MT Only: Confused by Contact Based Transmissions

[atpollard]

So, I was playing around with CT Striker to try and design some simple civilian vehicles ... and not liking the results too much ... when I decided to take a shot at using the Megatraveller Rereree's Manual.

The suspension and transmission for a wheeled vehicle are kicking my but, and the Consolidated Errata is making things worse.

So the goal is to start with something simple and see if I can actually follow the rules. I chose to build a 2014 Ford Expedition (a glorified 6-8 passenger box). I come up with a real world target volume of 16.7 cubic meters (aka kiloliters), a weight in the 2.6 ton (curb) to 3.4 ton (gvwr) range, with a 231 kW engine. I was not looking for anything closer than an order of magnitude, 1 significant figure match between the game and reality.

So some basic figures to start:
1 - Basic Hull Design (TL7; UCP 1.2 = 16.2 kl; box; Armor 1 - Comp.Laminate)
Weight (tons) = 1.64 x 0.44 x 0.25 = 0.1804 tons
Price (credits) = 3380 x 0.6 x 1.8 x 0.25 = 912.6 credits

2 - Power Supply (231 kW = 0.231 mW; Improved Internal Combustion; 10 hours fuel)
Volume (kiloliters) = 0.231 mW / 0.4 mW/kl = 0.5775 kl of Power Plant
Weight (tons) = 0.5775 x 1 = 0.5775 tons
Price (credits) = 0.5775 x 2000 = 1155 credits
Hydrocarbons (kiloliters) = .5775 x 0.025 x 10 hours = 0.144375 kiloliters

3 - Locomotion [HELP! Here is where numbers start to go sideways.]
Step 7: Contact-Based Suspension - TL 7 Wheels (By the book, no errata) 1.5%
Volume (kiloliters) = 16.2 x 0.015 = 0.243 kiloliters
Weight (tons) = 0.243 x 0.5 = 0.1215 tons
Price (credits) = 0.243 x 250 = 60.75 credits
Power (mW) = 0.243 x 0.02 = 0.00486 mW

Step 7: Contact-Based Suspension - TL 7 Wheels (By the errata v2.21) 1.5%
Volume (kiloliters) = 16.2 x 0.015 = 0.243 kiloliters
Weight (kg) = .243 x 0.5 = 0.1215 kg = 0.0001215 tons
Price (credits) = .243 x 12000 = 2916 credits
Power (kW) = .243 x 0.02 = 0.00486 kW = 0.00000486 mW

Step 7, the errata makes the numbers look much too small ... fraction of a kg suspension? ... 5 watts?

Step 8: Contact-Based Transmissions - TL 7 Wheels (By the book, no errata)
Volume (kiloliters) = 0.231 x 0.3 = 0.0693 kiloliters
Weight (tons) = 0.231 x 0.3 = 0.0693 tons
Price (credits) = 0.231 x 450 = 103.95 credits

Step 8: Contact-Based Transmissions - TL 7 Wheels (By the errata v2.21)
Volume (kiloliters) = 231 x 0.3 = 69.3 kiloliters
Weight (kg) = 231 x 0.3 = 69.3 kg = 0.0693 tons
Price (credits) = 231 x 5 = 1155 credits

Step 8, the errata is just crazy large.

So does anyone familiar with MegaTraveller vehicle design see where I messed up on Section 3 - Locomotion?

 

[Hyphen]

the problem is the MT rules miss this line from Striker:

"Wheeled and tracked suspensions occupy a volume with length equal to the length of the chassis and height of 1 meter."

And the follow-up is that width is determined by the designer, and affects ground pressure and therefore top speed over uneven terrain.

Try looking over my comments for robots here:
--> Tavonni Repair Bays
--> House Rules
--> Reconciling Robots, Part I – Run, Robot, Run!

It's really about legged robots, but contains quoted text from Striker and the discussion about the difference between suspensions & transmissions.

 

[Hyphen]

You may be selling the car short. ;-) The stats I have for the car are:

Length: 220 in = 5.6 m (approx.)
Height: 77 in = 2 m (approx.)
Width: 80 in = 2 m (approx.)

This suggests a 22.4 kl box, but then taking off approx. 2kl for the above-bonnet area leaves you with 20.4; let's say around 20 kl.

Wheels: 5.6 m (length) x 1 m (height) x 0.1 m (width) = 0.56 kl.

 

[atpollard]

3 - Locomotion [HELP! Here is where numbers start to go sideways.]
Step 7: Contact-Based Suspension - TL 7 Wheels (By the book, no errata)
Price (credits) = 0.243 x 250 = 60.75 credits
Power (mW) = 0.243 x 0.02 = 0.00486 mW

Step 7: Contact-Based Suspension - TL 7 Wheels (By the errata v2.21)
Price (credits) = 0.243 x 12000 = 2916 credits
Power (kW) = 0.243 x 0.02 = 0.00486 kW = 0.00000486 mW

Step 8: Contact-Based Transmissions - TL 7 Wheels (By the book, no errata)
Volume (kiloliters) = 0.231 x 0.3 = 0.0693 kiloliters
Price (credits) = 0.231 x 450 = 103.95 credits

Step 8: Contact-Based Transmissions - TL 7 Wheels (By the errata v2.21)
Volume (kiloliters) = 231 x 0.3 = 69.3 kiloliters
Price (credits) = 231 x 5 = 1155 credits

the problem is the MT rules miss this line from Striker:

"Wheeled and tracked suspensions occupy a volume with length equal to the length of the chassis and height of 1 meter."

And the follow-up is that width is determined by the designer, and affects ground pressure and therefore top speed over uneven terrain.

Try looking over my comments for robots here:
--> Tavonni Repair Bays
--> House Rules
--> Reconciling Robots, Part I – Run, Robot, Run!

It's really about legged robots, but contains quoted text from Striker and the discussion about the difference between suspensions & transmissions.

The question is "Did I make an error?" or "Does the errata need errata?"

For a fairly normal 3 to 4 ton passenger SUV,
Is the Contact-Based Suspension - TL 7 Wheels, 60.75 credits or 2916 credits? Does it require 5 Watts or 5 kilowatts

Is the Contact-Based Transmissions - TL 7 Wheels, 0.0693 kiloliters or 69.3 kiloliters (larger than the vehicle)? Does it cost 103.95 credits or 1155 credits?

Either I made an error or the errata bumps the numbers up by orders of magnitude ... I just can not find my error ... but I am reluctant to jump in and say the errata is broken and the book was correct.

 

[atpollard]

You may be selling the car short. ;-) The stats I have for the car are:

Length: 220 in = 5.6 m (approx.)
Height: 77 in = 2 m (approx.)
Width: 80 in = 2 m (approx.)

This suggests a 22.4 kl box, but then taking off approx. 2kl for the above-bonnet area leaves you with 20.4; let's say around 20 kl.

Wheels: 5.6 m (length) x 1 m (height) x 0.1 m (width) = 0.56 kl.

Yeah, I wasn't 100% sure how to treat the hood/bonnet.
I think that I assumed radical sloped front (-20%).

 

[TNE2300]

JTAS 14 has an article for civilian vehicles in Striker

it suggests the passenger compartment be considered a turret

it also suggests that power plants and cargo areas be allowed to have volumes of less than a cubic meter

 

[Timerover51]

Atpollard, if you are really interested in designing some civilian vehicles, I suggest you look at this Tech Manual to get a better idea of things. These are real vehicles from the Real World, not something from an article in JTAS or another game.

And for those who might want to see how well it works with a variety of vehicles, here is a link to the U. S. Army TECHNICAL MANUAL No. 9-2800, WAR DEPARTMENT Washington, 1 Sept. 1943 STANDARD MILITARY MOTOR VEHICLES.

https://archive.org/details/TM9-2800

Edit Note: The STANDARD MILITARY VEHICLE Characteristic Data Sheets from 1963, published by the US Army Tank Automotive Command can be found here. There is quite a bit of information, including ammunition loads and expected vehicle endurance.

http://cgsc.contentdm.oclc.org/cdm/compoundobject/collection/p4013coll11/id/879/rec/981

 

[elbmc1969]

Step 8: Contact-Based Transmissions - TL 7 Wheels (By the book, no errata)
Volume (kiloliters) = 0.231 x 0.3 = 0.0693 kiloliters
Weight (tons) = 0.231 x 0.3 = 0.0693 tons
Price (credits) = 0.231 x 450 = 103.95 credits

Step 8: Contact-Based Transmissions - TL 7 Wheels (By the errata v2.21)
Volume (kiloliters) = 231 x 0.3 = 69.3 kiloliters
Weight (kg) = 231 x 0.3 = 69.3 kg = 0.0693 tons
Price (credits) = 231 x 5 = 1155 credits

Step 8, the errata is just crazy large.

Actual weight of the 6R80 transmission is 245 lbs, but that's just the transmission itself, not the driveshaft, differential, etc. Still, that's considerably more than 69 kg!

With your by-the-book numbers, the transmission has a density of 1 g/cm^3, which is the density of water. i think that we can all agree that that is wrong. A transmission may not be solid steel, but it is still going to sink like a stone.

Step 8 errata is clearly wrong. Changed values are shaded, but the change from MW to kW is not shaded. The purpose of the errata was to make the contact-based transmissions more effective, not less effective. Correct volume is 69.3 liters, which is vaguely reasonable. Weight is 69.3 kg, which is obviously too low. Should probably be doubled to 140kg just as a start. Price sounds about right.

 

[aramis]

Actual weight of the 6R80 transmission is 245 lbs, but that's just the transmission itself, not the driveshaft, differential, etc. Still, that's considerably more than 69 kg!

With your by-the-book numbers, the transmission has a density of 1 g/cm^3, which is the density of water. i think that we can all agree that that is wrong. A transmission may not be solid steel, but it is still going to sink like a stone.

Step 8 errata is clearly wrong. Changed values are shaded, but the change from MW to kW is not shaded. The purpose of the errata was to make the contact-based transmissions more effective, not less effective. Correct volume is 69.3 liters, which is vaguely reasonable. Weight is 69.3 kg, which is obviously too low. Should probably be doubled to 140kg just as a start. Price sounds about right.

don't forget the volume of the suspension's movement volumes - the wheel wells and dead space around the arms, struts, and springs. Those also drastically affect overall volume. Oh, and also the accessways for grease-guns.

And, given the abstraction levels of Striker and MT - it also includes the volume of the ground clearance .

 

[Hyphen]

On re-reading I have a horrible suspicion that I've recommended the wrong units. It probably should be tons rather than kg, to match the rest of the MT unit changes (litres to kilolitres, kg to tons, etc.)

I guess I'll have to go back and look at those. (To be honest, my main focus was on robot legs...)

Oh, and regarding Will's comments about wheel-wells & so on: my guess is that that's why Striker's rules multiplied width by the entire vehicle length !

Not to mention that it's oriented to military vehicles(*), therefore the rules designers (Frank Chadwick?) would be expecting you to design a multi-wheel armoured car or ATV, therefore assuming the wheels run the entire length is appropriate.

(*) One of the secrets/consequences is that if you shoot at the front of a car using Striker's hit locations, you'll never hit the engine compartment! (Try it and see!) This is because most tanks have mid- or rear-mounted engines, and the rules are written to match...

 

[jec10]

IIRC, I pointed this one out to Don a long time ago David. I think you were a bit keen in taking the robots stuff and recommending it for the vehicles because the units are off (as you note).

 

[elbmc1969]

Oh, and regarding Will's comments about wheel-wells & so on: my guess is that that's why Striker's rules multiplied width by the entire vehicle length !

I've always thought that this was an oversight in the Striker design rules. Clearly, you should be able to design 4-wheeled scout cars and the like, so it shouldn't automatically be the entire vehicle length. The "other factors" mentioned aren't enough for me to buy it.

 

[aramis]

I've always thought that this was an oversight in the Striker design rules. Clearly, you should be able to design 4-wheeled scout cars and the like, so it shouldn't automatically be the entire vehicle length. The "other factors" mentioned aren't enough for me to buy it.

Looking at my car - a subaru - the tires are 14" radius, 4" wide, with minimum 2" clearance (actually 6" at rest loaded). there's a roughly ±30° swivel, 6" vertical clearance (inside the well) and 2" fore-aft clearance. so the swivel is an additional 2.4" clearance... the 0.04 cubic meter steer tire needs 0.11 cubic meters of space to operate.

Plus, the striker design sequence is based upon the bounding box... the losses from the top half are minimal - but the entire space under the body and between the wheels is dead space - and can come out of the top's somewhat excess volume. (keeping in mind that between 1/3 and 3/7 of the wheel diameter is below the body in most cases)

 

[Hyphen]

There's also the "Civilian Vehicles for Striker" article in JTAS #14 that basically says you need to mod the design rules before they are fit for civilian vehicles.