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Landing Gear Suspension?

DeeKaph

Junior Member
#1
Hi guys & gals .. I've poured over the interwebnets and can't seem to find anyone who's done what I have an idea for so I thought I'd throw it out there and see if anyone here has done it/heard of it and what you more experienced pilots think.

I'm got a Blade 350 QX2 (Ap Combo) I enjoy ripping around in but something that bothers me is the landing gear. I prefer flying in agility mode and so my landings aren't perfectly vertical - I enjoy coming in on a nice approach and touching down like a full scale heli would do (heels THEN toes). I'm actually pretty good at this, however, with the rigid landing gear on the QX2 (or any of the Blade quadcopters for that matter) the force travels through the frame and it tends to bounce no matter how gently you come down. There's also what I consider to be a design flaw in the skids - pointed toes.

blade_350_qx2_ap_combo_rtf_photo_drone_blh7900_5.jpg

Now, as far as I'm concerned there's a very good reason that full scale heli skids aren't flush at the front - when you skid it tends to catch on whatever you're landing on and tips the craft forward, causing the props to hit the ground and disaster ensues. In fact, the only crashes I've had with this bird so far have been from catching the toes on touchdown and rolling forward.

I also have a 1/10 truck and recently replaced the suspension system on it and it got me thinking - why is it that nobody I can find hasn't incorporated a pair of shocks from a RC truck into the landing system? Just enough to absorb some of the shock so that when you touch down you aren't sending the shock through the frame and causing it to bounce.

Just a thought, I'd appreciate any feedback you might have.
 
#3
The hobbyking x900 (which i have 2 of) have cushioned landing gears. Its a pretty slick design but wound'nt really work on your style of quad. I always run into the same issue as you when im flying my batbone, where the front legs dig in and it flips forward unless I land perfectly straight down. It has never happened with the x900 as they curve inwards and dont dig in because they collapse. When I first got the x900 I was afraid of snapping the tips of the landing gears(as it is only 1.5mm g10) off but it has never happened and it has seen some extreme crashes so the springs are definatly absoribing alot of that energy. A shock would be alot of added weight and I think a spring is the way to go.

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DeeKaph

Junior Member
#4
basically, weight. and because multi are so stable it's not really needed
Weight is always a consideration but would 59g really make that much of a difference in my flight time? The flight stability is dandy but it's the landing that's causing me to flip and no matter how light you touch down, with no shock absorption at all the force travels through the whole frame and causes a bounce and cause prop damage (and look ungraceful). I know a lot of pilots just let it "drop" when you get to the last six inches but landing but I often land on hard surfaces..
 

DeeKaph

Junior Member
#5
The hobbyking x900 (which i have 2 of) have cushioned landing gears. Its a pretty slick design but wound'nt really work on your style of quad. I always run into the same issue as you when im flying my batbone, where the front legs dig in and it flips forward unless I land perfectly straight down. It has never happened with the x900 as they curve inwards and dont dig in because they collapse. When I first got the x900 I was afraid of snapping the tips of the landing gears(as it is only 1.5mm g10) off but it has never happened and it has seen some extreme crashes so the springs are definatly absoribing alot of that energy. A shock would be alot of added weight and I think a spring is the way to go.

View attachment 39339
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The inward curve is what I'm really considering, whether it means modifying the existing gear or replacing the whole assembly with something of my own design with a better gear. Where are the springs located in that setup?
 

HawkMan

Senior Member
#7
a proper damper needs more than a spring though, just a spring can be as counter productive as just a shock absorber. in the case of that particular one,t he spring is probably weak enough it's not an issue anyway though.

but that's something you need to tune for the frame and landing gear, and sometimes even by the AUW. preferably, if weight wasn't an issue you would have one of those carbon T style landing gear, where the vertical tube was replaced with a fairly long oil shock absorber and spring, allowing the multirotor to sink down on the gear as it lands(kind of like when you put down a sizeable short circuit truck or dune buggy, it'll sink down as the shock absorbers take the weight). of course this ads a few technical challenges, the oil filled shock absorbers would add weight, if it matters would depend on the frame and size. And more importantly, on a truck, you have the whole suspension arms setup holding the thing together the shock absorber just does that. If it was the main Part of a T style landing gear, it would most likely bend on the first slightly hard landing since there would be no other support and it's not designed to take force like that, heck a hard crash and you bend them on cars to :)

alternative is to have a hinged T style gear that can "swing outwards, and have the damper in the joint. but for that to work, the skids need to be able to slide sideways when landing, or geometry just locks you up and you have no actual shock absorption again.

there's few easy solutions, especially for bigger heavier quads. Hence why most just suggest a gentle throttle curve on the hover and below down so you have really high resolution on the landing so you can land really gentle, and maybe in self level mode.

of course there's also the KISS solutions like Pool noodles around the skids, and some of the carbon and glass fiber gears come with special foam "tubes" to put on the front and end of the skids for damping. Simple, effective and light weight.
 

x0054

Senior Member
#8
Keep in mind that you also get the bounce because of the shock to the gyro while landing. If you disarm with a switch, try disarming just as you are about 1 to 0.5 inches away from the ground. You'll get a nice solid plunk on the ground, and you shouldn't get any bounce, other than from the springiness of the plastic gear.

Weight is the main reason you don's see oil shocks. You might actually see them on some of the really large custom made DSLR carriers, but on a small quad like yours, that 50+ grams is 5% of your total weight. That's 5% less flight time, 5% less agility. It does add up.

For a quick solution you can also ziptie or attache with epoxy some 10mm CF tubes. Cut them about 2 inches longer then the current skids. Should stop you from tipping.
 

nilsen

Senior Member
#9
I did a search on thingiverse and this guy has the idea of making the landing gear hinged at the top where it connects to the body then linking the bottom with a rubber band or similar so that the landing gear can open and absorb the shock.

http://www.thingiverse.com/thing:595399

I suppose it would be a balancing act to ensure that it isn't too stiff and also doesn't bounce.
 

HawkMan

Senior Member
#10
again that gear will have the problem I described above, if the skids can't slide sideways, the damping is locked and useless.

you'd need to double joint them
 

HawK86uk

Professional Amateur
#12
RAM, I might be missing something here, but those are just training rods to allow the copter pilot to learn his copters size etc. This shouldn't have any shock absorption element. If you look at the skids on the copter they're fixed solid material, so no shock absorption.. :confused:
 

HawkMan

Senior Member
#13
If the middle ball was "soft" and raised a bit, and mounted to the frame with a shock damper or spring or something, you could make that a limited shock damper landing gear, it woudl still have the issue that the balls have to slide outward as the get pushed up though.

You could also make the arms fairly soft and slightly "springy" and make sre the angle down do also give limited damping.
 

RAM

Posted a thousand or more times
#14
I used that image as an example. You can add flex by making the rods thinner so they bend more. The OP stated his real problem is tipping too much and driving the props into the dirt. His thought was to use a shock absorber. That might work but as others pointed out it will be more complex to build. A modified set of training rods would solve the tipping problem for him and could be angled downwards at the ends to give a little shock damping.
 

RAM

Posted a thousand or more times
#15
Something else to consider is using air instead of oil. This is something I am working on for my sons quad. Very simply, a tube in a tube. The smaller diameter tube gets capped on both ends. The larger dia tube is capped on one end only, and that end has a small hole in the cap. On a nice soft landing the air bleeds out of the tube and the other tube is pushed into it. A little harder landing and the air gets compressed a bit before it can leak out of the tube. Hopefully, less bouncy.

I can't find a good example but watch this video and imagine what would happen if you introduced a small air leak in the end of the tube.
 
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kah00na

Senior Member
#16
Put some rubber pieces on the underside of your landing gear - like the round things people put on the bottom of things to keep them from sliding around on a table. It won't be much but it may be enough to make your landings feel softer.
 

DeeKaph

Junior Member
#17
Wow some great input here, thanks guys!

I've been thinking about it and I think the added weight isn't worth the hassle of my original idea as it wouldn't just be the shocks themselves but the assembly to hold them, I recon on the light side I'd be adding at least 100g to the bird. And, using just springs will just make it bounce (as someone pointed out) so it would either have to be oil filled cylinders (like what I use on my terrestrial vehicle suspension) or some fancy integrated servo mechanism that loosened up the tension as the weight was set on the spring which would have to be controlled by flight data that I'm not convinced I can get high enough resolution out of at this point in technology. :p