based on my experiences taking off on water, i agree with the forum members who claimed forward motion was the culprit causing the forward pods to sink momentarily while the rear ones went airborne resulting on the flip.
P4 with Water Strider' flips into lake on takeoff
- Thread starter Don MacGregor
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No flight data log unfortunately, but I'm pretty inexperienced so it's entirely possible that although not intentional, some lateral stick was involved. Adding to the confusion however is that some flight tips actually suggest that to minimise surface tension, an 'angled liftoff' is actually their preference ?
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It's not uncommon for the quad to tilt even when you lift off without any forward motion. Sometimes one or more corners may release late from the water. When this happens, the angle of the quad will cause it to drift in the direction of the tilt. Here are some videos of quads with different flotation lifting off from water.
Typically water acted as glue on pods, from which craft might have also applied more power on one side to keep level when pilot sent command to raise up. Sudden asymmetric release must have caused flip. Find similar experience with heli having one landing skid stuck under mobile plattform. Its left skid suddenly released when pilot attempted with force to lift up to reposition aircraft.
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Let's blame everyone else and their sister....smh...
It is clear from the video that there was lateral movement. Try doing this on the ground: you will also flip.
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Well... if you ever done a slow Manuel take off from the ground you will notice the bird doesn't just go straight up. It drifts in a forward direction slowly with out even touching the right stick. I would seriously suggest you do more research yourself as you seem quite clueless in all of this
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John while some other design shape may or may not change the surface tension I don't think that matters. The pods are all the same. Therefore whatever surface tension there is will be equal on all four pods. As long as the overall drone then is relatively level it isn't going to make any difference on surface tension. I think the answer has already been pointed out. The drone was attempting to take off with some motion other than straight up.
I'd be interested to see what DroneRafts has to say on this matter.
Greetings everyone. I've only just now become aware of this thread through another customer, and I thought it was appropriate to comment. We want our customers to be happy and accordingly we offer a 30 day satisfaction guarantee. The OP has been in contact with us and we have issued him a refund. That said, we do believe the product performs as advertised and this behavior is not typical in any way. The drone was in forward motion during the takeoff and this forward motion led to a steep pitch angle which was rapidly corrected, which we believe was the true cause of the incident. (See below for a detailed account)
We hate to see anyone lose their drone in the water! So, we have studied the video very carefully. We also slowed it down to slow motion as well as frame-by-frame to see if we can understand what happened.
For anyone that isn't familiar with the WaterStrider, we have done extensive product testing, including hundreds of water takeoffs and landing in all kinds of scenarios on both calm, choppy, and ocean waters. This was all before we ever offered the product for sale. Since that time, we have sold many units that have had good reports related to water performance and we have continued flying and testing ourselves. There are thousands of successful Water Strider takeoffs and landings between us and our many customers all over the world.
The pods are carefully designed over many iterations to progressively shed surface tension during takeoff and there is actually very little surface tension. Both the P3 and P4 have plenty of excess power to handle this.
This report is the only instance of this behavior that we have ever had, nor have we seen this behavior ourselves. However, we still take any potential issues with the product very seriously.
Some Basic Observations About the Video to Understand the Sequence of Events
Here is what we believe happened based on careful study of the video.
Not powering down combined with a failure to neutralize the right stick before attempting the takeoff caused a high energy situation that resulted in over-correcting from the forward pitch attitude into a rapid aft acceleration too close to the water.
We don't believe that that the pods were 'sticking' to the water, although the forward pitch attitude (which pushed the pods down in the water) while moving forward likely resulted in the drone responding more aggressively to the sudden pitch control input change. With our production design, we've never seen the pods stick to the water much at all. In the video, the aft pods come off easily and the front pods clearly come off the of the water very quickly once the control input changes.
Recommendations
Cordally,
Adam
Head of Engineering and Technology
DroneRafts LLC
We hate to see anyone lose their drone in the water! So, we have studied the video very carefully. We also slowed it down to slow motion as well as frame-by-frame to see if we can understand what happened.
For anyone that isn't familiar with the WaterStrider, we have done extensive product testing, including hundreds of water takeoffs and landing in all kinds of scenarios on both calm, choppy, and ocean waters. This was all before we ever offered the product for sale. Since that time, we have sold many units that have had good reports related to water performance and we have continued flying and testing ourselves. There are thousands of successful Water Strider takeoffs and landings between us and our many customers all over the world.
The pods are carefully designed over many iterations to progressively shed surface tension during takeoff and there is actually very little surface tension. Both the P3 and P4 have plenty of excess power to handle this.
This report is the only instance of this behavior that we have ever had, nor have we seen this behavior ourselves. However, we still take any potential issues with the product very seriously.
Some Basic Observations About the Video to Understand the Sequence of Events
- The drone flies out facing away from the pilot
- The drone turns a bit facing the right side of the video
- The drone lands on the water facing the right side of the video
- The drone never de-energizes, meaning that the drone never really powers down below nearly a hover speed on the motors. It never really settles into the normal landing depth that a WaterStrider would sit at when carrying the full mass of the drone.
- The drone moves forward an estimated 3-4 meters and rotates close to 90 degrees left until the back is pointed toward the pilot. During this entire time, the drone still never really powers down.
- The drone then powers up further for takeoff. The aft pods lift completely out of the water while the front pods remain in the water. The front pods are actually getting pushed down into the water a bit. I estimate that the aft pods get to 3-4 pod heights above the surface of the water. The drone is tipped forward at an angle of probably 20-30 degrees with the front pods still in the water. It's a pretty aggressive angle. Then suddenly the front pods rapidly pull up out of the water and the rotation continues in a complete flip until the drone powers into the water upside down. The aft pods are the first thing to hit the water which accelerates the rotation as the drone hits the water.
Here is what we believe happened based on careful study of the video.
- The drone never really powered down completely after touchdown on the water.
- It was clearly traveling forward and rotating on the water under a bit under some power. This would require forward control (pitch forward) on the right stick and a bit of left control on the left stick (left yaw).
- At the point where the power gets increased for takeoff, the drone has stopped rotating in yaw but is still moving forward on the water. In order to do this, we believe it would have required pushing forward on the right stick to some degree.
- The forward inputs on the right stick are why the aft pods lift way out of the water while the forward pods remain in the water. This angle is approximately equal to a medium speed forward flight attitude. We do not believe that the front pods stay in the water because of surface tension.
- The aft pods were out of the water long enough (approx 1.5 seconds by counting video frames) that we believe he noticed the strange attitude and then pulled back on the right stick to correct the pitch angle. At this point the drone rapidly pitched aft, pulled the forward pods out of the water, and started toward a rapid acceleration backward. But, the drone never gained enough altitude above the water before the aft pods caught the surface of the water. Just prior to the aft pods catching the water (about 1/4 second), it appears that the pitch control was neutralized. However, at this point the drone is nearly perpendicular to the water and beginning to move aft pretty quickly. Because of the steep angle, it's unable to generate upward lift and descends downward until the aft pods catch completing the inverted flip into the water.
Not powering down combined with a failure to neutralize the right stick before attempting the takeoff caused a high energy situation that resulted in over-correcting from the forward pitch attitude into a rapid aft acceleration too close to the water.
We don't believe that that the pods were 'sticking' to the water, although the forward pitch attitude (which pushed the pods down in the water) while moving forward likely resulted in the drone responding more aggressively to the sudden pitch control input change. With our production design, we've never seen the pods stick to the water much at all. In the video, the aft pods come off easily and the front pods clearly come off the of the water very quickly once the control input changes.
Recommendations
- Review the tutorials and tips at Tutorials and P4 Flying Tips
- It is possible to taxi a bit on the water, but we consider this an advanced technique after significant experience is gained with water operations. Any fore-aft or lateral movement on the water should be stopped before attempting a takeoff or landing.
- During takeoffs and landings, the right stick should be completely neutral until well clear of the surface.
- After touchdown on the water, immediately shut down the motors. This can be done in two ways.P
- Pull the left stick down for 3 seconds to stop the motors. Be sure to keep the stick exactly in the middle so that yaw control is not simultaneously input.
- Pull the left stick down and then conduct the Combination Stick Command (CSC) that is used to start the motors.
- Pull the left stick to the bottom, inside corner and simultaneously press the RTH button on the controller. Warning: This will immediately stop the motors.
- Some of the older versions of the DJI Go app result in the P4 having a bit of trouble shutting down after landing. Make sure you are using the latest firmware for easy shut-downs.
- Practice takeoffs and landings with no input on the right stick on the ground before venturing to water.
Cordally,
Adam
Head of Engineering and Technology
DroneRafts LLC
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As the Op in charge of the bird that day, I just want to acknowledge how supportive and helpful the makers have been. As a noob it's entirely possible that less than optimum stick controlling caused the flip here. I'm still trying to muster the courage to try the pods again, with the insights above it will hopefully be a reality sometime soon.
I have a buddy up in Maine with a vacation house on a small lake, and the next time I go up there, I'm buying a set of these water striders from this fine company.
Its great to see water Strider address this incident. It very sad to see any drone go in the water. Does anyone have an idea where Ignacio Perez-Navarro, got the bottle (or tube) holders that he has in this post? Who makes them?
I always try to be positive, but all styles of water landing gear I've seen look like trying to strap a airplane wing on a motorcycle. Why would anyone want to land or take off from water? All other "cons" have been adequately described on this post. Water adhesion and forward stick did it.
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I suppose someone else said this same thing the first time pontoons were strapped to an airplane. I applaud anyone who is innovative enough to come up with new ideas that can help us fly safely whether on land or water.
Because, for one example, I don't have room on my skiff to easily land my quad and I don't want to hand catch it!
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Some of us are condemned to live in the woods where the open space is usually over a pond or lake.
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