Turn a SUP into a cruiser/fitness machine

I think I have now thought up a viable drive design that will engage two or more limbs for the type of exercise action that I am after
I will proceed to making a 34 cm drive pulley actuated by 4 ratcheting levers. One for each limb and the levers cross linkable with hand to leg return via string to pulley

Hoping that the 34 cm drive pulley can turn a much smaller pulley mounted on each axle and leaning towards using 40 cm rims for the wheels with 8 blades each that can be length adjusted to tune the whole setup. A 40 cm rim on this sup will just bite into the water at level trim

 

Why all the complications? Here is a 3D model of a commercially available elliptical road bike, as you can see there is no need for any ratcheting drives, it's an all lever affair. Free CAD Designs, Files & 3D Models | The GrabCAD Community Library https://grabcad.com/library/elliptical-bike-1
All you need to do is connect the forward pivot of the foot and hand levers to a crankshaft wich directly drives the sidewheels. That's how all oscillating cylinder steam paddlewheehlers operate. Or you can use it as is with the chain driving a sternwheel.
You will need a rudder, you actuate that via cable link connected to what are the brake levers in the cad model.
For outriggers a simple 2m crossbar with two rigid flotation aids on edge is sufficient.

Post 25 in this thread shows you an elegant way to make the sidewheels Converting Bicylce to Pedal Boat https://www.boatdesign.net/threads/converting-bicylce-to-pedal-boat.25486/page-2

 

Rumars, the elliptical or air walker style is what I originally asked about. In broaching the subject I also mentioned my concerns regarding how these bikes have a side to side motion as they move forward and how it may not be a good choice. Most responses seem to agree with this concern, and also it was pointed out to me that such a tall and heavy frame might make things ugly after a capsize. I let that idea go at that point

The air walker style is my preferred workout. What I am trying to do now is take that concept to a lower more recumbent position and also find an alternative to the framework to lower the COG and making it easier to roll back if it flips

 

You have outriggers, that takes care of transverse stability. Anyway, to insure the thing doesn't capsize completely you can fit a flotation device on top of the eliptical frame, for example a transverse bar with two inflatable exercise balls at the ends. Those will keep the entire thing floating at a ~45° angle and make recovery pretty simple as long as you are fit enough to climb back on board.
The motion you should be concerned about isn't side to side, it's fore and back, rocking can kill drive and the SUP is short.

For this project you should be able to weld aluminium or calculate and fabricate the frame in carbon fiber.

If you want to sit down while moving your feet and arms back and forth (the motion will not actually resemble the air walker or eliptical), your inspiration should come from wheelchairs. There you can find everything, from the old lever on a crankshaft system, to more complex things like the jackdrive or the completely 3d printed open source NuVu ratcheting drive.

 

Spent this evening messing with some ratcheting systems. A four limb cross workout is very doable. The ratcheting noise is unbearable. I can replace the ratchets with one way bearings from a fishing reel and these are noiseless. One awesome result was that while playing around with this, I saw a very simple way to make this a reversible system without any mechanical or electronic switching

I am now at a workable concept for a cross trainer drive that can go in reverse. Not just that but also when a motor is added to this system, forward throttle will not activate ratchet noise, BUT the one way bearings will not allow reverse under motor power. This will not be a problem as reverse will be instantly available under manual foot pedal

The motor will be attached with reduction gears with the hope to be able to get away with a small 5000 series BLDC. Since it will be always engaged, under manual power the motor would spin faster than the drive. This could be both a plus and minus. Could this be used to charge the battery? Would this make the drive too difficult to turn under manual? If this turns out to be a problem then the motor would need to be able to be disengaged

Except for the last bit, it's all pluses so far with the concept with and more. The unmanned craft would be under 50 cm in height making it less top-heavy than a full walker frame. Only metal parts would be 4 stainless drive shafts 8 mm x 500 mm, shaft end couplers, 6 rubber sealed stainless bearings, one hardened stainless or brass rod for crank shaft, 6 antireverse bearings, aluminium handle bar levers, aluminium foot pedals, any motor related parts and all the fasteners. All the other parts will suit printed PETG

The mechanisms in available cross trainer designs are difficult to bring to a SUP. Even prop based systems would be a pain with shallow water. Even in recommendations made so far there is always a need to add something to compensate for some limitations. I recognise the need for a system specifically designed for SUPs, one which doesn't impose any of the limits inherent in current systems

The above drive allows for rear wheel or all-wheel drive systems. The rear wheels will also do the turning, dog trailer style and the front axle is optional. That cuts the parts list almost in half as a start. For now, I'll focus on an RWD system to get the prototype on the water

 

Used the board for the first time today. My wide stout 84 kg is quite tippy. Sitting down and paddling is fine

I have a bunch of S698-2RS bearings. Stainless steel races with rubber seals. First step will be a pair of brackets out of PETG for running the axle across the board just behind the seated position

Any thoughts on a good way to retain the bearings in these inverted hangers?

 

I have made a start on designing parts for this in FreeCAD. Working out how it all comes together and all the main systems seem in harmony. Now to what I need this thing to do

Make use of the inflatable SUP
Improved stability and roll resistance
Lean seat, between astride and recumbent
Car topper by one person
Apart from the seat, a clutter-free deck (Axles, drive systems, frames and such)
Easily fitted or removed from SUP, secure
Four limb cross-linked manual drive
Electric cruise drive including charging
Can reverse without throwing switches and things
Simple and reliable steering, preferably without implementing an extra steering mechanism
Small total part count using very simple and direct systems
Mostly PE parts with a very small qty of marine rated metal parts
Drive system weight very very low to the deck level with a significant part below deck level
Be easily made by a home digital workshop/PCBway type orders
Exercise, fishing, cruising, beach fun
Sophisticated appearance in harmony with SUP aesthetics with some fun touches
Almost as easily cleaned and maintained as 6 lots of Alvey Luderick Special fishing reels after marine use, performed by one person

How is this for a list? Can this be done? One thing to consider is the amount of sitting back with a smoke thinking about the feasibility of each item before placing it on the list. The whole point of the list is going to be to bring it to fairly shine at the last 4 requirements

I think I have a design that can do it and I have made a start on it. Since there has been no interest in any sort of open source type on collaboration, I'll publish my results as I go and anyone wanting to experiment with anything similar will just have to work it out from pics or discussions here. Majority of items made will be of the printed type

 

Post photos of your progress so we can see, and offer more helpful suggestions. Verbal descriptions leave more questions than answers. Keep the weight down.

 

An aspect of designing things where everything comes and works together in harmony are parts that are efficient to make and use. Designing the axle hubs/bearing housings to meet all the requirements has been challenging. This includes the printing process, I have worked out a way to not need support layers and enable the easy care and meet drive train requirements. A lot of intellectual effort in this part so will be no close up pics of this one, but the design will be obvious

 

First step, get familiar with the roll characteristics. We have already used it neat. My frame is quite rolly polly on it. I'll try spreading a pair of amas out making the total beam 1.5 m. I'll make these out of pool noodles with an aluminium tube core and the cross-beams with very low profile box section


I have designed and made a beam end to see how it turns out. I have made it too heavy-duty so some redesign ahead

 

At this point in the design I have worked out the details for the manual power system and electric being delivered to the paddle wheels. If my drive can accommodate paddle wheels or dual props, is it worth chasing prop over wheel? The props would have to be under 25 cm diameter and ducted for safety and no rudders to fit the requirements list

 

The build is coming along well but due to a lack of interest, I will be continuing the project on the Sol forum as its more relevant to fishers rather than boat designers










Next I'll redraw the beam to a design that doesn't require lashings and some faired end caps for the noodles. Follow futere updates on Sol

 

You've done a good job Randy, it looks good. The simplicity is great, and I like your printed parts. Probably not much interest on here because there are bigger toys for engineers to play with, and it looks like you've got everything under control, with successful outcomes, and few questions. Ask here how to put a big motor on it and you'll get some interest. Good luck with your continued developments.

 

Thanks man. Some new pics


Replaced the beam ends with new ones with a loop at the end to not require lashings as well as nose cones. The noodles are very ineffective at that separation. They would need to be set wider or doubled up to offer any useable righting moment. It was an interesting experiment and help me to get a handle on added roll resistance. This is where I say goodbye to the noodles/outriggers

Moving on to the build and design of the fitness cruiser. I have been working out the fine details of the drive setup. These are going to be pneumatic tubes on 8" rims wearing blades printed in TPU. The rear wheels are the driven ones as well as provide steering. Both under manual and 2x 250w BLDC hub motors. The wheels will also provide the buoyancy function

I am very curious to build and test gyro driven foot controls as the foot pads of the leg levers on my xtrain drive system. This will allow max agility and total hands free as the drive can keep running on just leg levers alone and the gyro system allows instant switching or stacking human power with electric, direction with differential or any combination of those. Even more so if I enable AWD using another pair of hub motors for the fronts. This is for proof of concept to firstly see how taxing it is on the feet but dancers and driving enthusiasts should be fine

 

Randy,

With all these injuries and limitations you may be better off going to physio and following your specialists recommendations for exercise.
A full bodied, sliding-seat rowing setup may meet your recovery needs best.
You can get them for SUP's...

Best of luck.