Two kinds of repulsor drives?

The Silence and I · Post by **The Silence and I** » 2004-09-11 04:39pm

I was lying in bed thinking about getting up this morning when I mentally went over the pod race in TPM. I started thinking back to the moment when Anakin guns his engines to pass over a contestant at the place the track drops into a steep narrow gorge and something hit me: The pods don’t seem to use repulsor lift as it is described in many sources, that being anti gravity. When the pods passed over the cliff edge, their flight path was purely ballistic right up to the point when they reached the floor of the gorge where they decelerated sharply as if landing on a cushion.
This effect can be explained; design specifications might call for a creation of this effect as a part of the racing rules, but pod racers will do questionable things to get an advantage—add flame throwers, for example—I would think it an easy modification to have the repulsor simply maintain a particular altitude, say when you are about to pass a cliff. A pilot above the gorge could simply gun the engines and bee line for the next phase of the race, particularly if he knew where the check points (if any) are located.
Exploitable? Maybe, maybe not, but there are other uses for such a capability: if you are many meters in the air and stalling (Anakin’s tech-savvy might easily allow him to change the altitude of the repulsor drive when he risked falling to a not so pleasant end), or even something as simple as pulling up and getting above your opponent if he is trying to push your pod into a wall.
These observations suggested to me that repulsor drives on some small craft like pods or speeders (perhaps not swoops, or for that matter the cars on Coruscant) operate something like a modern hovercraft, only with force fields instead of air cushions. Lucas jokingly called the old orange blur under Luke’s speeder a “force field” and his vehicles do in fact move as if they are sitting on such a thing. This “variation” is seen mostly (if not solely) on Tatooine and may have something to do with the backwardness of the planet—for example a purely anti gravity drive will not care about the height of the local terrain, if you are set for 30 m above sea level and try to navigate a hill 35 m up, you will plow into the dirt. To get around this you need sensors that can accurately determine the local terrain features and adjust the drive accordingly…not hard to do with Star Wars tech, but perhaps hard to come by and maintain reliably on Tatooine.
Is this a valid observation? Flame away!

Praxis · Post by **Praxis** » 2004-09-11 05:09pm

I've always thought repulsors worked this way- they keep you a certain distance above the ground. Observe, the Podrace, Jabba's skiffs and sail barge (always the same distance above the ground), and the way almost every floating vehicle in Star Wars behaves.

The Silence and I · Post by **The Silence and I** » 2004-09-11 05:35pm

Yeah, that is what many to do*, but they go about doing it in a strange way: Speeders and pod racers on Tatooine have an all or nothing effect, that is, if a speeder drives over a cliff, it will drop like a stone until it approaches the bottum, where it declererates quickly to its normal position. (About Jabba's barges, I don't have ROTJ with me, so I cannot be certain how they act, I recall them following the contors of the ground, but don't quote me on that.) A true anti grav device would allow, even favor, a gradual, controlled drop. What we see is akin to turning the drive off and suddenly switching it back on a few moments later.
The need for dedicated sensors to help make sure the craft stays at the right distance is icing on the cake, I think, as many speeders on Tatooine barely go from A to B, complex sensors would beg to fail, leaving you in a spot o trouble.
What I see is readily explained by a hovercraft approach, but to get anti grav to work you have to introduce various other factors.

* To the best of my knowlege, all repulsor craft fall into one of two categories: The type mentioned above, including Federation Tanks, land speeders, pod racers and possibly Jabba's barges, and true anti grav, including Dooku's Swoop, cloud cars, Coruscant cars, remotes, Gun Ships at Geonosis etc which do not follow ground contors. Rather, they pick an altitude and stick with it, acting in every sense like an airplane today (except often they lack airfoils, thus proving they have repulsor tech)

Praxis · Post by **Praxis** » 2004-09-11 06:44pm

The Silence and I wrote:Yeah, that is what many to do*, but they go about doing it in a strange way: Speeders and pod racers on Tatooine have an all or nothing effect, that is, if a speeder drives over a cliff, it will drop like a stone until it approaches the bottum, where it declererates quickly to its normal position. (About Jabba's barges, I don't have ROTJ with me, so I cannot be certain how they act, I recall them following the contors of the ground, but don't quote me on that.) A true anti grav device would allow, even favor, a gradual, controlled drop. What we see is akin to turning the drive off and suddenly switching it back on a few moments later.
The need for dedicated sensors to help make sure the craft stays at the right distance is icing on the cake, I think, as many speeders on Tatooine barely go from A to B, complex sensors would beg to fail, leaving you in a spot o trouble.
What I see is readily explained by a hovercraft approach, but to get anti grav to work you have to introduce various other factors.

* To the best of my knowlege, all repulsor craft fall into one of two categories: The type mentioned above, including Federation Tanks, land speeders, pod racers and possibly Jabba's barges, and true anti grav, including Dooku's Swoop, cloud cars, Coruscant cars, remotes, Gun Ships at Geonosis etc which do not follow ground contors. Rather, they pick an altitude and stick with it, acting in every sense like an airplane today (except often they lack airfoils, thus proving they have repulsor tech)

How do we know that (for example) Dooku hadn't just been slowly increasing the altitude his repulsors were set to?

The Silence and I · Post by **The Silence and I** » 2004-09-11 06:52pm

Uh, I would say that is exactly what he was doing, as I placed his craft in the anti grav category. Meaning he has to increase the altitude setting if he wants to move up over something.
What was that supposed to point out (honest question, no offense)?

Praxis · Post by **Praxis** » 2004-09-11 08:41pm

Then it would be in the same category as the Podracer, no?
My point was that the Podracer is antigravity, just always set at a certain height.
Dooku's ship was constantly increasing the height.
I think they're all the same type, just with different settings (variable height, constant height).

Stark · Post by **Stark** » 2004-09-11 10:00pm

Its probably just a minor difference; for 'hover' vehicles, the system just keeps altering the repulsors to hold the vehicle steady at whatever height, while you 'drive' it like a car, but the flying ones have a different system which allows proper pitch/yaw/roll control and independent altitude control.

Winston Blake · Post by **Winston Blake** » 2004-09-11 10:32pm

The OT ICS says "Repulsorlift airspeeders and other such ground based craft are strictly limited in the altitudes they can reach, with most speeders offering only 2-50 metres of "float". Flight-grade repulsorlifts can carry a vehicle to suborbital altitudes, but only true spacecraft employ these powerful devices."

I think the idea of repulsors must have been inspired by the idea of a magnetic-like repulsion that acts against any matter. It's intuitive for landspeeders and podracers to act like they're on a 'cushion' if you think of it like that. However, when you look at TPM with Qui-Gon and Jar-Jar getting run over by an MTT, it looks like even the category of 'ground-pushing repulsors' are actually 'fixed altitude repulsors' (as in and Coruscant's overlapping skylanes) but with a very low flight ceiling.

So no, i don't think there's two kinds of repulsor drives.

Old Plympto · Post by **Old Plympto** » 2004-09-11 11:13pm

In the establishing shot of Dex's Diner, if you take a look at the right, you'd see the speeders that zip along the road past the diner fly over a cliff and immediately become one of the high altitude traffic lines. I used to think the high altitude speeders were of a different class of vehicles than the landspeeders, but this caused me to think otherwise.

If the speeders were keyed to fly at say 1.5 meters off the road, how it is suddenly able to switch over to 1 kilometer altitude without skipping a beat? Sensors that switch the altitude range? Or local transceivers that change the speeders' setting as they leave one area and enter another?

Winston Blake · Post by **Winston Blake** » 2004-09-12 12:54am

Old Plympto wrote:If the speeders were keyed to fly at say 1.5 meters off the road, how it is suddenly able to switch over to 1 kilometer altitude without skipping a beat? Sensors that switch the altitude range? Or local transceivers that change the speeders' setting as they leave one area and enter another?

I see it as being keyed to fly x meters from the center of gravity of the planet, with sensors that bob you up and down so you don't crash into stuff.

Actually i've found a slight problem with the 'one type' hypothesis. Under the Coruscant Taxi entry in the TPM ICS it says "Side-mounted, low power repulsors prevent collision and cushion docking". This really suggests 'matter pushing' repulsors, and kinda makes the MTT in TPM look odd.

The Silence and I · Post by **The Silence and I** » 2004-09-12 04:44pm

Praxis wrote:Then it would be in the same category as the Podracer, no?
My point was that the Podracer is antigravity, just always set at a certain height.
Dooku's ship was constantly increasing the height.
I think they're all the same type, just with different settings (variable height, constant height).

My point was if the pod racer is anti grav, and thus can arbitrarily change its height, why didn't Anakin use it to come out of his stall, why did no one take advantage of vertical movement? Why would an anti grav drive seem to shut off the moment you drive off a cliff, and suddenly switch on moments before impact? Why one static height above the ground? Surely there would be moments in a pod race where a slightly higher hover would be better (or lower)?

Winston Blake wrote:
Old Plympto wrote:
If the speeders were keyed to fly at say 1.5 meters off the road, how it is suddenly able to switch over to 1 kilometer altitude without skipping a beat? Sensors that switch the altitude range? Or local transceivers that change the speeders' setting as they leave one area and enter another?

I see it as being keyed to fly x meters from the center of gravity of the planet, with sensors that bob you up and down so you don't crash into stuff.

Actually i've found a slight problem with the 'one type' hypothesis. Under the Coruscant Taxi entry in the TPM ICS it says "Side-mounted, low power repulsors prevent collision and cushion docking". This really suggests 'matter pushing' repulsors, and kinda makes the MTT in TPM look odd.

(MTT?)
Well that looks like printed evidence (yay

) which is always good. I never said anti grav couldn't work much like seen on land speeders, if so used it should work just like you say. I simply observed that such a system would include potentially life-saving options and would likely act differently after clearing a cliff edge. With reliable sensors it would be superior to simple repulsion, which cannot save you from a long fall, but on Tatooine reliable sensors may be rare.
Another reason to use a simple repulsion system: hovering battle tanks/other vehicles (like in TPM), sophisticated sensors are not known for ruggedness, and the last thing you want to fail on a battle vehicle is its mobility. A jarring impact might disable sensors, and without them, you lose a lot of mobility, being forced to use the Mark I Eyeball, necessitating a slower speed. Meh, got to go do homework now.

Winston Blake · Post by **Winston Blake** » 2004-09-13 03:53am

The Silence and I wrote:
Winston Blake wrote: I see it as being keyed to fly x meters from the center of gravity of the planet, with sensors that bob you up and down so you don't crash into stuff.

Actually i've found a slight problem with the 'one type' hypothesis. Under the Coruscant Taxi entry in the TPM ICS it says "Side-mounted, low power repulsors prevent collision and cushion docking". This really suggests 'matter pushing' repulsors, and kinda makes the MTT in TPM look odd.
(MTT?)...

Multi-Troop Transport, the big elephant-like vehicles in the scene where all the trees and undergrowth is getting run over. As a land-sppeder-like craft (rather than a flight-repulsor-craft), i would have expected that MTT to have crushed Qui-Gon and Jar-Jar.

I don't get it. We have examples of pseudo-magnetic cushioning and examples of reactionless propulsion but that MTT is messing up my ideas.

Spanky The Dolphin · Post by **Spanky The Dolphin** » 2004-09-13 03:58am

Perhaps it's a focus thing.

Winston Blake · Post by **Winston Blake** » 2004-09-14 03:57am

Spanky The Dolphin wrote:Perhaps it's a focus thing.

I don't understand what you mean by that. Can you please explain a bit further?

The Silence and I · Post by **The Silence and I** » 2004-09-15 11:13pm

Perhaps he means pressure; the MTT weighs some (presumably) large amount but depending on how much area the repulsor covers, the force delivered to Qui Gon and Jar Jar may not be enough to cause injury. I've not done any calcs, but will watch that scene in a few moments and repost once I've some better idea.

Edit:

Linky

Linky II

Using these rough and dirty sketches I can guesstimate Qui Gon as being ~6 ft, then the whole transport is ~24 ft tall, or ~7.4 meters. It is also ~16 ft wide or ~5 meters. Based on eyeball conjecture with no basis in hard math it looks like the transport is 1.3 times longer than it is tall, therefore it could be about 31 ft or about 9.5 meters long.
This is at best informed conjecture, but I'd say a surface area at the bottum of roughly 47.5 m^2...
Now, the really not precise part: how heavy is this transport?
It's big, much bigger than any tank we have; I think 100 tons is not unrealistic, trouble is, no matter how off my area is, it can't make ~20,600 N/m^2 go away.
Basically, because it is very big, it is probably too heavy to allow a human to be under it unharmed; unless it is much lighter than I think (possible, it is hollow) or the repulsor has an area wider than the bottum of the vehicle.
Additionally the grass under the transport did not flatten as one might expect, Qui Gon's hair reacted violently as if a lot was happening-despite the slow velocity-but even Jar Jar was able to raise his head while under the MTT.

That said, looking at his face Qui Gon seemed very focused--he did not move at all and *could* have been exercising the force to protect himself and the idiot native he ran into.

Edit Two: (If no one responds after this I will stop bumping, honest!)

Going to sleep I realized I had missed a few important things above; that being the relative area of a human body, and how many newtons to a kg...silly little things, but any way.

See Linky

For diagram illustrating how the human body presents roughly 0.65 m^2 in the position Qui Gon was taking; I again assume he is 6 ft tall, or 1.82m. Qui Gon may be thinner than this illustration, but it is rough enough to begin with, using simple polygons, so any errors from relative body type are going to pale next to my method of measurement. Regardless, the point is Qui Gon should have presented less than a m^2 to the repulsor field.
For this 100 ton MTT (does anyone have a more firm figure than this?) that means--using .65 m^2--Qui Gon had to sustain some 13000 N, or about 1.4 tons of force. Something the size of a head would be pushed with some 1500 N or 150 Kg.
This is survivable, (I think) but too much for Jar Jar to lift his head and look around. But I think this scene is much closer to allowing a matter repulsor type drive than I originally thought. Being hollow the MTT may be lighter than the number I used, but more specifically, it is very tall, and unless the repulsor field is spread out somewhat beneigh it I think it would be dangerously unstable. More area obviously means less pressure, but most importantly, Qui Gon could have been using the Force under the MTT.

Meh, I get the feeling no one want's to discuss this...

Anyone have thoughts? Maybe there is another explanation? I'm all alone here!!!

The Silence and I · Post by **The Silence and I** » 2004-09-16 04:24pm

Of course silly me thought an edit would bump the thread, of course it didn't so here it is, the official BUMP!

Warspite · Post by **Warspite** » 2004-09-16 04:34pm

By the ICS, air is blown through grilles bellow the MTT (named "repulsor gas cooling system exhaust), hence why the grass and Qui-Gon's air was all over the place.

AS for stats:

Lenght: 31m
Height: 13m
Max. Ground Speed: 35 kph
Max. Lift Altitude: 4m