Hello all, first post here. I am building a composting trommel and could use some advice. The drawing is a rough sketch of where it’s going. I’m considering the motor for this now. I’m uncertain of the rotation speed and amount of torque it will need to run a belt and pulley.
I haven’t settled on a finished length. I have some 700cc rims on the way (listed as RIM WEI 700C 622x16.7 AS23X 36 SL/NMSW SV). I’m waiting until those get here to measure the inside diameter for 1/2 hardware cloth and the width for the fender washers to hold rivets and mesh. Haven’t selected rollers yet either. Base will probably be board, screws, and brackets with wheels on one end to move it around.
I have a circa 2015 dewalt 20vXR weedeater motor and controller/battery assembly I was gonna use but the lowest rpm is around 4000 lol. The control assembly is useful and the motor would be too if I knew enough to put a gear reducer on it. I’m fairly handy so if there’s a good technical solution I love a challenge and tinkering.
Looks unnecessarily long, my commercial one is a bit shorter than 1m (3’). It comes with a 400w motor which is enough. Also you would want the motor above it, so it doesn’t get all the dirt in to the bearings. Would also add a couple of aluminum angles along the length of the drum to lift and dropp the compost, helps breaking upp the lumps.
You are on the right track. Think about where your bigs are going to fall out on the lower end of your rig. I position mine so the bigs fall right back into my active bin once they exit the sifter. Also wise to think about ease of getting unsifted compost into the rig. 700 bike rims are good because you don't have to be very precise when loading with a shovel. The photo above looks like the opening to load material might be a bit small of an opening for my taste.
Generally speaking, the more efficient your process, the more fun you will have and the more often you will fire up the rig.
The motor is really where I’m currently stumped. I could source a motor from an appliance no problem. Im also ok with buying a new pulley motor but I wanted to see what is recommended first from this community before I went straight to that.
That sketch has a nice mad scientist energy with the offset motor and adjustable height, you're clearly thinking through the mechanics
For speed you want the drum turning slow enough that material actually tumbles instead of sticking to the sides, somewhere around 20 to 40 rpm is the sweet spot for most trommels. Torque depends on how much weight you load in there but a half horsepower motor with a big gear reduction gets the job done for a small setup
That weedeater motor at 4000 rpm is a fun puzzle though, if you enjoy tinkering you could chain a couple pulley stages to drop it down but it gets bulky fast. A cheap gearmotor from a treadmill or old washing machine has the reduction built in and they show up free all the time
Since you're already waiting on rims to measure for hardware cloth, I'd mock up the drum first and test how it rolls by hand. That'll tell you more about actual resistance before you commit to a motor
Oh I’m just buying things a peice at a time. I have time to consider everything at each step.
The main purpose is screening a fairly large amount of chip drop that’s been resting in 6inch deep x 3 ft wide strips against my fence line over the last year and it’s time to start taking it up to turn into beds and repurpose the undecomposed chip drop onto my garden area
That’s fun. I think I might look at doing a quick sifter after this using that dewalt motor and reciprocating arm on a radius maybe… dunno, it’s fun having gadgets to build things with.
I think you could keep it a lot simpler. I bought a readymade one on a stand. It has 2 compartments, but I have many big handles that I really easy to turn the thing. Halfway they have a bar which is not allowed to be filled more than the level of the bars. I turn it with ease once or twice a week at the most. No need for a motor because any more rotations would interfere with the process. I get the most beautiful compost out of them. Like black gold. No vermin can get in!
Great i love these builds.
Trommels are great but they also feel complicated compared to a shaker table.
You can make a double belt to reduce the speed on the motor. (Small circle - belt - big circle connected small circle - belt - trommel/rim.)
I have built a few of these, they are not for the faint of heart. I have found that the best motors for tromels are electrically speed controlled. The absolute best salvage motor for this application is from a treadmill.
I used rollerblade wheels for my base rollers, bike rims and 1/2 hw clothe for the drum. And a bike tube for the belt, just find the right size and cut the valve stem off. The stretch helps keep good contact with the drum.
You will definitely want your motor on the top or side with a shield to keep all the dirt off. The absolute crux of the build is going to be getting the power from the motor to the drum, a belt is usually best but make sure where the tension from the belt makes contact with the drum, the drum is supported so it doesn’t deform in shape. Also a major problem i kept having with one of my best tromels was the pulley on the motor filling up with dirt and crud then throwing the belt off, so i added a bracket that i shaped into a scraper that is mounted so it clears any debris out of the pulley, opposite of where the belt makes contact.
All that said if you build a good one it will become an invaluable garden and compost tool. The wife and I can sift 3-4 yards of soil out of our chicken areas and chip compost piles in a day (given they are ready for sifting).
I gave up pretty quickly on this because it was a massive hassle. I later built a table sorter that used a reciprocating saw
https://youtu.be/G1pGPLDPoMA
Now my systems I really wanted to sort worms from castings so you can use cheaper materials but just gives you an idea.
I made a small version of this with a 5gal bucket, your design is a much more useful size lol. For rollers I used straight caster wheels, make sure you have something to keep the drum in place/on track lengthwise. For the gear reduction the easiest way is to run the belt around the whole drum down to the motor pulley, but if you need more reduction the options are more pulleys, a gearbox, or chain reduction. One other problem I ran into was I had the drive pulley off to the side (was going for compact system) and it tended to pull the barrel up and off the rollers.
Good advice. I hadn’t though about restricting the barrel but now that you mention it, roller mechanisms like vacuum cleaners have those bushings on the ends to hold the center element and let the drum spin around the spindle.
I bet encasing the roller against caster wheels on top and bottom under spring tension might work
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u/wriky 1d ago
Looks unnecessarily long, my commercial one is a bit shorter than 1m (3’). It comes with a 400w motor which is enough. Also you would want the motor above it, so it doesn’t get all the dirt in to the bearings. Would also add a couple of aluminum angles along the length of the drum to lift and dropp the compost, helps breaking upp the lumps.