Drone legs

[platty]

I’m just curious about the DJI legs. I have a mini and an Air2s and they just have stubs at the rear instead of legs like the front. Why is that ?

 

[Cafguy]

The front legs are supposed to protect the gimble on the ground. BUT mine are always to short from the factory. I don't get fancy I just use a straw and extend them a little I suspect the back legs are designed short to give the props the best Bite when taking off.

 

[Yorkshire_Pud]

That I know of none of the 'Mavic style' drones have undercarriage on the rear arms.
I can think of several possible reasons.
1) Possibly they would create difficulties when folding the arms into the storage position.
2) with the Minis in particular it might be a weight consideration.
3) I'm probably over thinking this but consideration of the resulting "second moment of area", which relates to how the distribution of mass influences the speed with which it can accelerate its yaw and roll responses. That said, I have some add-on undercarriage for the mini that puts 'a lot' of mass at the outer ends of the arms and I didn't notice any difference in the yaw and roll accelerations so it probably isn't a consideration in practical terms.
4) 'three' points of contact is, in some ways, more stable and useful than four points of contact. Think camera and theodolite tripods.

 

[Cafguy]

4) 'three' points of contact is, in some ways, more stable and useful than four points of contact. Think camera and theodolite tripods.

I was always under the impression that the back legs were short to give the props the proper angle for taking off easily BUT I think you have something here The legs sort of make a tripod this way. makes for a much more stable landing

 

[Dbez1]

Looking at my Air2S here, I have leg extensions all around and I notice they keep the same angle as without. So, I agree that the angle must have something to do with takeoff efficiency. I think the really high end drones are not at an angle though.

 

[Yorkshire_Pud]

I do not think the chosen heights of the undercarriage are to do with the "efficiency" of each prop.
Rather I think they are chosen so that, when the drone is on the ground, the sum/total of the torques created by each motor is zero as is the sum/total of the horizontal thrusts being generated by each prop.
Note, if you look closely I suspect that you will find that none of the props are rotating about an axis that is perpedicular to the surface on which the drone is sitting.

If you put a drone on a tilted flat surface, start its motors with the CSC then SLOWLY throttle up I think you will find that it first lifts the 'downslope' motors/undercarriage, then, once the drone is nominally horizontal, it will then take off. I have done this several times.
BE CAREFUL if the initial tilt is significant just incase the upslope props hit the 'further upslope' ground.
In reverse, if you are careful controlling the descent speed, I think you will find that the drone will touch down the upslope undercarriage first then lower the downslope undercarriage. I might have done this.

PS if the slope is too steep the drone will not start its motors.

 

[Cafguy]

Plus- I suppose they could use any size legs they want and just mount the motors with the correct Thrust line. So theres that

 

[Yorkshire_Pud]

Plus- I suppose they could use any size legs they want and just mount the motors with the correct Thrust line. So theres that

True, a chicken and egg thing lol. I think there is a lot more to the design of these drones than meets the eye at first glance.

 

[Dbez1]

I do not think the chosen heights of the undercarriage are to do with the "efficiency" of each prop.
Rather I think they are chosen so that, when the drone is on the ground, the sum/total of the torques created by each motor is zero as is the sum/total of the horizontal thrusts being generated by each prop.
Note, if you look closely I suspect that you will find that none of the props are rotating about an axis that is perpedicular to the surface on which the drone is sitting.

If you put a drone on a tilted flat surface, start its motors with the CSC then SLOWLY throttle up I think you will find that it first lifts the 'downslope' motors/undercarriage, then, once the drone is nominally horizontal, it will then take off. I have done this several times.
BE CAREFUL if the initial tilt is significant just incase the upslope props hit the 'further upslope' ground.
In reverse, if you are careful controlling the descent speed, I think you will find that the drone will touch down the upslope undercarriage first then lower the downslope undercarriage. I might have done this.

PS if the slope is too steep the drone will not start its motors.

Yorkshire, I haven’t watched that closely but I will next time out. Thanks.

 

[Yorkshire_Pud]

Yorkshire, I haven’t watched that closely but I will next time out. Thanks.

It was a bit surprising the first time I saw it lol, it might have even been a hand launch, eeek.
I cup the drone with my fingers so that it doesn't slip, hence I might not have been as careful about my hand being horizontal as I should have been lol.

 

[Dbez1]

… I might not have been as careful about my hand being horizontal as I should have been lol.

At least it was a takeoff. After a couple hundred hand catches, I also was not as careful as I should have been and it took me two months to fully recover. I can laugh about it now.

 

[MA2 317]

and they just have stubs at the rear instead of legs like the front. Why is that ?

In addition to the stuff above, the antenne(s) are in the leg(s) so they get a clear signal from the controller.


.

 

[platty]

At least it was a takeoff. After a couple hundred hand catches, I also was not as careful as I should have been and it took me two months to fully recover. I can laugh about it now.

I guess it could’ve been worse if the blades were metal !

 

[platty]

I do not think the chosen heights of the undercarriage are to do with the "efficiency" of each prop.
Rather I think they are chosen so that, when the drone is on the ground, the sum/total of the torques created by each motor is zero as is the sum/total of the horizontal thrusts being generated by each prop.
Note, if you look closely I suspect that you will find that none of the props are rotating about an axis that is perpedicular to the surface on which the drone is sitting.

If you put a drone on a tilted flat surface, start its motors with the CSC then SLOWLY throttle up I think you will find that it first lifts the 'downslope' motors/undercarriage, then, once the drone is nominally horizontal, it will then take off. I have done this several times.
BE CAREFUL if the initial tilt is significant just incase the upslope props hit the 'further upslope' ground.
In reverse, if you are careful controlling the descent speed, I think you will find that the drone will touch down the upslope undercarriage first then lower the downslope undercarriage. I might have done this.

PS if the slope is too steep the drone will not start its motors.

Wow, it gets pretty technical. On my mini I had clip-on skids to lift the mini up a little higher off the ground. I haven’t noticed if that tilt was maintained or if the mini became horizontal to the ground. Will check it out.