View Full Version : pic: FRC488 - Six Wheel Drive Chassis
[cdm-description=photo]26122[/cdm-description]
A couple of questions:
Does that have any rocker in it? And is that 25 or 35 chain?
Why omniwheels on a 6WD?
Turning, I'd say. Instead of lowering the center wheel, why not use omni's? It's more stable and more maneuverable. (It's also easier to spin around by hitting.)
If the bumpers are back and the design is like 2006, then the next step is to add mounting to this frame that would allow the bumpers to be a structural element. If the rules allow forget home center plywood. Baltic birch "wood" be a good choice.
Cody Carey
02-01-2007, 22:32
Not necessarily more maneuverable, But I bet it is nice to have the 'bot spin around it's center set of wheels instead of whichever four happen to be touching the ground :rolleyes:
s_forbes
02-01-2007, 22:38
Wow, looks light! Do you have an estimated weight for the entire drive base?
And on the subject of omniwheels: It looks like with the setup you have it would be very easy to swap them for traction wheels if they are needed. I guess that would be decided in testing.
MikeDubreuil
02-01-2007, 23:07
Can you explain why you chose not to have a cross brace? I'm not a mech-e but I would guess you need one.
A couple of questions:
Does that have any rocker in it? And is that 25 or 35 chain?
The wheels are all in line -- there's no 'rock' at all. The chain is #25.
Why omniwheels on a 6WD?
Because the center wheel is not lowered at all, at least one outside set of wheels should be omniwheels to alleviate friction while turning. I chose to put a set on each end because there's no penalty to in line pushing force, generally, and I like to subtley encourage our drivers to avoid conflict. :)
If the bumpers are back and the design is like 2006, then the next step is to add mounting to this frame that would allow the bumpers to be a structural element. If the rules allow forget home center plywood. Baltic birch "wood" be a good choice.
I'm now looking at a mounting scheme that will accept bumpers and protect the wheels from impact. I've never put bumpers on a robot before, so I'm looking at examples of others' work to get an idea how to best accomodate the additional weight of the bumper assembly.
Not necessarily more maneuverable, But I bet it is nice to have the 'bot spin around it's center set of wheels instead of whichever four happen to be touching the ground :rolleyes:
Our 2005 robot had a lowered center wheel and the tipping action drove me and our drivers crazy. It's an impact to the system each time the robot's inertia shifts and that starts to lead to annoying things like loosened bolts and the like. Practically, it's cheaper and easier for me to make omniwheels than it is to make traction wheels and it's certainly cheaper than buying them.
Wow, looks light! Do you have an estimated weight for the entire drive base?
And on the subject of omniwheels: It looks like with the setup you have it would be very easy to swap them for traction wheels if they are needed. I guess that would be decided in testing.
As shown -- which includes everything but stiffening gussets and a base upon which to mount electronics, it's 29.5 lbs.
The omniwheels are riding on 5/8" keyed shaft, while the AndyMark performance wheel is broached for a 1/2" hex shaft. It'd be relatively easy to change out a set of omniwheels for a set of traction wheels with a little bit of forethought. Namely, I'd need to make some shafts that are 5/8" diameter with keyway on one end and 1/2" hex on the other.
Can you explain why you chose not to have a cross brace? I'm not a mech-e but I would guess you need one.
I'm waiting on the game before adding cross-bracing since I'm not sure if I'll need a scoop or something on one or both ends. I'd like to, if weight allows, put an aluminum plate (1/16" or so) across the bottom to add rigidity.
I noticed that the front and rear c channels are notched for the drive rails on top and bottom. This could be a weak point. Shouldn't the drive rails fit inside the c channel leaving the channel uncut ?
M -
Looks quite nice, and you have obviously put a lot of work and thought into the design. The efforts to minimize the total weight are obvious. The biggest concern you may have is strength in the event of an impact or collision. You might consider making the frame members out of rectangular tube instead of channel. Given the amount of material you are removing, the additional weight from the fourth side of the tube will be minimal, but there will a considerable increase in stiffness of the frame assembly.
Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?
-dave
Cody Carey
03-01-2007, 00:02
Oh goodness.
ChuckDickerson
03-01-2007, 00:15
Here we go again...
Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?
-dave
http://www.army-technology.com/contractor_images/man/man2.jpg
;)
Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?
-dave
Any crocs?
CRIKEY!
WATCH OUT!!! WE'VE GOT A DAVE ON THE LOOSE!!! SOS...SOS...SOS
Rich Kressly
03-01-2007, 09:23
M -
Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?
-dave
Who keeps letting him in? Security!!!
I love the simple approach to the 6-wheel drive. I'll be follwing up later if you use this to see what additional stiffening was used/needed. Good luck.
Who keeps letting him in? Security!!!
I love the simple approach to the 6-wheel drive. I'll be follwing up later if you use this to see what additional stiffening was used/needed. Good luck.
I took Dave's advice and added the fourth wall to the front and rear cross members as a start. Because these drivetrains are almost never operating absent some additional mechanism or superstructure, I try to incorporate those future additions into the design and allow for them to be used as support for the drive in the same way that the drive supports the mechanisms, if that makes sense. I try to design such that the finished robot appears organic -- not as if it was designed in pieces that were smashed together later.
Because of the holidays primarly, we haven't really done much of anything with our mecanum drive prototype. It still has no feedback system installed and remains difficult to drive. Most of the team agrees that, unless it appears to be a perfect solution for the new game, we'll stick with something more traditional like this drive, so there's a good chance you'll be seeing it somewhere.
Andrew Blair
04-01-2007, 20:34
Madison, I know that you have no broach capability, so I'm curious- where do you buy your #25 sprockets? I can't find any finished ones online, or in the Browning catalog.
Dan Petrovic
04-01-2007, 20:45
Not necessarily more maneuverable, But I bet it is nice to have the 'bot spin around it's center set of wheels instead of whichever four happen to be touching the ground :rolleyes:
Wouldn't the spinning of the robot automatically lift the front and back wheels up and equal distance from the floor? Kind of like when your arms raise up when you spin around.
Cody Carey
04-01-2007, 20:50
Wouldn't the spinning of the robot automatically lift the front and back wheels up and equal distance from the floor? Kind of like when your arms raise up when you spin around.
Maybe on a perfectly 4-way symmetrical robot, but in My team's experience, It stays on 4 wheels and rocks back and forth... Whichever four wheels happen to be touching are the ones the bot spins around. Kinda messes up high-speed maneuvering.
Madison, I know that you have no broach capability, so I'm curious- where do you buy your #25 sprockets? I can't find any finished ones online, or in the Browning catalog.
For this, we'll be ordering from McMaster-Carr -- part no. 2737T123. 5/8" bore was the smallest I found with a keyway for this particular sprocket. I didn't take a comprehensive look at many teeth counts, though, so I'm not sure how consistent the keyways are in 5/8" bore sprockets -- but I can't imagine why they all don't have one.
Andrew Blair
05-01-2007, 07:23
Ah, I see. We were going to be using 1/2" bore, and for some reason, no one on earth carries broached 1/2" bore sprockets. Thanks though!
Rick TYler
05-01-2007, 11:58
Wouldn't the spinning of the robot automatically lift the front and back wheels up and equal distance from the floor? Kind of like when your arms raise up when you spin around.
The last two years I worked on center-drive, 6-wheel robots and both times we purposely loaded one end of the 'bot with a LOT more weight for game reasons. This also had the effect of having the same four wheels on the ground most of the time. We had little fore-and-aft rocking and the robot wasn't tricky to steer at all. Having said that, Madison makes nice chassises -- er, chasses -- er, chassisses -- what IS the plural of chassis anyway? I'd hire her to consult on our chassis, but since I'm now on a VEX-only team, I think we'd be wasting her skills.
CE Mexican
05-01-2007, 12:25
M -
Looks quite nice, and you have obviously put a lot of work and thought into the design. The efforts to minimize the total weight are obvious. The biggest concern you may have is strength in the event of an impact or collision. You might consider making the frame members out of rectangular tube instead of channel. Given the amount of material you are removing, the additional weight from the fourth side of the tube will be minimal, but there will a considerable increase in stiffness of the frame assembly.
Just out of curiosity, what is the spacing between the wheel sets? Is it sufficient to cross a 20-inch wide, 16-inch deep, water-filled moat, should that capability ever be necessary?
-dave
I agree wiht what dave said about strenght, but on the contrary our team used aluminum channel for our frame and we didnt seem to have and problem with strength, and our frame took quite a beating during aim high this year
That looks very nice and pretty well engineered. My suggestions are that you only use one set of omni wheels. You have to admit that you will be getting in to conflict no matter what you do.
The frame does look pretty sound, but with all that material taken out, are you worried about bending at all? these bots go through some pretty hard hits.
But i am very impressed by your design and i look forward to seeing the end product after the next hectic 6 weeks =)
--Dan
CE Mexican
05-01-2007, 12:36
team 1783, which is my schools team, used a different drivetrain set up, we had designed a setup where each side had indepent suspension, and two wheels for each side. and this year (depending on the game) i have designed a three speed gear box that would be incorperated into our original design. also i was thinking about trying out a four whee drive design that would be built by me and a local shop. how many of you guys know about the xmods remote control cars at radio shack? well i got one for christmas (god only knows why) but i was looking at upgrades for it and i saw that they have a four wheel drive kit for them. and after hours of configuring, and designing i think that i can build the 4 wheel drive suspension and drivetrain for our robot.
Fred Sayre
05-01-2007, 12:59
The last two years I worked on center-drive, 6-wheel robots and both times we purposely loaded one end of the 'bot with a LOT more weight for game reasons. This also had the effect of having the same four wheels on the ground most of the time. We had little fore-and-aft rocking and the robot wasn't tricky to steer at all. Having said that, Madison makes nice chassises -- er, chasses -- er, chassisses -- what IS the plural of chassis anyway? I'd hire her to consult on our chassis, but since I'm now on a VEX-only team, I think we'd be wasting her skills.
And you of course, are welcome to come consult on our team any time :) Stop by if you feel you are missing out on the hectic 6 weeks that is FRC this season!
JaneYoung
05-01-2007, 13:16
what IS the plural of chassis anyway?
chassis, singular = chassis, plural
the plural would have a wee different pronunciation though
Richard Wallace
05-01-2007, 13:39
chassis, singular = chassis, plural
the plural would have a wee different pronunciation thoughOne chass-ee, two chass-ease.
Rick TYler
05-01-2007, 13:52
Ah, jeez, I know that the plural of chassis is chassis, I was just funnin' around.
For the record, in 2005 our bot had six wheels with 2WD, but last year our very heavy, very strong chassis had six wheels with 6WD. In case anyone cared.
I AM going through FRC withdrawal now that kickoff is near, but I also fell asleep last night thinking about softballs, so maybe I'm becoming a VEXer, too.
I would like to bring our new, nearly-all-rookie team to visit an FRC team during build, so maybe I will take 488 up on their offer. We also have had friendly comments from team members at 1318 and 492. I think the "F" in FIRST really stands for "friendly."
artdutra04
05-01-2007, 16:55
Having said that, Madison makes nice chassises -- er, chasses -- er, chassisses -- what IS the plural of chassis anyway? One can only venerate the intrinsic quagmires of the lexicon of the English language. :)
foundbobby
21-01-2007, 21:41
The wheels are all in line -- there's no 'rock' at all. The chain is #25.
Because the center wheel is not lowered at all, at least one outside set of wheels should be omniwheels to alleviate friction while turning. I chose to put a set on each end because there's no penalty to in line pushing force, generally, and I like to subtley encourage our drivers to avoid conflict. :)
I'm now looking at a mounting scheme that will accept bumpers and protect the wheels from impact. I've never put bumpers on a robot before, so I'm looking at examples of others' work to get an idea how to best accomodate the additional weight of the bumper assembly.
Our 2005 robot had a lowered center wheel and the tipping action drove me and our drivers crazy. It's an impact to the system each time the robot's inertia shifts and that starts to lead to annoying things like loosened bolts and the like. Practically, it's cheaper and easier for me to make omniwheels than it is to make traction wheels and it's certainly cheaper than buying them.
As shown -- which includes everything but stiffening gussets and a base upon which to mount electronics, it's 29.5 lbs.
The omniwheels are riding on 5/8" keyed shaft, while the AndyMark performance wheel is broached for a 1/2" hex shaft. It'd be relatively easy to change out a set of omniwheels for a set of traction wheels with a little bit of forethought. Namely, I'd need to make some shafts that are 5/8" diameter with keyway on one end and 1/2" hex on the other.
I'm waiting on the game before adding cross-bracing since I'm not sure if I'll need a scoop or something on one or both ends. I'd like to, if weight allows, put an aluminum plate (1/16" or so) across the bottom to add rigidity.
Nice design. What about having the wheels on the outside? Don't they need be protected some to avoid bent shafts and broken wheels?
foundbobby
21-01-2007, 21:48
Thread created automatically to discuss this image in CD-Media.
http://www.chiefdelphi.com/media/img/599/59935f4bff3e9d1c0462cc73ee03600b_m.jpg (http://www.chiefdelphi.com/media/photos/26122?)
Nice picture! We'll see you at SVR
Richard Wallace
21-01-2007, 21:52
Based on pictures in another thread (http://www.chiefdelphi.com/forums/showthread.php?threadid=52448) I think this is probably FRC Team 488's robot. Madison is a member of that team, and her team role is mentor.
Maybe I didn't understand your question?
Dominicano0519
21-01-2007, 22:01
team 1783, which is my schools team, used a different drivetrain set up, we had designed a setup where each side had indepent suspension, and two wheels for each side. and this year (depending on the game) i have designed a three speed gear box that would be incorperated into our original design. also i was thinking about trying out a four whee drive design that would be built by me and a local shop. how many of you guys know about the xmods remote control cars at radio shack? well i got one for christmas (god only knows why) but i was looking at upgrades for it and i saw that they have a four wheel drive kit for them. and after hours of configuring, and designing i think that i can build the 4 wheel drive suspension and drivetrain for our robot.
uhh did you just say suspension, as in springs and dampners suspension??
this is a carpeted field were talking about
Do you guys have a shaft coming out of the tranny for the middle wheel as well as 2 sprockets on the inside leading to the front and rear wheels? Are the sprockets inline? Wouldn't you need gears on the same axle as the sprocket to drive the sprockets in that case? Are the sprockets on the same axle? In that case how can your wheels be inline? Are the sprockets on the wheels on an offset?
Alright no more questions :D just curious.
Nice design. What about having the wheels on the outside? Don't they need be protected some to avoid bent shafts and broken wheels?
Teams have had success with similar designs in the past and our experience with the completed chassis yesterday indicates that, though we may want to protect the wheels, it's not a paramount concern given our strategy and design. In another game, or on another robot, it may be very important that the wheels are protected from damage and from the sort of wedging effect impedes motion that other teams with similar drives have seen in past seasons.
Nice picture! We'll see you at SVR
We hope you'll take a minute and stop by our pit to talk to the team. I'd be happy to talk more about our robot and answer any questions you might have -- as would anyone else on our team. We're proud of the work we do.
Do you guys have a shaft coming out of the tranny for the middle wheel as well as 2 sprockets on the inside leading to the front and rear wheels? Are the sprockets inline? Wouldn't you need gears on the same axle as the sprocket to drive the sprockets in that case? Are the sprockets on the same axle? In that case how can your wheels be inline? Are the sprockets on the wheels on an offset?
Alright no more questions :D just curious.
The gearbox at the center of each side has an output shaft that drives the center wheel. Two 18 tooth sprockets are coupled to that shaft and, via chain, drive the wheels at the front and back of the robot. Those sprockets are not in line -- they are offset 1/4". Our wheels remain in line because the sprockets on either end mimic the offset of their corresponding center sprocket.
Attached to this post is a cross-section of the gearbox that may help make the gearing arrangement a bit more clear. Excuse that the gears aren't meshed properly, please. :)
Brian Mocci
23-01-2007, 10:58
My favorite part about this design, something that no one has mentioned yet supprisingly, is the way that you extended your front and rear rails in order to protect the cantilevered wheels. Excellent design all around!
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