Newsgroups: comp.robotics Path: utzoo!utgpu!watserv1!watmath!mwtilden From: mwtilden@watmath.waterloo.edu (Mark W. Tilden) Subject: Re: Small Hovering Hobby Robots Message-ID: <1991Jun14.204833.9470@watmath.waterloo.edu> Organization: University of Waterloo References: <00949D78.A594B600@vms.csd.mu.edu> <26776@ttidca.TTI.COM> Date: Fri, 14 Jun 1991 20:48:33 GMT Lines: 209 The following are some articles I've kept on the subject. Might be still worth a read. ------------------------------------- To: outram@cernvax.cern.ch Subject: Re: model flying saucer - help/advice needed. Newsgroups: sci.electronics In-Reply-To: <1746@cernvax.UUCP> Organization: University of Waterloo Cc: Bcc: In article <1746@cernvax.UUCP> you write: > ___ > TOP VIEW : / O \ where 'O' is an engine. > |O + O| > \ O / > --- Limit it to three motors and install a microsequencer (rom based) to do high speed dynamic stabilization control for you. Nothing else is fast or light enough. Three motors gives you better lift area while simplifying the control problem to tripod balancing. The actual balance mechanism should be two loops of plastic tubing half filled with murcury (the other half with heavy oil). Paint the surface of the tubes half way with high conductive paint. Stick an insulated wire in contact with the murcury. Feed both outputs into a capacitance meter circuit and you have a damped stabilizer of reasonable accuracy. Far cheaper than building your own gyroscope. >Has anyone made one of these things before ? What difficulties where >encountered ? Yes, I made one out of carved styrofoam as a frame. Biggest problem is finding the ideal lifting fans. As for control, drive all fans from a single high-power electric motor (used in rc cars) driving triple magnetic clutches. You'll have to make these. Hope you have a Unimat lathe handy. The motor, as the batteries, must be mounted dead center. Using 100mA batteries, you can expect a maximum 2 min flight per charge. Longer if you want to run it by 'wire' of course. You will also want a speed regulator for the motor or control instability will result. Your biggest problem is weight and control. Too much weight and all you'll have is a floppy hovercraft. Control is also the major bitch. You require very high speed/accurate feedback to keep the thing from flopping hard. One of the things I did was install a deep murcury switch which only registered if the machine flopped > than 90 degrees. When triggered it replaced the balance circuit control with signals to level the craft at all costs. You won't have to slamm the thing into the ground too many times before you realize how handy this is. I'll tell you now, such a thing really isn't as fun as you might think. It is very difficult to control and if your motors aren't precessed exactly the damn thing is always spinning on you. This won't matter if you can find a gyroscope you can lift but otherwise you'll have hard times ahead. The only way around it is to leave the lift motors always stabilizing the outfit and install control vanes around the outside of the craft which allow retro-rocket like control. Works, but very boring, noisy and unstable. Anyway, that's my two cents. Good luck with it. -------------------------------- Newsgroups: rec.models.rc Subject: Re: Flying saucer - the beast emerges ! Summary: Expires: References: <1765@cernvax.UUCP> Sender: Followup-To: Distribution: Organization: University of Waterloo Keywords: In article <1765@cernvax.UUCP> outram@cernvax.cern.ch (Nicholas Outram) writes: > The craft will be powered by FOUR rc variable speed engines to >provide lift and small amounts of side thrust for horizontal mov- >ment. Two more small electric motors provide spin stability and >rotation capability. I suspect your craft will be far too heavy. Might want to reconsider three lift motors for better lift vs. effective area. As you're using a processor, fast calculation of the centroid of the device will be no prob. > Horizontal stability controlled by Mark Tildens 'mercury gyro' >idea. ... >-> I still need help of how to sense the rotation of the craft <- >-> Something like an electronic compass ?????? <- Just now I've had a better idea which might kill two birds with one stone: rotation and stability. Place 4 double contact mercury switches on a shallow bowl, the hub connected to a small stepper motor. The outside edge of each switch raised to a yet-undetetermined- angle. Rotate at a fixed speed (defined by uP) until the all switches *just* register closed at the outside edge. Any tilt will register as a open in the direction of lift and any rotation will be detected as uniform open contacts compared to the ideal spin motor value (this value being predetermined by experiment). Connections to the switches made by pickups on the outside of the dish. Granted rotation detection can only be made in the counter-stepper-spin direction but if the craft is designed to spin against this direction anyway, then the problem is solved. Granted also the signals coming back might require their own processor for correct filtering and control, but it's a neat idea. The range of values of rotation speed and switch angle should make up for the inherant errors generated by the switches. Wonder if it's practicable? >-> Also how do I convert small capacitance values to a form <- >-> easily input to a computer ????? (0-1nF)^ <- Make it part of a temperature-insensitive transistor based oscillator with a square wave output. Feed this signal into the strobe of a 8-bit latch (positive edge) and a delay line which will reset the 8 bit binary counter which is feeding the latch (at positive edge + a tad). The clock source for the counter must be a Xtal source timed to be approx 128 times faster than your transistor oscillator. Thus, if your t-osc frequency goes up or down, you have a 128 bit window to play in. A simple extension to this circuit will allow you to multiplex multiple capacitive inputs to the same output latch. As your lower 2 or 3 bits of your data will be random error, replace these with a binary value corrosponding to which capacitive tilt meter you're referencing. These will, of course, be driven by their own counter, the clock input from the t-osc. A five chip solution. Is all. ------------------------------------ Re: Flying saucers: >In one of yor artciles you made said that you have been able to construct >such a beast. Could you be a little more detail about these magnetic >clutches? You see, I'd like to make a platform with three rotors, and >I need some way to vary the thrust that each puts out for steering control. >My instaneous idea was to use three motors, and vary the speeds, but that >would be far too heavy. Second idea, use one central motor, driving var. >pitch rotors (mechanical nightmare and heavy). It would seem that >using one motor with three "clucthes" would be ideal, so any ideas in this >area would be greatly appreciated. Thanks, Jack Brooks >6843BrooksJ@vms.csd.mu.edu Yes, that's pretty close, I think. Magnetic clutches are available from a variety of industrial suppliers but the best thing is to find one at a surplus shop. They are small, rotary bearing shaped devices with two wires coming out of them. A good substitute is to find a source of pancake walkman motors and direct drive the shaft. If you short the leads from these motors, the back-generator effect causes a drag proportional to the efficiency of the motor. Pulsing this effect with a single transistor does a good job and is very energy efficient. Fast too. Only problem is the additional weight of the motors. My original flying creature was a flat thing made out of styrafoam. When all was said and done it was not really very exciting and took up far too much power. If I were to do another one, it would look more like this (side view): Magclutch and paddle - #------= Fan vanes and mount - = ----+---- =====|===== ----+---- = no-slip band drive - |----------|----------| drop frame and control- \_ | _/ \|/ Single hi-ef motor - [=] A single, low high-efficiency motor drives three lifting vanes by a no-slip band drive (nylon O-rings). The same shaft which drives the vanes also drives a free-rotating magclutch which is controlled by the onboard intelligence. I found that only a very small reduction in the available airflow to one lifter vane was sufficient to steer the device without damaging it's lifting ability. Saves on control vanes too. By mounting a small 'paddle' on the magclutch, you could limit airflow to any of the three lifters by a simple feedback control circuit. Also, if the paddle position can be controlled from side to side of a single vane tube, you can also control roll and direction. Unlike my original device, I now know that if the majority of the weight is 30 degrees below the lifting points, the device is self-stabilizing, so that helps. Neat thing about this design is that with the new 17% efficient solar-cells available, it could be entirely self-supporting. Could be. I'm sorry, are you building a flyer, hovercraft, model or full-size version? This idea is really only good for a model of some sort. Is all. Mark Tilden. -- Mark Tilden: _-_-_-__--__--_ /(glitch!) M.F.C.F Hardware Design Lab. -_-___ | \ /\/ U of Waterloo. Ont. Can, N2L-3G1 |__-_-_-| \/ (519) - 885 - 1211 ext.2454, "MY OPINIONS, YOU HEAR!? MINE! MINE! MINE! MINE! MINE! AH HAHAHAHAHAHAHAHAHA!!"