Alright, so I am new to robotics as well as this site, but here is a question I feel I have to ask. I need to ask because it will effect a future project I want to do when I am more experienced in Robotics.
Alright, so the theory behind this question has entirely to do with ground clearance with a treaded chassis. I notice that every bot with treads has very little ground clearance, and was wondering if there wasn't another way to do the chassis so you could increase the clearance and what kind of effect it would have on terrain options.
So, for reference I have a few pics of sketches. Please ignore my horrible drawing ability, as well as the pictures, as I took them with a digital camera at my desk, instead of using my scanner.
Image #1: Traditional Style (insofar as I have seen)
Image #2: My Design
Basically, the black lines are obviously the wheels and tread, and red is the chassis/frame for the bot. You can see in the second how it has raised the clearance by quite a bit. In the picture I used solid frames extending down to the lower wheels, but as I sit here, I am already thinking of how you could implement a shock absorption system to further enable rough terrain durability.
Basically, I just wanted to get some feedback to see if my idea is crazy, or if I am.
Edit: Thinking along another thought path (which I am prone to do) I came up with the idea of 4 treads on a bot (which I am sure isn't a new one) and was curious as to if there is a reason for not doing it, or does it just present to many problems? Image #3 is what I came up with.
What I gather from the pictures is that ground clearance is defined by the diameter of the wheels that carry the weight of the vehicle. The big ones in the middle of the track. Most LMR robots are too small to even have those wheels. So they only have the drive wheel and a free wheel (idler pulley). Just like this little wooden design: http://woodgears.ca/tracked_vehicle/index.html.
In your second image, you solve the problem by mounting the wheels on legs. But the wheels are very small (in comparison to the body). That vehicle will not be able to climb an obstacle like a threshold in the doorway. Place the lower two wheel closer together, like a tank has them. The front and back of the track now is diagonal and it will climb up and over any obstacle.
in ascii art:
BTW: I love the whyteboard/digicam design sharing technique!
Instead of using axles for the wheels try mounting the wheels on a standoff with an OD less than the ID of your wheel (you could also find a metal bar of the right diameter cut it to length and drill/thread it but that’s a bit beyond most of us). Then you won’t have any bars going from one side to the other. With the use of a sprocket and chain setup to drive the wheels you can create as much ground clearance as you want and still keep the classic \O^^^^^^O/ look to your treads.
The_keyword recently did something similar to this. Check out the video on this page and this picture. If he had opted for a chain drive setup instead of a direct drive (mount motors to wheel) setup he could have increased the ground clearance as much as he wanted (until that plastic sheet began to bend due to the laws of physics and leverage). You can do the same thing with the Tamiya trackset and get that classic tread look, just throw away the axles that come with it and use the standoffs.
NOTE: Using a bearing would be much better than placing the wheel straight on the axle but alas finding them can be hard and expensive. Just make sure you grease the standoffs (or whatever you use) and the wheel to cut down on friction. It shouldn’t be a problem on small scale projects like most of us are building.
This is a good design as it uses the three sprockets, with the upper one being the drive gear giving quite a bit of clearance depending on how the motor is actually mounted. This also has the drive gear slightly forward which helps with keeping the center of gravity pretty close to the center and low. Hootyhoo’s suggestion would also help giving additional clearance with mounting the sprocket/wheels on pegs/standoffs.