FlamingRCAirplanes
Elite member
Bro
How would you design a cyclocopter?
- Thread starter NickRehm
- Start date
2jujube7
Well-known member
As y'all have probably guessed, issues have cropped up during construction. I spent pretty much all of the weekend trying to figure out why I was getting 30% less thrust on the new rotors that I had built, but I have not confidently identified the issue yet. I made a few changes and it's being/printed constructed now, so we'll see where that leads me.
2jujube7
Well-known member
I'm pleased to announce that I've completed the last rotor. The max thrust produced by each rotor is 250g, 250g, 260g, and 320g. I think that the reduced thrust is due to a slight misalignment the airfoils on their bearings, but to fix it I'd have to remake 12 airfoils and not mess them up, so I'm just going to proceed. The cyclocopter should only need 150-175g thrust from each rotor to fly so it should be more than fine. I am running into issues figuring out how to hook up the flight control software so that it uses both the servos and motors, so I think that I'm just going to set it up as a quadcopter in the flight control software (librepilot via an old quadcopter CC3d) and directly mix in the servos via the transmitter mixes for yaw control only. I was planning to use dRehmFlight, but I already have the CC3d flight controller and I don't think that you can install dRehmFlight on it?
So really all I have to do in terms of the hardware is glue together the rotors and add some landing gear. Then of course make a gimbal setup thingy so that I can figure out the PID values.
CampRobber
Active member
That's looking pretty awesome.
One thing that kinda jumps out is that with no fuselage and just those two tubes, I don't think you have any torsional strength between the front and back. I'm not sure if that might cause flight dynamics problems.
It kinda seems like you're affecting a child/student attitude towards engineering.
The way a corporation looks at this situation, they just paid $$$$ to get that prototype built. Buying a brand new F405 is really cheap compared to totally rebuilding the prototype after RUD induced by a ten year old F103 running the wrong code.
One thing that kinda jumps out is that with no fuselage and just those two tubes, I don't think you have any torsional strength between the front and back. I'm not sure if that might cause flight dynamics problems.
It kinda seems like you're affecting a child/student attitude towards engineering.
The way a corporation looks at this situation, they just paid $$$$ to get that prototype built. Buying a brand new F405 is really cheap compared to totally rebuilding the prototype after RUD induced by a ten year old F103 running the wrong code.
2jujube7
Well-known member
This is a good point. It just turns out that I'm a high school student who is financing this by mowing lawns, so I don't really see the need to get a new flight controller if the one I already have works fairly well. Unfortunately I don't have a corporation or research school that is paying for this, so let me know if you hear that one of them wants a cyclocopter.
Yeah I agree that this probably isn't the stiffest setup. Just keep in mind that the tubes are pultruded carbon fiber, which are quite strong for the weight. Just testing by hand, the tube can take ~1000g in the middle (with both ends fastened) until it has a noticeable bend. At this scale where each rotor can output a max of 300ish grams (hover at 150-200g), I don't really consider the strength an issue. Sure, the battery and electronics in the middle might bend the shaft so that the front and back rotors are angled a few degrees, but in the grand scheme of things, fixing that would add more weight than the <5g thrust it would save.
CampRobber
Active member
What is the total weight of all those metal screws holding the rotor blades? Would nylon be strong enough?
2jujube7
Well-known member
They're M2x8 screws; each weighs around 0.2g. That adds up to 2.4g per rotor, which I'd say is pretty insignificant. I'm not sure how strong nylon screws are, but each blade is pulling around 270G of centripetal acceleration; with the blades weighing ~4g each, that's around 500g of shear stress per screw.
CampRobber
Active member
Ah that's not so bad. They seemed bigger in the photos.
2jujube7
Well-known member
Interesting phenomenon. A cyclocopter shoots out a plume of air that's canted from the angle normal to the ground. You can see that I need to add a substantial 20-30deg offset on the rotation of the rotor in order to get max thrust straight down. This was causing me problems yesterday when I was attempting free flight. I got the flight controller pretty much figured out and I have measured each rotor (while mounted on the cyclocopter) to 270-280g thrust each, but I'm still not getting enough thrust to takeoff. (Cyclocopter weight of 700g) I'm not sure what's causing the trouble, but something is, so I'm going to have to figure something out to do.
Below is a screenshot of paper that shows what I'm talking about. This data (computed not experimental) was taken with a cyclorotor diameter of 1.2m though, rather than my 0.15m, so I'm not sure how well the aerodynamics scale down.
I did build some landing gear with 5mm cf rods (the only size I have) Below is a screenshot from an attempted flight. The landing gear rotated a little, it's usually not in that orientation
Below is a screenshot of paper that shows what I'm talking about. This data (computed not experimental) was taken with a cyclorotor diameter of 1.2m though, rather than my 0.15m, so I'm not sure how well the aerodynamics scale down.
I did build some landing gear with 5mm cf rods (the only size I have) Below is a screenshot from an attempted flight. The landing gear rotated a little, it's usually not in that orientation
2jujube7
Well-known member
Exciting news: I broke a 4:1 thrust/weight ratio today.
Given Nick's success with fairly high thrust levels using the 2204 motor, I thought that I'd try it just to see what the thrust would be like. The thought is that it would have more torque than the 1808 motor that I'm currently using, but honestly I'm not sure how they would compare. I also chose a Goolsky 2204 1400kv motor (in comparison to the 1250kv I'm currently using) with the thought that it would also have slightly higher rpm and therefore thrust. To be honest, I'm not sure how a 2204 1400kv compares to a 1808 1250kv, so I just thought that it would be worth a try to see how well it would work.
I reached a max of 408g thrust, with the rotor weighing in at just at 100g. I need to do some soldering before I can test for the efficiency, but based on warmth of motor it seems pretty comparable.
EDIT: Just realized that this thrust measurement is based off of the thrust stand. As mentioned in the previous post, it is somewhat unreliable. The intrinsic value should be around 340g. However, that's still significantly higher than the previous intrinsic value of 280g thrust.
EDIT 2: Just tested efficiency and recorded values. The values are pretty much exactly the same as running it with the old motor. (+/- 3%) Yet as stated earlier, the max thrust peaks out 20% higher than the previous max thrust (330g vs 400g). I think I'm going to stick with this motor.
Given Nick's success with fairly high thrust levels using the 2204 motor, I thought that I'd try it just to see what the thrust would be like. The thought is that it would have more torque than the 1808 motor that I'm currently using, but honestly I'm not sure how they would compare. I also chose a Goolsky 2204 1400kv motor (in comparison to the 1250kv I'm currently using) with the thought that it would also have slightly higher rpm and therefore thrust. To be honest, I'm not sure how a 2204 1400kv compares to a 1808 1250kv, so I just thought that it would be worth a try to see how well it would work.
I reached a max of 408g thrust, with the rotor weighing in at just at 100g. I need to do some soldering before I can test for the efficiency, but based on warmth of motor it seems pretty comparable.
EDIT: Just realized that this thrust measurement is based off of the thrust stand. As mentioned in the previous post, it is somewhat unreliable. The intrinsic value should be around 340g. However, that's still significantly higher than the previous intrinsic value of 280g thrust.
EDIT 2: Just tested efficiency and recorded values. The values are pretty much exactly the same as running it with the old motor. (+/- 3%) Yet as stated earlier, the max thrust peaks out 20% higher than the previous max thrust (330g vs 400g). I think I'm going to stick with this motor.
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FlamingRCAirplanes
Elite member
I really like this thread. Just love readin about all this cool stuff. Great job man! Keep it up!Exciting news: I broke a 4:1 thrust/weight ratio today.
Given Nick's success with fairly high thrust levels using the 2204 motor, I thought that I'd try it just to see what the thrust would be like. The thought is that it would have more torque than the 1808 motor that I'm currently using, but honestly I'm not sure how they would compare. I also chose a Goolsky 2204 1400kv motor (in comparison to the 1250kv I'm currently using) with the thought that it would also have slightly higher rpm and therefore thrust. To be honest, I'm not sure how a 2204 1400kv compares to a 1808 1250kv, so I just thought that it would be worth a try to see how well it would work.
I reached a max of 408g thrust, with the rotor weighing in at just at 100g. I need to do some soldering before I can test for the efficiency, but based on warmth of motor it seems pretty comparable.
EDIT: Just realized that this thrust measurement is based off of the thrust stand. As mentioned in the previous post, it is somewhat unreliable. The intrinsic value should be around 340g. However, that's still significantly higher than the previous intrinsic value of 280g thrust.
EDIT 2: Just tested efficiency and recorded values. The values are pretty much exactly the same as running it with the old motor. (+/- 3%) Yet as stated earlier, the max thrust peaks out 20% higher than the previous max thrust (330g vs 400g). I think I'm going to stick with this motor.
2jujube7
Well-known member
I'm curious now. @Rcjetflyer2 I know that you've moved on to other projects, but our rotors are about the same size so it might be worth it for you to get a lower kv motor and a higher gearing ratio. With your over 2000kv motor (something like 2300 if I remember correctly) and 4:1 gearing ratio, you can calculate that the rotor was trying to spin up to around 7000 rpm. The actual should be closer to 3000 or 3500, but if I had to guess, it would be much lower than that as I bet that the motor is nearly stalled out. It might be interesting to check the actual rpm. I've been using a phone strobe light that measures up to 3000rpm and it has worked nicely.
^Or just found that you had a 1900kv and 3:1 gearing in a post a while back, but its the same 3000rpm. That's really interesting considering that I'm using 1400kv now with a 6:1 ratio.
I know that my no-load motor should be around 3000 rpm and with load it's just over 2000rpm. Our rotors have pretty much the same overall size, so it might be interesting to see what the efficiencies would be like if you increased the gearing/decreased motor kv. When I switched from a 4:1 to a 6:1, it made my motor significantly less hot and I'm fairly sure (it was a while ago lol) that it increased thrust.
^Or just found that you had a 1900kv and 3:1 gearing in a post a while back, but its the same 3000rpm. That's really interesting considering that I'm using 1400kv now with a 6:1 ratio.
I know that my no-load motor should be around 3000 rpm and with load it's just over 2000rpm. Our rotors have pretty much the same overall size, so it might be interesting to see what the efficiencies would be like if you increased the gearing/decreased motor kv. When I switched from a 4:1 to a 6:1, it made my motor significantly less hot and I'm fairly sure (it was a while ago lol) that it increased thrust.
CampRobber
Active member
I've been bitten by the cyclobug too.
Rotors are 3" radius by 5" long and 1.5" chord. Three for now. I've built one and it weighs 30g. I'm planning to use a 3S pack, 1606 2700kv (31800 rpm), 10:1 belt reduction (a #64 rubber band, lol) for 3180 RPM = 57 mph theoretical no-load tip speed. It's made out of PLA and BBQ skewer.
I'm curious about (1) aspect ratio (2) number of blades (3) whether to put the control rod forward or aft of the blade pivot.
2jujube7
Well-known member
Awesome, looks great!
(1) Doesn't really significantly impact the efficiency in terms of aerodynamics. Figure out the max blade width that you can do without a lot of bending, as bending is shown to reduce thrust.
(2) It depends. Less blades means higher efficiency, but more blades means lower vibrations. Based off of what I've seen, the middle ground is typically 3-6 with 4 being the most prominent at MAV scale and 6 being used on the larger (eg. 50lb+) ones.
(3) Not completely sure about this and I'm currently trying to write a paper about it, but I think forward. If it's backward it makes the blade pitch more on the top than the bottom, and if it's forward then it makes the blade pitch more on the bottom. Due to virtual camber on the bottom, it should be more effective to have a higher pitch there. This is not completely understood, and it might make sense to make one rotor then test both configurations. <= Actually this might be good to do before you build all four rotors. Lol it took me a year to get it to have a T/W ratio where it can lift a cyclocopter off, so you probably should iron out all the bugs before building all of them.
The above is just my understanding of what I've read and experienced. It may or may not be right (especially #3)
CampRobber
Active member
Interesting. I'd just been thinking in terms of mechanical design. Yeah, definitely doing thrust stand testing before building more.
CampRobber
Active member
NickRehm
Member
I think my design suffered from a combination of friction at the control linkages (too lazy to add one more set of bearings) and way too low gear reduction. You want to live on the left hand side to center of this plot for higher efficiency and higher power output:
If your motor is getting even remotely hot, you're on the right hand side which is the no-go zone for efficiency. I think I was like 95% to the right with the way my motor was loaded lol
If I were to redesign (when.... not if), I would probably ditch the belt drive and go to gear/pinion for as high gear ratio I can get.....then size the blades up until power loading stops going up. Belt drive was cool to showcase the low noise, but lead to too many problems getting a pulley large enough for the weight and it slipping....I would much rather it sound like a cheap rc car gearbox if it meant more thrust and efficiency haha
Happy to see you jump on board CampRobber!! Awesome progress
If your motor is getting even remotely hot, you're on the right hand side which is the no-go zone for efficiency. I think I was like 95% to the right with the way my motor was loaded lol
If I were to redesign (when.... not if), I would probably ditch the belt drive and go to gear/pinion for as high gear ratio I can get.....then size the blades up until power loading stops going up. Belt drive was cool to showcase the low noise, but lead to too many problems getting a pulley large enough for the weight and it slipping....I would much rather it sound like a cheap rc car gearbox if it meant more thrust and efficiency haha
Happy to see you jump on board CampRobber!! Awesome progress
CampRobber
Active member
In terms of *motor* efficiency yes, but in the bigger picture, if the motor is cold, you could have used a smaller lighter motor.
