43
votes
Why are bulldozers so slow?
I wonder why can't we engineer..
We CAN engineer a vehicle which is both fast, and has a lot of torque. (E.g. a tank, as you mentioned yourself)
The reason why we don't do this for a bulldozer (I.e. &...
- 757
36
votes
How do bike wheels keep turning when the rider stops pedalling?
The soft clicking sound you hear when coasting is the pawl going over the ratchet as in the picture below.
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29
votes
Is it possible for a bicycle chainwheel to have a fractional number of teeth?
Gear ratio
This is a Roller Chain drive system, and as such it's a timed system. The ratio between the two connected pieces depends entirely on the number of teeth on either end.
Even if you ...
- 1,116
26
votes
How do bike wheels keep turning when the rider stops pedalling?
it is called a freewheel.
Inside the sprocket gear, there is a mechanism that lets the chain engage the rear wheel only when it is moving faster than the wheel is turning; else the wheel will turn ...
- 22.1k
26
votes
Why are bulldozers so slow?
From memory, but pretty much realistic: a tank will use e.g. 1000 liters of diesel fuel just to move 100 km and will probably require a track maintenance afterwards. A truck with the same tank on its ...
- 499
23
votes
Accepted
Why does a gear have extra holes?
Different gears have different drivers for having holes.
One way you can categorize gears is by whether they are used primarily for transferring:
motion: transferring angular position and angular ...
- 24.3k
19
votes
Accepted
Is it possible for a bicycle chainwheel to have a fractional number of teeth?
I suspect that the answer to this is that, ultimately the gear ratio comes from the ratio of diameters of the gears rather than the number of teeth, although in most circumstances practicality ...
- 15.2k
17
votes
Accepted
Involute gear curve when root diameter falls below base diameter
In general, each tooth of an involute gear is made up of two curves: the involute curve and the root fillet. The involute curve is essential for gears to operate properly, and allows power to be ...
- 1,317
12
votes
Accepted
Why do tower cranes have gear shifts?
You need very slow speeds to make precise movements of the load. At high speed, the cables will stretch as the load accelerates and decelerates and then oscillate longitudinally, "bouncing" the load ...
- 12.5k
11
votes
Accepted
Is there a mechanism that can turn circular motion into alternating circular motion?
What about a crank-rocker mechanism?
(source: udec.cl)
When I am looking for inspiration for mechanisms, I have a look in the book Mechanisms and mechanical devices, by Neil Sclater.
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10
votes
Accepted
How does a (pulley based) continuous variable transmission (CVT) work?
Review of geared transmissions
In general, the idea of a geared transmission is depended on the gear ratio. The gear ratio $i$ affects many aspects of a gear transmission, and the following equations ...
- 24.3k
9
votes
Accepted
How to fix this gear
Oddly enough, this problem can be fixed using a set of car keys and your wallet. Here are the steps to follow:
1) put the keys in the ignition of your car, start it, and drive to the motorcycle ...
- 14.3k
9
votes
Accepted
How do bike wheels keep turning when the rider stops pedalling?
Basically several ratchets, below animation shows when you are not pedalling. In the other direction the ratchet will engage and provide force.
If you lift a bike and get the wheel spinning or just ...
- 206
8
votes
Accepted
How are high gear ratios achieved in a small space?
One simple way is to do the gearing in a number of stages in a gear train. Such a system uses gears which have two different gear sizes on the same wheel. In the example shown in the image below (...
- 6,386
8
votes
Is it possible for a bicycle chainwheel to have a fractional number of teeth?
A "44.2 tooth" gear still can only push 44 links of chain per revolution, which pushes a 16 tooth cog around 2.75 times. There's no getting around that.
I think that is the question that has everyone'...
- 181
8
votes
Accepted
How to reverse the direction of rotational movement on the same axis?
Option 1 - just reverse direction without affecting the speed: Bevel gears in differential gear setup, with the carrier (the axle on which the intermediate gears are located) fixed to the chassis.
...
- 6,125
8
votes
Accepted
Does a gear retain its mechanical advantage in a 1 2 1 ratio?
if you have them in line like the following picture then NO.
The first and the last gear will have the same speed and the same torque (actually slightly less due to losses).
if you wanted to retain a ...
- 24.3k
8
votes
Why does a gear have extra holes?
In addition to the other answers such as weight reduction and inertia, there are other possibilities:
Often there can be a precision machined hole for timing purposes. A common solution for some / ...
- 15.5k
8
votes
Why are bulldozers so slow?
Because the tracks or tyres and suspension needed for sufficient ground contact when pushing, dozing or grading does not match the suspension etc needed for higher speed situations.
Even the ...
- 15.5k
8
votes
Why are bulldozers so slow?
They need to be heavy for traction, which makes them too heavy for speed.
To have enough friction between ground and tracks, the machine needs to be very heavy. The Caterpillar D9 you mention weighs ...
- 1,943
7
votes
Accepted
What mechanism can make a shaft rotate in steps
Geneva drive
3D Printed Geneva Drive
Anchor Escapement (Clock Mechanism)
3D Printed Anchor Escapement
- 7,904
7
votes
Accepted
Meaning of O-slash in data sheet about gear diameter?
In the lower right corner of the document/drawing, you can see four (or five) lines of text upward: UNIT: mm
Another piece of useful information in the data panel is the scale, shown there as 3:1. ...
- 6,940
7
votes
Why does a gear have extra holes?
It could be for combination of reasons.
lubrication: the holes will both pump and let the lubricant pass through.
Reduced angular momentum reduces backlash and adds to gearbox responsiveness.
...
- 22.1k
6
votes
Accepted
Transform/change/convert rotation axis
The go-to solution is bevel gears. They are used when the shafts would intersect and allow the same ratios as normal gears.
You can also make one of the gears a crown gear so the other gear can be a ...
- 5,751
6
votes
Accepted
What is the relationship between drive shaft diameter and torque output?
No. Your basic problem is that "torque is proportional to radius" is wrong. Torque is the expression of normalized rotational force independent of radius.
For example if a motor can deliver 10 Nm ...
- 11.4k
6
votes
Accepted
How can I tell if a gear is pressed or threaded?
I decided that because of the lack of threads, it was more likely to be pressed on. So I whipped up a little shopmade gear puller, gave a little tug, and off it came. As it turns out, the gear and the ...
- 231
6
votes
Is "pitch diameter" the same as the distance between the centers?
Pitch diameter is the diameter of the pitch circle described by the mid point of the length of the teeth around the gear, as shown in this diagram:
The pitch circle defines the point where the teeth ...
- 236
6
votes
Accepted
How Much Efficiency is Lost in a Gear Train
Generally gear trains with lower ratios are more efficient due to reduced amount of sliding action between the gear teeth in mesh, so the compound gear train would probably be a better solution. That ...
- 2,347
6
votes
Why does a gear have extra holes?
Also someone may have to pick the machine up and carry it.
Reducing weight is not just related to the intrinsic function of the machine, its shafts and so on.
6
votes
Why are hydraulic systems widely used to multiply force ? won't a couple of gears do the job?
Power density. Modern hydraulic systems are way better compared to ropes and pulleys, gears, electromagnetic systems or levers.
Freedom of geometry. Put a cylinder somewhere, get a rubber hose to it, ...
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