Hi, Can anyone please explain how the M1A1 (AIM) decides which track to drive on a neutral turn? I have been driving one around at low speed, practicing getting it in & out of sheds and when neutral or pivot is selected, there seems to be no logic as to which track will drive and (where appropriate) which direction it will drive in.
Is there a simple method of determining which track will be driven?
I assume it works the same as the old M-60 did. If you put the transmission in Neutral (with the engine running, of course), then turn the wheel/steering bar to the left, the right track will drive forward that the left track will turn in reverse. This has the affect of pivoting the vehicle on it's center in place, rather than making and arcing turn.
If you watch this video, you will see both a German Leopard and an M-1 Abrams use neutral/pivot steer...
Hi greywolfghost, It's when performing pivot turns, sometimes one track will lock up and the other will drive in the appropriate direction, other times we get the 'true' pivot turn when both tracks drive in opposite directions. I wondered if there were preconditions, maybe moving from 'reverse' to pivot and then turning has a different effect to moving from 'drive' to pivot.
If the vehicle is in a "Forward Gear" and the driver turns left, braking is applied to the left track. The universal gear in the trans-axle transfers the power to the right track. Trying to "Neutral Steer" while in a backwards or forward motion of any speed could damage the transmission and break or throw a track, not to mention beat the crew to death inside. Just because the tank stops or turns, doesn't mean the people inside do. If the driver does something radical or stupid, he can smash the gunner's face against the sights and smash the ribs of the loader and TC against hatch rims - think about it...
I got my hand crushed once while crouching down inside trying to change a radio frequency. The driver suddenly pulled forwards then hit the brakes so hard the latch on the TC hatch busted and allowed it to drop on my fingers on the hatch rim. Luckily, it was really cold, so I had double glove liners in my leather gloves. Otherwise, I probably would have lost all the fingers on my left hand. No time for sickcall though. Just taped them all up and spent the next two weeks in the field nursing a very swollen hand...
Hey mate, I wasn't talking about changing to pivot whilst on the move - that'd be crazy!
What I am trying to get at is sometimes when we do a left pivot turn, the right track will be driven forward and the left track held, on other occasions, the left track is driven rearwards and the right track is held, or, both tracks drive in opposite directions.
Is there a 'logic control' in the transmission which decides which track is driven?
Planetary gears work the same in tanks as they do in the drive train/rear axle of a standard truck or car (that doesn't have limited-slip or posi-traction). When braking is applied to one side, to go around a corner, the planetary gears rotating around the driving shaft transfer the power to the outside wheel or track in the turn. If this didn't take place, the inside track or wheel would try to turn at the same rate as the outside track or wheel, putting bad stress on the system, possibly tearing up tires, tracks, axles and gears...
The same thing can probably achieved hydraulically in trans-axles that use oil rather than gears to drive the shafts, but the concept wouldn't differ much - -
Beyond that - you'll have to take the mechanic classes I sat through . . .
This message has been edited. Last edited by: greywolfghost,
Ahhhhh yes ... Marisa Tomei ... oh, and Joe Pesci.
< I wasn't talking about changing to pivot whilst on the move - that'd be crazy! >
Why ... we did it all the time ... coming to a 90 degree turn on a road (or even a city street), drop it to neutral, do the left or right neutral steer, drop it back to Low, and move on ... no problem! A 'normal' left or right turn on some of those narrow roads/streets, goes to wide. Of course this was an M60A1. The assumption, not knowing for sure, would be that the Abrams works the same ... or similar, at least.
I seem to remember in the M113 that one track would lock up and the other rotate just using the regualar drive sticks. However if you wanted both tracks to spin counter to each other in a proper pivot steer you had to grasp another pair of smaller sticks and punch the accelerator hard.
Isn't that what the OP is talking about?
I don't know the setup on the M1 specifically but maybe they automated it a little more with the controls so the engine knows the difference instead of the driver having to communicate via a different set of levers?
Erich, the smaller ones your thinking about were used when we would swim a 113.
If I remember right, the regular laterals would still let the track move some, but the other ones totaly stoped the track.
The only vech. that I drove that could do a pivot like the OP is asking about was the 551's we had at Irwin, and the only in first or second, after that it turned like any other track vech, big wide turns.
I understand the transmission system basics, but the M1A1 doesn't seem to consistently lock one track or the other when performing pivot turns. As I said above, sometimes both tracks will be driven, other times one will drive and the other won't. The end result is the same, the tank turns in the desired direction but the way it does it seems to be random. I'm an armament fitter, so it doesn't fall in my area of concern really, I'm just a bit mystified by it.
I know what you mean OP, the same thing happens sometimes with the M270A1 MLRS (which uses a Bradley chassis). I find that it helps if you floor the gas pedal while in pivot, obviously making sure to be gentle while turning the yolk...It seems like the inside track is more likely to lock up if you don't put much gas into it...
Originally posted by Nige: I understand the transmission system basics, but the M1A1 doesn't seem to consistently lock one track or the other when performing pivot turns. As I said above, sometimes both tracks will be driven, other times one will drive and the other won't. The end result is the same, the tank turns in the desired direction but the way it does it seems to be random. I'm an armament fitter, so it doesn't fall in my area of concern really, I'm just a bit mystified by it.
It has to do with the radial/planetary gear system. If one track is slipping because it is on looser or slicker footing, the gear will actually send most of the power to it because it is easier to move. If you had individual brake peddles for the tracks, the way some tractors do, you could apply the brake a little to the spinning track, and that would force the transmission to drive the stalled track more . .
Originally posted by Rocket_Redleg: I know what you mean OP, the same thing happens sometimes with the M270A1 MLRS (which uses a Bradley chassis). I find that it helps if you floor the gas pedal while in pivot, obviously making sure to be gentle while turning the yolk...It seems like the inside track is more likely to lock up if you don't put much gas into it...
bingo, when pivot is selected, sometimes it wont work properly (one track forward one reverse) unless you add some throttle, sometimes significant throttle.
Originally posted by greywolfghost: I assume it works the same as the old M-60 did. If you put the transmission in Neutral (with the engine running, of course), then turn the wheel/steering bar to the left, the right track will drive forward that the left track will turn in reverse.
GWG, not true, sorry to sharpshoot on that one Pard, but on M60 series tanks one track will lock up and the other one will pull the tank around in almost it’s own length. Best done on a hard surface too. I’ve seen more than one M60 series tank throw a track to the outside in muddy terrain because of that factor.
(The locked up track digging into soft wet and uneven ground or catching on a rock being the most common problem)
Now Bradleys, yes in neutral steer mode the tracks turn in opposite directions. I’ve seen Brads swap ends so fast it’ll make your head spin.
M60s will also have both tracks spinning in opposite directions in a neutral steer ... it just depends on how much "pedal" you apply. I didn't do too much driving of one, but as TC, had it done numerous times. Once, as a Loader, we were giving a demo at a German-American day in a large open area (surrounding one of our ammo dumps ... we were to come "flying" up to the area directly in front of the bleachers, traverse the turret to where the maingun was pointed directly at the crowd; the driver was then to do a neutral steer at fairly high speed, while the TC kept the gun on the crowd! We never moved from that position during the "spin" move. Other than the diesel smoke, they seemed totally amazed.
We were giving tank "rides" to the dependants (& some of the German civvies) afterwards. The rides developed into tank "races", until the Battalion XO came over and said to at least "wait until the General leaves!" Fun for a little while anyway.
Again, it had to do with the radial/planetary gear system, and the surface you were sitting on. The track that was supposed to turn backwards may appear just to be locked, because it seemed the forward-driving track always tried to do most of the work - but in "neutral steer", both tracks get power in opposite directions... It just may not be applied equally because of the traction under each track...
Once, while skirmishing along the border, a young 2nd Lt Plt Ldr got us lost in the wee hours of the morning, and we almost blundered onto the "fence." When he finally realized his mistake, with the help of a very angry young 11D40 who could read a map ( !), he ordered the whole platoon to pull into a farmer's field of rutabagas, do a pivot steer, and head in the opposite direction ASAP! Each M-60 pulled out there in the same place, did a 180, and headed off. By the time they were all done, there was a hole 4-5 feet deep as big as a house foundation, with all these crushed rutabagas piled to one side - nice PR! I just shook my head . . .!
!), he ordered the whole platoon to pull into a farmer's field of rutabagas, do a pivot steer, and head in the opposite direction ASAP! Each M-60 pulled out there in the same place, did a 180, and headed off. By the time they were all done, there was a hole 4-5 feet deep as big as a house foundation, with all these crushed rutabagas piled to one side - nice PR! I just shook my head . . .! 
