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This is our 2011 Drive Train concept. We are running custom transmissions with 6 motors (shown all as CIMs but 2 are Bane Bots) because we are too cheap/poor to buy Super Shifters. The wheels are driven with Gates timing belt which is run inside the tube. 4" AM wheels on 1/2 Hex Shafts. With our current gear ratio of 7.4 : 1 we should be able to move at around 12 fps.
Discussion
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11-01-2011 17:51
Stephen of REX
Re: pic: 2791's Chassis
Are the extra CIMS intentional? We're only allowed four this year.
11-01-2011 17:53
Vikesrock
Re: pic: 2791's Chassis
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Originally Posted by Stephen of REX
Are the extra CIMS intentional? We're only allowed four this year.
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11-01-2011 17:53
johnnyburns35
Re: pic: 2791's Chassis
are those cims? because your only allowed to use 4 this year...
11-01-2011 17:53
EricH
Re: pic: 2791's Chassis
My guess is they're FP stand-ins.
Not quite certain the bumper mounts meet the spec distance, but that may be because I don't know any dimensions. If those are 4" wheels, probably OK, otherwise take a close look.
11-01-2011 17:55
Sh1ine
Re: pic: 2791's Chassis
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Originally Posted by EricH
My guess is they're FP stand-ins.
Not quite certain the bumper mounts meet the spec distance, but that may be because I don't know any dimensions. If those are 4" wheels, probably OK, otherwise take a close look. |
11-01-2011 17:56
johnnyburns35
Re: pic: 2791's Chassis
sorry the other persons post wasn't there when i looked at it lol sorry
11-01-2011 18:01
johnnyburns35
Re: pic: 2791's Chassis
we are only allowed to use 4 CIM motors this year right because if we are allowed to use more then i have to change my layout?
11-01-2011 18:09
Chris is me
Re: pic: 2791's Chassis
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Originally Posted by Vikesrock
$10 says they represent RS775s through a CIMulator.
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11-01-2011 18:13
DMetalKong
Re: pic: 2791's Chassis
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Originally Posted by Vikesrock
$10 says they represent RS775s through a CIMulator.
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11-01-2011 19:11
Akash Rastogi
Re: pic: 2791's Chassis
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Originally Posted by DMetalKong
Where exactly are the CIMulators from? I've heard them mentioned a couple of times, but I've done a search on CD and a google search and I couldn't find a link.
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Very nice stuff Pinecone
(Idc how much I like your team, I still get to make fun of you!)
11-01-2011 19:16
Leav
Re: pic: 2791's Chassis
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Originally Posted by Akash Rastogi
AM's new product.
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11-01-2011 19:19
Akash Rastogi
Re: pic: 2791's Chassis
Oh my bad my bad. Mixed up the name with the CIMple Box from AM
11-01-2011 19:19
Chris is me
Re: pic: 2791's Chassis
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Originally Posted by Akash Rastogi
AM's new product.
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I wish it were an AM product though
11-01-2011 19:20
Aren_Hill
Re: pic: 2791's Chassis
http://banebots.com/
Banebots actually, not AndyMark
11-01-2011 19:41
JackS
Re: pic: 2791's Chassis
You can view some preliminary pictures with electronics here.
We are planning on using Anderson connectors to enable us to put the Victors much closer together than otherwise possible. Wire paths have yet to be drawn out.
11-01-2011 20:12
Navid Shafa
Re: pic: 2791's Chassis
A) Are you planning on running the chain on the inside of the frame?
B) Are the bumpers going to be mounted right onto the standoff blocks, without any other support?
11-01-2011 21:25
Sh1ine
Re: pic: 2791's Chassis
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Originally Posted by Navid Shafa
A) Are you planning on running the chain on the inside of the frame?
B) Are the bumpers going to be mounted right onto the standoff blocks, without any other support? |
The spacing between the edge of one stand off and the edge of the next closest stand off is always less then 8". Which is to say that the center points on the standoffs may be a bit more then 8, but if I am reading the rules correct "and no section of BUMPER greater than 8” may be unsupported)" just having material behind it suffices. And with a bolt holding it in place, and a generous amount of stand off to support the bumper from twisting, they should be good.
11-01-2011 21:51
Chris Fultz
Re: pic: 2791's Chassis
Nice work.
Something to consider. It looks like very little ground clearance.
If you have anything stick through the bottom plate, it could rub the carpet.
And, there is a small step in the carpet around the towers. There is a plate under the tower base, and then a layer of carpet covering it.
12-01-2011 01:47
Justin Montois
Re: pic: 2791's Chassis
Looks great. I love the belt running through the tube. Very slick.
12-01-2011 02:24
Leav
Re: pic: 2791's Chassis
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Originally Posted by 340x4xLife
Looks great. I love the belt running through the tube. Very slick.
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it's cool no doubt, but looks like a pain to maintain if you throw a chain...
A lesson I learned from my mentor a while back was to design for maintainability, as well as performance and looks.
12-01-2011 02:36
Chris is me
Re: pic: 2791's Chassis
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Originally Posted by Leav
I would actually say that is my least favourite feature about this chassis.
it's cool no doubt, but looks like a pain to maintain if you throw a chain... A lesson I learned from my mentor a while back was to design for maintainability, as well as performance and looks. |
This one will have a removable easy access window over the middle wheel. That and practice / belt changing drills should bring it down to 5 minutes - twice as fast as our previous dead axle drivetrain.
We also stress tested the drive. Stalled the wheels multiple times, ran it forward and back a bit with no signs of slipping or failing.
12-01-2011 02:49
rahilm
Re: pic: 2791's Chassis
Looking at the CAD with electronics, I just wanted to point out that the only legal bridge this year is the DAP-1522 included in the kit.
Looks like a pretty cool drive design with the 6 motors 
12-01-2011 03:08
Matt H.
Re: pic: 2791's Chassis
Why did you choose to use six motors in your drive train?
4 CIMs at a 7.4:1 ratio gives a maximum of 634 in-lbs of torque at the wheels. With 4 inch wheels, that becomes ~315 lbs of force to accelerate the robot. However, with a generous coefficient of friction of 1.5 your robot will spin its wheels at 180 lbs of accelerating force.
12-01-2011 03:14
Chris is me
Re: pic: 2791's Chassis
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Originally Posted by Matt H.
Why did you choose to use six motors in your drive train?
4 CIMs at a 7.4:1 ratio gives a maximum of 634 in-lbs of torque at the wheels. With 4 inch wheels, that becomes ~315 lbs of force to accelerate the robot. However, with a generous coefficient of friction of 1.5 your robot will spin its wheels at 180 lbs of accelerating force. |
Essentially, pushing power. 4 CIMs geared at 12 FPS draws a LOT of current. 4 CIMs and 2 BB isn't quite traction limited (60some amps last time I checked) but at least we won't stall out pushing mecanum bots and kitbots around a bit, and we'll have great acceleration.
12-01-2011 13:26
JesseK
Re: pic: 2791's Chassis
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Originally Posted by Chris is me
We're assuming about 1.3 for traction.
Essentially, pushing power. 4 CIMs geared at 12 FPS draws a LOT of current. 4 CIMs and 2 BB isn't quite traction limited (60some amps last time I checked) but at least we won't stall out pushing mecanum bots and kitbots around a bit, and we'll have great acceleration. |
If you use the line following sensors, where would you put them?
I only ask because the first words out of the student programmer's mouth was "I want my line followers here, here, and here", which correlated to the front corners of the robot and the center of the robot. In this setup, it looks like those sensors would interfere with the live axles (they're about an inch tall), though other modifications could be made.
12-01-2011 13:28
sdcantrell56
Re: pic: 2791's Chassis
Id be real careful gearing at 12fps. We did that last year with 4cims and 2fp's and often times our battery was totally dead with around 30 seconds left in the match. We later dropped down to 9.5fps with the 6 motors and it was much better. Just be ready to swap out gearing after testing. Otherwise this looks super awesome!
12-01-2011 13:58
Teched3
Re: pic: 2791's Chassis
I've always been an advocate of using smaller diameter wheels for a little better grip on the carpet. You also obtain a little lower CG, which helps on Sat afternoon. Was there a reason that your standoffs appear to be reversed from one side to the other, or just an oversight. are you using belt or chains to drive your front/back wheels? Your rendering is awesome, and is motivating me to learn a 3D modeling program. any suggestions for an old-timer? 
12-01-2011 14:17
Chris is me
Re: pic: 2791's Chassis
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Originally Posted by JesseK
Looks like a very solid setup.
If you use the line following sensors, where would you put them? |
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Originally Posted by sdcantrell56
Id be real careful gearing at 12fps. We did that last year with 4cims and 2fp's and often times our battery was totally dead with around 30 seconds left in the match. We later dropped down to 9.5fps with the 6 motors and it was much better. Just be ready to swap out gearing after testing. Otherwise this looks super awesome!
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That being said this is a valid concern - does anyone know how I could predict battery discharge rates using math? I have no idea how to do it.
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Originally Posted by Teched3
I've always been an advocate of using smaller diameter wheels for a little better grip on the carpet. You also obtain a little lower CG, which helps on Sat afternoon. Was there a reason that your standoffs appear to be reversed from one side to the other, or just an oversight. are you using belt or chains to drive your front/back wheels? Your rendering is awesome, and is motivating me to learn a 3D modeling program. any suggestions for an old-timer?
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This year, it's just under an inch and a half.
With the 9 foot tall arm we're working on, that could be pretty important.
12-01-2011 16:20
Matt H.
Re: pic: 2791's Chassis
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Originally Posted by Chris is me
That being said this is a valid concern - does anyone know how I could predict battery discharge rates using math? I have no idea how to do it.
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http://www.alliedelec.com/Images/Pro...A/610-0002.PDF
The last graph gives discharge characteristics. The C-rate or CA on the graph can be roughly calculated as Current Load/Rated Amp Hours so at your quoted 60 amps
CA~3.4
Visually extending the curve; you're right on the edge.
If you current usage rises to 80 amps with a greedy manipulator you'll almost certainly run of battery life.
Disclaimer: I'm not an expert on batteries and am only ~70% sure my interpretation of the C-Rate is correct.
Another method you could try is using Peukert's law.
Where the time to full discharge is approximated by:
t=H(C/(IH))^k
Here t is time to full discharge, C is the rated capacity, I is the current, H is the rated discharge time and k ranges between 1.1-1.5 for lead acid batteries (it is generally empirically determined, but we can use the discharge curves to estimate it)
Using the spec sheet again:
C=17.4 H=20 hours I=60 amps k~1.34
t~4.1 minutes
For 80 amps
t~2.8 minutes
So it all comes down to how much you want to trust the math. To me it looks like a very border line case especially if you have a high current (always on rollers, heavy lifting etc.) manipulator.
For more information:
http://en.wikipedia.org/wiki/Peukert's_law
13-01-2011 20:24
Chris is me
Re: pic: 2791's Chassis
That's pretty compelling, really. Though I doubt the drive will spend more than 30 seconds a match drawing maximum current, it is still something we should watch out for.
Our current plan as of today's meeting is to oder a set of pulleys to gear us for the more conservative 9.5 feet per second and to do extensive battery life testing. We've got a simple, probably low load manipulator planned - but we will still be careful. If during practice or competition we figure out we're going through batteries too fast - we'll swap those right out. Should take under 10 minutes.
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