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Old January 18th, 2003, 08:50 PM
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jfwking jfwking is offline
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Being a firm fan of vector/velocity based movements for ships I am planning on using such a system with an upcoming campaign. The rules in T20 are a little, erm, unclear on the subject so I am basicly going back to old rules for ship movement.

Question 1. What speed if any do people think is a safe or practicle maximum for space travel? A 1G ship that spends 60 minutes of constant acceleration can reach a speed of 45000 KPH. A 6G ship in the same time reachs a quarter million K per hour.

Question 2. Turning at speeds. I am looking at either speed/3 or speed/4 for the thrust needed to turn so a ship at speed 20 needs either 7G or 5G of thrust to turn a hex facing. I think this gives a good balance of manoverability to the high G ships while leaving the 1G merchants as lumbering around. Previous systems with half speed left ships far too unmanoverable in my opinion. Sugestions or ideas?

Question 3. Entering jump. A ship jumping at the end of a round cannot manover in any way as it must follow a precisely calculated course for the jump but what speed can it be doing. I prefer a slower speed, 10 or 15 hexes per round as the maximum for entering jump but I've not tried it before and as I am planning a ship combat heavy game I think it will happen. Any ideas on this one.

Helpfull advice or suggestions gratefully recieved.

Jim King
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Old January 18th, 2003, 11:24 PM
graden1 graden1 is offline
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Quote:
Originally posted by Captain Jonah:


Question 2. Turning at speeds. I am looking at either speed/3 or speed/4 for the thrust needed to turn so a ship at speed 20 needs either 7G or 5G of thrust to turn a hex facing. I think this gives a good balance of manoverability to the high G ships while leaving the 1G merchants as lumbering around. Previous systems with half speed left ships far too unmanoverable in my opinion. Sugestions or ideas?

Helpfull advice or suggestions gratefully recieved.

Jim King
Here's a reasonably "realistic" system I've used for movement in various space combat games. It gives results similar to vector-based systems, 'without all that tedius mucking about' with extra markers for previous/future positions.

1 hex = 10,000 km (15,000 for T20)
1 turn = 1,000 sec (1,200 for T20)
1g accel = 1 hex per turn

"Turn mode" = v^2/g; (v=velocity, g=accel)

This is just a basic calculation of turning radius, r=v^2/g. Each ship allocates its acceleration points at the beginning of the round, either to change its velocity (up or down), evasive maneuvers, or to change its heading. The "turn mode" is the number of hexes travelled between each 60-degree change in heading. A ship using all its acceleration to change course (but not velocity) ends up travelling in a circle with the calculated radius. (More like a large hex than a circle, really, but hey, it's a game, right?)

For a more "fast and loose" feel, add a ship's agility to its accel points, otherwise the "velocity squared" term in the turn mode equation makes it very hard to make large course changes quickly. On the other hand, it also makes for dramatic, short lived attack runs consisting of a single high-speed pass!

The hex size (km) and turn length (sec) can be re-calculated for any scale by choosing a turn length "S" and figuring hex size "H" = (S/10)^2.

This isn't a complete system by any means, but it's a good starting point, adaptable to many different games. I've used it often as a "fix" for games with broken space movement rules.

Hope you find this useful.

Thanx heaps,

DGv2.0
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Old January 18th, 2003, 11:45 PM
graden1 graden1 is offline
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Quote:
Originally posted by Captain Jonah:


Question 3. Entering jump. A ship jumping at the end of a round cannot manover in any way as it must follow a precisely calculated course for the jump but what speed can it be doing. I prefer a slower speed, 10 or 15 hexes per round as the maximum for entering jump but I've not tried it before and as I am planning a ship combat heavy game I think it will happen. Any ideas on this one.

Helpfull advice or suggestions gratefully recieved.

Jim King
The answer to this question I've most often seen (and used) is that momentum is conserved before/after jump. A ship leaves jump space with the same vector it had upon entering jump. This gets complicated because star systems can have large relative velocities. The big question is: How large, and in which direction? It's up to the referee/gm how much detail to use. I tend to randomize it, but if you're only dealing with a few systems, it might be worthwhile to have some data on their relative velocities.

The astrogator's goal, in most cases is to minimize travel time. So the ideal case is to go into jump-space with a vector which will minimize travel time from the "emergence point" to the ship's final destination. If the ship's point of origin and the destination system have a high relative velocity, this will have to be cancelled prior to entering jump space.

What this means is that the ideal velocity for entering jump will vary widely, depending on the situation. This brings us back to your original question: can a ship maneuver on the same turn it enters jump? In my games, I allow it, but it throws off a ship's vector upon leaving jump. If you want to discourage this, you might impose an increased risk of mis-jump in this kind of situation, which would limit this type of jump entry to "emergency" situations.

Which, now that I've thought of it, would be an interesting variant for my games, too.... [img]graemlins/file_22.gif[/img]

Thanx heaps,

DGv2.0
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Old January 19th, 2003, 03:04 PM
tjoneslo tjoneslo is offline
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A proper way to do a vector movement system is to use two counters per ship. A current location counter and a future location counter. Use the scale proposed by Digital Golem.

There are two phases during a turn, the acceleration phase and the movement phase. During the acceleration phase, the future location counter may be moved by 1 hex per G of acceleration of the ship.

During the Movement phase, move the current location counter to where the future location counter is, then move the future location counter an equal number of hexes (or squares) forward along the path.

1) The maximum possible speed is lightspeed, obviously, but a good limit may be 10% of lightspeed.

2) Turning: A ship may turn to any facing they like during the turn. Of course this implies using the above movement system.

The downside of DG's system is the requirement to constantly recalculate the "Turn Mode". Which may not be bad, unless your players are math-phobic.
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Old January 19th, 2003, 08:47 PM
graden1 graden1 is offline
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Quote:
Originally posted by tjoneslo:
A proper way to do a vector movement system is to use two counters per ship. A current location counter and a future location counter. Use the scale proposed by Digital Golem.

There are two phases during a turn, the acceleration phase and the movement phase. During the acceleration phase, the future location counter may be moved by 1 hex per G of acceleration of the ship.

During the Movement phase, move the current location counter to where the future location counter is, then move the future location counter an equal number of hexes (or squares) forward along the path.

1) The maximum possible speed is lightspeed, obviously, but a good limit may be 10% of lightspeed.

2) Turning: A ship may turn to any facing they like during the turn. Of course this implies using the above movement system.

The downside of DG's system is the requirement to constantly recalculate the "Turn Mode". Which may not be bad, unless your players are math-phobic.
Very true. I came up with the turn mode idea because I was tired of "mucking about" with all the extra vector counters. Sadly, I also had a few players who just didn't understand vector movement at all, and I was tired of trying (and failing) to explain it for them. [img]graemlins/file_28.gif[/img]

For those with math anxiety, I printed a turn mode table so they could skip the math, which was very helpful, especially when figuring out which way to round off the fractional turn modes! In the end, either system gives roughly the same results. Too much speed, and you're outa there. By the time you've turned around and come back, it's all over.

DGv2.0
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