OCCRA
Go to Post You must have a base on which to stand. Knowledge is the base that wisdom stands on. - Steve W [more]
Home
Go Back   Chief Delphi > CD-Media > Photos
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

photos

papers

everything



Off-season Caster Swerve Drive

owen.wilks.2471

By: owen.wilks.2471
New: 06-07-2018 11:07 AM
Updated: 06-07-2018 11:07 AM
Views: 2441 times


Off-season Caster Swerve Drive


This is a design that I have been working on for a while now that we plan to put on a t-shirt cannon as a summer project. Itís driven by 2 mini cims with a ratio 16:56 18:48 with a final speed of 16 ft/sec on a 6in pneumatic wheel. Turning is done by two 775 pros with a ratio (12:48) (18:48) (24:84) so it has the same turn speed as drive speed. The caster has a 3.25 offset and is using an SFX 4 by 4.75 thin section bearing (JU040XP0). We are going to be running the robot off 24 volts so we will be running the motors in series.


Recent Viewers

  • Guest

Discussion

view entire thread

Reply

06-07-2018 02:21 PM

ethanhavens0500


Unread Re: pic: Off-season Caster Swerve Drive

Is there a reason to use the caster design over a normal swerve?



06-07-2018 02:37 PM

Mark Wasserman


Unread Re: pic: Off-season Caster Swerve Drive

16 slots from the PDP.....

I'm not even going to try to convince anyone why castered swerve is an oxymoron and a bad idea, it just is..... sorry.



06-07-2018 03:09 PM

JohnFogarty


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by Mark Wasserman View Post
16 slots from the PDP.....

I'm not even going to try to convince anyone why castered swerve is an oxymoron and a bad idea, it just is..... sorry.
I mean, there are interesting things to think about...

https://www.chiefdelphi.com/forums/s...3&postcount=31



06-07-2018 03:15 PM

s_forbes


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by Mark Wasserman View Post
16 slots from the PDP.....

I'm not even going to try to convince anyone why <snip> swerve is an oxymoron and a bad idea, it just is..... sorry.
FTFY.

This seems like an overkill type of design for a promotional robot, not an FRC legal robot. You can do whatever you want in that case; more power = more fun! OP never even mentioned how many wheels they plan on using either, it might only be 3. Or 2.



06-07-2018 03:24 PM

tragicexpert


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by s_forbes View Post
FTFY.

This seems like an overkill type of design for a promotional robot, not an FRC legal robot. You can do whatever you want in that case; more power = more fun! OP never even mentioned how many wheels they plan on using either, it might only be 3. Or 2.
Don't know to much about the specifics but there are 3 wheels and I believe a triangular drive train.



06-07-2018 03:43 PM

AlexanderTheOK


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by Mark Wasserman View Post
16 slots from the PDP.....

I'm not even going to try to convince anyone why castered swerve is an oxymoron and a bad idea, it just is..... sorry.
Then why post?

Last I checked, no conclusion was reached in any of the CD castor swerve threads regarding the effectiveness of a castor swerve in an FRC context. Judging by your post history, you've not participated in any of those discussions, so you've either not read them, or decided that your opinions were already well stated by others.

In both cases, you really do need to explain why you think a castor swerve is a bad idea if you want to be taken seriously, and you most certainly should explain why you think it's an oxymoron. (which I would reckon is only possible if one misinterprets the operation of a castor swerve or the definition of "oxymoron")



06-07-2018 04:24 PM

hrench


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by AlexanderTheOK View Post
Then why post?

you really do need to explain why you think a castor swerve is a bad idea
As I replied to the most recent caster (not castor, which is vegetable oil) swerve drive posting, the purpose of rake and trail which results in caster is to make a following-wheel more stable while following, going straight.

The purpose of swerve is to be able to turn readily, at will. So making it harder to turn doesn't make sense. To me.

If you can tell me why you want to caster it, I'm listening.



06-07-2018 04:44 PM

AlexanderTheOK


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by hrench View Post
the purpose of rake and trail which results in caster is to make a following-wheel more stable while following, going straight.

The purpose of swerve is to be able to turn readily, at will. So making it harder to turn doesn't make sense. To me.

If you can tell me why you want to caster it, I'm listening.
The purpose of offsetting a swerve wheel has nothing to do with stability. It is merely a side benefit. There is also no trail in such a module, which is evident by just looking at it, so your reference to rake and trail in this post isn't actually relevant, as that's just not how caster swerves are designed and built.

I won't re-type the entirety of that thread, and I highly encourage that you reread it. Please take the time to understand the design and motivations before casting it away.

TL;DR: The purpose of offsetting the wheel is to allow fine adjustments through the steering of the module.

edit: Also, I hear others are partial to using olive oil for their drives, but once you go castor you never go back.



06-07-2018 05:48 PM

owen.wilks.2471


Unread Re: pic: Off-season Caster Swerve Drive

So yes, it is going to have three wheels. Also, the reason that we have chosen to overpower them so much is we know that the robot is likely to be over 200 pounds and we want it to have decent acceleration. The robot is also going to run on 24 volts instead of the normal 12, most of the standard FRC electronics can run on 24 volts but the motors can't. So we are going to run the motors in parrel, for example, the two mini cims will be run of one Talon SRX and one PDP slot this also allows us to use one slip ring per module. So the drivetrain will only be using 6 PDP slots. The reason we are choosing to do a caster drive is that it hasn't been seriously tested yet, we decided that this is a project that would allow us test casters without much risk.

-Owen Wilks

P.S. This design was never meant to be used in a real competition it is just a fun way to test the concept.



06-07-2018 05:52 PM

Tom Line


Unread Re: pic: Off-season Caster Swerve Drive

Wow. That looks like a very cool design. Let us know how it works out. I bet you learn alot about engineering swerves from it that you can take forward to competition. Just ignore the naysayers. There seems to be a lot of unnecessary negativity on CD as of late.



06-07-2018 06:59 PM

Bryce2471


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by owen.wilks.2471 View Post
Nice work Owen. It looks great! One suggestion I have is to add a rib in the middle of the slot for the 775 vents. It shouldn't block airflow, and will improve the motors' mounting rigidity.

Quote:
Originally Posted by Mark Wasserman View Post
16 slots from the PDP.....

I'm not even going to try to convince anyone why castered swerve is an oxymoron and a bad idea, it just is..... sorry.
I'm really curious what your motivations were for making this post. Please enlighten me.

Quote:
Originally Posted by ethanhavens0500 View Post
If you can tell me why you want to caster it, I'm listening.
Owen touched on the motivation for this application, but in a more general sense, an offset wheel would be used on a swerve for the same reason that one would be used on an unpowered caster: So that the structure it's mounted to can move immediately in any direction without skidding the wheel.



06-07-2018 08:28 PM

tickspe15


Unread Re: pic: Off-season Caster Swerve Drive

Cool design!

How did you go about determining the position of the idler pulleys?



06-07-2018 09:02 PM

ClayTownR


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by tickspe15 View Post
Cool design!

How did you go about determining the position of the idler pulleys?
Iíll offer what I do in Solidworks (it may be different in Inventor, which is what I believe 2471 uses):

Usually on the master sketch for the part, Iíll make a belt layout with the Input and output pulleys fully defined, but with the idler under-defined. Those pulleys are represented as circles with the pitch diameters (you can typically just look these up). Iíd then create a path-length dimension set to the tooth count times the pitch (ex: 80t HTD 5mm -> 400mm length). Iíd then drag around the idler until itís in a position I like, then dimension it into place. When making the plate itself, the idler usually doesnít get a hole but a slot, to make tensioning easier.

Feel free to pm me if you want more info or if I just donít make sense.



06-07-2018 09:14 PM

philso


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by owen.wilks.2471 View Post
So yes, it is going to have three wheels. Also, the reason that we have chosen to overpower them so much is we know that the robot is likely to be over 200 pounds and we want it to have decent acceleration. The robot is also going to run on 24 volts instead of the normal 12, most of the standard FRC electronics can run on 24 volts but the motors can't. So we are going to run the motors in parrel, for example, the two mini cims will be run of one Talon SRX and one PDP slot this also allows us to use one slip ring per module. So the drivetrain will only be using 6 PDP slots. The reason we are choosing to do a caster drive is that it hasn't been seriously tested yet, we decided that this is a project that would allow us test casters without much risk.

-Owen Wilks


P.S. This design was never meant to be used in a real competition it is just a fun way to test the concept.

Please verify the maximum input/battery voltage allowed on the current PDP manufactured by CTRE and the previous PDB to ensure that they will function properly in your proposed application.



06-07-2018 09:50 PM

tickspe15


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by ClayTownR View Post
Iíll offer what I do in Solidworks (it may be different in Inventor, which is what I believe 2471 uses):

Usually on the master sketch for the part, Iíll make a belt layout with the Input and output pulleys fully defined, but with the idler under-defined. Those pulleys are represented as circles with the pitch diameters (you can typically just look these up). Iíd then create a path-length dimension set to the tooth count times the pitch (ex: 80t HTD 5mm -> 400mm length). Iíd then drag around the idler until itís in a position I like, then dimension it into place. When making the plate itself, the idler usually doesnít get a hole but a slot, to make tensioning easier.

Feel free to pm me if you want more info or if I just donít make sense.
It doesn't look like they used a slot, so they'd have to know the exact positioning or have a plan to make custom sized idlers.



06-07-2018 11:16 PM

owen.wilks.2471


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by tickspe15 View Post
Cool design!

How did you go about determining the position of the idler pulleys?
ClayTownR you are correct we do use Inventor (2017) and use sketches to calculate the theoretical perfect belt path, but we also build in a way to adjust it.

So for the idler pulley between the 775 pro's the plan is a Delrin roller on a shoulder bolt that has been lathed down to provide the proper tension. It may take some adjusting to get perfect but will be a simple solution in the long run.

For the tensioning of the belt on the mini cim's I have implemented a solution is very similar to what team 192 has done with their belt gearboxes in the past.

Philso we are planning to control it with a hero board that can be run up to 28 volts and the matching PCB boards (I believe these can be run at 24 volts but am not 100% sure). Talon SRK can also be run at 28 volts, the electrical system is one of the main parts of the robot that we are still trying to figure out any advice would be greatly appreciated.

-Owen Wilks



06-07-2018 11:18 PM

owen.wilks.2471


Unread Re: pic: Off-season Caster Swerve Drive

ClayTownR you are correct we do use Inventor (2017) and use sketches to calculate the theoretical perfect belt path, but we also build in a way to adjust it.

So for the idler pulley between the 775 pro's the plan is a Delrin roller on a shoulder bolt that has been lathed down to provide the proper tension. It may take some adjusting to get perfect but will be a simple solution in the long run.

For the tensioning of the belt on the mini cim's I have implemented a solution is very similar to what team 192 has done with their belt gearboxes in the past.

Philso we are planning to control it with a hero board that can be run up to 28 volts and the matching PCB boards (I believe these can be run at 24 volts but am not 100% sure). Talon SRK can also be run at 28 volts, the electrical system is one of the main parts of the robot that we are still trying to figure out any advice would be greatly appreciated.

-Owen Wilks



06-07-2018 11:22 PM

pkrishna3082


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by owen.wilks.2471 View Post
advice would be greatly appreciated.
You will for sure want to have the pairs of motors in series, not in parallel. If you put them in parallel they’ll both run and 24V, which will likely kill them. If you put them in series they’ll drop roughly 12V each. You mentioned parallel in an earlier post and I’m not sure if that’s what you meant, so I just wanted to clarify.



06-08-2018 12:00 AM

owen.wilks.2471


Unread Re: pic: Off-season Caster Swerve Drive

Thanks, pkrishna3082

I work mostly on the mechanical side of the team and don't know much about electrical, so this is great advice and the results we wanted to see.

-Owen Wilks



06-08-2018 12:02 AM

AlexanderTheOK


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by pkrishna3082 View Post
You will for sure want to have the pairs of motors in series, not in parallel. If you put them in parallel theyíll both run and 24V, which will likely kill them. If you put them in series theyíll drop roughly 12V each. You mentioned parallel in an earlier post and Iím not sure if thatís what you meant, so I just wanted to clarify.
Yeah. It said series in the first post and parallel in the second post. Hope the second one was just a misprint. You'd be smelling mini cim for days!



06-08-2018 07:38 AM

hrench


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by AlexanderTheOK View Post
The purpose of offsetting a swerve wheel has nothing to do with stability.
the purpose of trail, as stated in the wikipedia article, is stability. To prevent 'wheel flop' and to center against wind forces. I've submitted an old BeDesign discussion to the image gallery so you can learn about this. I'm sure it will show up later today.

Probably you mean the reason this caster has trail in the design was not by intention to increase stability. But it will. If the trail is more than the wheel radius, it will be statically stable and dynamically stable.

Quote:
Originally Posted by AlexanderTheOK View Post
There is also no trail in such a module, which is evident by just looking at it, so your reference to rake and trail in this post isn't actually relevant, as that's just not how caster swerves are designed and built.
I think you mean there is no 'rake' in this design, as the rotational axis is vertical. "Trail" is the distance from where the rotational axis would intersect the ground to the point where the wheel contacts the ground. All casters have trail. The more trail, the more stable. The harder to turn. Why most swerves have none. And yes, you can have trail with no rake.

Here's a link to an online image of a caster where trail is illustrated and dimensioned:
http://photos1.blogger.com/blogger/2...600/castor.jpg

Again, I agree that you may have reasons to use caster in swerve. But I don't understand
Quote:
Originally Posted by Bryce2471 View Post
So that the structure it's mounted to can move immediately in any direction without skidding the wheel.
That doesn't make any sense to me. The wheel will skid if forces exceed traction. I don't know how caster helps that.



06-08-2018 11:17 AM

AlexanderTheOK


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by hrench View Post
Probably you mean the reason this caster has trail in the design was not by intention to increase stability. But it will. If the trail is more than the wheel radius, it will be statically stable and dynamically stable.
Quote:
Originally Posted by AlexanderTheOK View Post
The purpose of offsetting a swerve wheel has nothing to do with stability. It is merely a side benefit.
Funny how that's literally what I said.

Quote:
Originally Posted by hrench View Post
I think you mean there is no 'rake' in this design, as the rotational axis is vertical. "Trail" is the distance from where the rotational axis would intersect the ground to the point where the wheel contacts the ground.
You got me. I gotta take more naps to avoid mixing my my words up.

Quote:
Originally Posted by hrench View Post
That doesn't make any sense to me. The wheel will skid if forces exceed traction. I don't know how caster helps that.
You must have seen these links when going back into that thread. Please go down the rabbit hole. It's worth it from a purely "neat" point of view.

In short, on a conventional swerve, if two of your wheels are pointed in the wrong direction, you have to either wait for them to orient themselves, or deal with scrub.

A caster swerve can start moving immediately. There's no scrub because the incorrectly oriented wheels can contribute force in that direction by rotating.

Heck. ALL of your wheels can be pointed perpendicular to the direction you want to go, and you can still instantly go in that direction since they will all "shift" the robot in the process of rotating into position.



06-09-2018 07:41 PM

Nick_Coussens


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by AlexanderTheOK View Post
Funny how that's literally what I said.



You got me. I gotta take more naps to avoid mixing my my words up.



You must have seen these links when going back into that thread. Please go down the rabbit hole. It's worth it from a purely "neat" point of view.

In short, on a conventional swerve, if two of your wheels are pointed in the wrong direction, you have to either wait for them to orient themselves, or deal with scrub.

A caster swerve can start moving immediately. There's no scrub because the incorrectly oriented wheels can contribute force in that direction by rotating.

Heck. ALL of your wheels can be pointed perpendicular to the direction you want to go, and you can still instantly go in that direction since they will all "shift" the robot in the process of rotating into position.
This is probably the simplest and best way the potential benefit of caster swerve has been articulated. However, I'm not sure this is enough benefit to be worth it. As Jared had mentioned in the original caster thread, the downside is reversing direction by 180*. Caster swerve would inherently be worse at this then a regular swerve, and considering how often this specific maneuver occurs in FRC, even with swerve, I think dealing with this maneuver better outweighs the benefits of moving slightly faster in a change of direction normally with caster swerve.

Plus I believe a regular swerve will be inherently lighter, etc. etc.. it's a cool concept but the benefits seem to be far from outweighing the drawbacks.



06-09-2018 10:32 PM

AlexanderTheOK


Unread Re: pic: Off-season Caster Swerve Drive

Quote:
Originally Posted by Nick_Coussens View Post
However, I'm not sure this is enough benefit to be worth it. As Jared had mentioned in the original caster thread, the downside is reversing direction by 180*. Caster swerve would inherently be worse at this then a regular swerve, and considering how often this specific maneuver occurs in FRC, even with swerve, I think dealing with this maneuver better outweighs the benefits of moving slightly faster in a change of direction normally with caster swerve.
Yup, this kind of swerve only becomes advantageous when you need sub-cm accurate positioning. The advantage isn't so much speed as it is that you can move 5mm to the left without having to wait for all of your modules to spin to the right angles. I don't expect the GDC to ever create such a challenge, but if they do, the caster swerve will be a definite advantage.



view entire thread

Reply
previous
next

Tags

loading ...



All times are GMT -5. The time now is 02:26 PM.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi