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Unread 01-05-2008, 17:56
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Re: pic: 1726 NURC robot prototype

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Originally Posted by falconmaster View Post
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?
I did a search on Google for 'RC Boat Propellers' and I found this site. They have a variety of propellers in different sizes ranging from 30-60mm, which seems like the optimal size for this competition. They're also reasonably priced. I would start there.

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?
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Unread 01-05-2008, 19:12
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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!
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Unread 02-05-2008, 01:10
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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

Last edited by GUI : 02-05-2008 at 01:31. Reason: added video link
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Unread 02-05-2008, 15:28
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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.....
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Unread 02-05-2008, 22:11
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Re: pic: 1726 NURC robot prototype

Quote:
Originally Posted by GUI View Post
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
Awesome guys! We see that same thing about the plane props. We have used three bladed reverse pitch 12 inch props that we cut down to 4 inches inside a abs coupler as a shroud. The girls team LEGIT is using this idea
http://legitrobotics.googlepages.com/frame2
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Unread 03-05-2008, 00:16
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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.

Last edited by MrForbes : 03-05-2008 at 00:22.
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Unread 03-05-2008, 00:55
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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
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Unread 03-05-2008, 00:56
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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.
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Unread 03-05-2008, 00:59
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Re: pic: 1726 NURC robot prototype

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Originally Posted by falconmaster View Post
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.
Stock Drive Parts/Sterling Instruments is a good place. They're reasonably priced and have a big selection to chose from. Just be careful, we've gotten some bad stuff from them before.
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Unread 03-05-2008, 01:15
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Re: pic: 1726 NURC robot prototype

Thanks Jon.
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Unread 03-05-2008, 02:34
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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)
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Unread 04-05-2008, 02:55
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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
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Unread 04-05-2008, 13:36
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Re: pic: 1726 NURC robot prototype

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Originally Posted by TheOtherGuy View Post
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
Where is the night video? You guys are doing great!

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!
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Unread 04-05-2008, 13:23
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Re: pic: 1726 NURC robot prototype

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Originally Posted by squirrel View Post
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)
Thanks! We order some today!
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Unread 04-05-2008, 10:34
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Re: pic: 1726 NURC robot prototype

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Originally Posted by falconmaster View Post
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.
SDP-SI also has plastic and brass racks.
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