The world needs more robots with tank treads, keen to see some photos!

The treads are ordered, so something is going to get built around them!

The problem at the moment is the drive sprockets. To save weight, I want to use aluminium and can't find the right size (#35, 17 teeth, 1/2" bore) on-line. Does anyone know of a reliable free CAD download source? The ones I tried so far are either broken or want a paid membership .
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Is there a special tooth profile for sprockets not just semicircles?
if its circles Array polar in rhino should do the job for you
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Mechanical engineers build weapons, civil engineers build targets

Go to the SDPSI website, find the sprocket you want, then download the 3D CAD file (IGE), then you can just CNC one out of alloy.
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https://www.halfdonethings.com/

Thanks guys - I totally forgot about SDPSI
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Looking at the SDP/SI website it doesn’t look like they have 17t sprockets in #35 size.

My favourite online part server is: http://hpc.partcommunity.com/3d-cad-models/ its free and easy to use/navigate, you just make an account and it emails you the CAD files for the parts that you want and from experience you don’t get any junkmail or anything like that.

The sprockets are under the gears tab and just search for 3/8pitch for #35
It looks like the #35 17t sprocket model that they have doesn’t have a ½ inch bore, so you will need to slightly modify the CAD model but that shouldn’t be a problem, if it is just send me a PM and I can probably change it to what you need.

always wanted to build a tank something sounds great!
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Sprocket prototype:

Thanks to the magic of the interwebs and digital fabrication, the drive sprocket prototype is ready, already The sprocket will weigh about 31 grams, while the final item will probably have a smaller hub to fit inside an aluminium crush tube.



Thanks again for all the help! Its just dawning on me how massive these treads are. At 75mm wide, each link probably has a larger contact patch than the Colson wheels my other bots use - and there are 19 links in contact with the floor.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

If you are purely wanting more pushing power, maybe something like a Ducted fan could be a good option. Putting the 2kg into a big ducted fan powered by a monster Outrunner is going to improve your pushing power more than the tracks.

Are you having idler rollers all the way along? Otherwise you will only get decent traction from the areas that have a roller/some form of force pushing down on them.

Too late for a ducted fan - the treads are already on their way. There is some room for idler rollers; until I get the treads I don't know whether its better to use sprockets along the edge or rubber rollers in the centre.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

New Wheels:

I found some potential wheel upgrades for Sawnado at Hobbyking:



They are 99 x 42mm and quite a bit stickier than Colson wheels. They need a hub cast inside the tread, probably in a hard urethane. The extra grip should overcome the terrible weight distribution and make use of the extra motor power.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

quote:

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Originally posted by pilleya:
If you are purely wanting more pushing power, maybe something like a Ducted fan could be a good option. Putting the 2kg into a big ducted fan powered by a monster Outrunner is going to improve your pushing power more than the tracks.

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I'm sure someone will quickly prove me wrong, but I can't recall an effective ground-effect bot that used an EDF. There has been much talk and the theory is sound when the bot is on a smooth & flat floor, but suction is like magnetic hold-down; as soon as the bot is lifted slightly, the effectiveness drops off.

The other thing with tank treads is that the audience knows how they work and they have high visual appeal.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Tank treads are very cool.
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So even the rain that falls isn't actually going to fill our dams and our river systems

Killerhurtz had a reasonable "sucker".

But as mentioned before, the skirts needed are very vurnable.