Low RPM (Variable) - High Torque Electric Motor

[Sharpie_]

I am looking to build a wavemaker, based on a single constant piston. If you wish to see how effective it can be; simply take a water bottle and begin bobbing it in your tank. A 500mL bottle makes notable waves in my 120G. I don't like the idea of a ballast item bobbing in my tank, so instead I would like to try running a piston.

I was wondering if anyone knows of a variable speed electric motor with relatively high torque? Specifically between 0.5 and 5 RPM, and capable of lifting a piston of water OR displace roughly 500mL. I don't know how to calculate the torque needed to complete my task as the piston will be built around the motor.

 

[A Reef Scene]

Check out Hurst electric moters.

 

[Gandolfe]

I visited the Tampa Bay aquarium and that is one of the ways they make waves in their huge shark tanks, they have 3 big pistons that go up and down creating waves

 

[uncleof6]

http://www.baldor.com/products/servo_motors.asp

http://www.dynamotors.com/

I don't really see any point whatsoever in building a wavemaker for a home aquarium, a waste if you ask me, however this type of motor is fairly easy to come by.

 

[Sharpie_]

http://www.baldor.com/products/servo_motors.asp

http://www.dynamotors.com/

I don't really see any point whatsoever in building a wavemaker for a home aquarium, a waste if you ask me, however this type of motor is fairly easy to come by.

I prefer the undulating look as opposed to the stream an inexpensive powerhead produces. Not only that, but if I can build this the way I plan, I will have no equipment in the aquarium at all. If I had the money for an MP40 I would have one in a heartbeat. I feel like this project can be constructed with materials on hand + parts for less than 100$.

You seem knowledgeable when it comes to motors, do you think you could suggest a specific model? Or certain specs to look for to help my search? I was considering starting testing with a rotisserie motor.

 

[someone19]

If you wanted a proof of concept, you could try to setup a mass counterbalance. That way the motor only needs to create the new position, not exert as much force as blatantly picking it up would. Just a thought.

 

[reefergeorge]

A stepper motor would be nice. They have the same torque at any speed or position.

 

[d3snoopy]

A stepper motor would be nice. They have the same torque at any speed or position.

I tend to agree that you may want to look into a brush less motor rather than a typical servo motor. In a broad generalization, brush less motors hit their highest efficiencies at lower speeds than an equally rated servo motor. They do, however, require a bit more involved control.

You're probably looking at having to use gearing no matter what type of motor you choose, though, to get down to 0.5-5RPM.

If you're interested in more industrial-style motors, give maxon motors, mabuchi motors, and Pittman a look. You will be able to find motors with integrated gearing with them. You can also go down the route of looking into drill motors, since they will probably get you into the right RPM range.

If you're interested in looking at more of the hobby route, I like hobby-lobby. (not to be confused with hobby lobby.)

As far as sizing goes: I'd start by finding what will get you into the right speed range. Considering the gearing that you're going to need to slow a motor down to a reasonable speed, you're probably not going to have to worry a whole lot about torque. If you want to give yourself a sanity check, I'd try some sort of experiment.... get the piston that you want, and move it by hand to create the waves that you want. Try to estimate the speed and amount of force that you had to exert to make it happen, and power = force * speed... just pay attention to your units so you get power in the same units as the motors are specified in.

 

[BeanAnimal]

I am looking to build a wavemaker, based on a single constant piston.

There is a huge thread on this from 5 or so years ago...

We came up with several workable designs. The easiest is a push pull setup with a single pushrod and seal operated from a motor and bell crank.

Imagine an oil field pumpjack (grasshopper)...

You would use a standard 1720 rpm motor that is gear reduced to a few rpm. Easy to find on ebay.

 

[T Diddy]

I was always intrigued by this idea

http://www.youtube.com/watch?v=o5HB9qEGgBo

 

[kcress]

Well.. That was a worthless movie.

 

[T Diddy]

Well.. That was a worthless movie.

sorry you don't approve. maybe it will help the OP with ideas (as it was intended to do)

 

[kcress]

It was just so obviously a marketing vid with no interest in showing the mechanism.

Sharpie; You can easily measure the force required to insert your piston. Use weight to submerge it to a depth you want. If you're using a bottle just add water to it until it's at the depth you want. Then weigh it.

Using the excellent advice above about counter-weighting you can instead pre-weight your piston with something. Water or sand or ?

I'd pre-weight it with half the weight needed to reach your target depth. Weigh your piston from the full depth location then weight it with half-depth weight. The difference should be the force needed to push the piston all the way down.

If you don't possess a scale adequate to make these measurements you can measure the volume of water and convert that to weight since water is water.
Now that you have the vertical force required you can translate it to required motor torque via the arm length from your motor which yeilds ft-lbs, or ft-ozs, or in-lbs, or in-ozs. You want your motor system to always rotate in a full circle if possible because you cannot turn the motor on and off continually.

Grainger sells many DC motors that can be speed controlled with various RPM, and hence, torque ratings. I'd suggest you look for 1.5 times the torque your measurements suggest.

I'd pick something like this:
http://www.grainger.com/Grainger/DAYTON-DC-Gearmotor-2L009?Pid=search

 

[Sharpie_]

Thank you everyone for your input! I'm going to go ahead with the current suggestions and build the piston portion of the design and try to get some numbers.

Once again, THANK YOU!

 

[rwb500]

have you ever seen a tank without any traditional powerheads? Even the waveboxes you can buy that incorporate powerheads produce a lot of laminar flow. The wave effect is not the only thing circulating water. in terms of kicking up detritus and giving fish exercise (sounds dumb but makes me feel better about tangs and similar fish), the wave effect is practically useless.

 

[hebygb]

A Garage door opener is perfect for your application. You may find one for free or cheap on CL. I would love to see a drawing of your implementation... Although I love my Vortech pumps.

 

[BeanAnimal]

Other than the noise