Control 3 blimp motors

zumpner

My brother and I are putting together a UAV Blimp. We currently have...

Board of Education
BASIC Stamp
RC Blimp Kit
- 3 Volt Lithium Battery For Your Mach RC Airship (http://www.rctoys.com/rc-toys-and-parts/DF-3V123/RC-PARTS-BLIMP-BATTERIES-ACCESSORIES.html)
- Gondola for Mach 3 - MachIII RC Indoor Blimp (http://www.rctoys.com/rc-toys-and-parts/MACH-3-GONDOLA/RC-PARTS-BLIMP-BATTERIES-ACCESSORIES.html)
- White High Lift Blimp Envelope For Use Above 4000 Feet (http://www.rctoys.com/rc-toys-and-parts/MACH-HLENV/RC-PARTS-BLIMP-HELIUM-BALLOON-ENVELOPE.html)

We are planning on getting...

GPS
Compass

1) First question is, do we need motor controllers or can we use the ones provided with the RC Blimp Kit? If we must buy them, which would you suggest?

1 HB-25 Motor Controller (http://www.parallax.com/Store/Accessories/MotorServoControllers/tabid/160/CategoryID/35/List/0/Level/a/ProductID/64/Default.aspx?SortField=ProductName,ProductName)
* I'm thinking this will be way too heavy

2 Micro Dual Serial Motor Controller (http://www.parallax.com/Store/Accessories/MotorServoControllers/tabid/160/CategoryID/35/List/0/Level/a/ProductID/491/Default.aspx?SortField=ProductName,ProductName)
* Will 1 Amp be enough to power the motors?

3 Motor Mind B Enhanced (http://www.parallax.com/Store/Accessories/MotorServoControllers/tabid/160/CategoryID/35/List/0/Level/a/ProductID/66/Default.aspx?SortField=ProductName,ProductName)
* Firstly, this is expensive, secondly, is there room on the Board of Education?

2) My second question is about power. The RC Blimp Kit comes with with 3 Volt Lithium Battery. Will this be enough to power the motors and the BASIC Stamp / Board of Education?

3) My third question is about the BASIC Stamp itself. I know it can only do one thing at a time. Would that be a problem in this application? If so, would the PWMPAL (http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/saddle/List/0/SortField/4/ProductID/67/Default.aspx) be the solution or do I need to upgrade to the Propeller (http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/propeller/List/0/SortField/4/ProductID/332/Default.aspx)?

4) Lastly, are there any components that you can think of that I left out.

Post Edited (zumpner) : 7/27/2009 10:51:49 PM GMT

Mike Green

1) Without knowing what kind of motor controllers are provided, it's hard to say. Since the Blimp is R/C controlled, they probably use standard servo control pulses which should be just fine for the Stamp to control.

2) a 3V Lithium battery is fine for the motors, but it won't work for the Board of Education and the Stamp. You need 6 to 7.5V for that at a minimum.

3) a Stamp will work fairly well managing two servos and reading some sensors in between the servo pulse times. A PWMPAL or ServoPAL will help take some of the processing burden off the Stamp. A Propeller has several advantages. It will run off a 3V Lithium battery and it can handle a "bunch" of tasks.

Phil Pilgrim (PhiPi)

The components you've specified are not light-weight. Have you determined what the lifting power of the blimp will be? I came up with about 10 pounds for that particular gas bag filled with helium at STP, but I don't have full confidence that it's right. That number seems high to me.

-Phil

W9GFO

1 cubic foot of helium can lift about 1 ounce.

I calculate about 26 oz. gross lift.

I used a 36" sphere and a 21" cylinder with an 18" radius.

4/3 pi*r^3 = 24,417 cu in

pi*r^2*h = 21,365 cu in

Total cu in = 45,782 cu in or 26.5 cu ft

RC Toys said...
At over 4000ft some of our customers are unable to get the blimp to float due to low air density. If you are over 4000ft we recommend you purchase a high-lift envelope.

The high lift envelope only adds 2 cu ft (2 oz), I am doubtful that is has the lifting capability that you need.

Rich H

Post Edited (W9GFO) : 7/28/2009 12:13:09 AM GMT

zumpner

Thanks for the quick replies guys.

Mike, Thanks for the good info. The blip kit is actually on its way so I will have to take a close look at it when it gets here to see if it uses standard servo control pulses. Can you explain or point me in the right direction to learn how to interface with it? Also, lets say I need to get a motor controller, which one should I get?

Phil, by my calculations, I think the envelope will be able to handle a 6 oz payload. With the gondola, motors, gps, compass, batteries .... it's going to be VERY hard to stay under that weight, like you said. One thing I'm hoping will help is the 3rd fan on the bottom of the gondola. It will help keep neutral buoyancy by running constantly.

I was really hoping the 3v battery could run the whole show because of weight concerns.

Rich, thanks for the theoretical calculations. I'll let you know how it goes in the real world.

W9GFO

Other thoughts;

You could use a Spin Stamp by itself without the Board of Education. You would have to take care with how you hooked it up but you could save a lot of weight AND use that lithium battery to power it. If you can tap into the motor controller that is in the gondola then you wouldn't need anything else. It would be challenging.

GPS will not be of much use indoors - due to the plus or minus 15 ft accuracy (at best) and the poor signal that you will get while indoors. Outdoors would be very risky for this ultra light weight and low powered blimp - even in calm conditions.

There are RC blimps out there that would be much more appropriate for this type of project but naturally they get quite expensive ($1,000 and upwards).

You can get a weather balloon for less than $70 that will lift 3 kg. You would have to provide everything else but if you can deal with the spherical shape, it could carry most any controller, sensors and motors that you wished.

Rich H

zumpner

Rich,

Thank you very much for your thought. Very much appreciated. I had not thought about the weather balloon route and would definitely not be adverse to the aesthetics of it. I care a LOT more about the functionality.

To tell you the truth, this is more of a prototype kind of thing to get the guts working well. After this proof of concept is working, we were thinking about upgrading to the 1,000+ blips you mentioned.

I'll take a look at the Spin Stamp as well. Also, once everything is "working" off of the balloon code and motor wise, we were planning on ditching the board and hard wiring most everything.

Phil Pilgrim (PhiPi)

My gut reaction was that 10lb. was way too high. I now see where I went wrong: I used diameters and lengths instead of radii for the volume of a prolate spheroid. That reduces the volume — and lifting capacity — by a factor of eight. So 20 oz., which agrees fiarly well with W9GFO's figure. That's not much.

I'm not sure how advisable a weather balloon would be. You can't steer them or force them to rise and fall using aerodynamics, like you can with a blimp. You really need that prolate form, along with ailerons and a rudder, for maneuverability.

-Phil

Mike Green

If you decide to use a Basic Stamp, download the "Robotics with the BoeBot" tutorial which discusses servos and the Stamp at length.

If you decide to use a Propeller (including a Spin Stamp), download one of the servo control objects from the object exchange. The comments in the code are fairly detailed.

www.parallax.com/tabid/535/Default.aspx

obex.parallax.com/objects/category/7/ and subsequent pages.

W9GFO

Phil Pilgrim (PhiPi) said...
You really need that prolate form, along with ailerons and a rudder, for maneuverability.

Nah, even the real blimps use vectored thrust for low speed maneuvering. Sure, a proper zeppelin shape will move through the air better - and that is the preferred way to go - but there is no reason that a spherical balloon can't be steered in any direction desired, it just won't go very fast.

Rich H

erco

zumpner: With all due respect, it sounds like you guys are paddling toward the falls. I have been an airship freak my whole life. LOVE airships, even more than I love Basic Stamps. I'm a private pilot, I have flown the Goodyear blimp, I've sat in the very first unfinished Zeppelin NT in Friedrichshafen, and I built an R/C model of the NT for the Zeppelin company. R/C airships are neither simple nor trivial to build, although everyone assumes they are. Autonomous airship control is magnitudes harder. As a general rule, everything will be at LEAST twice as heavy as you expect, plus you need to plan extra lift for disposable ballast as your helium leaks out or becomes impure. To go outside, you'll need 10 times the motor power you expect, plus an emergency valve to dump helium when the wind inevitably carries it away. Any shape blimp or balloon will have unique momentum-related handling qualities, swinging like a pendulum, or·turning when you expect it to go straight. Check out·the Zeppelin NT, which has twin vectorable·main drive motors, plus two more·tail rotors, one vectorable.·Without building at least a half-size R/C scale model to learn how to control your airship, you can't begin to understand what is required and how to plan an effective flight control system. You'll need several gyros or accelerometers, PING modules, and several Stamps or a Propeller·chips·at a minimum.

I really hate to be a naysayer, but I'm trying to give you the benefit of my experience and some useful things to consider before you waste time and money. If you think·autonomous airships·are easy to build, ask yourself why everyone doesn't have one already. Just ballasting a model airship properly is a continuous and tedious process. Every time you add or remove weight, your airship's mass changes and your flight control parameters change. Modifying an existing R/C helicopter would be considerably easier. Alan Alda had an episode of his show (Scientific American Frontiers) perhaps 8-10 years ago, featuring a·Georgia Tech·contest for a UAV to pick up a ring on a football field. There was a German university with a spherical blimp that initially looked well-thought out but never stood a chance. The eventual winner: Stanford U with a helicopter. Try to find that old show before you spend a dime on any hardware. Here's the show transcript, the contest is at the bottom. http://www.pbs.org/saf/transcripts/transcript603.htm

Some more info and photos about that show at http://www.robots.org/newslttr/news0597/met0597.htm·near the bottom.

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·"If you build it, they will come."

Post Edited (erco) : 7/28/2009 5:35:04 PM GMT