paper: [Ri3D] The GreenHorns 2016 Present: Rivvet

[waterbott]

Originally Posted by Ginger Power

The turret would begin to drop when the angle between the ground and the shooter approached ~45 degrees as an estimate. I think if you're debating whether or not to add a mechanical brake to the shooter, I would recommend it. The reason I say this other than the back driving, the shooter would rock while driving, and especially while traversing obstacles. Stabilizing that seems like a good idea.

On the other hand... you could just ignore the rocking and then stall the articulation motor. Up to you!

What would you recommend as a means of dampening the rocking? Our team was contemplating using gas springs, an air cylinder, or even just elastic cord.

[Ginger Power]

Originally Posted by waterbott

What would you recommend as a means of dampening the rocking? Our team was contemplating using gas springs, an air cylinder, or even just elastic cord.

All of the above would be great for that purpose. It all depends on the geometry of your robot and where you can fit everything. Any of the options you listed can be as effective as the others if implemented correctly.

[bmammen]

Originally Posted by Ginger Power

We actually used a rotary servo like this one from AndyMark. We mounted a 4" piece of aluminum to it that acted as the lever arm. Our setup was slightly underpowered, but that could easily be remedied by using a stronger servo, and/or a shorter lever arm. Just be sure to do the math. Your trigger should be able to reliably push the ball into your shooter when your shooter is at any angle.

We have one of the REV Smart Servo's and the torque is good, but the speed is very slow - much slower than what we see on the robot you built. Were you using this particular servo, or one like it? Sec/60 specs on what you used would be great if you have it. Thank you guys so much for answering all these questions! Very much appreciated!

[bmammen]

Originally Posted by dradel

On the tubes do you know what od you went with off hand?
On the 2:1 vs 3:1 we figured that a mini cim is spinning around 6000 rpm so a 775 at 3:1 is also about 6000 rpm so should work out pretty much the same as you guys ended up with. We are going to use the versa planetary encoder to measure and set the rpm using a talon srx.
And leds in the tubes are a given!

Isn't the Versa Planetary encoder using the CTRE magnet that needs to be bored into a CIM shaft? Wondering how that would work on a 775 shaft.

[Ginger Power]

Originally Posted by bmammen

We have one of the REV Smart Servo's and the torque is good, but the speed is very slow - much slower than what we see on the robot you built. Were you using this particular servo, or one like it? Sec/60 specs on what you used would be great if you have it. Thank you guys so much for answering all these questions! Very much appreciated!

It wasn't exactly the REV Smart Servo, but it was similar in nature. I don't have exact specs because I'm not sure of the model, but I'm going to make an educated guess that ours has a lower gear ratio. Ours was also underpowered so that makes sense.

If you've got plenty if power but a low speed, you can increase the length of the lever that you attach to the servo. Sorry I don't have more info! That's the disadvantage of being 200 miles away from the robot.

[Ginger Power]

I'd like to clarify something that has bothered me. To articulate our shooter mechanism we used two 10:1 versa planetary stages for a 100:1 overall reduction. This is way outside the recommendations from Vex's Load Ratings Guide for a Cim motor. I apologize to any teams who may have gotten the idea to do this from us.

A much safer solution for articulating the shooting mechanism would be to use a Mini Cim motor in a versa planetary at a 108:1 ratio. This can be safely done by using a 3:1, 4:1, and 9:1 stacked up. It's still within Vex's recommendations and it provides a similar amount of torque.

Another solution would be to use the Gem 500 gearbox from AndyMark. I believe the joint at which the shooter articulates should be the strongest part of the robot. I will say from my experience with the Gem 500, it will have no problems, it's a tank.

Again, sorry if anybody copied this aspect of our design. I'd like to blame the sleep deprivation, but it was a result of our lack of experience. We've learned from our mistake and will do better next time!

[epicnun]

For the shooter, is it better to run a 3:1 gearbox with a 775pro then to do what you did with the mini-cims? Even though they will both be at around 6000 rpm?

[Ginger Power]

Originally Posted by epicnun

For the shooter, is it better to run a 3:1 gearbox with a 775pro then to do what you did with the mini-cims? Even though they will both be at around 6000 rpm?

The problem with what we did with the mini CIMs is that they were at their max speed. This means the speed of the wheels is completely dependent upon the battery voltage. 775pro's are lighter, and can be run faster than mini CIMs in this application. It is my belief that you will see better results with the 775pro's.

[gpetilli]

Originally Posted by Ginger Power

Not with a versa planetary I haven't done a 2:1 ratio before, so I'm not sure about the optimal way to do it. One way I can think of would be to drive a 16 tooth sprocket/belt off the motor and run a chain/belt to a 32 tooth sprocket/pulley on the intake wheels.

You could also just run the 775pro at 3:1 in a versa, which would still be faster and more powerful than mini CIMs at 1:1

I would recommend the Vex Cim-ile at 2.4:1 with the 775Pro
http://www.vexrobotics.com/vexpro/mo...s/cim-ile.html

Actually, this has the same exact mounting as the miniCIM so you could swap it out directly and do the comparison.

[mustangs2647]

So how tall was your robot when the shooter was down?

[Ginger Power]

Originally Posted by mustangs2647

So how tall was your robot when the shooter was down?

~14" We never had to worry about clearing the low bar. The top of the frame was 9" off the ground so we had high ground clearance with a low profile overall.

[gpetilli]

Originally Posted by bmammen

Isn't the Versa Planetary encoder using the CTRE magnet that needs to be bored into a CIM shaft? Wondering how that would work on a 775 shaft.

I dont think it is legal (or safe) to bore into a motor shaft. I hope you meant the versa planetary 1/2 hex output shaft - which would be fine.

[epicnun]

Originally Posted by gpetilli

I would recommend the Vex Cim-ile at 2.4:1 with the 775Pro
http://www.vexrobotics.com/vexpro/mo...s/cim-ile.html

Actually, this has the same exact mounting as the miniCIM so you could swap it out directly and do the comparison.

In the link it says the ratio for a 775pro with this gearbox is 12:29. Is that correct ratio or would we have to change the gears, and if the latter, where would I get the gears and which ones?

(I am really sorry if this is a stupid question. We are a rookie team trying to figure out what we are doing! haha)

[Coach Seb]

Thank you so much for this robot design, we build a shooter very similar to yours and it shoot very well... we also are using 775pro with 3:1 versa.

My question is around the elevation, maybe our framing is too heavy, but what would be a good recommendation to hold the shooter at the proper angle position mechanically while trying to aim at the target?

[Ginger Power]

There are a number of ways to articulate the shooter, and a number if those are covered in this thread, and in the white paper. The way I would recommend would be to get a gearbox with a very high gear ratio >100:1 and use that to drive a chain and sprocket setup which is connected to your arm. Two gearboxes I would recommend are the Versa Planetary from Vexpro, and the Gem 500 from AndyMark. Both can give you enough reduction.

You could also use a dart linear actuator to pivot the shooter. There are tons of possibilities!