Questions tagged [gears]

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44
votes
9answers
8k views

Is it possible for a bicycle chainwheel to have a fractional number of teeth?

Background In the world of bicycle motocross, also known as BMX racing, gearing is a hotly-debated topic. Since the bikes are all single-speed, gear ratio is a fixed number defined as ...
17
votes
3answers
39k views

Effective ways to drive a single shaft with multiple motors?

To head off the "why not use a bigger motor" question, I'm a high school mentor for an FTC (First Tech Challenge) robotics team, with a bit of a soft mechanical / hardware background. They're ...
14
votes
3answers
7k views

How do bike wheels keep turning when the rider stops pedalling?

I am very confused with something regarding bikes... How is it that a bike wheel continues to spin (either from momentum or from going downhill) when the rider is not pedalling, without also spinning ...
13
votes
1answer
1k views

How does a (pulley based) continuous variable transmission (CVT) work?

How does the (pulley based) CVT achieve the following? no requirement for a clutch fuel economy smooth gear transition
12
votes
6answers
6k views

Why does a gear have extra holes?

In a gear you normally have a center hole for the shaft to be put into. Why do some gears have holes surrounding that center hole? Is it for weight reasons? Does it add stability? Is it so you can add ...
11
votes
2answers
2k views

What is the mechanical element that holds a worm gear shaft in place called?

Here is an image of a worm gear. What is english word for mechanical element (two of them will be necessary for a worm gear) in which the worm shaft will "lie" and rotate? Here is one photo of the ...
10
votes
4answers
4k views

How are high gear ratios achieved in a small space?

I have a very basic understanding of how gears work, and while trying to learn more, I've run into a small point of confusion. If a 2:1 gear ratio is achieved by having twice as many teeth on one ...
9
votes
3answers
3k views

Mechanism of gear rotation

Is the smaller gear (pinion) always mounted to the input shaft when meshed with a bigger gear that is mounted on the output shaft? Are there places where the bigger gear drives the smaller gear?
8
votes
1answer
621 views

What does "tol" mean in a gear box?

In this NASA document, it is mentioned on page 221 (239 of the pdf) that a "23 tol gear box" was used. What does that mean? A google search for "23 tol gear box" (with quotes) comes up completely ...
8
votes
5answers
6k views

How can I get a stepper motor to engage with a freely spinning wheel?

I'm working on a project that uses a strong stepper motor to power a wheel that needs to be able to "coast" freely at times. The motor is too stiff when not engaged, and along with my gearing ratio, ...
8
votes
1answer
4k views

What is the benefit of additional planetary gears?

A planetary gear is a gear that rotates not around an axle but around another gear known as a sun gear, or star gear. I have designed prototype systems in the past that used a single planetary gear ...
7
votes
1answer
7k views

Involute gear curve when root diameter falls below base diameter

The answer to a question on involute gear curve calculations shows how the gear tooth curve proceeds as an involute calculation from the base diameter. If the pitch diameter is D = m.N where N is the ...
7
votes
2answers
5k views

How to mount a load-bearing gear shaft through a wooden plate

I don't have experience in mechanical engineering so I came here to ask for help. Here is sketch of one simple construction I want to realize: Here we have 5 cm thick wooden plate, 50 cm long and 35 ...
7
votes
1answer
6k views

Internal teeth involute gear pitch circles

I'm having some trouble figuring out how to design the corresponding internal gear for any particular spur gear. With spur gears, meshing is accomplished by having two gears with the same modulus (MOD)...
7
votes
3answers
1k views

Compound gear system ratio

This might be a stupid question, but I'm new to mechanics, so please bear with me. Suppose I have a compound gearing system defined in the image below (not to scale). The green gear is the driving ...
6
votes
4answers
3k views

What is the use of gears in a device with a fixed gear ratio?

From my understanding, there are two uses of a gearing system: to change the speed of output rotation (trading it with torque), and to change the axis of rotation. Now, in a car, for example, it is ...
6
votes
2answers
3k views

Is there a mechanism that can turn circular motion into alternating circular motion?

I'm trying to power and agitator (alternating circularly back and fourth) with a crank. I've seen a bunch of complicated mechanisms that do this, but I'm looking for the mechanically simplest method.
6
votes
3answers
14k views

Is "pitch diameter" the same as the distance between the centers?

I am designing gears in FreeCad, and printing then on a FlashForge Finder. I want to know if the pitch diameter is the same as the distance between the centers of the two gears. Both gears are ...
6
votes
3answers
1k views

How Much Efficiency is Lost in a Gear Train

I want to get a rough estimate for the transmission efficiency of two different gear trains. One is a one-stage gear train with 11.67:1 ratio (140/12 teeth) and the other is a compound two-stage gear ...
6
votes
1answer
222 views

How would you mechanically model an Earth-Moon like orbit?

I'm hoping to make a small mechanical demo (~10cm tall) that models an orbit that is similar to the Earth-Moon orbit - that is, only one side of the Moon faces Earth. I'm trying to keep it simple, so ...
5
votes
2answers
13k views

How do I calculate the gear ratio to lift a weight at a constant speed?

I have an 80 g·cm motor with a rotational frequency of 15,000 rpm. I want to lift a weight of 2 kg at a speed of 0.5 m/s. How do I calculate the gear ratio required?
5
votes
4answers
4k views

How to simulate car acceleration

I am a high school physics student and I've been trying to simulate the acceleration of a car as it fully accelerates from rest, but I'm finding it's much harder than I thought. Here was my first ...
5
votes
1answer
236 views

How can I tell if a gear is pressed or threaded?

I recently bought my first lathe (A circa 50s PREMO, Australian built with tapered roller bearings) and the spindle has a little bit of wiggle parallel to the axis of the spindle. I decided to pull ...
5
votes
1answer
2k views

Involute Gear Calculation

I've written a program to generate gears and write them to dxf files. I thought all was well until I looked at the mesh of two gears. From everything I've read there should be no backlash when the ...
5
votes
1answer
2k views

Determine the sign of torques for a planetary gear system

I am trying to calculate the power distribution of a planetary gear system, specifically a Wolfrom system like this one: In order to find the output power, I need to find the torque for the rings 5 ...
5
votes
4answers
2k views

Are there solutions for coupling a spline shaft to a round diameter shaft

I only have basic metal fabrication tools and do not own a mill or a lathe, but would like one. I took apart my cheap drill press to study whether or not I can convert it into a milling machine. The ...
5
votes
2answers
997 views

How to mount timing pulleys/belts for small DIY project

I'm building a rotating lamp for a small DIY project to learn about motors and timing belts/pulleys. As I am learning, finding parts that are small enough, fit a stepper motor shaft and reasonable ...
5
votes
1answer
571 views

How to transfer rotational energy into lateral energy only when rotating one way?

Is there a general way to convert rotational energy from a gear or something into lateral motion toward or away from the gear? I could use a piston type construction, but I only want the lateral ...
4
votes
1answer
1k views

Why do tower cranes have gear shifts?

Internal Combustion Engine powered cars need multi-speed gear shifts since their power is highly dependent on speed and engines have narrow usable power/speed bands. Some electric vehicles are also ...
4
votes
2answers
12k views

How to reverse the direction of rotational movement on the same axis?

I want to make a "gearbox" that will transform input rotational movement to an output rotational movement with the same speed but in the different direction (clockwise / counterclockwise) on the same ...
4
votes
2answers
2k views

Designing non-self-locking worm gear

I see that most worm gears are self-locking but I'm looking to make my own non-self-locking POM worm gear. It'll only be of module 1. Does anyone know what needs to be changed in order to make a self-...
4
votes
2answers
2k views

Why do single speed RC cars use a gearbox?

Being a mechanical engineering novice (I stick closer to solid state electronics), when I look inside of any toy-grade RC car, I see a series of different-sized gears between the motor shaft and the ...
4
votes
1answer
226 views

Are typical worms and worm gears self-locking?

Does anyone know if typical/common worms and worm gears self-locking (plastic or metal)? Are the self-locking ones specially designed (with specific angles) in order to be self-locking? By self-...
4
votes
2answers
9k views

Advantages and disadvantages of bevel gears

What are the advantages and disadvantages of bevel gears? This is what I've already found: Advantages: possibility to change operation angle Disadvantages: must be precisely mounted shafts' ...
4
votes
1answer
526 views

How does the optimal-gear indicator work?

Some modern cars, including models by BMW, Ford and Audi, have a system on the panel that tells the driver the next gear to use while driving, for optimal fuel economy. How does the vehicle decide ...
4
votes
1answer
258 views

How do Salad Spinners work?

I am curious as to how pump salad spinners work: not in terms of how they spin and use centripetal forces to get rid of water. I mean in terms of how the pump itself works. How does the 2D motion of ...
4
votes
1answer
423 views

4 Gears in a Circular Pattern - Calculating the Proper Distances for Meshing

I have recently been working on a gearbox for a robot. I have this pattern of 4 gears with each gear connected to its 2 neighbors. It looks like this: You will probably notice something though. ...
4
votes
1answer
7k views

Using a 'D' shaped shaft with a set screw

Suppose a 'D' shaped shaft with a 4 mm diameter like this type is fitted inside a module 1 (plastic) gear with a round hole with the same diameter. If the gear has a set screw, will this still be a ...
4
votes
1answer
663 views

Preload a worm gear?

I'm designing a 5 axis CNC, and preloading my lead screws has never been an issue for me, but for the first time, I find myself needing to preload a worm gear. How is this done, and what's the best ...
4
votes
1answer
586 views

Getting high RPM out of a low RPM motor

I'm trying to use a 1500 RPM-rated electric motor to accelerate a (light, 25kg) shaft up to 50 000 RPM. At these speeds I figure using a belt system or roller chains is out of the question due to wear ...
4
votes
2answers
687 views

comparing backlash of different mechanisms

I have a cylinder with a shaft in its center that I need to rotate at 120 RPM on 180°, for costing reasons, I would like, if possible, to reuse the same DC motor that I already use for another system. ...
4
votes
1answer
2k views

How to calculate if a motor is strong enough

I am building a machine for a project that should slowly tip a screen forward about 95 degrees, hold for a couple of seconds, and then slowly return to vertical. The design I am working on uses two ...
4
votes
0answers
75 views

Worm Drive Clutching Mechanism

Problem Description I have a project where I will need to be able to engage and disengage a worm drive (actually two of them). The worm drives are quite small. The worm gear is 49.2mm in diameter ...
4
votes
0answers
43 views

Efficiency of a planetary gearbox as a function of the lubricants viscosity

So I have a client that is asking about if they should switch from one lubricant to another in a planetary gearbox they have. The main advantage that this new lubricant has is that it has a much ...
3
votes
2answers
97 views

Can a hobby gearbox be used to mechanically amplify small forces for better force sensor resolution?

I am trying to configure a force sensor (a piezoresistive force sensor) in a device to measure small forces (less than 0.5 mN). This is difficult due to noise of the system. One of the ways I have ...
3
votes
1answer
1k views

What mechanism can make a shaft rotate in steps

I want to make a shaft rotate in 21 discrete steps, from a motor that is turning smoothly. I am thinking of some kind of simplified clock escapement type of mechanism. Or non circular gears. I ...
3
votes
1answer
1k views

Transform/change/convert rotation axis

I would like to know what mechanical parts can be used to convert a rotation movement from an axis to another. For example: You have the shaft of a motor rotating vertically, but you need to rotate a ...
3
votes
1answer
89 views

Gear acceleration and maintaining torque

If trying to achieve a 1:4 gear ratio, will a planetary gear system help reduce the loss of torque? Or is it essentially no different than the loss of torque when using a large drive gear to rotate a ...
3
votes
2answers
262 views

Why do we use bevel gears?

I understand bevel gears are used in situations were a 90 degree change is required, but I can't visually understand why. Why can't we just use standard spur gears at 90 degrees, what do we actually ...
3
votes
1answer
509 views

How can I produce two 180-degree intermittent rotations with a Geneva drive?

I would like to convert a continuous rotation into two 180° intermittent rotations. A standard Geneva drive layout can not do this, is there any variation of a Geneva drive that can do this? Above is ...

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