Legality of Downwards-Sloping Ramps

[Alan Anderson]

Originally Posted by Rick TYler

You all know that the season is over...?

"The" season? As one season ends, another begins. Lots of teams will be playing Logo Motion again before the next build season starts. Some of those games will have inspectors checking to make sure robots are still within the rules.

[bduddy]

Originally Posted by Chris Hibner

I'm not sure what you mean - could you please explain that.

I think what he's trying to say is that the minibot falling is illegal, or at least those are the implications of what he is saying. I maintain that this is ridiculous...

[Basel A]

Originally Posted by Chris Hibner

I'm not sure what you mean - could you please explain that.

With a downwards-sloping ramp, there are presumably 4 minibot energy changes (ignoring friction). Two kinetic increases, the downwards part of the ramp and the usage of the motor, and 2 decreases, going up the ramp and going up the pole.

You say that in net terms, the upwards part of the ramp outweighs the downwards part, but it's not about net change. To be purely technical, some of the kinetic energy from the downwards slope could be used going up the pole, just as some of the motor's energy is expended going up the ramp.

While the ramp doesn't give the minibot a positive net change in kinetic energy, that doesn't mean all the energy used to ascend the pole comes from the battery, which makes the downwards-sloping ramp presumably illegal.

[Jared Russell]

Originally Posted by Basel A

You say that in net terms, the upwards part of the ramp outweighs the downwards part, but it's not about net change.

Yes, it is. Energy is a quantity. You can't attribute specific moments in the minibot climb to specific Joules of energy from one source or another - it only makes sense to talk about energy in a net sense. And a downward sloping ramp with a higher "exit" than "entrance" is a net energy sink to the minibot, just as a level ramp is...

Ramps have some obvious and not-so-obvious advantages for minibot deployment. But energy (kinetic + gravitational potential) at the end of the ramp vs. the start is not one of them. (Now start talking about how the rate of energy conversion - power - of a DC motor varies with load/speed and you'll be on the right track).

[Kevin Sevcik]

Originally Posted by Jared341

Now start talking about how the rate of energy conversion - power - of a DC motor varies with load/speed and you'll be on the right track.

Which is the point of all ramp systems, really. It lets the minibot accelerate to or above the peak power point without struggling against the pesky foe gravity. Or so I imagine your thinking goes.

I think there's another contributing factor, however. Without gravity reducing your acceleration, the minibot comes up to speed much more quickly and spends much less time in the low-speed/high-torque operating area that makes it more likely you'll exceed your available traction and spin out. You also have more downforce from the minibot weight to increase your available traction. And you ultimately have control over your actual traction surface. I don't think I noticed any teams doing it, but you could design your ramp with a very thin coating of grippy material. That would give you the chance to really maximize your traction.

Basically, I think ramps are faster mostly because the minibot accelerates to operating speed faster and more efficiently thanks to no gravity and less wheel slippage.

[Chris Hibner]

Originally Posted by Kevin Sevcik

I think there's another contributing factor, however. Without gravity reducing your acceleration, the minibot comes up to speed much more quickly and spends much less time in the low-speed/high-torque operating area that makes it more likely you'll exceed your available traction and spin out.

Not only that, but you can argue that by spending less time in that pesky area of low-speed/high-torque, it also creates much less heat in the motors, keeps the internal resistance low, helps keep the battery voltage at that just-charged sweet spot, etc.

[jvriezen]

One thing I haven't seen addressed here, (at least not explicitly) is the following:

Consider a ramp that is horizontal, with an upward slope near the pole. Now, if the MB is initially stationed on the horizontal, and drives the ramp under its own battery/motor power, I see no problem whatsoever. However, if the host bot pushes, or propels the MB across the horizontal, then the HB is, in effect, providing energy to climb the pole. In fact, you can imagine (as was mentioned earlier) a HB that 'shoots' a MB horizontally which then is diverted up the pole and triggers without even having a MB battery or motor. Clearly illegal.

I would contend that if the HB provide impulse to the MB in anyway then the MB better not have any 'ramp' like device to steer the MB kinetic energy into upward direction. This technically would include kinetic energy from deploying the instant the HB reaches the tower base, because the drive motion of the entire HB+MB system will be giving the MB kinetic energy.

Our robot used surgical tubing to launch the MB horizontally to get it to the pole, but because there was no ramp involved, no problem. The MB literally made a 90 degree change in direction upon reaching the pole.

I would also contend that any ramp system where the HB does not 'launch' the MB, but the MB COG is higher at its start than at END OF DEPLOYMENT is getting some vertical gain outside of that provided by the battery.

[Ether]

Originally Posted by jvriezen

One thing I haven't seen addressed here, (at least not explicitly) is the following:

This has been addressed here explicitly.

Consider a ramp that is horizontal, with an upward slope near the pole. Now, if the MB is initially stationed on the horizontal, and drives the ramp under its own battery/motor power, I see no problem whatsoever.

The problem is Rule <G19>, which is quoted for your convenience in the original post in this thread. Read the highlighted part.

[jvriezen]

Originally Posted by Ether

This has been addressed here explicitly.



The problem is Rule <G19>, which is quoted for your convenience in the original post in this thread. Read the highlighted part.

I stand corrected. I see now that the horizontal kinetic energy in the MB gained while outside the deployment cylinder is above and and beyond the energy provided in the battery, and incidental motor/wheel rotation.