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To the left on your keyboard, theres a button called Caps Lock. Press it, and you can type without annoying people. Capital letters are most commonly used when screaming, something that you generally stay away from on a public forum.
But as Ian says, there are tonnes of diffrent windscreen wiper motors. Some might work, but theyre most likely too slow. Some cordless drills would work better.
Even the cheap 24v drills you can get from maplin or argos (and other places) have lots and lots or torque- arguably motor than WW motors.
As someone with no expirience with WW motors :sad: Can I ask what the output shaft usually consists of? Is it a simple keyed axle?
And yes, capitals are annoying, I also find it annoying when people use capitals on ebay or the for sale section of this forum, believe me- IT DOES NOT WORK :)
WWmotors usually have a shaft with a slight cone and then a thread on the end (either M6 or M8).
Sorry about the capitals :)
Note that the weight of the axe head is not particularly important (for power) in a pneumatic axe, as long as you have good ram speed. A lighter axe head also tends to make the robot jump less.
However, on an electric axe, the only way of getting a good level of enery into the axe is by having a very heavy head on the end of a long shaft. The motor is producing energy at a constant rate, so the longer the swing time, the more energy will be in the axe head at the end.
Ah, the master have spoken... :)
We ran a motor similar to a WW motor on 2meat hammers electric axe, and at 24v it provided just the right sort of whacking speed, about 2 hits a second.
We coupled the output shaft to a crank, and con rod to an accelerator copied from dominator. It worked fine in tests, but eventually tore half the teeth off the gearbox. I have tried replacing the gearbox with soemthing a little stronger, but have given up, and am converting it to pneumatics.
John,
However, on an electric axe, the only way of getting a good level of enery into the axe is by having a very heavy head on the end of a long shaft. The motor is producing energy at a constant rate, so the longer the swing time, the more energy will be in the axe head at the end.
The weight of the axe head doesnt have any bearing on the energy in the axe on impact. The problem part of your comment is that the motor is producing energy at a constant rate. The power (rate of energy) the motor is taking from the battery is Volts x Current - voltage is fixed but the current varies hugely. At start, it is very high (motor is stalled), and drops off as the speed of the axe increases.
On my axe weapon webpage (http://homepages.which.net/~paul.hills/AxeWeapons/AxeWeapons.htmlhttp://homepages.which.net/~paul.hil...xeWeapons.html) I have a spreadsheet for performing the physics of an electric axe: http://homepages.which.net/~paul.hills/AxeWeapons/MotorDriven.xlshttp://homepages.which.net/~paul.hil...otorDriven.xls. In this spreadsheet, you can alter the moment of inertia of the axe (which is the rotational mass), and see what energy you get after a certain angle (I chose 180 degrees in which case you may have to extend the table a bit). If you alter the moment of inertia, you find that the energy after a certain angle stays pretty much constant. The slight variation is because this calculation is using an iterative sampling approach rather than the pure maths which is rather hard!
Thats the theory that I worked out anyway. If you have any practical experimental results (and I know you have a lot of experience with these things) that disagree I would be very interested - it would mean my theory has a mistake somewhere!
If I can have an intuitive stab at what Johns saying (to see if Ive got the gist):
With a pneumatic axe, the amount of energy imparted to the weapon before impact is independent of its weight (and presumably depends on the energy of the air expanding in the cylinder), no matter the speed/weight trade-off.
With an electric axe, the more weight is present for a given sweep, the longer the motor will have to impart energy to it - and therefore the more energy the axe will have on impact.
i.e. a pneumatic ram imparts a given amount of energy regardless of how long it takes to expand, whereas an electric motor imparts energy (potentially) proportional to the time its running - with provisos about efficiency, variable gearing, etc.
Did that help, or have I just muddied the waters? (Its one of those things which could make sense, but could easily *not* make sense, too).
--
Fluppet
Youve got it spot on Andrew.
Paul, the energy delivered by an electric axe is pretty much proportional to the weight of the axe head, assuming that you optimise the gearing for a particular axe weight. You need to include a gearing factor in your spreadsheet, which you can adjust to get the maximum energy output. Judging by how flat the speed line is, it would produce much more energy with a gear reduction.
The motor is steadily churning out energy (OK, maybe not at an absolutely constant rate, although with the snail cam on beta we manage to keep the motor pretty close to max power output). The longer you can keep it feeding energy into the axe, the more it will have at the end. The way to make it take longer is to increase the weight of the axe head or increase the length of the arm.
Voltage x Current of course gives you the electrical power input to the motor, not mechanical power output. As the revs rise (and the current decreases), the efficiency rises. Hence it produces over 75% of maximum power within the centre 50% of the rev range. Which is nice for those of us making electric axes, as it means you dont have to get the gearing spot-on.