Minibot climb rate

[billbo911]

We have not received our FTC parts yet, obviously because the orders went in today :o . I have a couple quick questions and then a result of quick calculations based on assumptions.

What are the weights of the following items?:

NXT controller, Tetrix motor, 12v battery pack, HiTechnic motor controller.

I did some very ballpark calculations based on ideal situations. If we can build a robot weighing less than 5 Lbs, it should be able to climb the pole in less than 7 seconds.

Does that sound right?

[Brandon_Holley]

@billbo911

We have not received our FTC parts yet, obviously because the orders went in today :o . I have a couple quick questions and then a result of quick calculations based on assumptions.

What are the weights of the following items?:

NXT controller, Tetrix motor, 12v battery pack, HiTechnic motor controller.

I did some very ballpark calculations based on ideal situations. If we can build a robot weighing less than 5 Lbs, it should be able to climb the pole in less than 7 seconds.

Does that sound right?

What are you basing your calculations on? Overall output of the motors (ie: power)?

-Brando

[billbo911]

@Brandon Holley

What are you basing your calculations on? Overall output of the motors (ie: power)?

-Brando

Yep! I chose to run the calculations close the motor’s max efficiency. I also chose to use the largest wheel I could find that appeared to be legal.

[Chris_Hibner]

This calculation is actually very easy using the work-energy thorem.

Power = Work / Time

Work = weight * height

Therefore:

Time = (weight * height) / Power

Example:

Motor power: 8.43 W (Tetrix motor)
Efficiency: 0.85
Weight: 5 lb * 4.4545 N/lb = 22.27 N
Height to climb: 2.1 m
assume gearing for peak power.

then:

Time = (22.27 N * 2.1 m) / (8.43 W * 0.85)

Time = 6.53 sec

This is the FASTEST time. If you make the wheel big enough that the torque on the motor causes the motor to move away from the peak power point, the minibot will climb SLOWER, not faster. In other words, bigger wheels aren’t always better.

[billbo911]

@Chris Hibner

This calculation is actually very easy using the work-energy thorem.

Power = Work / Time

Work = weight * height

Therefore:

Time = (weight * height) / Power

Example:

Motor power: 8.43 W (Tetrix motor)
Efficiency: 0.85
Weight: 5 lb * 4.4545 N/lb = 22.27 N
Height to climb: 2.1 m
assume gearing for peak power.

then:

Time = (22.27 N * 2.1 m) / (8.43 W * 0.85)

Time = 6.53 sec

This is the FASTEST time. If you make the wheel big enough that the torque on the motor causes the motor to move away from the peak power point, the minibot will climb SLOWER, not faster. In other words, bigger wheels aren’t always better.

I looks like your numbers and mine are spot on. I took a different approach, but the result is the same within .1 seconds.:yikes:

Just so others can see where I got my numbers, I ran it through the JVN Calculator.

[BornaE]

Seems like everyone is forgetting the possible use of surgical tubing to shoot that bot up the pole much much faster.

Also you can use 2 TETRIX motors.

[billbo911]

@BornaE

Seems like everyone is forgetting the possible use of surgical tubing to shoot that bot up the pole much much faster.

Also you can use 2 TETRIX motors.

Who says we are forgetting?

[Brandon_Holley]

@billbo911

Yep! I chose to run the calculations close the motor’s max efficiency. I also chose to use the largest wheel I could find that appeared to be legal.

That’s how I would it approach it as well. 7 seconds doesn’t leave much time for lining up/deployment… Must Climb Faster

-Brando

[billbo911]

@Brandon Holley

That’s how I would it approach it as well. 7 seconds doesn’t leave much time for lining up/deployment… Must Climb Faster

-Brando

Again, you are spot on. With only 10 seconds to deploy the Minibot and get it to climb the pole… Every millisecond you shave off the climb rate, the better chance you have. Deployment has to be perfect. No slippage can be tolerated in the drive. It all has to be done right if you intend to grab the 30 points!

Think about dragsters. Getting off the line is just as important as how fast you go down the track. It’s all about “elapsed time”.

[Doug_G]

@billbo911

Again, you are spot on. With only 10 seconds to deploy the Minibot and get it to climb the pole… Every millisecond you shave off the climb rate, the better chance you have. Deployment has to be perfect. No slippage can be tolerated in the drive. It all has to be done right if you intend to grab the 30 points!

Think about dragsters. Getting off the line is just as important as how fast you go down the track. It’s all about “elapsed time”.

Yesterday we built a simple pole climber out of Vex parts with two 3-wire motors, 4 wheels, old vex microcontroller, and a battery. I’m hoping the FTC motors are more powerful (they’re specs say they are) because it takes it about 10 seconds to climb 10 ft.

The minibot challenge will be more difficult than people think this year, mostly due to the timing allowed for it.

[Brandon_Holley]

@Duke461

The minibot doesnt have to get there in those 10 seconds of alloted end game time. remember 469’s robot last year?
<G68> Scores will be assessed when the MATCH ends and all objects in motion come to rest, or 10 seconds elapses, whichever comes first.

You might be right, but it’s still a bit ambiguous. I’ll refer to Gary’s post
in this thread

I’m gonna need a clarification from the Q&A before I’d feel comfortable committing to getting an extra 10 seconds.

On the other hand, I want our minibot to be the first one to the top every single time, thus I’m not planning on our minibot needing an extra 10 seconds.

-Brando

[JesseK]

I think this shines the light on deployment mechanisms just as much as it shines the light on the climbing minibot. Teams won’t know if they’re lined up properly until the 10 second mark, which means that a missed deployment is as disasterous as a slow robot.

Good catch with the <G68> rule, though I don’t think it effects who wins the race. It would simply dictate whether or not last place always got the 10 points, even after the buzzer.

[RyanCahoon]

During brainstorming, my team used the minibots in the kickoff video as a reasonable estimate, which appeared to climb the pole in 4-5sec.

–Ryan

[Jibs]

@BornaE

Seems like everyone is forgetting the possible use of surgical tubing to shoot that bot up the pole much much faster.

Also you can use 2 TETRIX motors.

So the calculation above is based off one motor?

[TGA_Reaper]

Question: What is the estimated ideal weight for the mini bot?

[Doug_G]

@TGA Reaper

Question: What is the estimated ideal weight for the mini bot?

The first one we built was about 4 pounds. I think the final version we settle on will be more like 6-7 pounds.

[Hawiian_Cadder]

i think my team intends to use surgical tubing to launch the mini-bot to the top in less time than 1 second. last years kicker on our robot only contacted the ball for 3 inches and was able to kick pretty far. i think we will be doing something similar for this.

[TGA_Reaper]

@Doug G

The first one we built was about 4 pounds. I think the final version we settle on will be more like 6-7 pounds.

have you tried the heavier weight yet?

[indubitably]

What are the odds that a minibot launched by a slingshot will recieve a penalty?

I feel <G20> might be at risk as the slingshot might tap it after its initial release.

[JesseK]

Hmm, the calculations I’m getting from both of my ‘drag race’ calculators, adjusted for straight vertical ascent, comes out to just over 5 seconds. I’ll investigate…

@indubitably

What are the odds that a minibot launched by a slingshot will recieve a penalty?

I feel <G20> might be at risk as the slingshot might tap it after its initial release.

Please use the other minibot threads for this question…