Climbing -- battery or pneumatics?

[jake517]

Hello all,

My team has been trying to make our climbing mechanism work for a while now, and we finally have a solution.

Since the beginning, we have been planning on climbing the outside corner of the pyramid. Yes, we have to deal with the corner pieces sticking out, and yes we know that we will have to reach farther to climb. While we have had many obstacles to overcome, we finally found a simple solution that would allow us to climb the outside (and let any other teams climb inside the pyramid or on the faces of the pyramid.)

However, what we are concerned about is how much energy will we be using? We have been doing all sorts of calculations, but we still aren't sure if the battery will have enough juice for us to run around the field and defend, and still be able to climb the pyramid for 30 points (and then dump four frisbees for and extra twenty points at the top while we hang.)

Do any of you know if we should still go ahead and try to use the battery or should we be looking at pneumatics? We would like to try to avoid pneumatics if at all possible.

Thanks,
~4294

[tickspe15]

Pneumatics would have to run off the battery

[jake517]

Yes, we do understand that.

And that is a good point -- but will the pneumatics save us on battery-usage? Or will the pneumatics spend as much energy as a motor would use?

Thanks again,
~4294

[Patrick Flynn]

A lot of this is dependent on your climbing design. Is it reasonable for you to replace motors with pneumatics in the set up that you have designed? If it isn't then i think you've answered that question.
While looking at the battery to help you know if we think it'll make it through the match we'd need to know what motors you plan on using for climbing and how to use them.
It is also possible for you to charge up your pneumatics before the match with one battery and use a different one during the match.
As long as all other rules are followed, refer to this thread discussing pre-filling compressors. http://www.chiefdelphi.com/forums/sh...hreadid=112532

[CalTran]

Originally Posted by tickspe15

Pneumatics would have to run off the battery

I believe when he meant battery or pneumatics, he meant in the form running a winch uses massive amounts of power but is robust as opposed to pneumatics that use relatively low power but has to be engineered and have the right cylinders. Also, pneumatics is somewhat independent of the battery in that they just require the amount of air stored in your robot rather than the fluctuating power from the battery.

To answer the OP's question, I would say that this question is incredibly design dependent, and we would need to know a little more about your system. From what I can gather, your robot will be a defender-climber with no ability to shoot or do other functions. Based off of that knowledge, I do not believe you will run into power issues, as 4 motors on a drive train, provided your drive train is designed in such a way it is not constantly stalling, should have enough power come end of the match (or whenever you decide to climb) to winch your way up.

[jake517]

Our design is pretty simple, where we have two arms (sort of like ladders) that will have lead screws running through them, with two cims running on a shaft that will turn a chain (connecting to gears) that will turn the nut/lead screw.

Then with a cable and pulley system (which is kinda hard to explain without showing you our set up -- that is currently disassembled) the arms will extend at twice the rate we put into it. Basically, it is similar to a princton forklift that Lowe's uses.

So, by using a total of 6 Cims, and 2 window motors (which will be used for our second set of hooks that will keep our bot steady on the pole), we are wondering if we will be able to get enough torque and speed out of the Cims (which we can always gear properly later), will we use up too much battery juice on defending/pushing other bots and then still want to pull a 140lb robot up to the third tier.

If you still have further questions about our design, let us know.

Thanks,
~4294

[karomata]

My team is using battery power heavily by having CIMs lift our robot with a chain device, so it depends on the other operations of your robot, whether or not they will suck the life out of you battery during a match, and you may not have enough power to climb.

[Cory]

If you are not using pneumatics elsewhere and can pre-charge your accumulators and only use that much air, you wouldn't have to worry about your battery.

If you need an onboard compressor to refill your accumulators, you'll take a bigger battery hit. Compressing air is one of the most inefficient energy transfers out there.

[Tristan Lall]

If you're planning to use pneumatics to climb the pyramid, also plan on including something like this 72 L air tank and precharging it for a while.

[CalTran]

Originally Posted by Tristan Lall

If you're planning to use pneumatics to climb the pyramid, also plan on including something like this 72 L air tank and precharging it for a while.

How much does that thing weigh? If the shipping weight is somewhat accurate....that's massive (25lbs!)

[Bob Steele]

Originally Posted by Tristan Lall

If you're planning to use pneumatics to climb the pyramid, also plan on including something like this 72 L air tank and precharging it for a while.

Good points Tristan... although that tank might exceed the robot size.weight by itself... lol

Conservation of Energy says whatever work you do in moving the robot you have to provide energy to do that work... in joules...

If you make a simplistic assumption that you will be moving the center of your mass approximately 2 meters up from the floor. Assuming your robot has a mass of 68 kilograms... using 10 m/s/s as the acceleration due to gravity.... a rough approximation of the number of joules you will need to lift the robot is 1360.

Physics question for the day.... Can you store 1360 joules in a storage tank that you could have on your robot? Or multiple tanks....

This is a very basic look at the energy required... remember ...use your terms correctly... power is not energy... power is the rate at which the work is done. (Joules /second)

Now if you think you can have a tank (or tanks) that could store this potential energy.. how long will it take for the little legal FIRST pump to fill it? Also.. can you apply energy at the proper rate to do the work you want to do using this system in the time you want to do it.

Now after you get all of that done... you have to start dealing with the issues of friction (which will require more joules of work to overcome), other inefficiences in the transmission of energy etc.

If you wanted to lift this robot in 30 seconds you need to have power available equal to 45 watts (not including friction etc.)

Now if you are applying the power non-continuously (stopping at various points) you will have to adjust that power rating... say for instance you are pulling on a hook ... setting a hook ... putting the hook up to a new height... pulling again... you won't be operating at a continuous power...but if that is true... for some points you will have to operate at a higher power so now you will have to have a greater source of power... so that it can do the short strokes...

interesting isn't it?

Become an engineer and enjoy the process...

Look at what the cylinders have to do... the work they have to do...
figure out what it is and how quickly the cylinder will operate...

You are asking quite abit from pneumatic cylinders to do the 30 point climb
I am not saying it can't be done...

10 point hang with cylinders??? yes... doable...
30 point hang... difficult no matter what you do...

[mikegrundvig]

The hard part with cylinders isn't actually the pneumatics so much as the design of the climbing mechanism. A pair of 1.25" bore cylinders are more than capable of lifting our robot very easily. Due to the climbing requirement, we designed our robot to be under 100 lbs with both battery and bumpers.

Assuming you get a pneumatics design that works for climbing, then you just need to add tanks to ensure you have enough air volume. Our current plan is to have six 41in tanks and the small compressor on-board the robot. We will charge the tanks before a match. The compressor is there to ensure any leaks will not be a problem in the match or while queuing - we don't actually expect it to even come on until we are climbing and consuming gobs of air. The size of our two climbing cylinders far exceeds the ability to reasonably climb with just the compressor itself which is why we need the tanks.

[Mr V]

Originally Posted by jake517

Yes, we do understand that.

And that is a good point -- but will the pneumatics save us on battery-usage? Or will the pneumatics spend as much energy as a motor would use?

Thanks again,
~4294

Every time you convert energy from one form to another you end up with some losses. So without knowing the efficiency of all of the components that make up the system it is impossible to know which one is going to have the greatest net efficiency.

In general though using the a motor to do the work directly should be more efficient and thus use less battery power.

[wilsonmw04]

I've always wondered the legality of pre-charging with one battery and running a match with another. They have worded it so that it is legal this year. Interesting...