http://me218cboat.weebly.com/
http://www.stanford.edu/~rjandrad/ME218C/
and the spdl Terman Pond Flotilla (2 yrs ago)
http://www.stanford.edu/~rjandrad/ME218C/
and the spdl Terman Pond Flotilla (2 yrs ago)
Friday, April 29, 2011
Thursday, April 28, 2011
Mechanical Components that we can afford
Wow, great post Jackie. I understand the concerns about controllability, and I agree that it is important to be both fast and controllable.
I found some motors on Jameco's website that seem to fit our needs: 15k-25k rpm, reasonable torque and current, and low cost:
This one takes 13 amps, but would be very powerful, and it's only 6 bucks. (18krpm)
1.43A, 23krpm, $3
1.44A, 18krpm, $2
20krpm, 2.05A, $3
18krpm, 0.15A, $1, weak sauce
I'm a fan of either the beast 13A motor if we think we can handle the drive circuit, or the 20krpm 2.05A motor for a good mix of affordability and speed.
As for propellers and shafts, I think we should get decently large propellers and long (maybe flexable) drive shafts so we can keep the motor out of the water.
Bill of Materials
6 solder perf boards, 2$ apiece, 6 x 2=12$
14 board pins and mounts, 5c and 36c apiece respectively, 14 x 41 = 5.34$
18 2pin molex female connectors, 6c apiece, 6 x18= 0.96$
5 male & female 3pin molex, respectively 5c and 8c apiece 13 x 5 = 0.65$
something else accounting for 0.70$ (14 pieces)
total 19.65$, paid by Matt
Matt
14 board pins and mounts, 5c and 36c apiece respectively, 14 x 41 = 5.34$
18 2pin molex female connectors, 6c apiece, 6 x18= 0.96$
5 male & female 3pin molex, respectively 5c and 8c apiece 13 x 5 = 0.65$
something else accounting for 0.70$ (14 pieces)
total 19.65$, paid by Matt
Matt
$15 Batteries
$40.59 Shafts, Couplings, and Stuff Shafts at J&M
$5.29 ABS Sheet at Tap Plastics
$4 Velcro from Bookstore
$37.85 Motors, LED's, Button from Jameco
Random Thoughts on Designs and Components
After a quick chat with Ed, it seems clear that the best design is going to strike the right balance between speed and control. Apparently, in the past, getting a boat to go fast has not been a problem. I don't know what difference our particular fountain will make with the way the jets from above create currents. But in general, it sounded like a slow boat with quick, intuitive controls performed a lot better than the ones that went for raw speed alone.
We won't need to stay at an Atoll for too long to capture it, but we should allow time for errors and trying to position close enough. The RFID readers are reliable within only a few inches, so it might be worth investing in side propellers, especially if we have sensors on a couple sides of our boat and want to pull up to it sideways. That seems like the best plan to me because that allows us to simply drive in a ring around the whole fountain, especially if we can fit in the shallow section around the outside. And it would require less control and driving skill than having to face the front of the boat towards each RFID reader to tag an Atoll.
So, boat shapes. Higher level decisions seem to be between a single and double hull. Advantages of a double hull are stability and more flexibility with motor placement, since there would be a large space in between the two points that go in the water, possibly under our (waterproofed) electronics. Advantages of a single hull are mobility and a more compact size, since we do have to fit within the 72" perimeter requirement. One thought I had today was making a double-hulled boat, that was both wide and tall enough such that it could fit around an Atoll completely. The RFID signal would come from the inward sides of the two hulls. That would also be a way to block an opponent from capturing an Atoll we owned, if we decided not to go for more. Of course, with the Atolls being 16" wide already, it would be very difficult to fit within the perimeter, maintain stability, and leave enough of a margin to actually drive properly over an Atoll.
As for components, the things I see costing the most are good reliable motors (probably not the one that costs $100, sorry Matt) and the sensors we'll want in our remote control. Speaking of which, here are a couple accelerometers:
From Radio Shack, $35: http://www.radioshack.com/product/index.jsp?productId=2909788&CAWELAID=124299652
One of the reviewers even mentions using it on a model boat for automatic stability control (making sure the boat doesn't tilt too far to one side or the other). A cool idea, though it shouldn't be necessary if we get the mechanical design right (plus I don't think we'll be lacking in other code we have to write). Also don't think we can afford more than one of these and it'll probably go into the remote control. Anyway, this one is well-reviewed, but the technical specs are either non-existent online or hard to find.
From Adafruit, $20: http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=163&zenid=374729df98ba07ea843cc82c7806628b
Measures 3 axes (!) and seems pretty solid. Adafruit is also a pretty cool company.
Some other interesting sensors we can think about putting on the remote control:
Flex sensor: http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=182&zenid=374729df98ba07ea843cc82c7806628b
A different idea for a throttle: how much someone is bending some part of the remote determines how fast the boat goes.
Rotary encoder: http://www.sparkfun.com/products/9117
Doesn't have to be too expensive. If we can get a really solid/sturdy mechanical connection, I'm imagining a giant crank that you have to turn, or maybe a big wooden steering wheel like you find on old boats (eBay?).
There are lots more cool things out there, but that's all I have for now.
We won't need to stay at an Atoll for too long to capture it, but we should allow time for errors and trying to position close enough. The RFID readers are reliable within only a few inches, so it might be worth investing in side propellers, especially if we have sensors on a couple sides of our boat and want to pull up to it sideways. That seems like the best plan to me because that allows us to simply drive in a ring around the whole fountain, especially if we can fit in the shallow section around the outside. And it would require less control and driving skill than having to face the front of the boat towards each RFID reader to tag an Atoll.
So, boat shapes. Higher level decisions seem to be between a single and double hull. Advantages of a double hull are stability and more flexibility with motor placement, since there would be a large space in between the two points that go in the water, possibly under our (waterproofed) electronics. Advantages of a single hull are mobility and a more compact size, since we do have to fit within the 72" perimeter requirement. One thought I had today was making a double-hulled boat, that was both wide and tall enough such that it could fit around an Atoll completely. The RFID signal would come from the inward sides of the two hulls. That would also be a way to block an opponent from capturing an Atoll we owned, if we decided not to go for more. Of course, with the Atolls being 16" wide already, it would be very difficult to fit within the perimeter, maintain stability, and leave enough of a margin to actually drive properly over an Atoll.
As for components, the things I see costing the most are good reliable motors (probably not the one that costs $100, sorry Matt) and the sensors we'll want in our remote control. Speaking of which, here are a couple accelerometers:
From Radio Shack, $35: http://www.radioshack.com/product/index.jsp?productId=2909788&CAWELAID=124299652
One of the reviewers even mentions using it on a model boat for automatic stability control (making sure the boat doesn't tilt too far to one side or the other). A cool idea, though it shouldn't be necessary if we get the mechanical design right (plus I don't think we'll be lacking in other code we have to write). Also don't think we can afford more than one of these and it'll probably go into the remote control. Anyway, this one is well-reviewed, but the technical specs are either non-existent online or hard to find.
From Adafruit, $20: http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=163&zenid=374729df98ba07ea843cc82c7806628b
Measures 3 axes (!) and seems pretty solid. Adafruit is also a pretty cool company.
Some other interesting sensors we can think about putting on the remote control:
Flex sensor: http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=182&zenid=374729df98ba07ea843cc82c7806628b
A different idea for a throttle: how much someone is bending some part of the remote determines how fast the boat goes.
Rotary encoder: http://www.sparkfun.com/products/9117
Doesn't have to be too expensive. If we can get a really solid/sturdy mechanical connection, I'm imagining a giant crank that you have to turn, or maybe a big wooden steering wheel like you find on old boats (eBay?).
There are lots more cool things out there, but that's all I have for now.
Tuesday, April 26, 2011
Mechanical Parts for Consideration
Drivetrain options:
Fiberglass Propeller: http://www.amazon.com/1-34-x-2-06-Composite-Propeller/dp/B000UBZYH8/ref=sr_1_6?ie=UTF8&qid=1303883577&sr=8-6
Complete Drive Unit: http://www.hobby-lobby.com/multispeed_380_boat_drive_83_prd1.htm
Bow Thruster: http://www.hobby-lobby.com/scaledrives.htm
Exotic Ideas:
Ballast (good for stability of a monohull): http://www.hobby-lobby.com/racing_micro_magic_keel_ballast_34979_prd1.htm
Monohull(fasterand lighter): http://www.hobby-lobby.com/racing_micro_magic_hull_deck_hatch_34976_prd1.htm
Jet Drive: http://www.hobby-lobby.com/jetdrives.htm
Very expensive brushless motor: http://www.horizonhobby.com/Products/Default.aspx?ProdID=PRB4017#quickAccessories
Initialization
We just had our first meeting.
We discussed Atoll Capture Vehicle (ATV) design, and looked at the fountain. We decided that it would be a bad idea to go under the jets, and talked about using the calm 5.5inch deep channel along the sides for most of our navigation.
We worked on a basic timeline for the project, including major checkpoints.
26 April Today
28 April Questions for Ed
3 May Design Review ACV (finalize mass, buoyancy requirements)
Draft of Communication Protocol
6 May Working Draft of Communication
10 May Checkpoint 1
-ACV-CVC communication (read/decode, CVC simulated)
-Platform built, working propulsion and steering suspystems
-RFID rad and decode
17 May Checkpoint 2
-ACV-CVC-Atoll communication fully functional (commands, status messages)
19 May Project Preview
-successful driving and steering (CVC-ACV)
-recognize RFID's on Atolls
25 May Grading Session
Immediate action items (obtain the follow through legal channels):
- 2 PICs
- Accelerometer
- Potentiometers
- Wires for prototyping
- Motors
- Tricolor LED's
- Propellers
- Pink Foam
- Motor Drivers (LM293 D/NE or LM2800)
- perf board
- resistors
- parts organization bin
- molex
- batteries
-voltage regulators
- switches
- muli-strand wires in various colors
- LED's
- waterproof container
Questions for Ed:
How will the atolls display ownership?
Broadcast to everyone or just your team?
How close do you have to get to RFID tags?
How does the horn start the devices?
Do the devices need to sense the horn?
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