Cheap / cost-effective bi-directional motion mechanisms

This is my first post here. Hi everyone!

I’m making my first foray into automation since (partially) building a crappy robot from instructions found in a Boys’ Life magazine as a kid.

My project involves constructing a set of mechanisms to push small, relatively light objects off a conveyor belt moving at moderate speed. To maximize the number of diversion points on a given length of conveyor, I’d prefer to use bidirectional mechanisms capable of returning fast enough to push an object to the same diversion point twice in a row when required.

Fancy example:

I’d like this to operate at similar speed to the example.

The objects will weigh under 5 pounds, and the belt width/assumed stroke length for my prototype is 8", but I’ll ultimately want to use this on a wider belt, up to 18" or so.

I know that the options include solenoids, servos, and pneumatics (perhaps others I’m missing). My impression is that the upfront cost of the latter two is higher, but that they’ll consume significantly less power to operate.

I know that bidirectional motion would require at least two solenoids if I go that route, and it’s also been suggested to me that a single linear actuator might not have sufficient force on the return stroke (I know it would certainly be less, but most of the linear actuators I see online appear to be designed to push much heavier loads, as in hundreds of pounds, so I’m thinking I might get away with a single actuator for each pair of diversion points).

Anyway, I’m looking for the most cost-effective way to build this, both in terms of up-front cost and in cost of ownership.

I’m fortunate to have a friend who’s an experienced maker and able to assist with many aspects of constructing this thing in terms of the electronics, but he’s not as familiar with the mechanical aspects.

Apologies for any major omissions/mistakes/assumptions contained here, and thanks in advance for any and all advice!

Hey Kirbykrackle!

You could probably do it with a belt, a motor and some limit switches. I’ve made a quick sketch:

Let me know what you think of it

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Thanks! I’ll show that to my friend who has a better idea what he’s doing. He was also suggesting that a belt mechanism might be the way to go.

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Alright! Make sure to update me, I’m curious about your project!

Lock the rack in place and attach the push thingy to the sliding servo so you can have PWM control:

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Another idea is to put a bunch of servos along the roof that simply rotate-out a diagonal guide as required - the conveyor will motion the objects into the correct box. The guides move out of the way against a wall when not selected. You could even do this without a roof - just bolt the servos to the side of the conveyor system.

Thanks. I watched the demo video for this product, and it wasn’t clear if it was capable of higher speeds than what was shown (referring to when it was actually turned on, not when the motion was displayed manually). I’d like to get as close as possible to the speed in the example video. The price is also similar to that of the linear actuators at which I’d been looking, so if those are capable of the higher speeds (and I can get by with a single unit for each divert pair), those would seem to be stronger candidates. Power consumption is also a consideration, though, which is why I’v been looking beyond solenoids.

This second idea is pretty interesting. Of all the sorting systems I’ve looked at, only the “sweeper” type has mounted the divert mechanism above the conveyer rather than at the sides (or integrated into the “floor” in various ways). If it’s fast enough and can be done on the cheap, this could also bee a strong candidate.