paper: [Ri3D] The GreenHorns 2016 Present: Rivvet

[Coach Seb]

Thank you!

How would the position be steady with the gearbox? last we tried, we could not hold it in position....

Rookie team here... learning all to put this together ... appreciate your help..

[Ginger Power]

Originally Posted by Coach Seb

Thank you!

How would the position be steady with the gearbox? last we tried, we could not hold it in position....

Rookie team here... learning all to put this together ... appreciate your help..

The gearbox will be difficult to back drive if it's at a high enough ratio. That probably won't be enough to keep it from wobbling completely. In order to do that I think you'll need to use a brake mechanism. Another solution could be to employ a hard stop for your shooter at an angle that you know works from a certain spot on the floor. This hard stop will help reduce wobble. An additional solution (which could be employed in combination with either of the others) would be to stall your motors in a way that holds your shooter at a desirable angle. This won't prevent wobble, but it should help.

[Mr. B]

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)

The 12 and 29 are the number of teeth on the gears
so, 29/12=2.41

[gpetilli]

Originally Posted by epicnun

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)

There are no stupid questions. 12:29 is correct, which if you do the math (29/12 ~ 2.4:1). I believe you were originally looking for something near 2:1. Others have suggested versaplanetary 3:1, which is also a fine option - possibly easier to mount. You need to look at both in CAD and see which works better for you. The 2.4:1 will spin your flywheel 3.0/2.4 or 25% faster.

[greg7mdp]

Hi Ginger Power,

Rivvet is awesome, and our design is quite inspired by it. Unfortunately we are running way behind, and are having great problems with the articulation to rotate the shooting mechanism upwards. Since we want to be able to have the shooter operated via vision software, we need to be able to set a precise (and repeatable) upwards angle. Our current motors just tilt the shooter all the way up, and drop it when the motors stop. Also we have a motor on each side, and I don't think it is the best setup.

We have a GEM500 gearbox (unused yet), and I think we want to put a strong servo on it for repeatable settings. Is that a good idea? If yes what kind of servo could we use? And also how to extend the gearbox shaft so that it can be attached to the other side (maybe with a bearing?)

I apologize for the basic questions - I know nearly nothing about motors since I just started helping my son's team about 4 weeks ago (I'm a software guy).

[Ginger Power]

Thanks for the kind words. My first and strongest recommendation would be to abandon vision tracking and auto aimimg. 99% of teams are better off picking a spot on the floor (hard stopped against the tower, at the edge of the batter, or from the out works) and using basic robot-centric sensors to aim. For example a gyro on the arm to tell you what angle it's at. When the shooter goes all the way down you could have it reset the gyro so as to avoid gyro drift. Have a known angle for each shooting position. You will be more accurate as a result of this.

If you implement the Gem 500 with 3 or 4 stages on it, and have an external reduction via chain, you really shouldn't have trouble with back driving the gearbox. I would highly recommend plugging a Cim or mini cim motor into the Gem rather than a servo.

I'm sorry but I'm not sure I know what you mean by "extending the gearbox shaft to reach the other side". If you could explain what you mean by that I'd be happy to other my opinion on a solution.

[Boltman]

Thanks for your design we used it for our shooter, love it... I'm excited to see what we can do with vision and will see if we can build in redundancy without vision, we added to the front mini tomahawks from TeamRedracted . We trashed our shooter yeserday in practice but rebuilt it stronger today. If we get our scaler working we should be in good shape for San Diego week 1.

We are using bag and larger wheels.

[greg7mdp]

Thanks a lot for the fast answer, much appreciated. I wish I had a picture of our shooting mechanism to post, as I don't know how to explain it well. I'll try to get one tomorrow evening and post it

I understand what you say about vision tracking, but I think we could make it work if we had an accurate way to set the shooting arm vertical angle. I somewhat have it working on my PC, processing images (from a webcam) with OpenCV in one process and sending instructions using network tables to another process running a robot simulation with robotpy. I also run the same OpenCV image processing running on a raspberry pi mounted on the robot. However, without an accurate way to set the shooting arm vertical angle, this will never work.

Why isn't a servo a good solution? I thought it would allow for repeatable settings, but clearly I must be missing a big issue.

[Ginger Power]

Anything is possible with a dedicated software mentor and some time. I would never discourage a team from trying new things and growing their knowledge base. If vision doesn't work how you want, just be sure to have contigency plan!

I'd love to comment on a picture so I can give it a fair assessment. Here's what I can say: If your shooter is mounted on a live axle (for example a hex axle that rotates with the shooter) then you should easily be able to drive the shooter up and down via a hex sprocket on the live axle, and another sprocket on your Gem 500. I'd use #35 chain. You shouldn't need to direct drive the shooter axle, and doing so would be harder to implement I think.

There are benefits to being addicted to Chief Delphi. Quick replies being one of them.

[cadandcookies]

Just wanted to drop in and say thanks-- the Greenhorns robot was a key inspiration for 2667 this year, and I don't think we'd have built the same robot without yours existing.

We look forward to seeing 4607 at North Star Regional!

[Ginger Power]

Originally Posted by cadandcookies

Just wanted to drop in and say thanks-- the Greenhorns robot was a key inspiration for 2667 this year, and I don't think we'd have built the same robot without yours existing.

We look forward to seeing 4607 at North Star Regional!

Thanks Nick! That means a lot. Snow Problem's robot was amazing this year as well. I think we're really starting to figure out this whole 3 days thing. Too bad our teams can't do the same thing

[greg7mdp]

Thanks again for all the help. Here is a picture of our robot. It may look familiar... imitation is the sincerest form of flattery :-). We may have a solution for tilting our shooter, as we had some help today from a motor expert.