Hello all, What would be required to be able to control a simple 12Vdc grabber on the Blue2ROV? The operation requirements is just one function - open / close jaw. Could this operated on the Blue2 and could it be controlled from topside?
First you have to decide on an actuator. The simplest to interface with the rest of the system right now would be a servo that accepts RC PWM pulses as input. This could then be attached to the Pixhawk and controlled with the joystick. If you wanted to use hydraulics or a motor to actuate the grabber, then integration would require more consideration.
Thanks Jacob. Do you know if anybody has built a working manipulator for Blue2? Or do you know of any models that will work on Blue2?
Though there has been a lot of discussion about this on various topics in this forum, I have not seen a working solution yet. This one looks like it is getting close, though. We are working on our own manipulator that will be easily integrated on the BlueROV2, but it will be some time before that product makes it to the store.
Once I’m happy with the position and function of the robot arm on the sideplates there, it’s certainly possible to make a bolt on adapter that will fit a stock Bluerov2 frame. The arm location feels quite sturdy with the bottom plate attached.
The main difficulty with the robot arm other than the back mount, is going to be getting the servo wires through the penetrators/ Even the larger ones aren’t big enough to pass the wires through without pulling the plastic ends off first, which won’t be a big deal for me, but I can see some people might be concerned about. I plan to encapsulate the servo to arm connections outside the ROV in some sort of silicon seal. They should theoretically be fine even exposed directly to water though.
The servos themselves are going to be the waterproof ones blue robotics sells here, slightly modified. I will fill them with nonconductive mineral oil, replace the upper shaft bearing with a nylon bushing, and possibly re-pot the cable passthrough on the side of the servo if it looks like it is going to leak. The circuit board is already epoxy coated, the housing has rubber o-ring gaskets top and bottom, and the servo motor should work fine in mineral oil, so theoretically the whole thing should be pretty easy to get down do the 300ft deep range or deeper without too much problem.
I’ll probably release the arm mount files open source at some point, and maybe offer a few kits through a reseller somewhere or something if there is interest. Not sure yet.
Do you have a grabber in mind? I am looking at using a PWM linear actuator. Should be easier to waterproof using a double o-ring seal on the ram. I am interested in what you have so far.
Jacob, Just throwing this out there for your opinion. Could a spare thruster be slowed down enough to operate as a motor to turn a screw mechanism operating a modified simple bench vise such as the one in the picture? This would be the most basic actuator for a jaw function.Using a waterproof thruster would eliminate issues with depth. The only requirements would be mechanical. I have seen thrusters used as tooling motors on various systems such as Seaeye.
@adam Can lend more insight here, but my understanding is that the M200 motors windings are not optimized for this application. The motors don’t produce enough torque, and would need to be geared down. I think it would be possible, but maybe not practical.
Jacob is correct. You can definitely use tn M100 or M200 in an actuator an gripper, and we have had other customers do so. However, you will need to gear them down to get the torque you need for most applications.
Thanks for the response. Is down gearing a motor a difficult task?? Is a high torque servo more practical?
I’m essentially using a 2 axis + gripper variant of this one here: http://www.ebay.com/itm/6-DOF-Aluminium-Arm-Clamp-Claw-Machinery-Mechanical-Robot-Arduino-Control-Kit/132135647480?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D40130%26meid%3Dfe28162e3e054eaa90a9e8796f24232b%26pid%3D100005%26rk%3D5%26rkt%3D6%26sd%3D262875512530 but with waterproof Hitec digital servos modified for depth rating. You can see the rear servo in the frame pictures that were linked up above, along with the prototype of the rear bearing load transfer assembly. That’s since been replaced with a slightly shorter one. I’d add more axis but I don’t have the servo headers to use them.
Gearing down a motor is usually done using a planetary gear reduction gearbox. You should be able to find several hobby versions suitable for that need if you aren’t going too deep. I personally think it would be easier and less costly to depth rate one of the Hitec waterproof servos for this particular application.
Hey Tim. How do you plan to waterproof the servo shaft?
I’m hoping I will get a tight enough fit with the nylon bearing that it won’t be prone to leaking oil. There is room to also put a rubber washer under it as well. The mineral oil should be close enough to the density of water that it won’t tend to want to squeeze out under pressure. If it does. some sort of gasket may be required. Another option is filliung the upper section with servo greese entirely which should be less prone to leaking.
Hey Tim, sorry to be bothering you. How do you control direction (open/close) of the servo? Correct me if I am wrong but power comes from your battery, where do you take the PWM signal from and how do you control direction?
This is still theoretical since my rov is barely electrically complete yet, but the theory is to use the 3 of the 4 unused auxiliary servo outputs on the pixhawk itself. That will give me power and pwm signal to the servos. Direction will be bound to the controller, or keyboard buttons. Not certain yet. Other people are using those outputs with servos for other projects, so it should theoretically work.
I have tried, but no luck, in finding planetary gearbox for the M100 or M200 motors, except for custom build ordering and that was pretty expensive. Anyone who have a link to a site where they sell gearboxes that will fit ?
I am not aware of any gearboxes that will fit our motors without modification of customized adapters. It is unlikely that any are available- if you wish to gear down an M100 or N200, you will likely need to modify an existing gearbox or make your own! Vex robotics kits parts are often used for such things, though they may be a bit large. A planetary gearbox or worm gear drive will be more compact.
If you can locate one that will fit the shaft, I can design you a printable adaptor ring for it pretty easily if you like.
What considerations do you have for maintaining water-tight integrity for the control wires. water will push through the servo wire casing and make it’s way into your chamber.
This may not be a concern for depth’s <300 feet.
I’m aiming for depths of <=600ft and looking for options.