don’t believe the inherent danger is from the ball.
It is from the “cocked” mechanism.

If this mechanism is ready to shoot the ball…the mechanism, if tripped accidently, will impart the same force to whatever object or human body part is in it’s way.

Stored energy of any form can be quite a pain to deal with… no pun intended.

Here is the rule that I think is relevant to this discussion:

(R01) …… Teams must very careful when incorporating springs or other items to store energy on their ROBOT by means of part or material deformation. A ROBOT may be rejected at inspection, if, in the judgement of the inspector, such items are unsafe.

This gives the inspector considerable latitude in deciding the safety of the ROBOT.

Good luck to eveyone…

Hi Stu!!!

When you control the ball…you control the game… PELE

Exactly. The rules regarding safety are vague enough to give the judges/refs sufficiently leeway to keep us all safe – and that means you need to be really careful about putting that kind of load on springs.


I think that Most judges will allow robots to have “Springs” or other devices ont heir robot no matter what it is they do as long as it is confined and not able to dismantle another robot. Like if a robot had some device that shot 1+ feet in any direction thats outside of their starting box, they would probably deem it unsafe, especially if you need 7+m/s force to get a ball up.

I think the concept of launching has many people in first worried. The calculations we did about launching a ball came out to be
65-75 degrees is the ideal angle, but you need something about 7.8m/s just to get the ball over the rack when ur 3 meters away from it. Something that fast in Very dangerous in the wrong hands :stuck_out_tongue:
These numbers are similar to what we’ve come up with. I’m not sure where 22m/s came from…

From the rules:

CROSSING: The act of a TRCKBALL or ROBOT passing through the plane defined by a line (i.e.
LANE MARKER or FINISH LINE) when it is projected vertically upwards. A TRACKBALL or
ROBOT shall have CROSSED a line when all parts of the object, while traveling in a counterclockwise
direction, have completely passed through the plane.

and then contacts either the floor or another ROBOT before re-contacting the originating ROBOT.

Inherently, to hurdle one must also have a vertical projection on the ball. They have left the door open for teams to shoot the ball over the overpass. I think <R01> is there to ensure a compressed spring isn’t being held back by shoestrings or other objects that could easily release energy outside of the arena and really hurt someone. I do not believe it’s there to inhibit how you get the ball over the overpass.

You can’t be afraid to fail if you want to launch the ball. It’s a gambit, and the rules have technically left the option open for you. However, if you keep shooting balls out of the arena at refs, then perhaps they will deem your bot unsafe, but that’s your driver’s fault :wink:

22 ft/s is about 6 or 7 m/s

(English units vs. metric units)

Whoops :o

Well I guess it’s safe to say that the majority of us agree that any type of spring would be dangerous to use for this. The massive amount of force required requires a LARGE spring which are dangerous.

What I find interesting though is that so many people are getting different energy requirements for launching it though. I’ve seen numbers ranging from 5 J to 80 J. I know it depends on the angle but my teams estimated 7.5 J at 65 (I think degrees) is vastly different then then post above that gives that 80 J estimate.

If you figure that the mass of the ball is ~3.5 kg and you want to shoot it to a height of 2.5 meters (a little over 8 feet) then:

(3.5 kg)(9.8 m/s^2)(2.5 M) ~ 86 Joules

This is assuming that the horizontal componant of the balls velocity comes from your moving robot.

(posted by s_forbes on dad’s computer)

I believe you’ve misread the definition of CROSSING. For “it”, read “line”. The definition refers to projecting the line to indicate a theoretical flat surface through which a ball or 'bot will move. Imagine light shining straight upwards from the line. It’s not talking about throwing the ball.