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 quite simply, not putting our best foot forward leaves us open to shooting ourselves in the foot. - Jessica Boucher [more] |
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Here's FRC 1726's pending robot design for the National Underwater Robotics Challenge (June 6-8, 2008). We've spent some time brainstorming and reflecting on last year's competition, and came to several conclusions that greatly aided in the construction of this year's robot. We've shifted to on-board electronics, resulting in an incredibly smaller tether and a single-bodied design (less things to waterproof). So far, the design is both cost efficient and simple, allowing a small swarm to be constructed ( 
).
For more pictures on the build and robot, check out our photo gallery.
For a video of the initial test drive*, see our YouTube video.
Good luck to all NURC participants this year, and thanks Fredi and the entire Carl Hayden robotics team for hosting this wonderful event! 1726 can't wait to see everyone there!
*the robot drives pretty slow in this video, but after checking the battery voltage we realized they had close to no charge... we'll test it soon with fully charged batteries!
Discussion
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27-04-2008 11:39
Schnabel
Re: pic: 1726 NURC robot prototype
Holy crap that is so cool! What does it take to be in a competition like this? I would love to see robots like that working under water! Where is it that the competition is at? Maybe I can come watch.
27-04-2008 11:46
MrForbes
Re: pic: 1726 NURC robot prototype
The competition is in the Phoenix area
http://www.h2orobots.org/fallindex.htm
and this year's event is full (24 teams entered)
27-04-2008 13:23
davidmedeiros
Re: pic: 1726 NURC robot prototype
Oh wow that design looks really interesting!
I'm glad you guys finally got signed up. I can't wait till competition day to see how your design works
27-04-2008 14:09
falconmaster
Re: pic: 1726 NURC robot prototype
Fantastic guys! Keep it up. We are building our new one this year. Here is the team website with some picts so far
http://falconrobotics.design.officel.../pictures.aspx
We have two full sets of prop to build!!
We have a lot of work to do.
We also want you guys to be involved in the design of the next APASE competition. We will talk more later!
27-04-2008 14:28
Eric24
Re: pic: 1726 NURC robot prototype
Thats pretty cool, I want to make one now. BTW, what is that vex part that appears in picture 13 of the photo gallery?
27-04-2008 14:32
s_forbes
Re: pic: 1726 NURC robot prototype
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Originally Posted by Eric24
Thats pretty cool, I want to make one now. BTW, what is that vex part that appears in picture 13 of the photo gallery?
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27-04-2008 14:43
Eric24
Re: pic: 1726 NURC robot prototype
Thank you, thats very interesting, I might have to get me one of those so I don't have to worry about the micro controller all the time. And the size is another advantage for applications like these. 
27-04-2008 14:51
MrForbes
Re: pic: 1726 NURC robot prototype
The vex signal splitter is a neat thing, we're using it with 3 Banebots speed controllers to drive the T500 bilge pump motors. The batteries are two Vex 7.2v 2000mAH wired in series to provide nominal 14.4v. The splitter takes power from the speed controller's Battery Eliminator Circuit.
We looked at the signal on the tether output port on the transmitter using an oscilloscope, and it's a nice 6 channel PWM signal, on the red and green wires in the 4 conductor connecting cable.
I wonder if we can do some more compacting work to be able to fit more stuff in the robot...it's getting crowded in there! Wires take up a lot of room.
27-04-2008 18:20
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by s_forbes
That would be the Vex signal splitter. It's the non programable version of the vex controller, and it only has 6 pwm outputs and no inputs. Tiny, too!
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27-04-2008 18:26
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by squirrel
The vex signal splitter is a neat thing, we're using it with 3 Banebots speed controllers to drive the T500 bilge pump motors. The batteries are two Vex 7.2v 2000mAH wired in series to provide nominal 14.4v. The splitter takes power from the speed controller's Battery Eliminator Circuit.
We looked at the signal on the tether output port on the transmitter using an oscilloscope, and it's a nice 6 channel PWM signal, on the red and green wires in the 4 conductor connecting cable. I wonder if we can do some more compacting work to be able to fit more stuff in the robot...it's getting crowded in there! Wires take up a lot of room. |
27-04-2008 18:34
MrForbes
Re: pic: 1726 NURC robot prototype
That's an experiment that still needs to be done! I think Gary sees the need to do the experimenting, so maybe it will get done soon...
As for the signal splitter channels, it uses the 4 joystick axes to control the first 4 outputs, and the buttons for the last two. IFI suggests not using the last two channels with servos, as they seem to have some jitter at the neutral position.
27-04-2008 18:42
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by TheOtherGuy
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27-04-2008 18:55
kE7JLM
Re: pic: 1726 NURC robot prototype
How stable is it underwater? What keeps it in it up-right position?
Have you named it yet?
27-04-2008 18:55
falconmaster
Re: pic: 1726 NURC robot prototype
We did a little experiment. Modified Plane props, three blade reverse pitch 4 inch versus muffin fan 4 inch.
Plane 12v 4to 5 newtons at 8amps full throttle
Muffin 12 v 7-8 newtons at 8.5amps full throttle
We are building a second bot to assist the mother bot. We have not figured out what config. we are going with the little bot. On board batteries, off board??? we want a fast very maneuverable bot to help the lumbering mother bot.
27-04-2008 18:55
MrForbes
Re: pic: 1726 NURC robot prototype
quick answer for the current draw question...5 amps at 13v (with two 7.2v nicad packs in series)
27-04-2008 18:56
MrForbes
Re: pic: 1726 NURC robot prototype
a few pounds of steel stakes keep it upright (they are tie wrapped on the bottom skids).
I don't think they've come up with a real name yet, but I'm sure it will be highly technical when they do!
27-04-2008 19:11
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by squirrel
quick answer for the current draw question...5 amps at 13v (with two 7.2v nicad packs in series)
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You can get them at http://www.overtons.com/modperl/prod...ID=1009&r=view
In the pic it show a 750gph, they were lazy and used the same pic
27-04-2008 19:14
falconmaster
Re: pic: 1726 NURC robot prototype
Did you see the poster for this year, its going on the t-shirts! Look at the pics featured on the left.
28-04-2008 00:54
Jon Jack
Re: pic: 1726 NURC robot prototype
First off I'd like to compliment you guys on a nice, clean design. I think you guys are off to a great start. I'm interested to know if you guys have done any testing yet as I have a couple of concerns about your thrusters:
1) Your use of computer fan blades
From my testing at SeaBotix, I can say that fan blades are horribly in efficient. Especially in water. The blades tend to flex too much which cause for your performance to decrease, especially when you're moving at a higher speed. May I suggest using an RC/Model boat propeller. One advantage to this design is that you seem to have a lot of clearance to use a larger diameter propeller. Using a larger diameter propeller means you'll be able to move more surface feet of water per revolution, which means you can run the propeller at a lower RPM therefore cutting down your power consumption and making those batteries last longer. Also, there are a couple modifications you can make to an off the shelf RC/Model boat propeller to improve its performance and efficiency.
For example, make sure that you've gotten rid of ALL mold reliefs on the surface of the propeller. You may want to steal a page from the America's Cup boats and sand and gloss the propeller (spray paint gloss works just fine) then sand the gloss finish with a 2000 or finer grit sand paper. The gloss will cut down on the friction and the small grooves from the sand paper make sure that the water does not stick to the surface of the blade. If you do decide to make these modifications be very careful not to change the shape of the blades as that will effect the propeller as well. If done correctly you could increase your thrust by about 5-10%.
2) Water flow around the thruster
From some of the pictures I've seen, it seems like 80-90% of the propeller is being blocked by the thruster body. Remember that you want to keep as much of the area behind the propeller free from obstruction, increasing the flow of water and improving your performance. This will also help cut down on cavitation which will give the vehicle a much smoother ride. Cavitation not only sucks the performance out of a thruster, it also causes spikes in current draw (imagine running it in air/in water over and over again).
You can fix this by going with a larger diameter propeller. The more blade that is not being blocked by the thruster, the better.
3) The Kort Nozzle around the propeller
I found a picture in your gallery that had a very good picture of the thruster. One of the things I noticed was that your kort nozzle isn't wrapped very tightly around the propeller. You want this wrapped as tightly around the blades (with out actually touching them) as possible so you can concentrate and control the flow of water as much as possible. If there is a gap left between the nozzle and the blade the kort nozzle loses some of it purpose.
Anyways, I hope you find this as useful. Good luck to you and all of the NURC teams.
28-04-2008 01:29
s_forbes
Re: pic: 1726 NURC robot prototype
Great tips Jon, thanks a lot!
This is the kind of feedback that we always hope for when we post our projects for everyone to see. The help gained from a massive community of clever people far outweighs any competative advantages gained by keeping it secret.
01-05-2008 14:59
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by Jon Jack
First off I'd like to compliment you guys on a nice, clean design. I think you guys are off to a great start. I'm interested to know if you guys have done any testing yet as I have a couple of concerns about your thrusters:
1) Your use of computer fan blades From my testing at SeaBotix, I can say that fan blades are horribly in efficient. Especially in water. The blades tend to flex too much which cause for your performance to decrease, especially when you're moving at a higher speed. May I suggest using an RC/Model boat propeller. One advantage to this design is that you seem to have a lot of clearance to use a larger diameter propeller. Using a larger diameter propeller means you'll be able to move more surface feet of water per revolution, which means you can run the propeller at a lower RPM therefore cutting down your power consumption and making those batteries last longer. Also, there are a couple modifications you can make to an off the shelf RC/Model boat propeller to improve its performance and efficiency. For example, make sure that you've gotten rid of ALL mold reliefs on the surface of the propeller. You may want to steal a page from the America's Cup boats and sand and gloss the propeller (spray paint gloss works just fine) then sand the gloss finish with a 2000 or finer grit sand paper. The gloss will cut down on the friction and the small grooves from the sand paper make sure that the water does not stick to the surface of the blade. If you do decide to make these modifications be very careful not to change the shape of the blades as that will effect the propeller as well. If done correctly you could increase your thrust by about 5-10%. 2) Water flow around the thruster From some of the pictures I've seen, it seems like 80-90% of the propeller is being blocked by the thruster body. Remember that you want to keep as much of the area behind the propeller free from obstruction, increasing the flow of water and improving your performance. This will also help cut down on cavitation which will give the vehicle a much smoother ride. Cavitation not only sucks the performance out of a thruster, it also causes spikes in current draw (imagine running it in air/in water over and over again). You can fix this by going with a larger diameter propeller. The more blade that is not being blocked by the thruster, the better. 3) The Kort Nozzle around the propeller I found a picture in your gallery that had a very good picture of the thruster. One of the things I noticed was that your kort nozzle isn't wrapped very tightly around the propeller. You want this wrapped as tightly around the blades (with out actually touching them) as possible so you can concentrate and control the flow of water as much as possible. If there is a gap left between the nozzle and the blade the kort nozzle loses some of it purpose. Anyways, I hope you find this as useful. Good luck to you and all of the NURC teams. |
Thanks for posting your experience! Its right on. Please let us know where to get props. Do you think Seabotix might sell us just the props?
01-05-2008 17:56
Jon Jack
Re: pic: 1726 NURC robot prototype
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Originally Posted by falconmaster
You are so right about the fan blades, We have had a very hard time finding boat props the size we need. they are either too small or too big. Do you have any ideas where to get them. We find that plane props work, buy you need higher rpms. Ye sthey are not efficient, but they are better than none. We also found that if you use large plane props and cut the tips off they work even better. Find the highest pitch you can. I like the muffin fan idea and it is possible to find ones with blades that are not that flexible. I was even thinking of doing a bollard test with every other blade cut out. Just to see what happens.
Thanks for posting your experience! Its right on. Please let us know where to get props. Do you think Seabotix might sell us just the props? |
If someone is interested, I also found a site that sells Kort Nozzels and Kort Nozzle Propeller combos. If you can't find an off the shelf kort nozzle, the least you could do is use some PVC tubing that'll fit closely around the outside of the propeller. A step up would be if you can find something that is tapered towards the prop so you can concentrate the water column increasing your bollard pull.
What are the rules in terms of what motors teams can use on their thrusters?
01-05-2008 19:12
MrForbes
Re: pic: 1726 NURC robot prototype
No rules....basically we can do whatever we want, we are limited to maximum total power and maximum voltage.
We are limited by our budget, though! which is one reason we started out using the $15 bilge pump motors. another reason is that they come with a shaft seal that works ok at the depths of the competition.
We are also limited in time/fabrication abilities/etc so a pre-packaged motor is a big plus. Boat props work best when attached to a relatively long drive shaft, so the motor is a ways away from the prop, not like our current design. That's one reason we wanted to go with a larger diameter prop. Also I tihnk that efficiency is not going to be our ultimate goal..instead, we'll be aiming for a propulsion system that can accomplish the mission objectives in the required time, and have enough battery reserve to get the robot(s) back to shore. Budget again comes into the equation....
We had found the boat props already, but not the nozzles...very interesting!
Thanks for your input, we'll keep working on it and let you know what we find!
02-05-2008 01:10
GUI
Re: pic: 1726 NURC robot prototype
Today we put some 6-4 model airplane props that we had lying around on it to see how they compare, and it's quite a difference. The bot was quite a bit faster, though they were spinning noticeably slower than the fan blades, indicating higher motor loads. I think with with some sort of Kort nozzle (we need prop guards anyway, why not make them aid propulsion?) these propellers will do what we need. We are planning on testing with larger fan blades and possibly with cut down airplane props.
EDIT: Here's a video of the teste with the airplane props ( the vertical thruster is still using a fan blade in the video) http://youtube.com/watch?v=DeYNCOiSV4Q
02-05-2008 15:28
tseres
Re: pic: 1726 NURC robot prototype
guys, that is awesome, and it's cool to see something like that other then the rov-in-a-box. i think i may have a summer project.....
02-05-2008 22:11
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by GUI
Today we put some 6-4 model airplane props that we had lying around on it to see how they compare, and it's quite a difference. The bot was quite a bit faster, though they were spinning noticeably slower than the fan blades, indicating higher motor loads. I think with with some sort of Kort nozzle (we need prop guards anyway, why not make them aid propulsion?) these propellers will do what we need. We are planning on testing with larger fan blades and possibly with cut down airplane props.
EDIT: Here's a video of the teste with the airplane props ( the vertical thruster is still using a fan blade in the video) http://youtube.com/watch?v=DeYNCOiSV4Q |
http://legitrobotics.googlepages.com/frame2
03-05-2008 00:16
MrForbes
Re: pic: 1726 NURC robot prototype
They did another test drive today, and jokingly said they should name it "zippy" because it goes plenty fast. I even got to drive! after they'd run the batteries down, driving it around for over 20 minutes. That's with two VEX NiCd batteries wired in series, giving 14.4v nominal and 2000 mAH. We're thinking of just getting some 3500 mAH NiMH battery packs and it should provide plenty of power for the mission.
They've worked out a list of parts to buy to build two more robots...this will be fun!
The LEGIT robot is looking good! I hope they can get it in the water early and get some good practice, it really helps.
03-05-2008 00:55
falconmaster
Re: pic: 1726 NURC robot prototype
We got some 3200mh batteries lipo from tower hobbies
http://www3.towerhobbies.com/cgi-bin...&I=LXMDN3&P=ML
the link is not the right battery but it is the same brand
The three blade reverse pitch, pusher prop
http://www3.towerhobbies.com/cgi-bin...?&I=LXAPX4&P=7
and then we cut it to 4inch diam. to fit in abs coupler
03-05-2008 00:56
falconmaster
Re: pic: 1726 NURC robot prototype
Hey do you know where to get a rack and pinion set. We are needing a way to extend our arm in and out, screw drive is just not cutting it. We prefer plastic, but small brass will work as well.
03-05-2008 00:59
Jon Jack
Re: pic: 1726 NURC robot prototype
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Originally Posted by falconmaster
Hey do you know where to get a rack and pinion set. We are needing a way to extend our arm in and out, screw drive is just not cutting it. We prefer plastic, but small brass will work as well.
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03-05-2008 02:34
MrForbes
Re: pic: 1726 NURC robot prototype
I wonder if you could use the vex rack and pinion parts? you'd have to make a support thingy for it, and the stuff that it's made to bolt to is all steel (or aluminum), but you might be able to make something from plastic.
http://www.vexrobotics.com/vex-robot...gear-kit.shtml
also Lego comes to mind, I think they have some short stroke rack and pinion setups in some of the car sets? My son Steve might know, he still plays with Legos (and he's in college now)
04-05-2008 02:55
TheOtherGuy
Re: pic: 1726 NURC robot prototype
We made a quick little robot tour of our progress to date.
http://www.youtube.com/watch?v=IVfcqfdcpX8
We went on a shopping spree today and bought parts for the other additions to the team ( ) along with our new lighting system, some small 3watt apparently pre-watertight lights. Also, we finally took the 'bot for a test night swim and everything worked out perfectly, including the new "appendage" used for picking up objects!
I'll try to get some image up soon in the gallery, but until then you can check out the video
04-05-2008 10:34
=Martin=Taylor=
Re: pic: 1726 NURC robot prototype
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Originally Posted by falconmaster
Hey do you know where to get a rack and pinion set. We are needing a way to extend our arm in and out, screw drive is just not cutting it. We prefer plastic, but small brass will work as well.
|
04-05-2008 13:23
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by squirrel
I wonder if you could use the vex rack and pinion parts? you'd have to make a support thingy for it, and the stuff that it's made to bolt to is all steel (or aluminum), but you might be able to make something from plastic.
http://www.vexrobotics.com/vex-robot...gear-kit.shtml also Lego comes to mind, I think they have some short stroke rack and pinion setups in some of the car sets? My son Steve might know, he still plays with Legos (and he's in college now) |
04-05-2008 13:36
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by TheOtherGuy
We made a quick little robot tour of our progress to date.
http://www.youtube.com/watch?v=IVfcqfdcpX8 We went on a shopping spree today and bought parts for the other additions to the team ( ) along with our new lighting system, some small 3watt apparently pre-watertight lights. Also, we finally took the 'bot for a test night swim and everything worked out perfectly, including the new "appendage" used for picking up objects!I'll try to get some image up soon in the gallery, but until then you can check out the video |
We are in the process of making the new ROV for this year. We are calling it Amanda, Tell you the story later. Basically a slightly improved version of last years. We are also making a second ROV much smaller as an assistant. We will post pics soon. We hope to be in the water soon and test as well.
Also, if you want strong magnets, break open non functioning hard drives and use those magnets, they are very strong and light!
04-05-2008 13:55
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by Hachiban VIII
SDP-SI also has plastic and brass racks.
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04-05-2008 14:14
MrForbes
Re: pic: 1726 NURC robot prototype
On the left is a list of stuff, go to "gears" then "racks" and you'll hopefully find something like this
https://sdp-si.com/eStore/Select.asp...SearchPattern=
but it's a frames web page, so you need to see all the frames at once, and I can't link to all of them at once!
04-05-2008 14:17
Vikesrock
Re: pic: 1726 NURC robot prototype
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Originally Posted by falconmaster
Tried looking, can't find it. Nice website though!
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11-05-2008 20:07
MrForbes
Re: pic: 1726 NURC robot prototype
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Originally Posted by falconmaster
Where is the night video?
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http://www.youtube.com/watch?v=TrQC1tjaLe0
Sorry it took so long!
12-05-2008 23:29
falconmaster
Re: pic: 1726 NURC robot prototype
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Originally Posted by squirrel
I finally put some night video on youtube
http://www.youtube.com/watch?v=TrQC1tjaLe0 Sorry it took so long! |
23-05-2008 22:33
Andrew Bates
Re: pic: 1726 NURC robot prototype
How did you run both the video and the info for the VEX robot controller on the same tether?
23-05-2008 23:06
TheOtherGuy
Re: pic: 1726 NURC robot prototype
Yes we are; we're using the twisted pairs of CAT-6 cable to prevent any interference, although we recently bought some more flexible cable for the miniROV with untwisted solid wires, and the signals work just fine on that tether.
23-05-2008 23:41
MrForbes
Re: pic: 1726 NURC robot prototype
The signal from the video camera goes up the tether on one twisted pair, while the signal from the vex transmitter goes down the tether on a different twisted pair. Network cable (cat5, cat6) has 4 pairs, phone cable usually has 2 or 3 pairs.
23-05-2008 23:43
Andrew Bates
Re: pic: 1726 NURC robot prototype
Ok cool. Are you using a webcame or one of those circuit board cameras(not sure what the name is).
23-05-2008 23:47
MrForbes
Re: pic: 1726 NURC robot prototype
We're using some board cameras from SuperCircuits. although of the 3 we bought, the last one didn't work, so we need to get some more.
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