Have you guys got any suggestions on how best to motorise this soil sifter? Picture at
I left the large flat area (size just under 50x40 cm) so that a drive could be added but I am not sure what motor and mechanism would be best. Any recommendations?
Easy. attach a motor to the side fo the sieve, put an offcentre weight on the shaft. Vibration will do the job. You might need to add some rubber to allow the sieve to move both ways a bit.
NT
You mean to get it to jiggle up and down? Unexpected idea! I had in mind getting it to shift sideways - hence the runners. And the grille's bars are "rough" in that direction. The idea is to use them to help break up clods of soil.
Incidentally, the sieve is sized to allow other, normal garden sieves with finer meshes to be inserted, so it doesn't need to use the rough mesh in the photo!
jiggle it sideways. So mount the motor with shaft pointing up or down. (I expect any direction would work.)
NT
I saw one a while back powered by an electric drill set at screwdriver speed. The drill had a crank with a shaft to the sieve a bit like the pushrods on a steam loco.
Mike
I'd certainly be more inclined to go down the geared motor plus crank route than the high speed eccentric.
On my clay soil, it wouldn't work. I feel it is too fragile for regular use. Sorry to be negative, but I'd go for a washing system with water. Similar to gold mining operations.
With clay soil you need an initial stage to squash all the lumps and break them into a size that will fit through a suitable size mesh, otherwise you'll throw away 90% of the soil along with the stones that you want to remove :-)
If you are going to wash the soil to leave the stones behind, you need a
*lot* of water and a *lot* of space where the water-and-soil can drain away and dry, and then you need to break up the "mud flat" once it's dried.I have "fond" memories of digging my girlfriend's garden. The soil was nice and sandy, but there were lots and lots of layers of sandstone which had to be removed. Big ones were easy, once you'd prised them out of the ground, but there were lots of small 2cm x 2 cm stones. And my girlfriend though it was "stupid", "laughable" etc to use any form of sifting (eg through a piece of chicken wire in a frame), so I had to pick each and every one out by hand :-(
Agreed. I could use a pushrod to drive the sled back and forth. In the one you saw was the electric drill providing /direct/ drive to the pushrod?
Based on manual sieving the time to send the sled a full cycle (out and back) of roughly 1 second would be about right. So perhaps some gearing to reduce the motor speed (and increase its power) might be better. Not sure how best to do that, though.
The soil here is also clay-based. And I know it's hard to work with. When wet it clumps. When dry it can set hard. I have even had to take a pickaxe to some of it where a fork could not be driven in!
However, I can be sure that there won't be a problem because the soil can be sieved manually.
I might add diagonal bracing to the sifter to make it stronger but thought I would see how it performed with motor drive first and only add bracing as needed.
On that I might be tempted to make a steel 'A' shaped horizontal frame that goes either side of the sled then joins in the middle on the flat deck, ideally with a guide going though a bearing at that point. Then it would be quite easy (if there was enough room for the required travel) to couple a suitable power / rpm motor with a offset pin and a con-rod to the end of the A frame.
I'm not sure it would need full travel of the track and finding the sweet spot of travel and speed might be key (and could vary depending on what was going on).
Cheers, T i m
Yes, the resonant frequency (sweet spot) will almost certainly vary according to the mass of soil in the sieve, so you want the motor to have a variable speed. I'd opt for a mechanism with a variable motor speed, and start with a mechanism that has a very small amount of travel in case the travel increases a lot at resonance: make the mechanism very strong to withstand the forces of a few kg of soil vibrating backwards and forwards.
I wonder if it could be tested (at least) using an old / cheap-new reciprocating saw? Whilst you may not be able to change the stroke length (it would be far less than the 200mm or so it looks to be available on the frame) it should be reasonably appropriate and they are often variable speed and assuming the blade travels linearly, could be directly coupled to the sled (via a suitable A frame / reinforced bar etc).
Once this sifter is mechanised I wonder if it would need some diagonal / longitudinal support between at least two legs at one end and the main 'chassis' to stop it 'racking' from inertia (something it wouldn't do if manually actuated of course)?
Cheers, T i m
I bet if it was heavily laden with soil and you started moving the sieve by hand at its resonant frequency it would rock pretty violently. Maybe splayed-out (rather than vertical) legs and a heavy weight low down on the chassis would be necessary to reduce this.
What do you think of a mechanism like this:
The surprising thing there is that the drill is running slowly enough that the drive is coupled directly. I would have thought that some gearing would be more appropriate.
Say a reasonable rate for the sled would be 1 or 2 cycles per second. That would need the wheel to turn at between 60 and 120 RPM. A drill would, I guess, probably be happier at four or five times that so would need to be geared down.
Good guess at the size. There's a max of 170mm of movement.
The oscillation rate of a reciprocating saw is higher than I had in mind. That said, do you think such a sifter would be better with a short travel and high oscillation rate?
Probably. I thought I would try it out before deciding whether to add diagonal bracing. Such bracing would be easy to put on later.
...
Oops, sorry, max travel is just over 225mm. You were even closer!
There's definitely no high-speed whistle from a drill running at normal speed and using reduction gearing. I wonder if the drill is only going at that speed because it's working very hard, even though it "wants" to go much faster. Lack of back-EMF from a slow rotor may not do the drill much good and may draw much higher current than normal. I can't hear any noise over the constant humming/droning which could be the noise of the digger.
Attach the tray to a traic'd down reciprocating power saw?
The great majority of that movement will simply be wasted. There's a reason that's not how it's usually done.
NT
ISTR it had about a 15cm disk mounted directly in the chuck with a conrod bolted about 25mm in from the edge. That would give about 25cm throw. With the drill running a screw-driving speed it wasn't that fast.
Mike
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