h a l f b a k e r yFlaky rehab
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No. For many, many reasons no. Here are the top 3. |
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1. Rotary hammer mechanisms don't increase total torque,
they just concentrate it in a spike.
2. Those torque spikes will break things.
3. Using a lower gear will achieve the same effect in a
manner less offensive to man, beast and machine. |
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It's a tire axle -- how are you seriously going to break it? You
can't break things unless you're over-tightening something,
like a screw -- and a tire axle is not tightening like a screw
does. |
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Nextly, the torque spikes can at least help lurch forward a
tow-load that is stuck. |
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Well, an axle will be built to handle a certain amount of
torque + a safety factor. A rotary hammer will display no
torque
for most of the rotation then a sudden spike of ~10x the
input torque. So, since you're building a 300bhp V8 rotary
hammer, you're input torque will be ~300lb/ft. In 1st gear
we have a ~5:1 torque multiplier effect of gear ratio,
you'll need a differential/hub capable of handling 15,000
lb/ft (10x) plus the safety factor and probably plus some
more for shock loading. You have to handle peak torque,
not average. |
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There's no way you get away with this without a 10x
overbuilding of the whole transmission after the hammer. |
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What advantage is this over a standard low range
gearbox? |
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This impact hammer torque mechanism would be attached
directly to the axle(s), and not to the transmission. The
impact rate (BPM - Blows Per Minute) would be electronically
controlled, therefore there wouldn't be any need to involve
the transmission or its fragile gearing. |
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//It's a tire axle -- how are you seriously going to break it?// well, speaking for Murphy, and from experience, you'll break it on a steep pitch of a hill about 30 miles from town. In the dark. |
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//help lurch forward a tow-load that is stuck// somebody shouldn't have sent it to me in the first place. |
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So, if a normal gearbox transmission is equally good at delivering different torques at different speeds, the logical conclusion is that we can dispense with the gearbox entirely and have a pure hammer-torque transmission. It should be continuously variable from standing start to full speed at constant engine revs. Could be noisy though. |
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Yeah, because of noise and wear, I would only use this impact
hammer method for towing, rather than normal driving. As for
whether it's continuously variable or not -- this is more the
opposite of CVT, in the sense that it's electronically-pulsed.
You could dial up the pulse rate according to whatever way
you want, since there's no gearing or belts. |
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I for one have always wanted my car's wheels to be
doing a "burnout" no matter how gently I push the
pedal. |
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As per [sninctown], the sudden impact will break the
traction of your tyres, so this will be both loud and wear out
your tyres faster, while getting you nowhere. |
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Maybe the impact hammer method could asymmetrically
hammer in a somewhat more downward direction while
applying its torque-spike effect. That might increase the
traction of the tires, due to the asymmetric downward force
on them, thus reducing the chances for burnouts/slippage. |
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Powertrain engineer here. Presuming this was
somehow coming out of your engine crank, you
would break your accessory drive, your timing drive,
your motor mounts, and probably many ancillary
items hanging on the engine. |
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Your clutch damping springs would absorb some of
the impact load before bouncing off of their stops,
but wouldn't last long, either. |
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If somehow you designed a clutch that would take
this punishment, your transmission would
experience a lot of unpleasant gear chatter shortly
before beeaking gear teeth. |
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[RayfordSteele] That would be your job as a //Powertrain engineer// to sort out those minor niggles. Now lets get back to the sensible business of designing this thing. |
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Afraid that sorting out those minor niggles would be the job
of a physicist, or better-than average magician. |
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The point of the impact in an impact wrench is to apply a
very high torque for a shot time to overcome static
friction. As everyone else pointed out, if you put that in
the driveline, as described, if by some chance you have
the system designed well enough that it doesn't break, it
will simply cause the tires to slip. |
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Now for general on road towing, I don't think there is any
shortcoming in a standard transmission, but sometime you
need additional towing force, with less peak force on the
tires (limited by traction). This might be useful for tasks
such as stump pulling, but most of all for truck tug of war
competitions. You could employ a concept similar to an
impact wrench, but rather than a rotary system, the
hammer action needs to be linear front to back. A first
pass design for this might be to have the (heavily
reinforced) trailer hitch mounted such that it could slide
forward/back slightly, and have it held forward by a stiff
spring. As the truck pulls against a stubborn load, the
spring compresses. When the tires start to slip, a signal is
sent from the traction control system to the "jackhammer
system", that repeated accelerates a large weight
forward until it bounces off a stop rigidly connected to
the moveable trailer hitch. With this, the force on the
majority of the truck and the friction on the tires would
be set by how fast the weight is accelerated forward, but
the peak force on the trailer hitch is based on it being
hammered forward by this weight. |
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I can think of a lot of situations where this wouldn't be
that useful. For example pulling a car out of the ditch
generally requires a force for a long enough period of
time to get the car up the steep incline. Pulling a stump
could be improved, but only if the stump couldn't flex
enough to absorb the individual impacts. The place I can
see this being highly effective would be in a truck tug of
war. As long as you use a strong enough chain (not a
stretchy rope), it will either jerk the opponent backwards
breaking their traction on each impact, or more likely,
since the truck has so much inertia and the acceleration
is so sudden, it will simply rip the trailer hitch from the
opposing truck. While dragging the opponent backwards
is considered the normal mode of winning, I think tearing
their bumper off also counts. :) |
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