28 replies to this topic

[Mott]

How come engine size is the only thing that impacts a mech's top speed? Why doesn't the weight of the mech factor in as well?

Say i build a mech with 2 weapon groups I'm happy with (Lasers & Ballistics) and it has a couple missile hardpoints i don't want to use, so i leave them open and also don't have to add any ammo for them.

It's sitting 10 tons underweight... yet the top speed doesn't change despite it being somewhere between 10%-25% lighter, depending on the chassis.

It should increase say, an Atlas' top speed by 5-7kph and a Hunchback's top speed by at least 20kph.

Kind of a weird, oversight imo.

[Buckminster]

It's one of those "that's the way it was done in the tabletop game" carryovers. Speed = engine size / mech weight.

I suppose we could sit here and ponder the physics of it, but the reality is just that's the way it is. So you might as well use all that weight!

[990Dreams]

Just assume weight is factored in.

Or we can say the engine has a "safe operation limit". So a 45 ton Mech can have the same speed as a 50 ton Mech by cranking the maximum operation limit up a little.

[Modo44]

PGI did not even bother with fast running animations for mechs. I would not expect dynamic max speed changes any time soon.

[AaronWolf]

DavidHurricane, on 20 January 2014 - 07:44 AM, said:

Just assume weight is factored in.

Or we can say the engine has a "safe operation limit". So a 45 ton Mech can have the same speed as a 50 ton Mech by cranking the maximum operation limit up a little.

This is what I assume. Or else all my HBK's would have been running far faster when I first had them, rather then dumping the giga-XL's in.

[BLOOD WOLF]

Modo44, on 20 January 2014 - 07:45 AM, said:

PGI did not even bother with fast running animations for mechs. I would not expect dynamic max speed changes any time soon.

what do you mean by fast running animations?

[Mechteric]

It would just get too complex, because then as you take damage and lose armor and weapons an limbs in combat you might also gain speed. Of course we don't even have all the other factors that actually might make you lose speed either, such as if you lose an arm, that could make your mech heavier to one side and make it harder to run faster actually, or what about things like critical hits to leg and foot and hip actuators or even to the engine that should make you slower as well.

I guess these are things that would be nice for immersion and realism but not a requirement to be faithful to the tabletop RPG (which had no means to handle some of these complexities).

[990Dreams]

My K-Town senses are tingling.

Anyways, I just assume that there is a maximum operation limit like I said. The advantages of that:

• It fits real technology
  
• It satisfies the question
  
• It opens up new modules for speed boosting

Edited by DavidHurricane, 20 January 2014 - 07:51 AM.

[CMDR Sunset Shimmer]

Mott, on 20 January 2014 - 07:37 AM, said:

How come engine size is the only thing that impacts a mech's top speed? Why doesn't the weight of the mech factor in as well?

Say i build a mech with 2 weapon groups I'm happy with (Lasers & Ballistics) and it has a couple missile hardpoints i don't want to use, so i leave them open and also don't have to add any ammo for them.

It's sitting 10 tons underweight... yet the top speed doesn't change despite it being somewhere between 10%-25% lighter, depending on the chassis.

It should increase say, an Atlas' top speed by 5-7kph and a Hunchback's top speed by at least 20kph.

Kind of a weird, oversight imo.

A hunchback with a 200 engine will move faster than an Atlas with a 200 engine. Tonnage does matter... your not understanding how engines work.

I'd post all the math, but I'm not in the mood to be bothered. Needless to say, the Weight of the mech determines how fast a specific rating of engine will cause it to go.

Meaning your post is moot anyway, since you're saying that weight doesn't impact things, when it fact, it's the biggest mitigating factor. If it wasn't, an altas with a 300 engine would be going 120kph... like a jenner with a 300.

[Bagheera]

Because changing weight does not effectively alter top speed in vehicles. If you take a bunch of weight off of your car it does not have a higher top speed because top speed is a function of engine RPM, transmission (and differential) gearing, tire size, and motive power loss along the driveline. Weight changes only measurably impact accel/deccel and turning characteristics. Not top speed.

I have a 30 year old landcruiser that weighs about as much as an Atlas. I could lighten it all day long but it would still be limited by 3400rpm redline, a 4 speed transmission, and 31" tires. Top speed is just math, really.

TLDR: Just because you make a mech that is slightly underweight does not mean that the machinery operating the legs will be able to articulate any faster.

[Buckminster]

There's also the assumption that unused hardpoints equals unused weight. I know that if I don't use all of my hard points, my mechs still tip the scales at their chassis max - I'm adding a bigger engine, more armor, bigger guns, more heat sinks, AMS, and so on.

[Modo44]

A proper system would base the max speed on the gyro+legs assembly, limiting it for every chassis. As equipment (like ammo) was removed and parts destroyed during battle, the current maximum speed could be adjusted accordingly, up to the preset limit. The logical limit happens to prevent 100kph Atlases and other shenanigans.

BLOOD WOLF, on 20 January 2014 - 07:47 AM, said:

what do you mean by fast running animations?

If you have a mech with double basics, put a big engine in, and watch it in 3PV. The derpy movements are simply sped up walking animations -- not actual running.

Edited by Modo44, 20 January 2014 - 08:01 AM.

[TercieI]

I strongly suggest you find a use for the rest of the weight, if not the hard points. Due to this very issue, there's simply no reason not to. Any optimized build will be right on weight (or in a couple very peculiar cases, no more than .5 ton off).

[Mott]

Cool posts.

To the few comparing mech engine/structure to automobiles - good points, i should have been more specific and related it to acceleration, turning, etc. Although when geared for high speed weight absolutely plays a factor in how fast a machine can go top-end.

But, mechs can't be compared to any mode of RL transportation or RL war machines. They are fusion powered and propelled by hydraulics and myomer musculature.
Because of this they are more comparable to a human body. And most human bodies come with nearly the same heart, etc.

A 300lbs man will not be able to run as fast as a 150lbs man, if both are in normal health and we're barring freaks of nature.

However, without changing the engine (heart & lungs) of the 300lbs man, it is possible to make him significantly quicker by having him shed weight.

A mech is similar, and a mech's speed is not limited by "gearing", it's limited by the resistance placed on it's structure by weight.

Terciel1976, on 20 January 2014 - 08:24 AM, said:

I strongly suggest you find a use for the rest of the weight, if not the hard points. Due to this very issue, there's simply no reason not to. Any optimized build will be right on weight (or in a couple very peculiar cases, no more than .5 ton off).

No worries there, i never leave mechbay underweight by more than 0.5T

Edited by Mott, 20 January 2014 - 09:35 AM.

[Rushin Roulette]

Jade Kitsune, on 20 January 2014 - 07:52 AM, said:

A hunchback with a 200 engine will move faster than an Atlas with a 200 engine. Tonnage does matter... your not understanding how engines work.

If you would have bothered to read the full OP, then you would realize that your reply completely missed the point. As per your annalogy, the OP is asking why an Atlas with only 90 tons filled and 10 tons unused moves just as slow as the Atlas filled to the brim weighing in at 100 tons.

Im afraind this is one of the "Its just so" things with Science fiction/lore. You can explain it however you want in a logical way and it would still just be filling in the blanks of the logic with guesses. For example it could be because the actuators and Myomers inside the mech are not swapped out with differign weight, but they still have a maximum speed limit they can move at.

[Koniving]

Consider this: The mech's weight is supposed to be maximum carrying potential of the battlemech. Even so, the engine and the joints can only go so fast.

[Durant Carlyle]

In the lore, a BattleMech is designed for a certain performance envelope. Its control computers are programmed to not let the performance go outside that envelope because structural integrity (the legs) would be compromised.

The control computers have to be completely reprogrammed for the planetary conditions when gravity varies from the 1.0G standard.

One book in the Jade Phoenix trilogy has a Summoner (70-ton Clan OmniMech) on an airless moon with reduced gravity. The control programming was done incorrectly, and the 'Mech went beyond its designed parameters -- because of the light gravity, it went too fast. This resulted in one of its legs breaking off at the knee.

That is why 'Mechs that are lighter than they were designed to be do not actually go faster, or turn better, or accelerate quicker.

Edited by Durant Carlyle, 20 January 2014 - 09:48 AM.

[sC4r]

well yea now imagine for a second someone buys boarshead and puts in nothing but xl400

[MetalBacon]

On topic, mechs should gain speed as their limbs and torsos are blown off. Or as ammo is used. Maybe even give an option jettison ammoless limbs. Also why not have an option to direct the lift thrusters into a horizontal position. GUNDAMNS.

[Durant Carlyle]

MetalBacon, on 20 January 2014 - 09:54 AM, said:

Non-BattleTech spewage which may or may not be sarcastic.

Not just no ... HELL NO!