Hi Core Forum,
I’m a completely new user to this space so I’m incredibly grateful to anyone who responds. I’m looking to build a small lightweight submersible treadmill that I can place in my bath to help my labrador in her recovery from some surgery.
What I need to find is a motor (I imagine probably a servo or maybe stepper) that can operate completely submerged and drive a single axel that will drive the treadmill base. I guess ideally this motor would need something like 20-35kg of torque and does not need to have high RPM capability as the treadmill only needs to be used to encourage the dog to walk while submerged, not get them up and galloping.
If anyone has ever tackled something like this in the past I’d love any recommendations on suitable motors that might work for my intended purpose.
Thanks in advance Core forum crew 
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Hi Grayden,
It definitely does sound unusual 
You say its for recovery from surgery … so I’m guessing it doesn’t have to be too elegant if it’s only for a few months use ? Will the bath be used for anything else for the duration (ie does this gadget need to be removable) ?
I cant help with the engineering or electronics beyond saying that I expect submerging electronics or motors is likely to give a lot of difficulties (and maybe some mild electrocution). Might it be feasible to keep the electronics above water and use something like a car drive belt to move the motion down under the water ? Hmmm, that might make too much disturbance in the water, so maybe a mitre gear or bevel gear to translate the horizontal rotation 90 degrees to vertical rotation, then another at the bottom to translate back to horizontal rotation.
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Hey Donald,
Thanks so much for your reply. Since posting this I have begun to think about the problem and also considered whether it might be possible to bring the electronics up above the water instead and your idea of a belt drive might just be what I need.
As for the slapdash nature of the apparatus, yes I’d say we’ll only need to use it for about 12 months at most to hopefully get her back on her feet full time. And the bathtub we’d be using is the household bath so it would need to be removable.
Assuming that I can figure out a way to move the electronics above the water and drive the axel the next major thing I think I’ll need to tackle will be driving the belt while underwater. A lot of cheap treadmills rely on tension and friction between the axel and belt to perform the rolling action. However, I’m not sure if with the addition of lubrication from the water, if this style of system might not create enough friction to continue to function.
I’ve actually found a treadmill supplier that sells treadmill parts and I’m starting to wonder if with an extruded aluminium frame and some parts from them If I could make it all work.
https://www.mytopia.com.au/treadmill-roller-with-pulley-9859/
https://www.mytopia.com.au/treadmill-running-belt-6544/#product_tabs_additional_tabbed_contents
Happy to hear your thoughts though.
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Just throwing out a crazy idea. How about using a small submersible pump and a water wheel (if you’re adept in building one). The bathtub should be deep enough to feed the pump. Again, the danger of losing the doggy baby to an electrical mishap is always there.
Another idea would be a non-submersible pump (or a dual mode submersible, non-submersible one - which would also protect the pump from the splashed water) kept in a shelf or outside, with water from bathtub connected and feeding a water wheel by some sort of hose.
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Hi,
Interesting situation. A couple of questions:- How submerged will the dog be? Completely? Up to her/his tummy? That will affect the buoyancy and, consequently, the torque required (in N.m) by your motor. Also, how much does your lab weigh?
What you could do, assuming the bath is spare, is put a penetration through the side of the bath and put a drive shaft through. Maybe it’s your ‘human’ bath though!
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Hey Gerard,
Thanks for your reply. The dog would be submerged about halfway into the bath, just above her belly.
She’s about 30kg which is why I thought something in the 20-35kg torque range would be ok as this probably accounted for the lack of weight pressing down due to buoyancy but probably didn’t run me too short if I’d undercalculated.
As for your idea of a shaft through the bath unfortunately yes this is our human bath. However, it looks like we might have just secured a property today that has a large outdoor area that might allow for more of a purpose-built tank with the type of shaft you’re talking about.
I’m just not so sure how confident I am of my water tighting skills that might be needed to make this work. This is a great solution though and it certainly gives me ideas to think about. Since posting this request I’ve since been told by our vet that this solution is in high demand for people like us. He apparently gets asked regularly if there is a solution like this available for at-home use so I’m beginning to think on more of a product to market scale so I really appreciate your input.
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Hi Grayden
What a great idea. As this would be an occasional use item the sale market might be pretty limited. You may be better off making just a few for hire. Local vets may be interested if they could hire something like this for relatively short periods or point their clients in your direction…
When you get it all working don’t forget the lubricants for all your moving bits. It will be under water so you might need something like water pump grease ( used to be an automotive water pump grease) or similar which won’t dissolve or mix with water.
Cheers Bob
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Hey Grayden,
Another option for holding lots of water could be some large containers from Bunnings.
I have some good experience with the high power motors with gearboxes from Pololu, there are a few ratios to choose from: https://core-electronics.com.au/131-1-metal-gearmotor-37dx57l-mm-24v-helical-pinion.html
I like the idea of using a belt or chain to transmit energy, though having a dog with long hair this might become an issue. If you do travel down the road of drilling a hole, I would have a look at how the drive shaft of a boat remains water tight.
Submerging the electronics definitely wont be the greatest idea especially if you grab the 24v motor that I linked above, Flitetest have an amazing video on waterproofing some RC electronics: Flite Test | Waterproofing Electronics - YouTube
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I think the belts/chains would be a safety issue and could end badly. You’d need to integrate the mechanics/electrics and have them sealed well away from the dog.
The tub from Bunnings is a good suggestion.
One consideration is that the animal on the treadmill will be almost neutrally buoyant so it’s a fine line as to how much water the pet is immersed in. Too much water and doggie floats, too little and he’s probably not going to benefit as designed by putting him in the bath in the first place.
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Horses are exercised by swimming in a pool. They are held back by a bungee cord and just naturally swim while going nowhere. I was told by a chap who did this that nine out of ten horses love it while the tenth hates it.
Done at Labrador scale it might be a useful treatment for you canine pal. Can’t think where Arduino would come into it, but.
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Thanks Robert,
You’re actually bang on the money, I was thinking it would be more of a product that could be sold to vets to hire out or at best build a few and hire them via vets who want to refer my product. So funny that we’re on exactly the same page.
Thanks for your input around the lubricants this wasn’t something I’d yet considered but as soon as you said it I though I instantly realised this would be something I could overcome using plumbing and lubricant that I already have from another project. But thank you so much for flagging it.
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A little lateral thinking. There are hydraulic motors, driven by pressure. And pumps. Place all the electronics in a box outside the bath with an electric motor driving a pump. A couple of hoses from the pump to a hydraulic motor on the treadmill. I have no idea if suitable parts exist or what they cost, but as an idea it has the advantage of isolating the electrics from water, and no belts or other unnecessary moving parts. There’s plenty of air driven motors and that may be an alternative. I suspect it would be harder to set a speed with an air motor. Water is basically incompressible so the treadmill speed would be determined by the electric motor speed.
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