Vehicle Drive Trains

[archhealer]

On the chart for DTU power, size, etc., it states that the thrust output is PER ep put into the DTU. Does that mean that without increasing the size of the drive train, you can put more ep in and get higher thrust output? Or do you need to increase the size of the DTU to provide the required thrust? It's very unclear.

Also, I'm a little confused about the whole "Multiples allowed" bit on that table. Is that just for determining off-road speed and/or backup systems, or does it have some other function? When you add wheels to a vehicle, does each pair count as another DTU or does each pair just increase the size of a single DTU?

It's very possible these questions have ready answers, but i'm still kinda new to T20 and they're giving me headaches.

 

[tjoneslo]

The answer to your first question is no. The purpose of the Thrust Output per EP is to note the conversion of EP (generated by the power plant) into thrust (used to move the vehicle). Think of in the reverse direction, to get x thrust requires y EP supplied to the collection of DTUs.

Second question: You are correct, the purpose of multiples is only for off-road speed and "back up" units. If you read the damage charts in the combat sections, you can damage or destroy the drivetrain. If you have more than one, you only break one, leaving the vehicle still partly mobile.

The size of a DTU is fixed, but the number of DTU's in a wheel (or set of wheels) is up to you. That is, if your vehilcle has four wheels, each wheel can have one, two, five, ten or whatever number of DTU's. In fact each wheel can have a different number of DTU's (strange but true). The vehicle's speed is determined by the total number of DTU's.

If you have more questions, this is my area of expertise.

 

[archhealer]

Ok, so if a hypothetical DTU (These numbers are just simple easy ones for this example) took up 1 vl, provided 1 th/1ep, and cost 1 cr, and I need 10 thrust, the total DTU would be ten times the size, cost, and energy requirement of the base unit. And if I want to increase my off-road speed, I install two of these, both operating at once (Thus taking 20 ep) but still only providing 10 thrust, so my max speed is the same, but off-road is faster, and if one is damaged, I still have 10 thrust avialable.
Alternately, I can have only one operating at a time, using the second only if the first is incapacitated, so I still can lose one and have 10 thrust, but the system only needs 10 ep to operate.

So, new question on these: To design a vehicle that uses rails (Monorail, locomotive, etc.) which DTU would you all suggest? It seems to me that wheeled would be closest, but wouldn't the DTU base unit be smaller, to account for the fact that steering is not needed, and would the controls also be reduced in size/cost due to the fact that they only need to consist of "Go", "Stop", "Reverse"?

 

[veltyen]

Ahhhh. I understand now.

Multiple drive trains are NOT just multiplied through. That would be somewhat excessively expensive. The cost and space of additional drivetrains are listed under each drivetrain that can have multiple.

As for rail it is tracked obviously. Some of the tracked DTU space/cost is buried in the ground however rather then part of the vehicle itself.

 

[jonathonbarton]

*boggle*
*TRACKED*!?!?!?
I can't imagine that... A locomotive, with better off road performance than a Chevy Caprice?
I think the only similarity is that they're both called "tracked".

I'd stick with Wheeled. But the need for steering is still there - just not in the "power assisted rack and pinion" sense. I'd assume that the mechanism to allow the trucks (on a locomotive/train car) to articulate sufficiently to go around a fairly tight corner (in a yard, or on a mountainside) take up the similarly sized space traditionally used by the steering rack, etc. on a ground car/Wheeled AFV.

 

[veltyen]

Um... Railway tracks?

Part of the track is the track buried in the ground, instead of having a continuous looped track you have one nailed down. Otherwise basically the same machine. And offroad speed is great for locomotives, offtrack speed however is sadly lacking...

Since part of the drive is part of the landscape there is no offroad speed of course. Like trying to drive a car with wedge shaped wheels, leaving part of the DTU behind just doesn't work.

 

[veltyen]

Getting back to the original question, yeah I would use a track, but with only 20% of the volume and 50% of the price. The rest needs to be sunk into the rail infrastructure that bears the vehicle. Depending on rail system (dual rail, monorail, dual rail with external supplied power, maglev guide and so on) the percentage externally supplied would change, down to quite small amounts for some systems.

 

[archhealer]

Hmm, it never occured to me to count the rails or tracks themselves as part of the DTU. I think what I'll do is account for the section of rail immediately under the vehicle (Thus not counting the rest of the the possibly thousands of miles of track) as some of the VLs of the Drive Train, but not use those particular VLs to calculate speed (Possibly about 20% less, as Veltyen suggested.) or cost of individual vehicles. That way, It is included in the calculations for EP and Thrust, as they well should be, but not for mass of the vehicle being moved (You odn't move the tracks with the train, unless somethings wrong). Yeah, I think I like that. Thanks!

 

[archhealer]

I just realized I have another (I know, I know, I'm nit-picky) question about calculating vehicle drive trains.
When it says that you divide the total thrust (TH) by the number of wheels/props/tracks/etc. attatched to the drive train, I presume that A). that only applies to POWERED wheels and such, since not all vehicles by far are four-wheel or more drive.
Secondly, does that mean that if you have a four wheeled vehicle producing 100 total thrust, you only accellerate as if you had 25 thrust, or is the "Thrust per wheel" claculation only used in determining remaining thrust if a wheel is disabled/lost? The latter is the one I'm inclined to go with, as the former would make all drive trains immense, both in size and expense.

 

[far-trader]

I think you're right about the thrust per (device) being intended to calculate thrust after taking damage, but it seems the system wasn't put in place in the book for actually doing damage to the drive train parts (TA3 does).

As for the the first part of the question, my easy-way-out assumption is that all vehicles are in fact all-wheel drive. If you have 6 wheels they all have power, hence the division of thrust.

This should provide better offroad speed than two wheel drive and I recall seeing a mod somewhere but can't find it (added to off-road speed depending on the number of extra powered wheels).

EDIT: And there it is

Right at the bottom of the Offroad Speed table pg. 253. Add 5kph per pair after the first. So...

If you want to make a simple two wheel drive vehicle (for example) don't apply the additional volume and cost calculation for wheels over the first pair and don't add the offroad speed bonus.

If you do apply the extra volume and cost as per the design rules then you're buying all-wheel drive and get to add the bonus.

 

[SanDragon]

Ummm.. a tracked vehicle is, well... a tank!!!

A self-propelled, self-contained vehicle.

Not a rail road track.

 

[jonathonbarton]

That's what I was thinking...

How can you possibly account for an indefinite volume of "track" suspension? And if you're going to go that route and reduce the volume by some 50% or so, why not just stick with the lesser volume required in a wheeled suspension? (at least, according to the Striker rules I know off the top of my head - a wheeled suspension requires less minimum volume in comparison to tracked)

I'll invert your argument for tracks just to be pissy, because it's my friday night and Elton John says Saturday Night's Alright For Fightin'

Tracks are just a road for trains...that's why they're called Rail-ROADS.
Roads are a separate entity from Suspension Design.

I still say go with a fullsize wheeled suspension and drivetrain, treat the rails as a specialized road, and give the train *zero* off-road capability.

 

[SanDragon]

Okay. It's okay to be umm- pissy. I was afraid I came off a little blunt. Sorry for that.

It depends on what you want.

Wheels are faster but have little off-road capability.

Tracks have off-road capability, but aren't fast... Unless half the vehicle is power plant!

 

[archhealer]

Originally posted by far-trader:
[

EDIT: And there it is

Right at the bottom of the Offroad Speed table pg. 253. Add 5kph per pair after the first. So...

If you want to make a simple two wheel drive vehicle (for example) don't apply the additional volume and cost calculation for wheels over the first pair and don't add the offroad speed bonus.

If you do apply the extra volume and cost as per the design rules then you're buying all-wheel drive and get to add the bonus. [/QB]

Er, ok, but wouldn't you still add the vl and cost, after all wheels aren't free and they're kinda big, even if they just roll, but only divide the thrust between powered wheels?

 

[far-trader]

Well I'd say, to keep it simple, ignore the added volume and cost requirement for extra wheels that aren't adding to the thrust performance (per the offroad speed adjustment). Put it down to the basic part of the wheel drive train calculation. As long as you don't see some abuse coming from an 18 wheeled vehicle with only 2 drive wheels, and in the basic rules there is none that I can see. Even with the addition of the rules in TA3 for targeting wheels I'd say such an attack ignores the simple extra wheels and only targets the actual drive wheels. Or not, since iirc the effect of shooting out wheels is more a handling problem result than speed.

 

[jonathonbarton]

Originally posted by SanDragon:
Okay. It's okay to be umm- pissy. I was afraid I came off a little blunt. Sorry for that.

Oh, HEAVENS NO, sir... I wasn't being pissy with you...I'm in complete agreement.
It's Veltyen that's off his nut.

 

[veltyen]

You know, I would normally take that kind of statement as fightin' words.

But you are close to the first person to spell my name correctly, so I'm having a hard time getting angry

 

[BetterThanLife]

Originally posted by far-trader:
Well I'd say, to keep it simple, ignore the added volume and cost requirement for extra wheels that aren't adding to the thrust performance (per the offroad speed adjustment). Put it down to the basic part of the wheel drive train calculation. As long as you don't see some abuse coming from an 18 wheeled vehicle with only 2 drive wheels, and in the basic rules there is none that I can see. Even with the addition of the rules in TA3 for targeting wheels I'd say such an attack ignores the simple extra wheels and only targets the actual drive wheels. Or not, since iirc the effect of shooting out wheels is more a handling problem result than speed.

I am not so sure about that Dan,
Losing a wheel is both a speed and a handling problem. (Especially if you lose the wheel at speed.) As far as multiple wheels with limited number driven, that is how a train and an 18 wheeler work. The extra wheels are not part of the Drive and thrust but they are part of the suspension. However the rules don't take into account unpowered wheels for volume or handling. Wierd! I guess I never noticed before.

Perhaps in a revision they should seperate the drivetrain from the suspension.

 

[far-trader]

It's a simplification due to the lumping of suspension and thrust into one as you note. My suggestion seems imo the best way to do it without a redesign of the vehicle design rules (which unless craftily done would mean all the vehicles to date are wrong, or wronger ), and could go on to affect the craft design rules.

Extra wheels that don't add to the thrust don't have volume, cost, or required energy input. They don't add to handling or offroad speed or any other effect. Saying they can't be targeted is the easiest way to handle the TA3 rules.

This is also the way TA3 handles building towed trailers btw. You designate the towing capacity of the vehicle just as if it were onboard cargo capacity. The only thing a trailer has is empty vl and the cost of the chassis for that vl.

An example:

You want to build a trailer for the jeep. All you do is pick a vl and pay for the chassis and that's all the trailer costs. No drivetrain. No wheels. No nothing. Now it must have some wheels of course but they don't add to the performance in any way or require any power, all that comes from the jeep. So we just ignore them except as color/descriptive.

To determine the performance of the jeep when towing the trailer you have to recalculate the drivetrain thrust for the total vl of the jeep and trailer. In MTU I allow the extra energy the power plant has in abundance to be used for towing, so you can still get up to the top speed of the basic jeep if your trailer isn't too big by putting extra power into the drivetrain.

Another example:

A big rig tractor trailer truck. Pick the full vl of the tractor and trailer. Select the top speed desired and build to that. Insure that all of the design requirements fit in the tractor part of the vl and your trailer is just an empty vl ready for hauling cargo. You could recalculate the performance of the tractor by itself (i.e. not pulling a trailer) but it would still be limited to the top speed, it'd just take less power to get there (and so you'd use less fuel).

That's the way I see it, hope I explained it clear enough for everyone to see what I mean. It looks like the intent of the rules as they are so far between the book and TA3 at least.

 

[tjoneslo]

Yes. As the author of TA3, I can state that far-trader is correct. And I like his idea about the extra (non-powered) wheels.

The T20 vehicle design system is a compromise between the full gearheadedness of something like GURPS Vehicles or Striker or the MT design system and the full effects based design system like D20 Future. The more you poke at it, the more holes you will find. I found several cases where I just waved my hands and said "it's an abstract system".