Alright this is a reach but worth a shot. First time posting on a thread like this. I’m a mechanical engineering student that is working with a sponsor who wants us to build an automated fly fishing system for someone who is paralyzed from the waist (correction: neck down). The biggest concern is how to achieve the linear motion necessary, yes we have simplified this art form to only 2 degrees of freedom. This linear system needs to have a speed of about 11 in/s, carry about 10 lbs, and be able to hold a linear force of about 15 lbs. we have found that ball screws can hold the weight but can’t achieve the speeds and a belt drive can do the speed but can’t hold much weight without skipping. Does anyone know of a linear rail belt driven system configuration that can achieve this? The idea now is to use a nema stepper and a belt and pinion system. How could I keep the belt from skipping at high speeds and and have the gantry wheels hold this weight? This is the first time we have designed a linear system like this. Any help and suggestions would be greatly appreciated.
Put the person in a sit on top kayak. It is empowering and easier. There is so much less math involved. Although I am not personally paralyzed from the waist down, I have helped many people with missing limbs and other mobility issues catch fish from one. I fly fish from a sitting position from mine quite successfully in the ocean, lakes, and rivers and I am a truly horrible fly fisherman technique-wise.
This is a great suggestion. Although I did not catch my mistake. I misspoke. The person is paralyzed from the neck down. A fully automated system is what’s needed. Fishing from a kayak is pretty fun. Though I prefer a raft as I can take my dog with me.
As you have noted there are not really any good solutions in the way of linear drives. Have you considered a belt driven rotary drive?
I appreciate the suggestion. If you mean a belt driven linear rail system with a carriage then yes. The thing about those is that we can get the speed needed but not the ability to carry weight. If you have any ideas about a belt system that can carry weight i would love to hear them. I’ve been looking at specs and diy systems can reach 6 m/s but at a cost of only being able to carry a pound or so on the gantry. Unless we do a custom system that’s $2k and has the accuracy of +/- 1 micron, accuracy like that is not needed with a proof of concept system like this, then I’m kind of stumped. Right now I’m looking at rack and pinion systems but again speed and weight carrying ability is an issue.
A diagram of what you're trying to do would probably be helpful. In terms of a linear system, I'm envisioning a pair of semi-parallel actuators, holding the rod at each end of the handle, and when one punches forward the other one flies back, flicking the rod forward extremely fast. Otherwise a rotary axis coupled with some kind of spring tension would probably make more sense. I am, however, in no way, shape or form, any kind of fisherman or fishing-adjacent person, so I could be miles off. Hard to engineer something without pictures!
So basically we have a wiper motor with an encoder on it to basically make it a stepper motor for the angular motion. This wiper motor would have a coupling to attach the rod to the motor. The motor would be mounted on a cart along with the reel and possibly the electronics. Since this picture it has been decided to mount the Electronics either remotely or on the linear rail. This whole system would be on a cart or gantry. In the pic the angular motion system is mounted on the blue plate and the gantry is the purple box. This angular motion would create the 10 am to 2 pm motion for casting. Now there is also a linear travel involved when casting. The rod moves about 20 inches in a straight, straightish, line. This is where the linear rail comes in. Linear rail is the grey rail system you see. The main question is how to drive this gantry linearly. It has been found that this linear system will have to stay in place while holding the fighting force of a 5lb trout, say 10 lbs in the horizontal direction. The wiper motor has proven to hold this amount of force since it has a torque rating of 14Nm. The linear rail system will also have to move the 10 lb gantry, estimated to be 10 lb but should be as light as possible, about 11-20 in/s. This would be a continuous forward and back motion. The system has no inclination and will be mounted flat. So basically, how can I drive this thing without blowing up? Lead screws are out, too slow. Belts are still on the table, can do the speed but start to skip with too much weight on the gantry. Chain drives might be able to do it, speed maybe weight maybe. Loud and possibly dangerous though. It would be a direct drive so speed and torque are key. So maybe a nema 42 high torque motor and a belt drive system? But how do I keep the system from skipping and thus loosing steps. Can it still go fast with all this weight? So many questions....sorry if this is now a novel.
Ok, so, first assumption to test: does the linear rail even need to be active while reeling in? If it just sat parked up against the hard stop at the front, what difference would it make? If it just sat there wobbling back and forth in the middle of the rail, would that few inches make a difference to the reel motor that's actually pulling the tens of feet of line in? Could that additional motion, in fact, not be a sign of the struggle and communicate the excitement to the user? If it's a perfectly smooth, automated experience, and it's not just an excuse to sit there and go through a case of beers, I'm not sure it'll hold too much interest over the long term. You're not only creating a robot, but one that effectively interfaces with an individual, so that should be considered too. In terms of driving it fast enough for casting, I'd consider springs and a small flywheel for control that can also help decelerate the carriage at the other end. You can use a small motor to slowly crank the spring up for the next casting (or a bigger one for repeated recasts) with heavy planetary gearing and a screw. But in terms of actually moving, you need massive acceleration with a good size load, which isn't gonna happen with steppers, you'd be better off with a servo. The problem with plain motors is the massive current inrush you need to get them instantly flying. Too many of those, you're depleting a battery pretty quick. Unless you figure out some kind of recovery braking, instead of just dumping the deceleration energy through a resistor. A small 18v compressor (augmented with solar?) and a pneumatic actuator may not be off the table either. That's probably the best actual motion technology to use for this kind of purpose. The only issue might be noise, which fish are really sensitive to.
Forgo the belt and go with a continuous loop of spooled wire to drive it. Based on a spool with a 3” circumference moving 12” in one second only requires 240 rpm on the stepper which is doable. The issue is determining the size of the stepper required.
To fly fish, you’ll want to control both rod speed, distance of travel and stripping out more fishing line as you progressively swing the rod more and more and then you’ll want to “release” the line to send it or “shoot it” for the most realistic motion. You’ll want a radio controlled control box of some sort that has control of the rod speed/distance and line control (stripping and shooting). I believe if the person has control of their mouth, they can use a mouth joystick type apparatus and a button to send the line. ideally, you could build modified mouth joystick that has a button you bite down on. You release your bite a bit and it strips the line... then you completely / quickly release your bite and it would ‘send’ the line. Bless you for working on this! It’s a terrific example of engineering challenge that matters to real people!
