We are definitely finish with CADing our robot and just want to release a teaser. It’s not like we are still designing our climber mechanism or anything. This is just the drive train of our robot, a complete CAD model of our robot with all of our game winning mechanisms will be posted soon.

What size wheels/what wheels are you using?

We’re using 8 inch wheels. The gearbox we ordered’s ratio was a little extreme so we wanted to offset it with larger wheels.

You can also offset it with different ratios.

The idea behind getting the 8 inch wheels was to increase our robot’s speed while still having a large gear ratio(and thus torque) for pushing matches.

Yeah, but we already had the gear ratios purchased and because of our budget thought it would be a better idea to instead purchase larger wheels. We decided to get two inch wheels so we can still have plenty of friction despite not being able to have as many wheels in the entire frame.

Larger gear ratio does not mean more pushing power. It means more pushing power for a given size wheel assuming your whole system is not traction limited (wheels slipping). Compared to a typical 4 inch wheel drivetrain, you guys are using twice the reduction and twice the wheel circumference meaning theoretical pushing torque and speed are the same. The reason you do not see alot of teams using large wheels is because of the additional tradeoffs made in the process of using them. A larger wheel will be heavier, more expensive, and take up more space and in a game like steamworks where space is at a premium, teams will generally choose to deal with the minor issues smaller wheels pose like wheel wear over the above listed issues.

You may want to find the JVN calculator and plug in your motor, gearing and robot weight and see what you get. It will help you get a better understanding of how these parameters interact. Try different gear ratios and wheel sizes too.

In our current configuration we are 16.6 fps in high gear and 4.5 fps in low gear.

The gear ratio + wheel diameter act as a combined effect to convert torque at the motor to linear force at the wheel contact patch.

Twice the ratio and twice the wheel diam will get the same force in a classic sense.

In reality, the smaller wheel (within reason) will get more force as less reduction was needed (likely) and you’re throwing less away from inefficiency of gears/chain/belts.

In terms of dynamics you’ll also be a tad faster as there is less inertia to spin up (this really compounds with more gear reduction).

The thing people are trying to point out is that, ignoring efficiency, small wheels geared for these same speeds (not the same ratio, the same output speed) would push with just as much force / torque / “power”. In reality, since it requires less of a gear reduction to get a smaller wheel to these speeds, they will be more efficient and actually produce slightly more force / torque / “power”.

Essentially, increasing the size of your wheel “undoes” your gear reduction - for a fixed gear ratio, the bigger the wheel, the faster you go and the less force you push with. Remember force equals torque divided by distance (wheel radius).

Another way of saying it is that the power output of a given set of motors is limited.

Thank you, at the time of purchase we understood it would make a difference to our reduction, but assumed it wouldn’t be as large as it is. Now that we have a tool that makes the calculations much easier we have a much more accurate understanding. We are already working on a solution, but it wouldn’t have happened in time without your guy’s help.