3D Printed ROV – Manipulator
Even though this was just going to be a small observation ROV I still kind of planned on adding a small manipulator to it anyway. The only problem is I will only be able to control either the manipulator or the tilt for the camera at one time. I’m going to try and make the manipulator easily removable and with modular grippers.
My first thought was to use a scaled down (50%) version of the manipulator a printed before so I printed that first because all the design work was already done. I also wanted to try some other options…
… so there’s this version which I designed based off the gripper I made out of a Radio Shack Armatron that I used on my Seafox because I really like the parallel gripper design better I think.
The gripper design uses a worm gear setup just like the original Armatron. I did add some hooks to the grippers tips to add some versatility so you could close them stick them in a hole and open the gripper to grab the item with the hooks.
The main arm and housing will be made from PVC Pipe and Fittings and use a shaft seal much like my Seafox manipulator. (The shaft is not shown in these diagrams.)
There are quite a bit of bits and pieces to this design because I am incorporating a clutch into the motor. The Original Armatron Gripper had springs on the fingers that wouldn’t let you stall the motor when it was closed all the way, my clutch design will accomplish the same idea. This may limit the gripping force but being as this is such a small Rov I won’t be lifting much anyway.
The clutch is basically just a slip clutch, the triangle surface on the green part mates with a corresponding cut out on the orange part and when the force is to much the entire motor pushes back against the spring and the mate is broken.
This is another view showing the mating surface of the orange part.
The modular part will use easily changeable gripper heads. This one being a golf ball grabber.
This design could be used as a soil or water sampler. These are easy to print so the possibilities are endless.
For the arm portion I started by squaring up the ends of a piece of 3/4″ PVC Pipe.
Next I trim off a small section of a 1/2″ PVC Coupler. (This will be the front section of the main arm housing.)
Then I turn the coupler around in the chuck and chamfer an angle on the front edge. (This is purely for aesthetics.)
Next its on to the seal seat piece. I start by trimming off the flange of a 1/2″ PVC Plug.
I then drill and bore out an area to create the seat for the actual seal.
Turning that part around in the chuck I have to turn it down just a bit so it fits inside the 3/4″ pipe.
These are the machined parts so far.
The seal is pressed into the seat at this point. I’m using a 3/16″ shaft so this is a 5mm Yamaha motorcycle oil seal. (I’ll have to find the part number and update this later.)
Using a PVC primer and glue the seat piece gets glued into the pipe (seal facing out) and then the front section gets glued onto the seat piece. (I couldn’t take pictures while assembling it because I need to stick the pieces together while the glue is fresh.)
This is how the seal should look.
After that the assembled piece goes back in the lathe just to clean them up.
The main housing all cleaned up and I’m ready to work on the internals.
This is an exploded diagram of the Internals.
Colored parts explanation from left to right.
- Purple/Grey part is the seal/seal seat part that was glued into the main arm housing.
- Yellow is a bushing to hold the shaft centered (I didn’t feel a bearing was needed on this one.)
- Orange is the shaft side of the slip coupler.
- Green is the motor side of the coupler.
- Grey is the 10 RPM gear head motor.
- Red is the spring cap (this holds the spring centered and away from the motor terminals.
- Next is the spring.
- Light blue is the internal motor housing.
The internal motor housing (cut away view) is designed around the motor. It has flat internal sides to keep the motor from rotating, a center post for the spring, as well as wire exits.
Here are the actual 3D printed pieces ready to be assembled.
This shows how the spring cap keeps the spring centered and away from the terminals and wires.
The two halves of the slip coupler. The amount of force required for the coupler to slip is depended on the spring used. (I used a ball point pen spring.)
Once everything is assembled in the internal housing the bushing will be glued in place. The bushing slip fits into the seal seat piece when assembled.
The entire internal housing then will slide into the main arm housing and be held in place with a end plug. (not shown yet)
Oops I just noticed I grabbed the wrong motor off my bench while designing this… (too many projects going at once) I grabbed a 10RPM motor instead of a 30RPM. (I think this is a 30rpm anyway. ) At only 10 RPM’s the fingers would take like 1-2 minutes to fully close. The 30 might be a bit too slow too but it’s all I have at the moment so that’s what I’m using. The only problem is it larger so it just barely fits in the main housing so now I have to go back and redo the motor housing. At least everything else should still work. Well back to the drawing board…..
OK that was easier than I thought… Here’s the redesigned motor mount. It’s no longer a complete internal housing and the flat sections are going to be real thin but I’m still hopeful it will work out.
Everything looks pretty much like it should still fit and work out. I just have to print a the new mount and a new spring cap before I’ll find out for sure.
Here is the other printed gripper. Everything was printed in PLA with the exception of the pads on the fingers. I printed these out of a flexible rubber material so they would have better grip. It uses some 4-40 and 2-56 screws for assembly and a 1/8″ stainless steel rod for the gripper shaft.
The gripper shaft has a flat spot ground in it for the 4-40 set screw on the worm gear.
This smaller shaft of the gripper will mount to the motor shaft though a coupler. This will allow the grippers to be easily changed out when needed.
I next cut a 6″ long piece of 1/2″ PVC pipe to use as the arm of the manipulator. Using the gripper assembly I mark the location of the mounting holes for the gripper. The first mark is for the mounting screw and the second mark will be the access hole for the coupler set screw.
After drilling several holes through the arm on both the top and bottom the arm is glued to the motor housing portion of the manipulator. (some of the holes are for drainage because the arm portion of the manipulator is not water tight.)
A quick test fit of the gripper is next to make sure the set screw access hole is in the correct position.
I am using a piece of 3/16″ stainless steel rod for the motor shaft. Again a flat section is ground into the shaft for the shaft slip clutch coupler set screw.
Next the bushing is placed on the shaft and the shaft is inserted into the housing and through the seal.
I then mark the center location of the set screw in relation to the motor shaft.
I made a coupler out of aluminum to join the smaller gripper shaft to the larger motor shaft. I then mark the location where the motor shaft needs to be cut as well as how far in inserts into the coupler.
After cutting the shaft to size and grinding another flat on that end (not shown) the shaft is reinserted into the motor housing. I temporarily attach the coupler to a scrap piece of the gripper rod so I can insert it into the arm and affix it to the motor shaft.
I secure the set screw in the coupler to the motor shaft through one of the holes in the bottom of the arm.
With the motor shaft and coupler in place I can go back and trim down the gripper shaft to length and grind the set screw flat on the end. (this is done with the shaft removed from the gripper)
Then is just a matter of sliding the gripper in place, securing it with a 4-40 flat head screw, and tighten the gripper shaft to the coupler.
Next it’s on to mounting the motor. I first have to print a new motor slip clutch coupler first as this motor shaft is a different size.
Next is was on to the end cap. This is another 1/2 Plug that is turned down to fit inside the 3/4″ Pipe.
My original idea to keep the motor from rotating was just to use a couple of pins to attach the motor mount right to the end cap so I made a template to dill some holes in the edges of the cap.
This Rov is not going to deep so I just use the epoxy method of sealing the through wires. (I did strip the section of the wires that will be in the epoxy to combat any leaking through the wires jacket if it gets nicked.)
Here the epoxy is setting up. (I finally found a use for the larger manipulator.)
The pin idea ended up looking a little sketchy so I ended up cutting a section out of the end cap and redesigned the mount to have a mating surface so it should be stronger now.
Here’s how the mount and end cap go together.
I cut the wires just long enough to leave room for the motor to slide back and forth a bit. After soldering them on the motor its time to put this thing together.
Here’s the scary part about this… once the end cap is glued on there is no going back. There is no fixing any problems and it’s pretty much a disposable housing if anything goes wrong. (Which is why I didn’t want to risk just using the small pins to keep the motor from rotating.)
Here is the assembled manipulator… as you can see I changed the length of the arm too. When mounted to the Rov it would have stuck out to far and I want to keep the Rov relatively small.
So far everything is working, here is a quick GIF of it in action… It’s still kind if slow (I think a 60RPM motor would be better but I couldn’t find one small enough.) The grip isn’t the strongest either because of the slip clutch but its better than stalling the motor every time it closes to far.
I printed up some different fingers too with optional finger pads. The top fingers (mounted one) have round tip pads while the bottom fingers have pointy tip pads that might grip better. I still need to run some test to see what works better.
Here we have the golf ball grabber. This one actually has a wider opening which I could use the other fingers on if needed. Next I have to figure out how to mount it to the ROV. I have some different ideas for that too I want to try…
STL files for this design are available on Printables and can be found HERE.
Now it was time to start work on some Lighting.
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