Michael C
Graduate Poster
"95-98% efficiency": very nice.
Down wind faster than the wind
- Thread starter my_wan
- Start date
"95-98% efficiency": very nice.
I'll agree to that. I was going to suggest the same thing, again in the spirit of competition!
John Freestone
Graduate Poster
John Freestone
Graduate Poster
I see, fair dos.
It's difficult to comment much without really understanding how you envision it, and I'm sure you know what you're doing and understand all the loads and stuff a lot better than me. I'm just kicking the idea round. I would have thought that a broken thread could reach an indefinite distance, as it would continue to unwind from the emptying spool (on the prop shaft?) while the prop is still spinning. I guess a spring-loaded device could activate a brake on the prop, which normal tension on the thread would keep away or something. I was thinking more of loops unwinding rather than breaks, for instance if something slows the cart's travel momentarily, before the prop slows as well, or if there's an odd gust of wind, but maybe I'm imagining very unlikely scenarios or the wrong forces. It's your neck.
Sure, but I was thinking of gears you can change during running. I guess that's not an issue given your interest.
Well, I think there are some bike shaft-drive designs. I don't know the efficiency figures. But I was thinking of the bevel first and then some sort of inline hub gear system, or even a shortish chain drive and derailleur. Obviously not going to match up for your purposes.
Dan did.
...and you've almost changed your mind.Now I've given you several.
Dan O.
Banned
- Joined
- Feb 14, 2007
- Messages
- 13,594
I received my cart yesterday and assembled it last night - good way to bring in the New Year!
I ordered a variety of parts with my cart to do some extended testing - extra wheels and props to check various advance ratios and such.
In the following list, the break-even speed is followed by the prop diameter and pitch. Here are the initial results:
6.2 mph with 15x7.5
6.8 mph with 12x8
7.2 mph with 12x6
8.8 mph with 12x3.8
9.3 mph with 10x8 with 4 blades
My cart is still breaking in as it runs, so hopefully with a little tuning and some more running time the cart will get more efficient.
By the way, don't tell humber but I added 4 AA batteries to the front of the cart for traction instead of the single 9 volt one. I know that is only 6 volts but I figure that means that my actual break-even speed will be 2/3rds of what the list shows with 9 volts.
I ordered a variety of parts with my cart to do some extended testing - extra wheels and props to check various advance ratios and such.
In the following list, the break-even speed is followed by the prop diameter and pitch. Here are the initial results:
6.2 mph with 15x7.5
6.8 mph with 12x8
7.2 mph with 12x6
8.8 mph with 12x3.8
9.3 mph with 10x8 with 4 blades
My cart is still breaking in as it runs, so hopefully with a little tuning and some more running time the cart will get more efficient.
By the way, don't tell humber but I added 4 AA batteries to the front of the cart for traction instead of the single 9 volt one. I know that is only 6 volts but I figure that means that my actual break-even speed will be 2/3rds of what the list shows with 9 volts.
John Freestone
Graduate Poster
Nice one. Happy New Year. You're one of a small but growing elite, apparently.
Break-even speed - that's where you achieve over-unity and this thing starts making energy from thin air, isn't it? I can't remember if it's fusion or fishin', but you know...
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Yes, John, that's right! Once the cart was over-unity, I checked my power meter reading for the house, unplugged the treadmill to let it gain some more speed and then plugged it back in. I now have the treadmill motor generating power, as the power meter reading is now at a lower level. As soon as I can get the kids off the video games I can run that power back into the grid and make some money off this thing.
Hey, maybe I should have let it build more speed before plugging it back in!
ThinAirDesigns
Graduate Poster
- Joined
- Nov 10, 2008
- Messages
- 1,058
And all that from the kinetic energy stored as you first place the cart on the belt. Amazing.
JB
Christian Klippel
Master Poster
Hey mender,
don't forget to lubricate the belt's surface, to increase the performance! You know, we already learned that slipping wheels work far better. It will make your meter go backwards even...
Greetings,
Chris
ThinAirDesigns
Graduate Poster
- Joined
- Nov 10, 2008
- Messages
- 1,058
Oh drat -- Christian is right Mender ... I totally spaced.
Yes, it's NOT just the kinetic energy as I previously stated -- it's also the slipping.
Kinetic and slipping. I'm straight now.
JB
Yes, it's NOT just the kinetic energy as I previously stated -- it's also the slipping.
Kinetic and slipping. I'm straight now.
JB
Hold on there. What about hopping? Are you guys forgetting about hopping? That's the real secret to this thing.
It's just a hop, slip and a humb away from hovering over its own wormhole before departing from our reference bound universe! As soon as it transcends the laws of KE translational exchange, it will instantly depart from the energy well in which it is trapped at light speed and vanish upstream in time.
Down to 2.5" wheels with rubber tires, left off the batteries ("dead" weight anyway) and now it achieves windspeed at 5.5 mph.
Humber, feel free to substitute one of the other terms that you use (groundspeed, shorespeed, treadmill speed, observerspeed, etc.) to describe this condition.
Down to 2.5" wheels with rubber tires, left off the batteries ("dead" weight anyway) and now it achieves windspeed at 5.5 mph.
Humber, feel free to substitute one of the other terms that you use (groundspeed, shorespeed, treadmill speed, observerspeed, etc.) to describe this condition.
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ThinAirDesigns
Graduate Poster
- Joined
- Nov 10, 2008
- Messages
- 1,058
I'm sorry guys -- I feel like a real goldfish here.
Kinetic, slipping AND hopping.
That's it then.
JB
Kinetic, slipping AND hopping.
That's it then.
JB
New test: treadmill inclined at 2.7 degrees, check break-even speed with different props.
10.2 mph with 12x8
8.1 mph with 15x7.5
Analysis: larger prop influences a larger mass of air, reducing the speed change needed to develop the same force. Same amount of cart drag is present (tested against a scale at a variety of speeds, is pretty consistent from rest through the speed range at about 14 grams). Area of bigger prop is 58.3% more than smaller prop. Momentum imparted to air because of the higher speed with smaller prop per square inch is 58.6%. F=MA still applies!
Variables not accounted for, difference in prop pitch and efficiency - but the numbers were surprisingly close.
Net force is the same for both props, as indicated by the cart climbing the incline ever so slightly. Distinctly different speeds needed, no wheels sliding.
I'm running my cart with the prop at the front (prop oriented correctly of course) because I have a load cell at the back of the treadmill that the cart gearbox rests against for force measurements. The small wheel on my cart momentarily goes into a wobble every so often and noticeably slows the cart. Other than that, the cart runs quite consistently and readings from the load cell are also consistent. I'll refine the test a little more.
10.2 mph with 12x8
8.1 mph with 15x7.5
Analysis: larger prop influences a larger mass of air, reducing the speed change needed to develop the same force. Same amount of cart drag is present (tested against a scale at a variety of speeds, is pretty consistent from rest through the speed range at about 14 grams). Area of bigger prop is 58.3% more than smaller prop. Momentum imparted to air because of the higher speed with smaller prop per square inch is 58.6%. F=MA still applies!
Variables not accounted for, difference in prop pitch and efficiency - but the numbers were surprisingly close.
Net force is the same for both props, as indicated by the cart climbing the incline ever so slightly. Distinctly different speeds needed, no wheels sliding.
I'm running my cart with the prop at the front (prop oriented correctly of course) because I have a load cell at the back of the treadmill that the cart gearbox rests against for force measurements. The small wheel on my cart momentarily goes into a wobble every so often and noticeably slows the cart. Other than that, the cart runs quite consistently and readings from the load cell are also consistent. I'll refine the test a little more.
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Most human-powered airplanes in the past 35(?) years have used Berg chain, as DanO noted. This is a pair of steel cables with plastic buttons molded between them so that it will work with standard bicycle sprockets, but can also do things like twist 90 degrees between the sprockets, such as you'd want to do between an axle (or pedal crank) and a prop shaft. It's a pretty simple solution, but the big drawback is that if you're sloppy about the design, the chain will jump off of the sprockets from time to time. Not a big deal if you're just doing short hops around an airport, but a very big deal if you're over water, miles from land. I imagine this was a matter of great concern for Gossamer Albatross. You can't really use a derailleur with Berg chain, but you could change sprockets when you aren't moving.
Some HPAs have used shaft-drive with bevel gears. No practical way to change gear ratios at all (unless you want to get much more complicated and heavy), so Daedalus used a variable-pitch prop to accomplish that purpose. It's not such a big deal to pick the gear ratio that you want in the first place. The Daedalus gear boxes were custom-made, using hardened steel helical bevel gears and aluminum shafts, and they were pretty delicate. Loading them up in the wrong direction (such as by holding the pedals stationary while the wind tried to turn the prop) was an invitation for a trip back to the gearbox guy for repairs. (That was for the prototype, I'm not sure we ever had to have the gearboxes on the final planes overhauled, but we were pretty careful with them by then as well.) Aside from that, reliability was excellent and efficiency was obviously quite good. Since weight is less of a concern for a prop cart, it may well be that motorcycle parts would work in that application, and they should be damn sturdy. A motorcycle transmission may even work if variable gearing is desired.
Spool transmissions have been used to some extent in human-powered vehicles, and they do have some promise, but they seem to me like more hassles than they're worth. Yes, there was that helicopter in Seattle that used them, but a lot of the concern there was that because they needed to transmit the drive over such a long distance (they used small props at the rotor tips to turn the rotor), any other solution would have been prohibitively heavy. And although they did get some sort of brief hover, it's not really an example of a wildly successful design. I also worked (obliquely) on another HPV back in 1981 that was supposed to used a spool transmission, and I don't think that crew ever really got it to work. You have to be careful when winding up the spool, because you need to keep a fair amount of tension in order to get it to work right, and in operation, there's a possibility of the last turn of the string burying itself into the pile and then jamming or snapping. They aren't problems that can't be overcome, but they're more of a headache than it might seem at first glance.
If I were making rules, I wouldn't require that the machine be able to run indefinitely without some kind of "rewinding", but I would require that the entire apparatus go along for the ride, thereby precluding any stakes in the ground that don't get pulled up during operation.
Some HPAs have used shaft-drive with bevel gears. No practical way to change gear ratios at all (unless you want to get much more complicated and heavy), so Daedalus used a variable-pitch prop to accomplish that purpose. It's not such a big deal to pick the gear ratio that you want in the first place. The Daedalus gear boxes were custom-made, using hardened steel helical bevel gears and aluminum shafts, and they were pretty delicate. Loading them up in the wrong direction (such as by holding the pedals stationary while the wind tried to turn the prop) was an invitation for a trip back to the gearbox guy for repairs. (That was for the prototype, I'm not sure we ever had to have the gearboxes on the final planes overhauled, but we were pretty careful with them by then as well.) Aside from that, reliability was excellent and efficiency was obviously quite good. Since weight is less of a concern for a prop cart, it may well be that motorcycle parts would work in that application, and they should be damn sturdy. A motorcycle transmission may even work if variable gearing is desired.
Spool transmissions have been used to some extent in human-powered vehicles, and they do have some promise, but they seem to me like more hassles than they're worth. Yes, there was that helicopter in Seattle that used them, but a lot of the concern there was that because they needed to transmit the drive over such a long distance (they used small props at the rotor tips to turn the rotor), any other solution would have been prohibitively heavy. And although they did get some sort of brief hover, it's not really an example of a wildly successful design. I also worked (obliquely) on another HPV back in 1981 that was supposed to used a spool transmission, and I don't think that crew ever really got it to work. You have to be careful when winding up the spool, because you need to keep a fair amount of tension in order to get it to work right, and in operation, there's a possibility of the last turn of the string burying itself into the pile and then jamming or snapping. They aren't problems that can't be overcome, but they're more of a headache than it might seem at first glance.
If I were making rules, I wouldn't require that the machine be able to run indefinitely without some kind of "rewinding", but I would require that the entire apparatus go along for the ride, thereby precluding any stakes in the ground that don't get pulled up during operation.
DDWFTTWRA rules:
1. Minimum weight To Be Determined.
2. Maximum "sail" area TBD.
3. Average height of "sail" from ground TBD.
4. Total C of G of vehicle to be used in calculating DDW velocity and finishing position.
5. Variable speed or pitch mechanisms allowed.
6. Ground interface must travel with vehicle (no stakes, etc.).
7. Adequate brakes required - TBD.
8. Minimum distance capability of drive system (finite systems allowed).
9. No energy storage before start allowed.
10. Energy storage after start is allowed.
11. Contest will begin with an unassisted start in a stationary position.
12. In case of #10, start is considered to have occurred when the start signal is given.
13. Maximum "reset time" for mechanism after return to start line of 30 minutes if multiple runs are required.
14. In the case of a course that isn't aligned perfectly with the prevailing wind, all vehicles must complete the course within a designated time or at the same time to equalize any adverse effects from that misalignment.
15. Maximum deviation from intended line of travel will not exceed 5 degrees at any time and will be within twenty feet laterally of expected line of travel at the finish line.
16. All efforts must be made to avoid contact between vehicles and/or drive systems when multiple vehicles are on course at the same time. Intentional interference causing a loss in performance or position of another vehicle shall result in forfeiture of that contest segment.
17. Throwing of small objects and/or fruit during the event is not considered interference of the vehicle's performance as long as it impacts the driver or crew members only. However, rule #4 applies to the objects thrown.
Rules are subject to revision without notice.
1. Minimum weight To Be Determined.
2. Maximum "sail" area TBD.
3. Average height of "sail" from ground TBD.
4. Total C of G of vehicle to be used in calculating DDW velocity and finishing position.
5. Variable speed or pitch mechanisms allowed.
6. Ground interface must travel with vehicle (no stakes, etc.).
7. Adequate brakes required - TBD.
8. Minimum distance capability of drive system (finite systems allowed).
9. No energy storage before start allowed.
10. Energy storage after start is allowed.
11. Contest will begin with an unassisted start in a stationary position.
12. In case of #10, start is considered to have occurred when the start signal is given.
13. Maximum "reset time" for mechanism after return to start line of 30 minutes if multiple runs are required.
14. In the case of a course that isn't aligned perfectly with the prevailing wind, all vehicles must complete the course within a designated time or at the same time to equalize any adverse effects from that misalignment.
15. Maximum deviation from intended line of travel will not exceed 5 degrees at any time and will be within twenty feet laterally of expected line of travel at the finish line.
16. All efforts must be made to avoid contact between vehicles and/or drive systems when multiple vehicles are on course at the same time. Intentional interference causing a loss in performance or position of another vehicle shall result in forfeiture of that contest segment.
17. Throwing of small objects and/or fruit during the event is not considered interference of the vehicle's performance as long as it impacts the driver or crew members only. However, rule #4 applies to the objects thrown.
Rules are subject to revision without notice.
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