Any Track geeks out there?

#1
Something occurred to me a while back but didn't know whom to ask before my ARRSE enlightenment.

Since MBT's tend to be rear engined and hence the drive sprocket at the back, the tensioned track is beneath the road wheels.

Most APC's, IFV’s and some weird israeli tanks have the engine and drive sprocket at the front so the tensioned track is above the road wheels and not in contact with the ground or unfortunate/stubborn inf that it flattens.

I had been wondering if there was any significant advantage/drawback to either config. Obviously both work when the veh is reversing so it can't be HUGE problem?

P_T
 
#2
Not that I know a lot about the subject, but wouldn't the tensioned track be above the road-wheels in both cases?

MsG

EDIT. As you were! Yes, forwards and all. Sorry about that.
 
#3
Having driven both vehicles with the drive sprocket at the front and rear, as long as the track is correctly tensioned then there is little difference.

Unless you don't maintain correct track tension and have a severely slack track, I think then you'd notice a difference/have troubles.
 
#4
If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?

mmm?
 
#5
Arte_et_Marte said:
If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?

mmm?
I'm sure a driver mech will be along shortly to scratch his nuts and utter the DS solution of 'fcuked if I know'...
 
R

Reversionary_Modes

Guest
#6
pull-through:

Since MBT's tend to be rear engined and hence the drive sprocket at the back, the tensioned track is beneath the road wheels.
If so why, when the track is tensioned during track-bashing, is it the portion of the track not in contact with terra firma that becomes taut?

Arte_et_Marte

If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?
Surely the track is stationary relative to the ground, but not the vehicle. Otherwise, the AFV would have to remain stationary while the ground moved. Always thought it was the RAC kept the world spinning.
 
#7
Arte_et_Marte said:
If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?

mmm?
After 10 minutes of head scratching I think you're right, the MBT is in effect 'laying' its tracks (hence the H class on a license being for a 'track laying vehicle steered by its tracks') so the track link on the ground is stationary while the track link above it is moving.

Ohh err my head hurts :study:
 
#8
Silly question, if a vehicle is travelling at 30mph all its components have the same forward velocity.

Magnus Pike, tennis ball, why doesnt it smack me in the face when I throw it in the air on the back seat of the car travelling at 70mph.
 
#9
Bollock-chops said:
Silly question, if a vehicle is travelling at 30mph all its components have the same forward velocity.

Magnus Pike, tennis ball, why doesnt it smack me in the face when I throw it in the air on the back seat of the car travelling at 70mph.
Now I realise why I deserved the fail in physics :oops:
 
#10
R_M

As the nature of the post would suggest, I'm no figure of authority on armoured ops but presumably during track tensioning: the bit of track suffering the resistance of the atmosphere, against the bit that 60-odd tonnes of steel is pushing into said terra firma is rather an unfair fight?
 
#11
Pull through, you are confusing the issue, yes the track that has 60 tonnes on it will be marginally thinner, also a tad longer, the track without loading will be in a neutral state with neither external vertical or horizontal loads, assuming the vehicle isnt moving.
 
#12
Bollock-chops said:
Silly question, if a vehicle is travelling at 30mph all its components have the same forward velocity.

Magnus Pike, tennis ball, why doesnt it smack me in the face when I throw it in the air on the back seat of the car travelling at 70mph.
I've always wondered the answer to that. Can the resident physicist enlighten me?
 
#13
lofty_lofty said:
Bollock-chops said:
Silly question, if a vehicle is travelling at 30mph all its components have the same forward velocity.

Magnus Pike, tennis ball, why doesnt it smack me in the face when I throw it in the air on the back seat of the car travelling at 70mph.
I've always wondered the answer to that. Can the resident physicist enlighten me?
Because yon tennis ball is already travelling at the environmental velocity of the car and everything else in it, thus it's not affected.

MsG
 
#14
Agreed, i've either massively confused the issue, my self or both. I have exactly zero knowledge of track tensioning practice, beyond the fact that doing it wrong results in stationary targets. I would however be interested to learn - hence the post.


***********************


Hold on there I've just re-read the thread. All further statements refer to PURE mathmatics and theoretical mathmatical mechanics, otherwised referred to in reality as: "that crap that I learned at school and never though I'd use again"

When the veh is statioanry and stable there will be no tension on the tracks generated by the drive sprocket, front or back.

If the length/tension of the tracks is shortened/tensioned, the shortening willoccur where the resistance to movement is least. In this case, where the tracks do not have to push against the earth beneith them.

Whilst the veh is moving, (for a rear engined veh) the track below the road wheels is always taught. For a typical APC the track above the road wheels is effectivly transfering the energy.

P_T
 
#15
Arte_et_Marte said:
If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?

mmm?
30 mph? wot the feck you on about? Proper tanks do 21.5 mph.5fwd 2 rev with a real clutch. Dreaming git.
 
#17
Arte_et_Marte said:
If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?

mmm?
Not necessarily, the vehicle has a linear velocity whereas the track has a rotary velocity. If you wanted to find the true speed of a track you would need to measure its length then use this figure as the circumference of a circle. You could mark a single link and measure its RPM at a given speed, these could then be used (with a bit of maths) to work out the true speed of the track.
 
#18
spaz said:
Arte_et_Marte said:
If your MBT is travelling at 30 mph and at a point on the ground the track is stationary, is the track at the opposite point at the top of the track travelling at 60 mph?

mmm?
Not necessarily, the vehicle has a linear velocity whereas the track has a rotary velocity. If you wanted to find the true speed of a track you would need to measure its length then use this figure as the circumference of a circle. You could mark a single link and measure its RPM at a given speed, these could then be used (with a bit of maths) to work out the true speed of the track.
Not really, you are confusing a track with a wheel, a single point on the outside of which truly moves in a circular motion. It is more helpful (I would suggest to consider a track as a series of individual track links. Therefore the majority of their movement is either straight forward or backwards in relation to the AFV hull. As previously stated for a tank moving at 30mph, a track link at the bottom of the track will move backwards at 30mph in relation to the hull, but will be stationary in relation to the ground. A link in the top of the track will move forward at 30mph in relation to the hull but 60mph in relation to the ground being covered. This will continue until the links reach the back and front sprockets or idlers respectively, when they will change direction of movement in relation to both hull and ground.

In relation to the original question, it is easiest to consider two examples, CR2 (rear drive sprockets) and WR (front drive sprockets). Admitidly there are some differences 2 versus 1 pin tracks (although both are "live" tracks) and of course the suspension (hydrogas versus torsion bars) and also the lack of automatic track tensioning system on WR (i.e. manual cranking rather than flick of a switch). However, if you look at the handling characteristics of WR compared to CR2, the slack in the track concentrates between the front drive sprocket and the first roadwheel, this means that there is little pressure being exerted on the front suspension (other than by the wieght of the vehicle, which makes WR much bouncier when it starts or stops than CR2. However, on the plus side, as the distance between the front sproket and the first roadwheel is small, there is less lateral twisting in the track and so the track is much less prone to be thrown left or right between the sprocket and the road wheel than along the length of the top rollers on CR2 where the slack accumulates on a tank. This means that the WR is far less likely to throw a track during low speed manouvring, even if it is reletively slack, which is common on WR which has no hydraulic track tensioning system and has the less efficient torsion bar suspension. Clearly all of this is reversed when the AFV is reversing (no pun intended).

Ultimately, where the drive sprockets are on the hull does not make a great deal of difference, when compared to the other issues such as suspension type, track to vehicle weight and power to weight ratios. All design features are selected to ensure the best balance of characteristics for that type of vehicle. So for a tank, to provide a very stable platform to fire out to accurately long distances from while moving. For WR, something less complex, lighter, with a reasonable ride (personnally, I think WR is deeply uncomfortable cross country and makes me feel sick). Designers will choose to mount the nengine and gearbox in the back or front of the AFV to enable the required functionality of that vehicle. So a WR had to have the engine in the front, because the dismounts go in the back. Most tank producing nations put the engine of MBTs in the back of the hull, to give a better weight balance, thus giving better cross country mobility. The Isrealis put the engine and gearbox in the front of the Merkerva (apparently) because the frontal arcs were more likely to be engaged and Isreal could better aford new tanks than new crews to put in them (i.e. they were prepared to have a higher risk to the engine by putting it in the line of fire than the crew, who sit behind it). This comes with the added advantage, that the Merkerva is able to have a small additional crew compartment at the rear of the vehicle. This was (at the time) seen as a unique Isreali design requirement and resulted in a tank optimised (from the start) for asymetric warfare or counterinsurgency rather than the the tank on tank battles, which other tank producing nations optimised their designs for. Who's the fool now!
 
#19
Research carried out by "Caterpiller" has shown that the best place for the drive sprocket is in tne centre of the none ground contact area of the track, and so came up with this
 

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#20
Not that I'm doubting you T66, but armed only with my 0.00 knowledge of tracky things, surely a civvie thing designed to work at <10mph will have significantly different design parameters than a warry thing intended for use at >30mph for MBT's and >40mph for IFV's, where incoming fire is more of a problem than chavs lobbing rocks / stubborn ground-mounted rocks?

P_T
 
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