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Unread 12-07-2018, 07:46 PM
Noah Bamberger Noah Bamberger is offline
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Drivetrain design for difficult terrain

As I am relatively new (started in 2017) to FRC, I have never designed or tested a drivetrain to cross bumpy and difficult terrain. My team has some struggles in 2016 with a modified KOP chassis, as we could cross the obstacles but could not turn very well. I'm looking for any tips or processes about drivetrains that can deal with this kind of terrain, more specifically for tank drive. Any examples would also be very much appreciated
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Unread 12-07-2018, 07:58 PM
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Re: Drivetrain design for difficult terrain

2016 was the most recent year with difficult terrain and arguably the year with the worst terrain. I highly suggest you look at videos and robots that did well that year. The Blue Alliance would probably be a great place to start.
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Unread 12-07-2018, 08:02 PM
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Re: Drivetrain design for difficult terrain

Team 254's technical binder from 2016 has some nice models of their drive train. It's very simple, just tubing and axels with a belly pan. There's no need for the custom gearboxes where you're at now, but slap something like evo shifters on it and get going.
Just make sure there's very little gap between the wheels and don't try to make a perfectly designed out drive train with gaps that "shouldn't ever get stuck in theory." like we did and then, of course get stuck on the moat.
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Unread 12-07-2018, 08:21 PM
Noah Bamberger Noah Bamberger is offline
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Re: Drivetrain design for difficult terrain

Quote:
Originally Posted by StAxis View Post
Team 254's technical binder from 2016 has some nice models of their drive train. It's very simple, just tubing and axels with a belly pan. There's no need for the custom gearboxes where you're at now, but slap something like evo shifters on it and get going.
Just make sure there's very little gap between the wheels and don't try to make a perfectly designed out drive train with gaps that "shouldn't ever get stuck in theory." like we did and then, of course get stuck on the moat.
So I know in 2016 254 had an 8 8" wheel design which worked really well, and 1538 had a 10 6" wheel design which worked as well. Is there any benefit to going with more 6" wheels as opposed to less larger wheels or vice versa? I have also seen some teams using a steel bellypan, is that necessary or is 1/8" aluminum fine?
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Unread 12-07-2018, 08:29 PM
ngreen ngreen is offline
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Re: Drivetrain design for difficult terrain

2016 we didn't add wood rails until after week one seeing another team use them but it really smoothed out the crossing. Our large pneumatics wheels, 10" iirc, really made crossing most of them not to bad. I think unique designs i.e. rocker bogey style might be wasted effort. I will say the 8" 4 wheel designs could probably cross more gracefully which was needed somewhat for autonomous.

Larger single steps can be overcome several ways, see 2004. The multiple step problem is something that is a little more vexing.

edit: I can't recall too much issues with bellypans, but maybe others remember. I think we were high enough it didn't matter.

edit2: Here you can see our robot that year (and the rails underneath). https://www.youtube.com/watch?v=OpEfWgsq5HU

One of my favorite reveals in 111 2004 robot and how it when smoothly on and off the platform: https://www.youtube.com/watch?v=NHw0j0lFBnw

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Unread 12-07-2018, 09:03 PM
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Re: Drivetrain design for difficult terrain

So, here's some tips that I've picked up over the past few years...

1) Use pneumatic wheels - Make it easier to cross terrain and makes the crossing easier on your drivetrain.

2) Add as many wheels as your length will allow - Whether it's an 8WD with 8" wheels, 10WD with 6" wheels, etc. you want to prevent your chassis from bottoming out over the terrain.

3) Use a larger drop for your center wheels - With pneumatic wheels you typically need a larger drop. I would say 1/4" at minimum.

4) Make sure your wheels have a leading edge - If a piece of terrain is particular tall, you can risk your frame running into the terrain first. So give your pneumatic wheels the leading edge and let them pull you over the terrain.

In 2016, it seems like 8WD with 8" wheels had a pretty smooth time crossing defenses, but many successful teams had 6WD with 8" wheels as well. As long as your frame has enough clearance, you can use whatever setup best suits your design.
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Unread 12-07-2018, 10:17 PM
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Re: Drivetrain design for difficult terrain

In 2016 we used the kitbase with the 8" pneumatic wheel kit for crossing the defenses. As long as you have clearance and the wheels filled up you should be good.

After out competition we added more leading edge to the front wheels and added wedges as well. As you can see here

https://imgur.com/GYWmRG5

The only crossing defense we had issues with was the rockwall, and it was mostly because of the space between the wheels.

Take a look around The Blue Alliance for more teams and what they did that year. I know quite a few teams used more smaller pneumatic wheels or a combination of pneumatic and colson wheels and those solutions worked well as well.
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Unread 12-08-2018, 09:54 AM
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Re: Drivetrain design for difficult terrain

With AndyMark's release of 8" pneumatic wheels with 1/2" hex bore, I am interested in how WCDs would handle a terrain-based game. Considering that the product page calls it a "perfect choice for building a WCD style drivetrain", I'm wondering if any teams here did a WCD in 2016 with pneumatic wheels. Are there any special considerations that you implemented to modify the WCD? I'm mostly concerned about the cantilevered axles going over terrain over the course of a season, but I'm not sure if that's something I actually need to be worried about.
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Unread 12-08-2018, 10:19 AM
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Re: Drivetrain design for difficult terrain

Pneumatic wheels can handle just about anything as Team 3875 proved in this match:

https://www.youtube.com/watch?v=21q3_17ymqM&t=1m45s
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Unread 12-08-2018, 10:37 AM
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Re: Drivetrain design for difficult terrain

Quote:
Originally Posted by pkrishna3082 View Post
With AndyMark's release of 8" pneumatic wheels with 1/2" hex bore, I am interested in how WCDs would handle a terrain-based game. Considering that the product page calls it a "perfect choice for building a WCD style drivetrain", I'm wondering if any teams here did a WCD in 2016 with pneumatic wheels. Are there any special considerations that you implemented to modify the WCD? I'm mostly concerned about the cantilevered axles going over terrain over the course of a season, but I'm not sure if that's something I actually need to be worried about.
We ran eight 6" pneumatic wheels in 2016 with no issues due the cantilever. We did modify the drive base, putting shock absorbing springs with about 1" of travel on both ends. In hindsight the shocks were an unnecessary bit of extra work, it would've been fine without them.
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Unread 12-08-2018, 01:20 PM
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Re: Drivetrain design for difficult terrain

We did some careful planning with our wheel spacing in 2016 to ensure that there was no position in which we could high-center on any of the obstacles. It resulted in an odd frame length, but the effect was great: We had no fear about hitting any of the obstacles at speed.

Our wheels were cheap: 8" harbor freight pneumatics, with press-fit hex hubs that we spun on our lathe. They were extremely heavy, but they allowed us to bounce over obstacles with no issues whatsoever.
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Unread 12-08-2018, 01:38 PM
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Re: Drivetrain design for difficult terrain

Quote:
Originally Posted by pkrishna3082 View Post
With AndyMark's release of 8" pneumatic wheels with 1/2" hex bore, I am interested in how WCDs would handle a terrain-based game. Considering that the product page calls it a "perfect choice for building a WCD style drivetrain", I'm wondering if any teams here did a WCD in 2016 with pneumatic wheels. Are there any special considerations that you implemented to modify the WCD? I'm mostly concerned about the cantilevered axles going over terrain over the course of a season, but I'm not sure if that's something I actually need to be worried about.
4901 ran a chain-in-tube setup with the center direct-driven, but chose to support the other end of the 8" pneumatic wheels due to the loads. A couple teething problems with chain at Palmetto, but once dialed in it got through Orlando and SCRIW and demos with little maintenance.
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Unread 12-09-2018, 09:28 AM
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Re: Drivetrain design for difficult terrain

So, the inevitable question, What about tracks?

We ran tracks with great* success in 2016 (once they were sorted out.) The key to using tracks in a robot and it still being able to turn well is 2 fold. First you still need a drop center, though not as large a drop as pneumatic wheels, (AM rhino tracks have this) and you need a very low center of gravity (don't build a tall robot and put your battery on your belly pan)

The main advantage of the tracks is smoothness of crossing and the lesser need for ground clearance (in a situation where the obstacle can be mounted by both tracks at the same time)

Some disadvantages though, it does require more energy to turn, even if it has a low CG and is stable when turning. (as compared to a standard drop-center 6 or 8 wheel drivetrain) It takes up more space inside the robot, it is heavy, and the tracks may want to jump off if they are not properly tensioned and guided.

That said, I would choose them again for the smoothness and ease they afforded us getting over the defenses.

EDIT: and please just use belts similar to those sold with the Rhino units (we used Brecoflex belts that we had lying around). Those tracks that are sectional and you put together however many links you want do not have much traction and are not smooth at all.
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Unread 12-09-2018, 10:05 AM
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Re: Drivetrain design for difficult terrain

Quote:
Originally Posted by fargus111111111 View Post
So, the inevitable question, What about tracks?

We ran tracks with great* success in 2016 (once they were sorted out.) The key to using tracks in a robot and it still being able to turn well is 2 fold. First you still need a drop center, though not as large a drop as pneumatic wheels, (AM rhino tracks have this) and you need a very low center of gravity (don't build a tall robot and put your battery on your belly pan)

The main advantage of the tracks is smoothness of crossing and the lesser need for ground clearance (in a situation where the obstacle can be mounted by both tracks at the same time)

Some disadvantages though, it does require more energy to turn, even if it has a low CG and is stable when turning. (as compared to a standard drop-center 6 or 8 wheel drivetrain) It takes up more space inside the robot, it is heavy, and the tracks may want to jump off if they are not properly tensioned and guided.

That said, I would choose them again for the smoothness and ease they afforded us getting over the defenses.

EDIT: and please just use belts similar to those sold with the Rhino units (we used Brecoflex belts that we had lying around). Those tracks that are sectional and you put together however many links you want do not have much traction and are not smooth at all.
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Unread 12-10-2018, 11:30 AM
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Re: Drivetrain design for difficult terrain

254 had a pretty sweet drivetrain in 2016. Well, they do every year, but in 2016 it was just super KISS. 8 inch wheels, simple wheel spacing, and a slight raise to the front wheel. All on a 2x1 WCD. Slap your own gearbox on it, modify the size and be done with it. I like to follow Corsetto's golden rule number 1.
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