Racing tracked vehicle

[Kemenb]

Hello everybody!
I'm new to this forum, and to tracked vehicles, but not to building RC cars.
I'm building something what I always wanted-fast tracked vehicle, my requirements:
-fully adjustable suspension
-wide tracks, racing look
-slipper cloutch on each track
-2 motors (more power, easier to build)
-good airflow-cooling
-my goal speed is 100 km/h



This started as 500 mm long vehicle and grow to just over 1 meter and 480mm wide. I plan on using 2x Castle Creations Mamba XL ESC and 2x CC 2028 brushless motors, the power will be supplied with 2x turnigy nano tech 8s 5000 mAh li-pos. Shock absorbers are rear Carson Gas Devil. Whole vehicle is build from 7075 6mm thick aluminium, suspension arms are 10mm thick. Track is also build from 10mm thick aluminium with rubber pads. So far the vehicle weights 33 kg fully loaded, but I want to lower the wight down as much as possible. I found out that RPM uses nylon, how thick nylon should I use, or is there any better material?

My second problem is gearing, castle creations doesn't want to release any data about their motors, all they say is "you can run in 10hp 1:5 baja range" and that it is 750kV. I took a look at 1:5 baja transmission and try to match their gear ratio. Pinion gears range from 12-18T, spur gear is HPI baja slipper clutch, 57T. Baja has a second set of gears to lower gearing ratio, so instead I used smaller track drive sprocket, Baja tires are 180mm across, my track drive sprocket is around 90-100mm. Will this work, or will I burn the motor?

Drive sprockets on some of the photos are not up to date, this are the marching sprockets for the track:




Suspension arm travel is 100mm, ride height (without gravity) ranges from 80-120mm or even 150mm if you don't mind having suspension arms in almost vertical position.
Track tensioner (not sure if this is the right word) is in front and has 2 shock absorbers to help keep the track tight and in place.



Some screenshot have 2 types of track, the one with chain was too heavy-10kg even without all the parts, so I decided to use the other one with aluminium base and rubber pads (5 kg). Below from left to right you can see aluminium base and 3 types of rubber pads, the firs is very simple, second is monster truck style, the third is proline octa grab tire inspired. Does any one have any idea how to make this pads?



Can I use V tail mixer and car radio to operate this vehicle?
Any help will be very appreciated.

[jdflute]

For those speeds I would say you need a high density rubber track similar to those used on industrial conveyor belt systems. The project will either succeed or fail with the building of the tracks and sprockets so get that sorted first.
There is a lot of parts and friction with a tracked vehicle and it is very easy to throw a track or shred a gear box, so I wishyou luck.
Don't know whether the motors will work or burn out that will have to be trial and error I think.
The best thing is to start simple, create aand test prototypes and learn from your mistakes. I guarantee that the finished product will have changed significantly from your first design.

Jd

[Andy in Cheltenham]

I'd go for bigger road wheels. they would rotate slower than tiny wheels and would ride better.

[Kemenb]

Great! Now we are getting somewhere, I was wondering why most of the tanks use big road wheels. How big wheels are we talking, twice the size? Currently they are 50mm across.

@jdflute: I also goggled your suggestion, but making a mold for rubber track will be very expensive, I'm still searching for a track that is 100mm wide and is commercially available, maybe I will find something.

Keep the ideas coming

[Andy in Cheltenham]

I don't think there would be an ideal size. Just make sure they fit nicely into the area available. Use them to return the track as well. have a look at the T34 design from WW2. Simple and effecient. Your biggest problem I reckon would be centrifugal force on the tracks themselves.

[jdflute]

I wasn't suggesting you make the track, look for off the shelf industrial belt sytems, intralox is a place to start

Jd

[Kemenb]

Found something, I'm just skeptical this will survive 2 motors, 10hp each, I'll do some more research:
http://www.rctankcombat.com/tanks/T010/

I have another question, what are the benefits of having drive sprockets in front or in the rear of the tank?

[jdflute]

None, it's more likely to destroy your track quicker.

[Hein SA]

Hmmmm Very interesting... Would like to see it run

[Kemenb]

Does any one own 1:4 scale tank? Would those tracks hold be tough enough for my project?

This road wheels are as big as I can go without having to redesign whole thing, tires just pass the next swing arm mount by few mm (my guess around 5mm). I also marked them, hopefully you can see them better.