View Full Version : pic: 148 Follower Wheel Assembly
Brandon Martus
21-01-2009, 19:23
[cdm-description=photo]32440[/cdm-description]
Jonathan Norris
21-01-2009, 19:24
Totally unnecessarily awesome... :cool:
Ice Berg
21-01-2009, 19:30
How is this going to measure ground speed if it can't touch the ground?
It can.
The GDC has ruled that similar devices do not count as "traction devices" in the Q and A.
NoahTheBoa
21-01-2009, 19:33
It was asked in the Q&A and they said that if it does not provide traction than it can touch the ground. The actual rule says that the rover wheels are the only thing that can provide traction, not the only thing that can touch the ground.
synth3tk
21-01-2009, 19:34
How is this going to measure ground speed if it can't touch the ground?
I'm no mechanical engineer (no, really, I'm not) but I'm assuming this will either touch the KOP wheels or somehow be attached along the route of the chains, without touching the ground.
NoahTheBoa
21-01-2009, 19:43
Here is a relevant Q&A on the subject
Question:
Can any part of your robot...other than the FRC supplied wheels...make contact with the playing surface if their intention is not to provide traction to propel or stop the robot?
GDC:
Yes.
http://forums.usfirst.org/showthread.php?t=10919
Joe Ross
21-01-2009, 19:45
We were planning to do the same thing, but with all vex components, including the new encoders. Hadn't gotten to it yet.
Fabulous use of VEX parts in a very elegant package. I think we'll be seeing a lot of similar assemblies this year.
Humm - how much bigger than the green gear is that omni wheel? The reason I ask is because on the carpet, the wheel may sink in enough to allow the gear to grab some carpet fibers.
Also, is it just pivoting off the robot frame from that empty set of holes, and thus using gravity to keep it in contact with the floor?
NoahTheBoa
21-01-2009, 19:59
If you are just using gravity to maintain contact with the ground have you tested to see if it slips at all when driving on the regolith?
danshaffer
21-01-2009, 20:03
Beautiful assembly!
Have you tested whether it will stay on the ground under its own weight? If not, may I suggest gas springs!
Akash Rastogi
21-01-2009, 20:24
Correct me if I'm wrong, but are those delrin sideplates? They look very nice. Good luck with this. =)
Greg Needel
21-01-2009, 20:26
I like the fact that black gear is an ABS rapid prototype. Want to clue the world into the right pitch for interfacing with a vex gear?
AdamHeard
21-01-2009, 20:35
Soo.... will Vexlabs be selling these?
Humm - how much bigger than the green gear is that omni wheel? The reason I ask is because on the carpet, the wheel may sink in enough to allow the gear to grab some carpet fibers.
Also, is it just pivoting off the robot frame from that empty set of holes, and thus using gravity to keep it in contact with the floor?
We had a similar plan, and were thinking if gravity wasn't sufficient, a rubber band to add a slight amount of tension would be easy enough.
=Martin=Taylor=
21-01-2009, 20:53
Here is a relevant Q&A on the subject
http://forums.usfirst.org/showthread.php?t=10919
Well... one could argue that the friction in the side-ways direction from this device COULD be used to stop the robot from sliding sideways...
But it would be one anal inspector to call you for that :)
artdutra04
21-01-2009, 21:00
I like the fact that black gear is an ABS rapid prototype. Want to clue the world into the right pitch for interfacing with a vex gear?I'm about 95% sure it's 24 diametric pitch.
Edit: Yup, they're 24 DP.
Brandon Holley
21-01-2009, 21:27
wow JVN this looks VERYYYY familiar....ours looks almost identical...
NoahTheBoa
21-01-2009, 22:32
Well... one could argue that the friction in the side-ways direction from this device COULD be used to stop the robot from sliding sideways...
But it would be one anal inspector to call you for that :)
I think that since it's an omni wheel the sideways friction won't be enough to slow a 120 lbs+ robot.
DonRotolo
21-01-2009, 22:35
Very nice! But why such a big green gear? I'd have used a smaller gear and a similar green gear on the encoder. I am curious.
Also, I think we'll be stealing the idea! (kinda sorta) Thank you!
Don
NoahTheBoa
21-01-2009, 22:42
Very nice! But why such a big green gear? I'd have used a smaller gear and a similar green gear on the encoder. I am curious.
It looks to me like it's a 1:1 ratio. Would make programming a bit easier without the extra math to account for the gear ratio.
Humm - how much bigger than the green gear is that omni wheel? The reason I ask is because on the carpet, the wheel may sink in enough to allow the gear to grab some carpet fibers.
Also, is it just pivoting off the robot frame from that empty set of holes, and thus using gravity to keep it in contact with the floor?
It's 1/8" bigger radially. It should be okay, if there are problems during testing I'll tweak things a bit. We plan to spring load it down. Spring tension, TBD. Surgical tubing, of course.
We were planning to do the same thing, but with all vex components, including the new encoders. Hadn't gotten to it yet.
The electrical engineers on our team say I have an "encoder mental block" where I refuse to model them into the final design. I had a heck of a time cramming them into Tumbleweed last year. This year we knocked em out almost immediately so they'll keep their mouths shut.
Soo.... will Vexlabs be selling these?
How much would you pay for one? ;) I'm starting my own company KarthikJohn.
We had a similar plan, and were thinking if gravity wasn't sufficient, a rubber band to add a slight amount of tension would be easy enough.
I think with some down-force this should get pretty good grip on the regolith.
I'm about 95% sure it's 24 diametric pitch.
Edit: Yup, they're 24 DP.
Yes, 24DP. We just modded the VEX 60t Gear Model to make the coupler piece. Works pretty well.
The side plates are laser cut ABS, 1/8" thick (cut on our small 12x24" laser, not the big one that does the sheet-metal.) The coupler is 3D printed ABS on our Dimension SST. I feel pretty darn spoiled.
Probably could have gone with a smaller package, but we've got plenty of room in the drivetrain to mount it. Like Raul said, if the 60t gear catches some carpet we may change it. I'm not real concerned. *Shrug* This was done quickly and the design group moved onto other things.
-John
Andrew Bates
21-01-2009, 23:54
Why not use the larger omni wheel? It would get the wheel away from the gear more. Also the larger omni probably has a less likely chance of slipping...
Travis Hoffman
22-01-2009, 00:02
The electrical engineers on our team say I have an "encoder mental block" where I refuse to model them into the final design. I had a heck of a time cramming them into Tumbleweed last year. This year we knocked em out almost immediately so they'll keep their mouths shut.
"Knocked out"....the encoder models or the EE's? :p
"Knocked out"....the encoder models or the EE's? :p
This year the encoder models... but thanks for a good 2010 plan.
AdamHeard
22-01-2009, 01:18
How much would you pay for one? ;) I'm starting my own company KarthikJohn.
-John
Not counting the cost of the encoder, I'd say $25-30 probably.
CraigHickman
22-01-2009, 02:10
Not counting the cost of the encoder, I'd say $25-30 probably.
Ditto on this. With encoder, depends on the accuracy/type of the encoder.
Jared Russell
22-01-2009, 07:18
Looks strikingly similar to something we're making...
How much would you pay for one? ;) I'm starting my own company KarthikJohn.
Where would you put this company? Halfway between Toronto and Greenville is...I dunno...Kokomo?
Kingofl337
22-01-2009, 10:59
With a few modifications you could use the US Digital encoders that come in the kit.
martin417
22-01-2009, 11:35
Why not use the larger omni wheel? It would get the wheel away from the gear more. Also the larger omni probably has a less likely chance of slipping...
This what we are doing. Not because of the slipping issue, but for "smoothness" of rotation. The large Vex omnis have two sets of rollers, offset to the sides for a smooth roll. The small ones would tend to go bumpity-bump as it transitions between the rollers. We thought the smoothness would be better for the encoders.
Very nice! But why such a big green gear? I'd have used a smaller gear and a similar green gear on the encoder. I am curious
Why gear at all? ours is a direct drive set-up.
Wow, maybe this was NOT worthy of showing off. Sounds like almost every team in FIRST has something "identical" or better back in their shop. Color me corrected.
-John
PS - Of course I was joking about starting my own company and selling these.
Jonathan Norris
22-01-2009, 12:01
How much would you pay for one? ;) I'm starting my own company KarthikJohn.
John that sounds like a lot of work for you... we all know Karthik isn't allowed to design anything that would actually go on a robot! :p
Chris Fultz
22-01-2009, 12:05
How much would you pay for one? ;) I'm starting my own company KarthikJohn.
Do you want to forge a partnership with CollinChris?
It's a family business. Right now we have no products, we just intend to steal good ideas from Chief Delphi posts and set up shop. Right now we are producing a cool wheel follower assembly that it appears you have copied... :) (our lawers will be contacting you for the patent infringement)
Tom Line
22-01-2009, 12:26
Wow, maybe this was NOT worthy of showing off. Sounds like almost every team in FIRST has something "identical" or better back in their shop. Color me corrected.
-John
PS - Of course I was joking about starting my own company and selling these.
Well, if it makes you feel any better, we don't have all that fancy-smancy vex stuff, so ours looks gargantuan compared to yours. :D
Sounds like almost every team in FIRST has something "identical" or better back in their shop.
Just like all the roller claws "identical" to 1114's last year, right?
AdamHeard
22-01-2009, 15:17
Wow, maybe this was NOT worthy of showing off. Sounds like almost every team in FIRST has something "identical" or better back in their shop. Color me corrected.
-John
Aww. I'm sure this will be the coolest looking follower wheel I'll see all year, "identical" in function isn't really identical. Last year we were "identical" in function to 987, but they were clearly better (in design, looks and performance).
PS - Of course I was joking about starting my own company and selling these.
Aww. lame. Sometimes we can blinded by awesomeness.
The Lucas
22-01-2009, 15:37
Wow, maybe this was NOT worthy of showing off. Sounds like almost every team in FIRST has something "identical" or better back in their shop. Color me corrected.
-John
PS - Of course I was joking about starting my own company and selling these.
Have you tested to see what percentage of your total robot traction the follower wheel represents? (like the GDC posted)
The TEAM must be prepared to provide test data verifying that the maximum sensor traction is not more than 5% of the maximum traction of the ROBOT (acceptable validation methods would include test data logging total drawbar pull both with and without the sensor in place).
I am not saying that I think this will represent >5% of robot traction, I would be surprised if it did. I am only curious because my team has yet to test our Way-Better, Uber-Awesome follower wheel we build out of Joe's spare Vex parts :rolleyes: :D
Ben Piecuch
22-01-2009, 19:24
John,
Are you running any sort of bushing on the vex shaft? Or, are you just letting it ride on the 1/8" hole in the ABS? (I'm having a hard time finding a flanged bushing for an 1/8" shaft)
Very pretty, thanks!
Bengineer
FRC1350
Andrew Bates
22-01-2009, 19:32
I bet they are just letting it ride in the hole. In the VEX system the bearings are just delrin with round holes so this plate essentially is the same thing.
Rickertsen2
22-01-2009, 22:07
I like it! Let us know what the accuracy of this turns out to be. A measuring wheel is something i always wanted to try. I'm assuming the remaining two holes are a pivot for this thing hang off of.
Just a word of warning about those greyhill encoders, they are very fragile and if subjected to remotely harsh conditions have a tendency to "go crunchy". Have a spare on hand.
John,
Are you running any sort of bushing on the vex shaft? Or, are you just letting it ride on the 1/8" hole in the ABS? (I'm having a hard time finding a flanged bushing for an 1/8" shaft)
Very pretty, thanks!
Bengineer
FRC1350
We're just running it in the ABS. VEX shaft is designed as a "rounded" square profile so it works great in that application.
-John
Dan Richardson
24-01-2009, 09:46
Every time I see a teaser/picture from 148 I feel like a tiny kitten who is lost in wonderment and amazement of the string spinning from the fan. I spend about 30 minutes pawing at the screen saying "I can haz?"
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