Rule 3.b.: 3.500kg and 5.000kg measurements

[gmatyja]

We're preparing for the new season, and our team is considering signing up to be event supervisors at a few tournaments for Air Trajectory B. We've noticed the 5.000kg mass limit seems rather specific. In the past years, have teams teams brought masses to tournaments near the 5.000kg limit? What is the appropriate grade of scale and calibration that should be used?

[bernard]

I prepare my setups so that if a device is over a requirement, there is no question about it being over. Target locations will be as precise as humanly possible, but device squares may. be a millimeter or two over so that if a device doesn't fit, it's without question too large. With scales and timing devices, you can consider the precision and accuracy of your device as well as what you might allow. I might have a scale that reports to 0.1 g but how much should I trust the number it displays? Did I calibrate my scale to a 5,000 g? I certainly don't expect teams to be calibrating their scales and realize the error in my or their scales, so I might allow 0.1 g, 1 g, 5g, or 10 g of forgiveness depending on all the factors—magnitude of the measurement, my equipment, and effect on performance in the event. That way if a team's mass reads 5.015 kg, it's more likely than not out of spec. If it's 5.001 kg, I'll probably allow it with a warning for future tournaments—it's a gamble between a marginal advantage and a very high penalty.

[gmatyja]

Is there any guidance on who will be placing the participants' masses on the scale? Are the masses exempt from the principle that only the participants should be touching or manipulating the devices?

[bernard]

Is there any guidance on who will be placing the participants' masses on the scale? Are the masses exempt from the principle that only the participants should be touching or manipulating the devices?

Handling any part of a participant's device risks damage of their device by your hand. I allow participants to place objects on the scale. If I believe adjustments need to be made for an accurate weighing, I advise them of what needs to be adjusted.

[knightmoves]

I prepare my setups so that if a device is over a requirement, there is no question about it being over. Target locations will be as precise as humanly possible, but device squares may. be a millimeter or two over so that if a device doesn't fit, it's without question too large. With scales and timing devices, you can consider the precision and accuracy of your device as well as what you might allow. I might have a scale that reports to 0.1 g but how much should I trust the number it displays? Did I calibrate my scale to a 5,000 g? I certainly don't expect teams to be calibrating their scales and realize the error in my or their scales, so I might allow 0.1 g, 1 g, 5g, or 10 g of forgiveness depending on all the factors—magnitude of the measurement, my equipment, and effect on performance in the event. That way if a team's mass reads 5.015 kg, it's more likely than not out of spec. If it's 5.001 kg, I'll probably allow it with a warning for future tournaments—it's a gamble between a marginal advantage and a very high penalty.

Thanks, Bernard, for some wonderful common sense!

I'd guess most ES will use the same scale for this as they'd use for weighing the sand for the balsa event - a scale that weighs to 20-30kg, and reads 1g precision. And I'll bet almost none of them have a suitable set of calibration weights.

And whilst I applaud Bernard's approach, I'd caution people that not all ES will follow his example. You'll find plenty of people who will say "the rules say 5.000kg, which means not more than half a gram over 5kg as measured by my scale. So I'd advise people to go deliberately underweight by 10-20g, to accommodate uncertainties in an ES's scale.

[Suhrit]

Hello,

I was wondering if i can bring a bike pump outside of the launch area to power my pneumatic piston?
I was thinking of using my pneumatic piston to release a weight that drops on an air chamber to launch the ball.
Is that against any of the rules?
Also does the pneumatic cylinder and the bike pump count as part of the 5 kg for Div B because it is not powering the device directly.

Thank you

[knightmoves]

You want to use the piston and bike pump as a trigger device? No air connection between the bike pump and the launch mechanism?

There is no reason you shouldn't use a pneumatic trigger device. It would be an unusual choice, but the rules do not prohibit it. Note that bike pumps don't usually have a long enough air hose to have your entire body safely outside the exclusion zone when you launch.

Your trigger device cannot contribute any energy to the launch, but if all you do is operate a pneumatic piston to release your weight, then you should be OK.

[redscience]

I have a related question about the measurement of the falling mass.

Do all the parts of the falling mass need to be removeable for weighing or can one or more parts remain attached to the assembly as long as they can be weighed as a combined unit with a spring balance to prove that they are within 5.000 kg?

In our case, the ‘falling’ mass is 3 parts, A,B,C. A and B are attached to the air chamber to provide a platform for putting additional removeable weights (C) and also to seal the air chamber between A and B. Our team can weigh A+B+C using a spring balance and demonstrate that it is within weight limits. However, we can’t remove A&B from the assembly to weigh. Our team would love a clarification so we can move ahead with further improvements to our build and prepare for competitions ahead.

Rule 3.b says
3.b. The launching force must be entirely supplied by gravitational potential energy from a falling mass less than or equal to 3.500 kg (Division C); 5.000 kg (Division B). Any part of the device whose potential energy decreases and provides launch energy is considered part of the mass, with exception of items of nominal mass such as strings and thin membranes/plastic container walls. The falling mass may consist of discrete parts, which together count as the total mass

Based on that, our understanding is that in our case
* All three, A,B,C consist of parts that provide the potential energy
* All discrete parts A,B,C need to be accounted for for total mass <= 5.000 kg
* It doesn’t stipulate how the masses can be measured, or that they have to be disassembled for measuring.

[SPP SciO]

I have a related question about the measurement of the falling mass.

Do all the parts of the falling mass need to be removeable for weighing or can one or more parts remain attached to the assembly as long as they can be weighed as a combined unit with a spring balance to prove that they are within 5.000 kg?

In our case, the ‘falling’ mass is 3 parts, A,B,C. A and B are attached to the air chamber to provide a platform for putting additional removeable weights (C) and also to seal the air chamber between A and B. Our team can weigh A+B+C using a spring balance and demonstrate that it is within weight limits. However, we can’t remove A&B from the assembly to weigh. Our team would love a clarification so we can move ahead with further improvements to our build and prepare for competitions ahead.

Rule 3.b says
3.b. The launching force must be entirely supplied by gravitational potential energy from a falling mass less than or equal to 3.500 kg (Division C); 5.000 kg (Division B). Any part of the device whose potential energy decreases and provides launch energy is considered part of the mass, with exception of items of nominal mass such as strings and thin membranes/plastic container walls. The falling mass may consist of discrete parts, which together count as the total mass

Based on that, our understanding is that in our case
* All three, A,B,C consist of parts that provide the potential energy
* All discrete parts A,B,C need to be accounted for for total mass <= 5.000 kg
* It doesn’t stipulate how the masses can be measured, or that they have to be disassembled for measuring.

Rule 2.b. says, "The device must be impounded with the mass(es) detached," so I don't think that plan will work. Plus, the ES will insist that everyone's mass is measured on the scale they provide, and wouldn't allow you to use your own scale to demonstrate.