| From: | "Chrysanthos Kanellopoulos" <xchrysk-at-otenet.gr> |
| Subject: | Fw: Track Questions [TANKS] |
| Date: | Tue, 17 Oct 2006 07:20:57 +0300 |
| Reply-To: | tanks-at-rctankcombat.com |
|
Loose tracks without rollers work like this in high
speeds. Without return rollers, the track is practically a wave that is
exhausted somewhere in the middle due to the weight of the track. This is what
makes tracks flapping. Again, the weight of the track works as a
secondary tensioner. attached jpegs.
With return wheels, the wave is carried all the way
to and over the front wheel, causing an undesired extra loose track in the
front. Not good. All of the above applies for high speeds. My tank has no
speed controller so it drives at 5 km/h or rough terrains. In scale 1:6
that would be translated to 30 kms/h, but my tank is only 50 cms long, so it is
in scale 1:10 or 1:12 and real life speeds of 50 and 60 kms/h respectively - on
rough terrains!!
Loose tracks are good for another reason:
Tolerance. If a rock is caught between the track and the wheels, there is space
for it to go around the drive wheel and finally ejected. You cannot do this with
tightly tensioned tracks, and of course you cannot do it with a friction drive
system, that requires properly tensioned tracks (the guys here who use a
friction drive do other, wonderful things though). Yet the friction system won't
allow the motors to stall in case a rock jams between the drive wheel and the
track.
CHrys
----- Original Message -----
Sent: Monday, October 16, 2006 10:18 PM
Subject: Track Questions [TANKS] Hey Michael,
I've noticed from experience that rear drive (for my primitive models) is
safer. It depends more on laws of nature. With a rear drive, like in T-34s and
Universal Carriers, and Abrams, and a number of other vehicles, the sagging is
on the top, and the weight of sagging track stretches the track. With a
rear drive system you can enjoy all the benefits of a very loose track, on a
rough terrain. Nothing is on the way. WIth return rollers, there is a lot of
extra track, a surplus of loose track to cause problems, potentially, like throw
a track.
With a front drive, the "sagging" of extra track, is
between the drive sprocket and the front ground wheel. See in attached jpeg what
happens with an obstacle ( I experienced it with my first RC all steel
Sherman). As you said, the drive sprocket PUSHeS the track over the obstacle,
and in between the sproket and front ground wheel. In my Sherman the track was caught there and wound around the back of
the sprocket. Di-sa-ster!
The vehicle won't roll over the rolling "ramp" of sloping track in this
front part. The front ground wheels will suffer a major shock. The tank actually
has to climb one step up.
In the other jpg, you see how the weight of the track (with blue , in the
middle, above) works as a secondary tensioner. It stretches the track from
either side / direction around the wheel. WIth red arrows, the force of the rear
drive system, always PULLS the track from the front of the vehicle. The track is
pulled firmly, yet with some tolerance and elasticity, from both red and blue
forces around the front and rear wheels. And yet, with a rear drive, I drive my
tank on very rough terrains with very loose tracks as shown in the third
attachement.
I hope that helps
CHrys
2 I've
noticed that full-scale tracked vehicles can be either front-drive or
rear-drive. The engine seems to be always at the same end as the drive
wheels, but I'm not sure whether, in general, the engine location determines the
drive-wheel location or vice versa. (I did read once that the Merkava is
front-engined, and thus front-drive, in order to provide additional protection
for the crew from frontal assault.) It seems to me that, if you want
to have slack in the track---see previous question---the track system will work
better FOR FORWARD TRAVEL if the drive wheels are in the rear. I say this
because the drive wheels cannot push the track, only PULL it. (Is that
comment clear?) Anyway, does anyone have anything to say about this
topic?
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