Is the VHT's 105mm Cannon a Rail-Gun based on Ammo Storage?

[ShadowLogan]

Officially in the show the dialogue only ever establishes that the big gun in the arm shield is a beam weapon (laser specifically), however the 2E Palladium RPG and the RT.com Infopedia (which is justified due to trajectories seen in animation) have it as a cannon firing high velocity shells (48 in the 2E RPG, 60 in the RT.com Infopedia). This being the Palladium Boards, I am going to use the RPG payload as there is a payload difference between it and the RT.com Infopedia (plus it being the smaller payload if it can't be made to work...).

So the question is where would the VHT-1 store the ammunition for it's 105mm cannon? The place with the most volume available would be the torso* (maybe even the nose/B-mode tailcoat), however due to the battloid mode option for sustained firing (even at reduced ROF) this will require a complex feed mechansim to navigate the shoulder and upper arm to the shield w/n the range of motion of any joints, where if it was a Gladiator Mode only weapon it could feed in from what would be the top of the sheild in B-Mode and we wouldn't see it (unless the B-Mode option is only possible due to a pre-chambered round and it won't reload in B-Mode in actual practice). Now such a feed mechanism might be doable to navigate all those joints, but I would think that it would work best with a smaller sized round (105mm is over 4 inches in diameter, and this ignores the length of the shell/round) and be subject to added complexity.

*Torso break down in Spoiler

Spoiler:

For a quick simple math lets use 1/2 the Battloid Mode Height to determine the "height' of the torso section, now this does include negative space for the area on either side of the head, but we are also not including the "Tailcoat" which might also be able to store (it holds connection gear for the EU gunpod, and lights), so for a quick simple assement lets call it a wash since that space could be used also. The Width is based on the Gladiator Mode (narrowest mode, T-mode likely includes when the hoverjets are deployed), and the Length is the Battloid. This gives ~7.95m^3 of volume, if an ammo bin is here it would have to share space with various other systems (acuators, pilot cavity, etc).

Now if the 105mm cannon's shells are stored here, and assuming the Shells are standard NATO (105mm diameter with 617mm length), you could fit 1,488 shells. We need only 48 (for 2E RPG, 60 for canon) shells, which only need ~0.26m^3 (~0.32m^3 for canon). Which would still leave over 7m^3 of volume to give over to other aspects.

If the Shells are shorter than the NATO length, well they just become even easier to fit.

The use of the legs or the alternate arm and/or arm shield is even more demanding for the feed mechanisim, and it has to contend with very limited volume given it also has to share the feed mechansim and payload with other systems that we know are present in these locations.

This only really leaves the Right Side Arm Shield (location of the cannon) and/or arm. I estimate the upper arm location (which connects to the shield) is approximatly 1/3 the length of the shield, and just as wide/tall as the shield (which makes sense given transformation). Now not all of that space is available, you will lose some of that to the limb actuators on the shoulder and elbow (plus any additional "muscles" that might be present). For simplicity let's assume that only 1/2 of the available space can be repurposed for ammunition storage though I think that might be generous (as such I split the results later).

I estimate the size of each Arm Shield to be 3meters long (it appears to be ~1/2 the length in transport mode) by at least 0.125m wide and
0.125m high (the bore of the 125mm Beam Cannon that is also housed here without apparent modification). Technically I am ignoring barrel thickness and the armor plating thickness so width and height are off. The armor thickness is of less concern IMHO as that is already pre-allocated space I don't have to factor in again later. The Barrel thickness is of more concern as it reduces the internal volume of that space, though it will increase the available space, plus space is lost as I am ignoring the possibility of gaps between the barrel and inner wall of the shield compartment. It also holds a barrel that is 1.75m long, as determined by the difference in length for the T and G modes of the VHT (the sole reason for the difference in length), this doesn't include any loading mechanisim or firing chamber (which logically has to be big enough for a round).

Based on these numbers I am going to use two different approaches to determine if the required quantity can be made to fit: available volume and available length.

By Available Volume. If we treat the 105mm barrel and the arm shield as both simplified rectangular cubes (which they are not), how many 105mm diameter rounds can you fit in the remaining volume with no consideration for how they are stacked, the number in parathesis is for the upper arm (all fractional numbers rounded down):
-NATO standard length (617mm) can hold x5 (+1 in UA)
-at 1/2 the NATO length can hold x10 (+2 in UA)
-at 1/3 the NATO length can hold x15 (+4 in UA)
-as 105mm long cylinder can hold x30 (+8 in UA)
-as 82.95mm long cylinder can hold x38 (+10 in UA)
-as 66.15mm long cylinder can hold x48 (+13 in UA)
-as sphere it can hold x45 (+12 in UA)

By Available Length. If we subtract out the barrel length from the arm shield, and stack the shells infront of each other in the remaining length, number in parthesis is for upper arm (all numbers rounded down):
-NATO standard length (617mm) can hold x2 (+0 in UA, yes none fit)
-at 1/2 the NATO length can hold x4 (+1 in UA)
-at 1/3 the NATO length can hold x6 (+2 in UA)
-as 105mm long cylinder (or sphere) can hold x11 (+4 in UA)
-as 82.95mm long cylinder can hold x15 (+6 in UA)
-as 66.15mm long cylinder can hold x18 (+7 in UA)
-at 26mm long cylinder can hold all x48 (+19 in UA, @20mm long can hold all x60 from RT.com Infopedia in the armshield alone)

So can we put 48x 105mm diameter shells into the Right Arm Shield/Upper-Arm? The answer is yes, provided the shells are short enough in length. That means one of four scenerios is at play (five if you count it doesn't exist and they should all be beam weapons, six if you want to say an invisible/unseen external magazine drum is at play or seven they have undisclosed "macguffin" technology that can take several forms or eight the ammo is stored in the torso):
-the ammunition is telescopic/caseless (this can reduce the length of the round, but it is highly questionable if it could reduce a cannon shell that much)
-the ammunition is using more powerful propellant materials (like seen in SLAP rounds?)
-the ammunition is some combination of the caseless and more powerful propellant
-the ammunition requires no propellant as the weapon is actually an electro-magnetic mass driver (rail gun) firing a canister that can be configured for a variety of roles.

All of these have some basis in the 2E REPG setting. We know the ASC has caseless ammunition (M-33 pistol), they use SLAP and LEAP projectiles (more energetic propellant?, this also includes the M-33), and they have electro-magnetic mass drivers (Tri-star's 220mm Rail Cannons).

So I guess the question is which seems the more plausible explanation to to how the VHT-1 carries all that ammo:
-rounds apply caseless ammunition and/or SLAP/LEAP technology
-electro-magnetic propulsion for the shells (allowing them to be reduced in size)
-conventional shells stored in the body/nose of the tank that feed in from the top of the shield (as in B-Mode), with the Battloid Mode being rectoned into having only 1x round w/o transforming back to G/T (or give it a complicated feed mechanisim to overcome this)

Weapon Configuration Tangent Option in Spiler

Spoiler:

Side Thing I looked at during this to preserve the idea of a projectile launcher in the shield was to ditch the cannon and use missiles (which are projectiles) that would run the length of the shield and launch Vertically from them in T/G modes and horizontally out the side in B mode, this requires the missiles to be guided, but you could install in the Right Arm Shield (left would be reduced due to the tri-cannon by some percentage unless you want to ditch it):
-24x 125mm Missile (size of the later PBC cannon)
-28x 105mm Missile (size of the cannon's shell)
-38x 78mm Mini Missile
-42x 70mm Mini Missile
-50x 60mm Mini Missile
-15x 190mm SRM (technically won't fit)
-16x 180mm Grenade used by the TZ-IV Weapon Cluster (technically won't fit, it's considered a Mini Missile for damage purposes)
-16x 178mm SRM on the Tomahawk (I point this out due to the TZ-IV being a Mini Missile with larger diameter, but we have an SRM with smaller)

The 125/105mm option would require a purpose built missile at this size (none exist in RAW descriptions in 2E RT AFAIK), so it might be classified as a Mini-Missile OR Short Range Missile as I'm not sure which based on just known examples of diameter and range categroy. The 190/180/178mm options won't fit the existing shield, though if the shield could be increased in size outward (in T/G Modes it would increase the width and possibly the height) then it would be an option.

Using the Mini-Missiles as replacements would result in a drop in firepower (damage x total payload) and range compared to the cannon. To preserve as much of the firepower/range of the cannon in missile form I think requires using Short Range Missiles, you would still come up short in terms of payload without some assistance from the second arm shield (at ~75% capacity you could meet the cannon's capacity between the two shields).

IMHO this idea seems more at home with a new variant/model based on the main VHT-1 model than as a method to to address any issues with the VHT-1's projectile cannon. While such a unit might not have the RPG's range and power for the missiles (LRM/MRM), it would still make a decent stand-in for a Phalanx-style Destroid for short-range engagements in terms of payload.

[Rabid Southern Cross Fan]

Does a rail-gun recoil when fired? If it does, then it should be possible that the Spartas does have a rail-gun for its main gun until its supplanted by the 220mm beam cannon.

[Jefffar]

Railguns recoil, but do so considerably less than a gas expansion gun of similar power

[ShadowLogan]

Does a rail-gun recoil when fired? If it does, then it should be possible that the Spartas does have a rail-gun for its main gun until its supplanted by the 220mm beam cannon.

Yes, and I don't see why it wouldn't generate recoil. Now the amount of recoil of the system is questionable if it would explain the recoil seen in the show*, but we also don't see it eject spent casings either which would also need an explanation. A Railgun-type system offers an explanation for no casing to be ejected and would be easier to fit the official required number of shells since they can be smaller than conventional shells (no propellant) and possibly even caseless ammunition option.

220mm is from the OSM? RT.com doesn't actually list the replacement size of the beam cannon. One of the reasons I want to stick with the 2E RPG's listed sizes as much as possible since this is the RPG forum. However, if that is the size of the beam weapon instead of PB's stated 125mm, that would mean you would have even more space to work with in the arm shield (and upper arm if necessary) somewhere between x4 and x5. Still not enough to account for 48 (or 60) standard NATO 105mm length, but at 1/2 the length you'd have 47x rounds in the shield and 4x more in the arm based on available volume if the width/height is adjusted to 220mm instead of the RPG's 125mm. And anything smaller than 1/2 the NATO length would have an even easier time (at a 1/3 the length you'd have 70x in the shield).

*I would also think that any attempt to quantify it will require to many assumptions to be considered reliable.

[glitterboy2098]

i've generally assumed it uses a caseless ammunition system, which would explain the lack of casings and how when we do see shells, they seem to be the "big and lofting" style of a howitzer or tank gun rather than smaller projectiles and flatter trajectories you'd get from a high velocity railgun.

the 2nd ed RPG goes with a 105mm cannon, which is what the robotech.com entry gives it. the site and the RPG also have a later model equipped with a particle beam cannon instead, which i think was done to explain why Sean was fawning over "the new model" the unit got after Dana was assigned as its leader.

[Rabid Southern Cross Fan]

Thanks to Teddy Gorospe on FB (for hooking me up with a downloaded copy of the Japanese Pioneer LD/DVD release) the animation in Bio-Psycher/Mind Games shows that the barrel of the Main Gun,forward of the "square" is the part that actually recoils. Everything abaft of it is the housing. So there should actually be a good deal of space inside the arm shield. Of course, the RRG suggested that its main gun uses liquid propellant, so the rounds would already be much smaller. However, nothing says that the original 105mm couldn't have been upgraded at some point to a railgun (and considering the housing abaft of the "square", that would be where the magnetic coils would be located I would think).

In fact, its funny that the gun should be (based on the scene from Danger Zone) capable of launching ~10cm missiles as well. While the dialogue says they need to hit the base of the tower with a "hyper magnetic particle beam", perhaps that's fancy grunt speak for a warhead like a Proton Torpedo? And, as an added wrinkle (just for fun) it is stated in the script for The Sentinels Episode #5: The Battle for Fantoma that Wolfe's hovertanks fire missiles at the Invid. (although the text is unclear, I think the Spartas are supposed to be outfitted with the Battloid-mode Vernier Augmentation System). The start of the script for Episode #6 Hunter's Moon has Wolfe's hovertanks being reloaded with missiles.

[ShadowLogan]

i've generally assumed it uses a caseless ammunition system, which would explain the lack of casings and how when we do see shells, they seem to be the "big and lofting" style of a howitzer or tank gun rather than smaller projectiles and flatter trajectories you'd get from a high velocity railgun.

This assumes of course that the VHT's "Rail Gun" is being used to fire high velocity projectiles, it could be firing lower velocity projectiles for any number of reasons (available power being just one).

I guess the question to consider is if the caseless ammunition can be made such as to allow a VHT to carry the listed quantity of ammunition in what ever location you place the ammo storage. I do think that a Railgun-style system offers the best chance of meeting that requirement since it can go with a smaller projectile.

While the dialogue says they need to hit the base of the tower with a "hyper magnetic particle beam", perhaps that's fancy grunt speak for a warhead like a Proton Torpedo?

This makes me think of Lunk in Ep84 when he tells an Invid Shock Troopers to "eat laser" and then fires off a volley of missiles. So perhaps the UEEF and UEDF developed single use disposable beam weapons that could be mounted as a warhead for a variety of projectile types to use in place of shaped explosive?

And, as an added wrinkle (just for fun) it is stated in the script for The Sentinels Episode #5: The Battle for Fantoma that Wolfe's hovertanks fire missiles at the Invid. (although the text is unclear, I think the Spartas are supposed to be outfitted with the Battloid-mode Vernier Augmentation System). The start of the script for Episode #6 Hunter's Moon has Wolfe's hovertanks being reloaded with missiles.

It's also possible the REF has their own version of the VHT that is equipped with conformal/internal missiles like the Logan is depicted with in the Sentinel comics (also piloted by Wolfe).

And it isn't like the UEDF version of the VHT doesn't have potential room to mount missiles in either arm shield by 2030 with the introduction of the all beam weapon configuration (partial for one prior to this, unless you have optional configurations for the arm shield). And I did speculate on an all missile configuration for the arm shield (2nd spoiler at the end in original post), which would become easier if the size of the housing factors in the 220mm size instead of the 125mm size in the 2E RPG since you could then use the standard 190mm diameter missiles without redesigning the shield housing or having the missiles partially exposed or a custom missile size or going with a lot of Palladium-type mini missiles.

[glitterboy2098]

2nd ed has mini missiles in the arm shields of the invid era "wideowmaker" variant of the VHR-2 Myrmidon, so i could see a variant of the larger Spartas having Minis or even SRM's in there instead of the projectile firing weapons. probably using a variation of the same 'stacked in a tube' launcher system seen on the VF-1 'super' arm modules and thruster packs.

honestly, i don;t see why the mecha's arm shields couldn't have been designed with modular internal connections so you could more easily pull the weapon out and fit in a new type.

[green.nova343]

The 105mm cannon on the VHT is using energy to transfer momentum & kinetic energy to a projectile at rest, so yeah, there's going to be recoil.

And...to be honest, even if it's doing it with a railgun, I suspect the physics is going to say "if you transfer momentum X to projectile Y, it's going to generate recoil force Z", regardless of how the transfer occurs (gas expansion from a fast-burning propellant, electromagnetic conduction, etc.). I suppose it might vary a bit depending on how quickly the energy/momentum is transferred to the round...but I wouldn't be surprised if, because of the fairly small size of the VHT, they didn't include some sort of recoil suppression system (like they use in real-world low-recoil versions of the L7/M68 gun that are mounted on light tanks & some of the lighter wheeled AFVs).

[glitterboy2098]

The 105mm cannon on the VHT is using energy to transfer momentum & kinetic energy to a projectile at rest, so yeah, there's going to be recoil.

And...to be honest, even if it's doing it with a railgun, I suspect the physics is going to say "if you transfer momentum X to projectile Y, it's going to generate recoil force Z", regardless of how the transfer occurs (gas expansion from a fast-burning propellant, electromagnetic conduction, etc.). I suppose it might vary a bit depending on how quickly the energy/momentum is transferred to the round...but I wouldn't be surprised if, because of the fairly small size of the VHT, they didn't include some sort of recoil suppression system (like they use in real-world low-recoil versions of the L7/M68 gun that are mounted on light tanks & some of the lighter wheeled AFVs).

this is pretty much how it works. the main difference is how that recoil expresses itself.. in a cannon, the recoil is from a single explosive action, while in a railgun or coilgun it is from the (relatively) gradual acceleration along the length of the the barrel. which means in a railgun the recoil occurs over a slightly longer time and builds from lower to higher in that time. mind you, its the difference between one fraction of a second and several fractions of a second, so in practice the difference is barely noticeable to a human user.

and both conventional and railgun versions would require recoil handling systems. we see the VHT's main gun 'retract' a bit into its housing each time it is fired so it does seem to have some degree of recoil suppression. though the tank itself doesn't move much despite its relatively light weight (it weighs 26.4 tons "dry" (unloaded and unfueled), so probably between 28-30 tons ammoed and fueled up), while the 105mm on a modern tank (such as this Leopard I tank, which weighs 40 tons) all tend to have very noticeable shudder or rock back despite the gun being mounted in a recoil handling mount that moves as much as the VHT cannon does. suggesting either it is using a lower velocity projectile (which would seem to argue against a railgun, since there would be little advantage there) or some form of semi-recoilless design (like the M1128 Stryker Mobile Gun system, which uses a 105mm tank cannon [in fact, the same M68A1 105mm that the 2nd ed RPG gives the VHT] modified to include a longer stroke recoil system and a degree of gas redirection to reduce the recoil. though it shakes the 18 ton vehicle pretty bad when firing still.)

we see the muzzle blast on the VHT seem to run down the barrel back towards the mecha (not a normal behavior for a canon of any kind) which is partly why i think it is a conventional gun. that odd shaped blast would be part of the recoil supression system, part of the propellant gasses being redirected to offset the recoil. which combined with the recoil system in the mount (in fact the same actuators which extend and retract the barrel for battloid mode probably work as a recoil handling system as well) and the hover thrusters providing their own degree of counter-thrust, would enable the visuals we see.

[Jefffar]

The movement of the muzzle may be related to the reloading system as well. Teh transformation systems of the VHT require a moving barrel, so might as well make that part of the reloading cycle instead of trying to move the feed mechanism to match the barrel.

[Sambot]

I'm not sure how the rounds would be stored along with the ammo feed system, the reloading system, and the recoil suppression system, the mechanism that moved the barrel in and out, and room to store the barrel.

However it's done, I would say they're caseless rounds with an advanced propellant. I have wondered if it's a chemical laser and the "recoil" is part of loading the next round of chemicals. Then it gets upgraded to a laser directly powered from the tank.

[ShadowLogan]

2nd ed has mini missiles in the arm shields of the invid era "wideowmaker" variant of the VHR-2 Myrmidon, so i could see a variant of the larger Spartas having Minis or even SRM's in there instead of the projectile firing weapons. probably using a variation of the same 'stacked in a tube' launcher system seen on the VF-1 'super' arm modules and thruster packs.

While squeezing in Mini's into the arm shield is certainly possible, the question would have to be considered if that would be a good substitution/replacement for the main cannon (outside of IMUs) when you consider range and (game mechanic) damage options between the two approaches, a consideration that doesn't seem to exist for the SRM as range and damage. You might be able to account for the damage with a larger payload, but the range isn't as easily adjusted for.

suggesting either it is using a lower velocity projectile (which would seem to argue against a railgun, since there would be little advantage there)

I agree the projectile is a lower velocity. However, I think the main advantage of the rail gun is that it allows a reduction in the physical size of the ammunition which might be a necessity to get the required ammunition into the VHT.

A conventional self-propelled gun (example the Japanese Type74) is a bit bigger than a VHT in transport mode (by two dimensions for the Type74), and when using 105mm cannon only fits in 30 rounds (the American M7 from WWII more than doubles the payload and similar dimensions). However the VHT also has to account for systems not present in these conventional vehicles that begs the question if there would be enough room to fit the required number of conventional rounds in the required quantity in what is essentially a smaller package that also has to account for systems not present in these real world counter parts like the hover system, additional large weapons (tri-cannon and rifle), it's 2500hp power plant (Type 74 is 300hp), transformation systems, automation systems (the conventional vehicles also have multi-person crews), etc.

have wondered if it's a chemical laser and the "recoil" is part of loading the next round of chemicals.

Recoil could be the result of the chemical reaction itself that powers the laser as it can occur in a combustion chamber and generate exhaust gases (in at least one type of Chemical Laser).

[Sambot]

have wondered if it's a chemical laser and the "recoil" is part of loading the next round of chemicals.

Recoil could be the result of the chemical reaction itself that powers the laser as it can occur in a combustion chamber and generate exhaust gases (in at least one type of Chemical Laser).

Cool!