Tracked Vehicle Drive Sprokets

[Folkbox1]

Are there any benefits to having the drive sproket at the front of the vehicle rather than at the back? I can envision some benefits to having the drive at the rear but many have had the drive at the front (even with a rear engine which seems a strange thing to do to me - the extra weight and compexity of driving the front sprokets from the other side of the turret).

Does it if fact make any difference at all?

[ferny]

hi Darren.

It all depends on what the AFV is designed for.

here are 2 examples:

British Army Warrior, infantry fighting vehicle with the back used forthe troops so engine and transmission is in the front.

Chally 2 MBT huge engine to move the beast so its at the back also the turret ring is pretty big as well.

I thing the germans had other ideas with thier tank design but im no expert on them!

Hope that helps.

Jon

[ChrisITA]

As brits we do seem to be the odd ones out in preferring rear mounted engine and transmission (including the sprockets)

I have always assumed the choice to put the sprockets at the front was down to engineering reasons. With the sprocket at the rear the tank moves by the sprocket pulling the track from under the road wheels. With only a short section of track between the last road wheel and sprocket, I imagine this puts a lot of strain on the track. With the sprocket at the front, the track is pulled by the sprocket along the top run from the idler with less tension

There is also the issue of steering control. In German tanks this was done directly by a relative short system of hand and foot actuated levers into the actual gearbox and transmission. In British tanks this system had to run from the very front of the tank to the very rear. The longer it is, the more opportunity for something to go wrong

Having the transmission at the front would also seem to make it vulnerable to fire (seeing as tanks try to send most of their time facing the enemy), but the flip side of that is that its that much more metal in front of the crew. In british tanks the only thing that seperated the crew from fire was the frontal armour

Swings and roundabouts I guess

Chris

[Andrew Jones]

As brits we do seem to be the odd ones out in preferring rear mounted engine and transmission (including the sprockets)

I have always assumed the choice to put the sprockets at the front was down to engineering reasons. With the sprocket at the rear the tank moves by the sprocket pulling the track from under the road wheels. With only a short section of track between the last road wheel and sprocket, I imagine this puts a lot of strain on the track. With the sprocket at the front, the track is pulled by the sprocket along the top run from the idler with less tension

There is also the issue of steering control. In German tanks this was done directly by a relative short system of hand and foot actuated levers into the actual gearbox and transmission. In British tanks this system had to run from the very front of the tank to the very rear. The longer it is, the more opportunity for something to go wrong

Having the transmission at the front would also seem to make it vulnerable to fire (seeing as tanks try to send most of their time facing the enemy), but the flip side of that is that its that much more metal in front of the crew. In british tanks the only thing that seperated the crew from fire was the frontal armour

Swings and roundabouts I guess

Chris

Should in fact be the other way around, much less strain on the track with a rear drive sprocket, the track on the ground does not in fact move at all. It is not pulled from under the road wheels ,but the tank rolls along it and it is then lifted by the sprocket. You will notice with a tank with rear drives that the upper run is not under tension and usually hangs slackly, ie Cromwell, JS 3, KV etc, whereas with a front sprocket the top run is taut ie Sherman ,this must put a greater strain on the track and running gear.

[ChrisITA]

Should in fact be the other way around, much less strain on the track with a rear drive sprocket, the track on the ground does not in fact move at all. It is not pulled from under the road wheels ,but the tank rolls along it and it is then lifted by the sprocket. You will notice with a tank with rear drives that the upper run is not under tension and usually hangs slackly, ie Cromwell, JS 3, KV etc, whereas with a front sprocket the top run is taut ie Sherman ,this must put a greater strain on the track and running gear.

this mighty be true if there is any power in the roadwheels, but there isn't, they're just free rotating wheels on axles. The power being supplied by the sprocket

The road wheels rotate and move the tank forward by this rotation because the track is being pulled rearward from under them. This puts all the pressure of pulling the track on a few links, rathern than spreading it over half the run.

The Cromwell track does not really sag, it only touches the top of the centre road wheel when correctly tensioned. The Sherman track would sag to a similar extent (ie very slightly) where it not for the track skids.

Sag or lack thereof has very little to do with which end the sprocket is positioned at and much more to do with a combination of track design (the Sherman's design promotes less wear on the track pins so less sag) and maintenance (British tank crews were required to adjust the tension on track every day if not directly involved in action)

If it was true that front sprocket tanks experience less sag then Panzers wouldn't experience sag, whereas most photo evidence famously points that they suffer from it significantly

Chris

[mrcooljules]

i built 10 armourfast cromwells recently...knew something was wrong but wasnt sure what

i put the tracks n wheels on wrong side, so went from rear to front drive lol.....

i had used superglue so was a nightmare to rip em off n then scrape clean to fit again

[Dads203]

By putting the drive sprocket on the back you can keep the engine and transmission as one unit, so its easy to lift out and replace in the field if it should fail.

Nearly all modern MBTs have this design apart from the Merkava. The Merkava carries an infantry section in the rear so it had to have the Powerpack in the front to allow for the troop

compartment in the rear. Same design as modern APC's, as the rear compartment is for troops and not engine/gearboxes.....

HTH

Dan

Edited December 7, 2010 by Dads203

[ChrisITA]

By putting the drive sprocket on the back you can keep the engine and transmission as one unit, so its easy to lift out and replace in the field if it should fail.

Nearly all modern MBTs have this design apart from the Merkava. The Merkava carries an infantry section in the rear so it had to have the Powerpack in the front to allow for the troop

compartment in the rear. Same as modern APC's, as the rear compartment is for troops and not alot else and not engine/gearboxes.....

HTH

Dan

A very very good point indeed. The Abrams and Leopard can swap out the engine in minutes I believe, because the engine and final drive just slides right out. Mind you, its a shame we didn't think of that in WWII! Would have saved REME many man hours, and the Russians

[Dads203]

A very very good point indeed. The Abrams and Leopard can swap out the engine in minutes I believe, because the engine and final drive just slides right out. Mind you, its a shame we didn't think of that in WWII! Would have saved REME many man hours, and the Russians

I worked on AFV's for 10 years of my army career. Nothing like a packlift to cheer you up especially in the field when its raining.

[Derbyeomanry]

I think the type of track dictates whether/how much it will sag or not. Most US WW2 tanks used live track - the track pins were rubber bonded inside the track block. Adjacent track blocks were joined with end connectors which made for quite a stiff track unlike other types which were joined together using a track pin leaving the track loose and flexible a bit like a watch strap.

Shermans/Grants/Stuarts were rear engined with a prop shaft running through the hull to the gearbox/diff which transferred drive to the front wheels. The gearbox was next to the driver so linkages were short and simple. However this made the tanks quite high as the prop shaft had to run beneath the turret basket

Rear engine/gearbox necessitated the use of long, complex linkages from the driver compartment to the gearbox. I believe some Brit tanks used compressed air to work gear cahnge mechanisms.

The non-driving idler wheel was used to tension tracks whether at the front or rear

Neil

[spike7451]

Ahhh yes,,,the Sprocket.Loads of fun!

Strangfellow bar,RAF Mount Pleasant 1989.

Idea was to fit thru the sprocket completely..Some people had....trouble..

Edited December 7, 2010 by spike7451

[ferny]

I have been through (almost) one of them in the Crab and Sprocket!

[spike7451]

I have been through (almost) one of them in the Crab and Sprocket!

Does my bum look big in this?...

[Folkbox1]

This puts all the pressure of pulling the track on a few links, rathern than spreading it over half the run.

Surely this is not true! Is not the tension the same for each link whether it is a short run to the drive sprocket or a long run from the last road wheel?

[ferny]

I worked on AFV's for 10 years of my army career. Nothing like a packlift to cheer you up especially in the field when its raining.

You forgot to mention in the dark aswell!

[derek burton]

Or a troop track change(Chieftain), oh and by the way we can change that busted suspension spring while we are at it, i used to hate that the way it used to ping and ring as you tightened it down scarred me to death.

dont forget, track to the back same track, track to the front other ****.

Dek.

[ferny]

Can't beat a bit of track bashing!

[pigsty]

Surely this is not true! Is not the tension the same for each link whether it is a short run to the drive sprocket or a long run from the last road wheel?

I'm sure it's not true, too. While the entire vehicle is moving forward by means of the track being fed forward and the road wheels rolling over it, the sprocket is only trying to move the track against the ground resistance; it's not trying to lift the weight of the vehicle or drag the track out from under it. Plus, while track stretches, that's a result of wear over time. It's not elasticated, so pulling over a greater length doesn't distribute the force any more usefully.

We had this discussion over on Armorama and I think we came to the conclusion that there are advantages to either layout, but the main determining factor these days appears to be having as short a transmission path as possible. It's very rare to find an armoured vehicle now whose engine is at the other end from the sprocket. I'd post a link to Armorama but it would take an age to find it, I'm afraid.

[Dads203]

Or a troop track change(Chieftain), oh and by the way we can change that busted suspension spring while we are at it, i used to hate that the way it used to ping and ring as you tightened it down scarred me to death.

dont forget, track to the back same track, track to the front other ****.

Dek.

Pad changing was even better, 87 ish pads each side to change..... Nice!

[davidelvy]

A very very good point indeed. The Abrams and Leopard can swap out the engine in minutes I believe, because the engine and final drive just slides right out. Mind you, its a shame we didn't think of that in WWII! Would have saved REME many man hours, and the Russians

The Americans did with the Hellcat. Saw it on that excellent series on tank restoration, the name of which eludes me.