# Best Gear ratio and motor for belt system

Hello, we want a belt to move two cargo balls up to our flywheel/shooter.

• We want the belt to move a ball up 12 inches per second
• The diameter of the pulley is 1 in
• When the pulley turns 1 revolution, the belt moves π inches
• π inches / sec = 1 rev / sec =
• 12 inches / sec = 12 / π rev / sec ≈ 3.8 rev / sec = 229 rev / min = 229 RPM
Therefore we need the pulley to spin about 229 RPM. What’s the best motor and gearbox ratio to accomplish this. Not sure if a NEO 550 is overpowered.
Thanks!

Neo 550 is a good choice. You can just divide motor speed by desired output speed and get the reduction. In this case, any where from 36 to 48 to 1 will be fine. There shouldn’t be much torque needed so I would err on the fast side and pick 36:1.

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As a rule of thumb in FRC: there is no motor that’s “overpowered” for a solution, only underpowered ones. You can always turn the voltage down on a “too-big” motor.

As for gear ratios, @jhajel is right. Something around like 40:1 would do the trick. Drop the reduction a bit if you think it’s too slow, raise it if it’s getting stuck or the motors are getting too warm.

Protip that isn’t exactly what you asked for: For a NEO 550 or a 775pro, make sure you use the current limiting features offered on the SparkMAX and Talon SRX, those motors can burn up quickly if they draw too much current for too long. A 775pro can hold 40A for a match, a NEO 550 can hold about 20A. More than that and you’re going to start learning how to identify motors by smell.

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Why so slow?

Idk we may try multiple speeds to see what works best

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I would go much faster for the belts. Ideally if your shooter can handle it, you want the feed fast enough for the balls to exit the shooter in under a second, even under .5s

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A Johnson PLG motor is 410rpm. Small light weight and the gearbox is already installed, no need to assemble.

Might be a good application. You can also run two off one controller legally if you are short on motors.

We used one on our adjustable hood shooter last year and on our pizza spinner in 2020.

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This depends on the recovery time of your shooter.

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A 42 watt motor feels quite underpowered for a transfer

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Have you ever used or tested a PLG?

its literally a 42 watt motor that’s enough to say that its quite underpowered

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Underpowered? Sorry, mate, that’s the Denso throttle motor.

42W is plenty for some applications. Whether you have such an application on your robot is another story. (Color wheel could have been a prime 42W job last couple years, for example.)

Part of this competition is learning how to use the resources you have. If you have 20 Falcons on your robot, and you’re constantly browning out, you aren’t using those resources effectively. Figure out what you’re using a Falcon for that you could be using a weaker motor for, put the weaker motor in, and let the limited power help you open up the rest of your robot. Doesn’t have to be a PLG… but it could be.

If someone figures that they can use a 42W motor to move balls around inside their robot effectively, and it works, then they didn’t need more power, and you can’t say that it’s underpowered. (Well, you can. But don’t say that when you’re right in front of their shooter while they’re testing it, see?)

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No offense intended, but this is what I’ve tried to teach my kids to recognize as a ‘used car salesman’ moment. Do you have the math to support that 42 watts will not provide the required torque, speed, and acceleration of the desired application? Because in an engineering context those are the type of answers that are required, even when you feel like you know the answer at a gut level.

It’s always easy to say ‘more power’. Yet elite teams regularly utilize smaller motors, because using the right motor for the job saves weight and battery power. (And I’m not suggesting for a moment that we’re an elite team - my answer to motor questions is often ‘will a falcon fit?’).

As an aside, I’m doing a project at work. It’s been a month long data gathering exercise over several major manufacturing plants. All to compare different types of conveyors for a future plant application. It’s utilized 4 people, large amounts of database time, and all to come down to an answer that we suspected was correct from the start. But it is worth knowing that when a director asks why you did something, you have the proof to validate that you know how to do your job.

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That little motor is used to lift the rear door on big SUV’s when you push a button or wave your foot under the bumper.

You’re 100% right.

What’s a cargo ball weigh? Half a kilogram?

W = dU = mgh = 0.5 kg * 9.81 m/s^2 * 1.0 m = 4.905 joules to lift one about three feet.

dt = W/P = 4.905 J / 42 W = 0.12 seconds.

If you double that time to account for frictional losses and whatnot, you’re at a quarter of a second to lift a cargo ball three feet using a 42 watt motor, which is four times faster than the spec requested (though I agree they should want to change that spec from “one second” to “as fast as our shooter can handle”.)

Every task doesn’t need 400 W thrown at it. We often use BAG motors on intakes and things, because 150 W is often overkill, too.

When choosing a motor for a given task, how much do you want it to be loaded? We’ve tried to shoot for about 10-20% of stall torque.

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This is anti-thetical to the engineering process we’re trying to teach the kids in our program.

Over-certainty without data is a dangerous combination to be throwing at problems. In my particular profession (computer engineer by trade) I spend a lot of time either proving or dis-proving the bro science that spills around our industry in the form of quips or soundbites.

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It is also important to note that since the PLG is a gear motor that 45w and 4.1 N/M of torque is the true output, after the frictional losses of the included transmission.

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Yeah, but there’s belts 'n stuff to move, so doubling isn’t unrealistic.

“Without data you’re just another a*****e with an opinion”.

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