Design a tracked bot

Lynxmotion Rovers, Sumo, and Tracked
1

Hi all,

I am planning to design a tracked bot in order to test my AGV autodrive software.
This is the first time that I use tracks so I have some question, could you explain me more, please?

My bot have to carry an electronic box that have 30cm x 20cm dimensions and about 3Kg.

What is the corret tracks lenght in order to carry this box?
How many sprocket have I to use?

Thanks.

2

It will depend onj how far apart your sprockets are.

For instance if you place your sprockets 12" apart, and use the 9 tooth (2.14") sprockets, you will need 30.8" of track per side. This means you would need to buy 3 sets of track since they are sold in 23" lengths. To save costs you could reduce the distance.

If you make them 8.5" apart you can use one set of 21 link track (23") per side. Meaning you can save some costs.
Your total length from end of track to end of track once assembled will still be 10.7", still sufficient for you size. Sprocket center to center would be 8.5".

Something this small can use the 2" wide track. It would be lots. And one pair of sprockets at each end would be good.

So you would need:
2 X 2" wide 21 link tracks
4 X pairs of 6 tooth sprockets
2 X pairs of idler mounts (to mount the idler sprockets)

Then the hubs and motors of your choice.

3

Thank you very much, evolution.

For the locomotion I am planning to use two gearmotor, is better a front or rear transmission?

4

I’d suggets putting one motor in the front and one in the back opposite of each side. That way you wont have problems counterbalancing the robot and power is coming from both one front wheel and one back wheel, allowing better driving on difficult surfaces.

5

I disagree.

Having motors on opposing corners will cause unnecessary rotational tweaking along the line of symmetry (between the two motors).

Don’t forget to take into account the rotational energy produced by the motors as well, and how that rotational energy also affects balance. The attitude of a vehicle can be greatly affected by centripetal force.

Furthermore, if you are going up a hill with your tracked vehicle, it would be good to have equally weighted rear sides for better traction. If one rear side weighed more than the other, then the tracks wouldn’t have equal traction.

If balance is your concern, use the battery to distribute out the weight, not kooky motor placement. QED.

6

should have took that into account, my bad :blush:

7

I have to agree. I’m not a fan of using a motor in the front and back on opposite sides. If you have any ratcheting in the tracks this can also cause adverse effects.

If the motors span across the entire chassis on a small bot, it would be fine. But the bigger you get, the heavier your motors and batteries become and the more torque and momentum you are throwing around. And keeping the components symmetrical is best.

8

Hi all.

I also think that having motors on the same axix could get less problems, but it could be better front or rear transmission?

Thanks

9

I was going to start a new thread on material choices for a tracked robot, but I think I will just add to this one instead!

First of all, I am looking at using Aluminum (a 7075 or 6061 alloy) vs. Lexan.

If you look at the physical properties of the alloy versus it’s density, aluminum is a far better choice than the Lexan in every way. (Other than lightning resistance!) However aluminum has about twice the density of Lexan. Is aluminum to much for a Johnny-5 style bot? One might argue that you could use aluminum with half the thickness, and still have a stronger material, but once its thin enough, the aluminum becomes to flexible/maleable to use. Anyone have thoughts on this?

10

Yes, I also have thought about aluminium for the robot chassie.

I think that could be a good solution and could increase the chassie resistance.
One problem, for hobbiest like me, could be related to the cutting of aluminium panel but once resolved it the design should be very reliable.

11

We use 0.120" lexan which has about the same weight as 0.060" aluminum. They are both relatively strong, but the lexan has much more flex. Lexan requires reinforcing aluminum bars or angles to make a rigid structure. Knowing this weakness and how to compensate for it makes lexan a useful material.