Need Specific Help Regarding Mathematics and Motor Choice of Arm

[MAXOFLIFE]

Hello! My team has hit a road block and it would be amazing if we could have some online help. In last year's game our team had very poor organization and planning, which lead to a robot that barely functioned and practically broke itself to do so. This year I'm trying to make the change of delicately planning our designs so that we don't waste our small funds on components that will break or not work due to our designs.

As practically a rookie team, we wanted to stay simple so that we can do one job and do it well. We're using the Rhino Treads from AndyMark and our main goal is to have this arm on the front so that we can open the portcullis and push down the cheval de frise so that we can handle all defenses except for type category C.



Our main problem is lack of understanding when it comes to choosing which gearboxes should be used. Using the JVN calculator has lead us far, but we've hit another road block.



Why are there 8 red boxes under Driving Gear and Driven Gear? Shouldn't there only be 1 driving gear and then a continuation of how those gears connect?

Thanks for taking the time to read this post and possibly give your input!

Also, please comment if our design seems wonky. It was the first thing we imagined the arm and are completely open to suggestions.

[EricH]

I'll answer on the 8 boxes. For each gear pair in the gear train, the driving gear is the one that is GIVING the power to the next one. Each driven gear is receiving the power. If you have 3 gears, all in line, 1, 2, and 3, gear #1 is driving only, gear #2 is driving (#3) and driven (by #1), and gear #3 is driven only. If you are only using 1-2 reductions, set anything that's left to 1:1 ratio.

So, let's see if I read your setup properly: Two 10:1 reductions followed by a 4.67:1 reduction (the 18:84 change), with two mini-CIMs going into it. Then a 2.5'-3' arm, lifting 10 lb... I think that will work, maybe a tad overpowered but more is better than less in this case.

[Knufire]

There's 8 red boxes (4 pairs) so you can do up to a 4 stage gearbox in the calculator. More often than not you'll only have a 2 or 3 stage gearbox, so you can leave the last set at 1:1.

Looking at the calculator, it seems like you plan on putting the miniCIM in a Versaplanetary with two 10:1 stages, and then an 18T gear on the output of the Versaplanetary driving an 84T gear connected to the arm. If this is the case, you have filled the calculator out correctly for this scenario.

If the scenario I said above was indeed correct, I'd caution you to maybe switch to a less powerful motor. The miniCIM is overkill for this application, which isn't in itself bad, but it also exceeds the load rating for a 100:1 Versaplanetary. You can find the load rating guide here: http://content.vexrobotics.com/vexpr...s-20151221.pdf

[MAXOFLIFE]

Originally Posted by EricH

I'll answer on the 8 boxes. For each gear pair in the gear train, the driving gear is the one that is GIVING the power to the next one. Each driven gear is receiving the power. If you have 3 gears, all in line, 1, 2, and 3, gear #1 is driving only, gear #2 is driving (#3) and driven (by #1), and gear #3 is driven only. If you are only using 1-2 reductions, set anything that's left to 1:1 ratio.

So, let's see if I read your setup properly: Two 10:1 reductions followed by a 4.67:1 reduction (the 18:84 change), with two mini-CIMs going into it. Then a 2.5'-3' arm, lifting 10 lb... I think that will work, maybe a tad overpowered but more is better than less in this case.

Originally Posted by Knufire

There's 8 red boxes (4 pairs) so you can do up to a 4 stage gearbox in the calculator. More often than not you'll only have a 2 or 3 stage gearbox, so you can leave the last set at 1:1.

Looking at the calculator, it seems like you plan on putting the miniCIM in a Versaplanetary with two 10:1 stages, and then an 18T gear on the output of the Versaplanetary driving an 84T gear connected to the arm. If this is the case, you have filled the calculator out correctly for this scenario.

If the scenario I said above was indeed correct, I'd caution you to maybe switch to a less powerful motor. The miniCIM is overkill for this application, which isn't in itself bad, but it also exceeds the load rating for a 100:1 Versaplanetary. You can find the load rating guide here: http://content.vexrobotics.com/vexpr...s-20151221.pdf

Thank you! If we continued with this design, would switching to 1 miniCIM be more efficient? Also, how does the belt system in our design play into the math for calculations?

[kitare102]

Originally Posted by MAXOFLIFE

Thank you! If we continued with this design, would switching to 1 miniCIM be more efficient? Also, how does the belt system in our design play into the math for calculations?

Switching to only one miniCIM will use less power, but make your arm accelerate slower as it pulls the portcullis. Efficiency of power shouldn't be an issue, but it's possible efficiency of time will be hurt moving to one motor. That being said, you should be able to get a fairly responsive arm to move using just one miniCIM. MiniCIMs are fairly heavy, and gearboxes to handle 2 CIM profile motors have to be larger, so moving to one miniCIM will save a notable amount of weight if that's a concern.

As for the belt, you'll have a reduction where the "driving gear" value should be the number of teeth on the pulley connected to the gearbox and the "driven gear value" should be the no. of teeth on the dpulley connected to the arm's axle. In your spreadsheet currently, the 18 and 84 could represent an 18t driving pulley and an 84t driven pulley.

Right now you have two 10:1 reductions in your spreadsheet. AIf those are versaplanetary stages, I'd like to point out that the user guide for that system suggests not using two 10:1 reductions with a miniCIM. However, due to the relatively higher rigidity of the teeth of lower reduction stages, a 100:1 reduction composed of 2 5:1 stages and a 4:1 stage (for example) is greenlighted. If you're using a different system, disregard this paragraph (though checking out user guides is always good).

[ahartnet]

In addition to what others have said, make sure you:
1) have the arm load and length set correctly. 22 lbs sounds like a pretty heavy arm and your picture indicated 2.5 feet, but your spreadsheet picture has 3 feet.
2) where is this located in the robot? make sure you're still meeting rule G18 about extending past the frame perimeter.

[MAXOFLIFE]

Originally Posted by ahartnet

In addition to what others have said, make sure you:
1) have the arm load and length set correctly. 22 lbs sounds like a pretty heavy arm and your picture indicated 2.5 feet, but your spreadsheet picture has 3 feet.
2) where is this located in the robot? make sure you're still meeting rule G18 about extending past the frame perimeter.

We used those values to ensure that we would have enough power if we added a few extra parts to the arm or modified it's length.

[Ether]

Originally Posted by kitare102

Switching to only one miniCIM will use less power

Would you please show your calculations.