- #36
blixel
- 52
- 1
there is a Lowe's by where I live so I came by to look at their springs so I would know what values they are using. Their springs are listed just by their safe working load in pounds. Is that the same as lbs/in?
Dr.D said:I see that in your spread sheet, you show the mass in pounds. This simply will not work right.
If you use feet for length,
then
velocity is in ft/s
acceleration is in ft/s^2
weight is in lb
mass is in slugs = lb-s^2/ft
energy/work is in ft-lb
g=32.174 ft/s^2
The key is be consistent.
Dr.D said:A block with a weight of 1 lb has a mass of M = W/g = 1/32.174 = 0.031081 slugs.
If the item weight is W = 0.128906 lb, the mass is M = W/g = 0.128906/32.174 = 4.006527*10^(-3) slug
Now, look at your units on the KE:
KE [=] M*(L/T)^2 [=] (M*L/T^2)*(L) [=] lb-ft
where
[=] means "is dimensionally equal to"
Without checking your final arithmetic, yes, the last result above, KE=0.3084 ft-lb looks correct. (note that the order of the units makes no difference at all, so that ft-lb is equivalent to lb-ft)
Dr.D said:I was thinking earlier, however, that you may have used the wrong mass value. You based your mass on the weight of the projectile only, but it should include the "chair" and (1/3) the total weight of the spring. This will modify your calcs above by a little bit, but not too much. The spring weight is, of course, initially unknown. You can start with an estimate, and iterate the calculation with closer and closer values as you learn more.
JBA said:Apparently now US spring manufacturers now allow both US and SI units to be used, below is an online catalog for Lee Springs, who I have used for years for off-the-shelf spring purchases. Just click on the style of spring you want and you will see how to do a selection using either US or SI units.
http://www.leespring.com/
As a retired american engineer who is required to use SI for many problems on this forum, SI is just as frustrating for me as US is for you.
JBA said:Honestly, it is not very intuitive for me as well. In the past I have been able to simply leaf through a copy of the catalog to search for a close match to my requirements but this online catlog makes that approach totally impractical; so, below are is the input I used and the result based upon my #23 post solution for the 45° case. You bring up the extension search app by clicking on the picture of the extension spring in the list of spring types on the left side of the page.
View attachment 114667 View attachment 114668
JBA said:The minimum torque required will be your design spring load at it initial installed deflection x the radius of the motor shaft gear and the maximum torque required is the spring load at full design deflection times the motor gear radius.
ALERT: WHAT YOU HAVE HAVE SELECTED IS A CRAFTSMAN 11543 HAMMER DRILL. ARE YOU SURE YOU WANT HAT TYPE OF DRIVE? UNLESS YOU ARE VERY FAMILIAR WITH AND HAVE USED THIS TYPE OF DRILL, I WOULD NOT THINK SO; NOR, WOULD I RECOMMEND THAT TYPE OF DRILL FOR YOUR APPLICATION.
JBA said:Apart from the function issue of the hammer action of this type of drill, I would expect that its torque far exceeds your requirements i.e. at its rated torque of 420 in. lb., if you put a 1 inch diameter gear or pulley on its shaft, it will be able to pull a maximum of 420 x .5 = 210 lbs of force which I am sure far exceeds the maximum spring load of your device.
At the same time, it does have an adjustable speed and you can get a standard variable speed hand drill with that function; but, I would think that any of those will also far exceed your max load requirement.
So if I understand this whole thing correctly, the motor I got, plus a https://www.amazon.com/gp/product/B00UMK4NKG/?tag=pfamazon01-20 would allow me to control the speed of the motor?JBA said:An inexpensive standard adjustable speed battery powered hand drill's speed can be adjusted all the way from 1 rpm to it maximum rated speed; and, if you are using the above type of drive then having a excess of torque available is not an issue.
Look for that type of drill and you will find one much less expensive than the one you specified above.
Below is an example of the type of drill I am describing.
http://www.homedepot.com/p/BLACK-DE...PIPHorizontal1_rr-_-205152814-_-202891148-_-N
JBA said:As an adendum on the torque requirement issue, the best place to begin addressing this is to establish the diameter of the sprocket wheel you want to use for you chain drive and multiply that times your maximum spring load and work backwards from that.
blixel said:So if I understand this whole thing correctly, the motor I got, plus a https://www.amazon.com/gp/product/B00UMK4NKG/?tag=pfamazon01-20 would allow me to control the speed of the motor?
JBA said:I wasn't under the impression that you already had a motor, I thought you were considering getting the drill you referenced.
JBA said:I missed the "I got" part of that post statement.
What you keep describing as a motor, because of your application is in reality for the outside world known generally as a "Hammer Drill" and you should use that name for it in your posts so that other do not confuse it with simple electric motors.
In that respect, the controller you are looking at is not suitable to be used with a battery operated hand drill or hammer drill. That controller is meant to be used with standard DC electric "motors".
At the same time , what you are overlooking in the spec sheet for your purchased hammer drill is that it is a variable speed unit all within itself. If you will look at the speed listing on that spec sheet you will see:
View attachment 115102
Never the less do you really know how a "Hammer Drill" works? They specifically designed for drilling into hard materials using carbide tipped special drills for that sole purpose like concrete so as soon as they come under torque they start a hammering action along with their rotation, like someone hammering the drill into the hard material with a hammer. They do not deliver the smooth rotation that you need for your mechanism.