Legality of Downwards-Sloping Ramps

Excellent post Kevin. Reps to you.


I guess as long as the minibot’s starting position on the slope is lower than the end of the ramp on the deployment end, there isn’t a net gain in energy, so it skirts around the rules.

It seems like the slope just gives the motors a break, they aren’t exactly the best so it’s a good idea to have them run as little resistance as possible before running up the ramp and pole.

I’d call it legal, but there’s a lot of illegal things I’d try to call legal too :smiley:

One thing that I haven’t seen mentioned is that there are two fundamental parts to a ramp: the downward sloping part that gets the minibot to the pole, and the upward sloping part that transforms the horizontal movement into vertical movement. I think they have been regarded as the same, but they should be regarded separately.

The downward sloping part should be considered legal, I think. Energy-wise, it’s no different from storing the energy in a spring, or however else you’re getting the minibot to the pole. A downward sloping ramp with a horizontal end seems perfectly legal to me.

The upward sloping part is the part that transforms any horizontal momentum into vertical momentum, and this is the part that I think is illegal. This is the piece that separates “Energy for vertical movement” which is forbidden in G19 from energy for horizontal movement, which is necessary to get the minibot to the pole.

I hope there’s no flaw in my logic.

Nope, not quite.

Minibots are to use only the power in the battery, delivered through the motors. Springs (for traveling along the pole) would be considered illegal, for example–though certain types of springy material could be used for latches. So the downward portion would be illegal–gravitational potential energy is not listed as a legal minibot upwards power source (though it’s the primary method for getting down).

With respect to the second part of your argument (upward ramps), there are actually 2 holes. The first is that ramps were considered legal at multiple events. Translation: either multiple inspection and ref crews really screwed up, or there’s a legal way to do it.

The second is this: Power for vertical motion only comes from that battery, through those motors. The fact that it starts out horizontal does nothing to the motors providing all of the vertical motion. Somehow, that horizontal motion gets converted to vertical–in this case, by a stationary part of the hostbot that the minibot runs on.

In other words, it’s precisely because the minibot is supplying all of the energy that the upward ramps are legal, and because it is not supplying all of the energy that the downward ramps are illegal.

We should keep in mind in your examples, practical implementations for weight and size which plays heavily on the actual advantage gained. Also it should be noted that the GDC did allow motors to be running throughout the match if a team wanted to use that approach. (Q&A 2/1/2011)

He was using hyperbole in those examples to make a point. He clearly stated that:

Kevin addressed the above point in his post:

G19 etc. state that the minibot must move up the pole with electric energy provided by the battery AFTER deployment. Deployment starts when the minibot crosses the cylinder. Ergo, any ramp system where the minibot starts a significant distance away from the cylinder is putting significant energy into the minibot system before deployment starts. It’s kinetic energy stored in the inertia of the battery and frame,

Rule allows the minibot to store up kinetic energy in its spinning motors and wheels prior to start of deployment. That is a separate question from using those running motors to store up kinetic energy in the body of the minibot prior to start of deployment; a point which GDC did not clarify when asked, and which is at the heart of much of this discussion.


You all know that the season is over and that there are other more deserving expired horses to beat, right?

Like what, for example? :slight_smile:


I think one point to be made is that even if there is a positive change in net gravitational potential energy, any decrease that is converted to vertical kinetic energy is still illegal.

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

“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.

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…

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.

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).

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.

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.

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.

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.


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.