Crawler tracks

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bullestock
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Re: Crawler tracks

Post by bullestock » 23 Jan 2012, 21:40

marcoloca wrote:
hassenplug wrote: I would connect the motor to the middle hub to give it good ground clearance, but only if the track goes around 90 degrees of the hub. Less than that, and it may slip.
Sorry, I don't understand "goes around 90 degrees of the hub"...
The track needs to touch the hub (wheel) for at least a quarter of the hub - look at this picture:

http://en.wikipedia.org/wiki/File:Track ... ram%29.png

Here, 1 and 4 would be good places to attach the motor, but 5 and 6 would be bad choices, because there is too little contact between hub and track.

h-g-t
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Re: Crawler tracks

Post by h-g-t » 23 Jan 2012, 23:05

If your vehicle is mainly moving forward, driving the back (wheel 5 on the diagram) is best.

The lower track is being pulled straight by the rotation of the drive wheel so is less likely to jump off the wheels.

Of course, when going in the other direction it is being pushed so not kept tight.

If it will spend the same time in either direction the the 3-point solution (top wheel driven) should be better but there is greater chance of the track jumping the drive wheel.

You might be able to get round this by having another wheel (with a tyre) on top of the track pushing it down onto the sprocket.

Alternatively, you could have a tensioner wheel (either inside or outside of the track) which keeps it all fairly taut.

This could be on a pivot and operated by a rubber band or spring).
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marcoloca
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Re: Crawler tracks

Post by marcoloca » 25 Jan 2012, 14:54

bullestock wrote: The track needs to touch the hub (wheel) for at least a quarter of the hub - look at this picture:

http://en.wikipedia.org/wiki/File:Track ... ram%29.png

Here, 1 and 4 would be good places to attach the motor, but 5 and 6 would be bad choices, because there is too little contact between hub and track.
Thanks, now I understand! I'll see tomorrow in the laboratory =)
h-g-t wrote:If your vehicle is mainly moving forward, driving the back (wheel 5 on the diagram) is best.

The lower track is being pulled straight by the rotation of the drive wheel so is less likely to jump off the wheels.

Of course, when going in the other direction it is being pushed so not kept tight.

If it will spend the same time in either direction the the 3-point solution (top wheel driven) should be better but there is greater chance of the track jumping the drive wheel.

You might be able to get round this by having another wheel (with a tyre) on top of the track pushing it down onto the sprocket.

Alternatively, you could have a tensioner wheel (either inside or outside of the track) which keeps it all fairly taut.

This could be on a pivot and operated by a rubber band or spring).
Our robot must turn and go backwards sometime... I think it's better trying to connect the motor to the middle high hub. Other more complicated methods are unsuitable for our simple robot, sorry =)

h-g-t
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Re: Crawler tracks

Post by h-g-t » 29 Jan 2012, 16:30

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spillerrec
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Re: Crawler tracks

Post by spillerrec » 30 Jan 2012, 00:08

What is the advantage of positioning the threads in this kind of triangular fashion? I would think that to get maximum grip you would want to have as much tread touching the ground, however a triangular design would reduce this a little.

Just to make sure it is mentioned, the rubber tracks do require quite a bit more power to turn them, because of the internal friction in the tracks. The thread links do not have this issue but since they are of plastic they have very little traction on hard surfaces.
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h-g-t
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Re: Crawler tracks

Post by h-g-t » 30 Jan 2012, 02:22

I think the main advantage is that the lower track is under tension whichever direction you are going.

It might also help to improve ground clearance under the centre of the vehicle by keeping the gears, differentials, etc higher up.

Probably does not improve the stability by putting weight up higher though.
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jwiger
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Re: Crawler tracks

Post by jwiger » 11 Feb 2012, 20:38

I would connect the motor to the middle hub to give it good ground clearance, but only if the track goes around 90 degrees of the hub. Less than that, and it may slip.
Sorry, I don't understand "goes around 90 degrees of the hub"...
The track should contact 1/4 (25%) of the driving wheel hub, or more. I would recommend the front or back (anterior or posterior) since most track designs (re: a bulldozer) have almost 1/2 (50%) of the wheel hub in contact with the track.
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pepijndevos
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Re: Crawler tracks

Post by pepijndevos » 13 Feb 2012, 21:22

mightor wrote:At my robotics club we have competitions and the robots with the tracks often find themselves unable to make a pivot turn on the rubber mats due to the friction. I've seen tracks split or just come off the little wheels. Keep that in mind :)

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mightor
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Re: Crawler tracks

Post by mightor » 14 Feb 2012, 11:33

We get together in Sint-Katelijne-Waver in Belgium. It's quite close, about an hour from R'dam. More info: http://wiki.robotmc.org/index.php?title=Hoofdpagina

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