Testing Trident with attached Payloads

payloads
testing
drag
gopro
performance
mount
trident

#1

I wanted to start posting little tidbits about development we’re doing on Trident on the forums, and I realized that a quick set of tests I did recently to see what size of payloads we can fly with would be a great start.

Alright- I had some fun with this.

At first, I attached just an empty GoPro case (mostly filled with water to make it neutrally buoyant - I’ll use an actual GoPro with supplemental flotation later) to the bottom of the ROV as shown. To my delight, Trident handled it very well, and I could hardly notice a difference in performance. This was all at night which makes it harder to notice subtle details, but I’d say the only noticeable difference is that the pitch was a bit off, but that was easily correctable by adding a slight amount of vertical stick- almost none at all.

Since that went so well, I figured “ah heck- let’s put something bigger on” so I hot glued on a plastic box I found (which would also be flooded) and took that for a test drive. Okay- well, this configuration didn’t work so well. If I were flying very slowly I could just about make it across the length of the 20’ pool without hitting the bottom or the surface, but for the most part it pitched up (yes, up) like crazy once any speed was added.

At this point I was on a roll, so I rummaged around for other stuff around the lab to glue on the ROV and found a Pelican 1010 case. I attached this case roughly where the GoPro was and let it flood. Despite the noticeably larger size, this test also went very well. I was certainly able to notice that the ROV was more pitch sensitive (I couldn’t decide if it wanted to pitch up or down) but I was able to control it pretty well on the stick. At low speeds I didn’t even need to use the stick very much and the whole thing flew pretty gracefully in straight lines. When I turned, I noticed a lot more roll than before. Anything but slow turns will be a bit sloppy, but still very doable.

Finally, I decided to try an idea I had been thinking about for a while which was to mount the big box (which has the dimensions of 185 x 120 x 45mm) to the back of Trident, behind the fins. I used some scrap acrylic and a bunch of duct tape to do this. This is the test that really got me excited- Trident flew beautifully! As I suppose one might expect, it turned a little slower than usual but certainly it was fast enough - maybe it would take 1.5 seconds to turn 90 degrees. Where it really shined was the tracking during forward flight. I guess this is also intuitive, but having the drag behind the vehicle and aligned with its CG along that axis caused it to fly like an arrow. I could point it to a part of the pool (both in heading and pitch), and by only pushing on the forward joystick it would go straight there. I envision that for larger payloads such as side scan electronics, fancy scientific sensors, acoustic positioning transducers, etc, there could be a bracket that screws into the bottom and runs straight back for things like this to mount on. I don’t see any reason payloads couldn’t even be comically large compared to the vehicle- it’s got plenty of power and the performance falls off pretty gracefully. I half considered taking an empty Trident shell and and taping it onto the operational prototype backward just to see what would happen, but then I realized I was very hungry for dinner and that the FroYo place up the street was about to close.

I plan to do more precise testing once we have dynamically accurate prototypes ready (this prototype has a different CG and slightly different geometry than what we’ll ultimately have) but I am feeling pretty good about attaching stuff to Trident and and doing transects. Especially if we can add some hydrodynamic cowling, it seems that even fairly large items can get strapped onto the bottom without major issues.


Searching this forum for Trident Threads
#2

Hi Eric

First off thanks for sharing this, :beers: it great to hear feedback of how the system is going
It also raises a couple of questions.

To add versatility to mounting - [I know you have talked about the potential for mount spots (I assume some sort of threaded “nut” in the injection housing)] have you considered designing into the injection housing some sort of standard V or T slotted makers beam system to allow things to be added? rather than gaffer tapping on a bit (yes I know it was just a trial and great to see the quick and dirty results)

Also if the Trident is going to be capable of using wifi to communicate with external payloads, the wifi would typically only travels through 100-150mm of water so the location of the “aerial” will be important or an eternal plug where the payload could be connected to

Interested to hear your thoughts
Scott


#3

Hey Scott- thanks for the encouragement!

You’re correct that the mounting concept we’ve been working with is to include periodically spaced threaded inserts (basically embedded nuts) in the bottom of the vehicle. With this system, a slotted rail could be added after the fact, but would not be built in. You’re also right that using double sided tape was just for quick and dirty prototyping- I would not suggest using such things with an expensive payload in the field!

We’re still working on what the exact spec will be for the size and separation of these holes. My guess is that it will end up being something like M3 holes spaced 50mm apart in either direction.

As for the WiFi comms, the 10cm or so of water that we can transmit through shouldn’t be a problem as I expect payloads to be mounted against the side of the vehicle. Since WiFi travels just fine through plastic and air, one can think of any non-water (i.e. plastic) material between the ROV and the payload like a tunnel for radio waves. For now, I want to keep the electrical power for payloads separate from the ROV’s power system to reduce risk, so payloads should have their own power source. I expect that the main payload people will fly with initially will be GoPro cameras.

Also, at a holiday party the other night we decided to get really carried away and attached two very large water-filled tubes (actually toy crayon-shaped piggy banks someone got at a dollar store) to either side of the the ROV with duct tape. These have as much (perhaps more??) mass as the entire vehicle itself and are equivalent in size to pretty serious side scan transducers with electronics. As it turns out, the vehicle flew pretty darn well with them too! Trident has plenty of power, so as long as it’s drag is balanced, it seems to have quite a bit of payload capacity while maintaining speed and stability!

Anyway, thanks again for the questions- keep them coming!

~E


Payload Interface: Mechanical (Trident Kickstarter Update #10)
#4

Hi Eric

Thanks for the reply

Just a thought if you are going to use M3 (although M4 is a more “standard” size in engineering) are they going to be using Long/Coupling Nuts so that you get greater thread engagement so you don’t rely on just 4 threads to hold on to those precious payloads

Also you may need something at the base of the nut so someone overzealous doesn’t screw a bolt in so hard that it punches through the plastic body below the nut

As for spacing’s maybe a couple specifically set up to take GoPro mounts (as you indicate the most likely basic payload) mmmm maybe down facing by 2 and front facing at the top by 2

PS I like how you are trialling the new missile launch payload option :smiling_imp:


#5

Scott- Thanks for the advise. So, you think M4 would be more common? I think that would be doable, and we’re already planning to use M4 for the tether attachment (more on that later). I tried doing some googling to find info on commonly used thread sizes but didn’t find much. Also, where did you find those groovy anodized GoPro mounts? I’m still shopping around for options there…

e


#6

I have no stats on M3 V M4 but it seems like there is a lot more M4 stuff out there (no science just experience)

As for the mounts I just Googled “aluminium gopro mount” I have something similar on my 2.6 ORov for holding the GoPro for SfM stuff

http://www.dx.com/p/aluminum-alloy-skating-surfing-board-mount-fixed-socket-for-gopro-hero-3-3-2-black-silver-318106#.Vmzt2kp97IU


#7

Hi!

I would like 2 brass M4 fittings on each side or 4 below.

The main thing i would like to add to my Trident is some kind of sonar/transducer, since that would increase it’s usage for me a lot.


#8

Is the aim of this testing to understand which mounting position is most effective (allows the most payload and least effect)?
Do bottom mounted ‘payloads’ make any sense?


#9

Yeah- we’ve been doing testing to figure out what our maximum payload capacity can be and how those payloads can be best mounted. I’ve been aiming to carry small payloads like GoPro cameras, but got curious about how capable the vehicle would be at carrying larger payloads. For smaller payloads (up to around the size of a Pelican 1010 case) mounting on the bottom seems not to have many major effects on performance, but I’ve also found that larger payloads (even as massive as the vehicle itself) can be carried if balanced with the center of drag.


#10

Hi all. late to this thread but great to see. I’m looking ta using the Trident for marine teaching labs and really like the idea of proper attachment points for payloads. The side mounted payload capability would be something that would be very useful for us.


#11

Eric, Any update on payload mounting? Will there be any side mounting nuts?


#12

Eric, I’m following up Jim Scholz question on Oct 7 ! Are there Any update on payload mounting? Will there be any side mounting nuts?


#13

Thanks Eric, I’m also keen to find out where this goes.

I am planning to build upon your previous work by creating and testing a payload “even as massive as the vehicle itself” with my two side mounted payload modules to support laser measurement devices, GoPro cameras, 360degree cameras, ultrasonic sensors and perhaps even manipulator arms by the sounds of it.

In the absence of hard points on the sides, I propose two thin straps for securing the modules either side of Trident using the bottom hard points for the primary connection and two tensioned top straps to create a “snug” friction fit with the assistance of cast silicone interface pads (or modelling clay) between Trident and the modules to reduce drag.

I expect to hit some hard limits at some stage…but nothing that a little more power and some additional thrust couldn’t fix.


#14

Hi, So I got my Trident recently, finally got it out for a test dive and it was fantastic! in relation to attachments. My GoPro doesn’t fit with the M3 mounts on the trident but I noticed in Kickstarter update #10, there was an image of a square adaptor, that screws into four of the m3 holes and has a GoPro attachment. Is it possible for OpenROV to provide an stl of that design so I can try to 3D print it for my use?


#15

When I purchased my GoPro, it came on a large black plastic base plate in the box. It is just big enough to fit so I plan to use this base plate with some flat washers to clamp it to Trident.