Alternative for powered raising saw head on LT25

[kelLOGg]

This is the parent thread which in more helpful.
http://www.forestryforum.com/board/index.php/topic,16775.msg240849.html#msg240849

Bob

[AnthonyW]

I wasn't following the reason for the link, until I found the posting on calculating the torque required. Slick, very slick. Will do tomorrow if time permits.

I prefer to not have the motor attached all the time for two reasons. (1) I don't plan on having the power source available (ie., mounted to the mast or head) so I won't have power down which brings us to (2) during hand cranking, I would be reverse driving the motor's gear box, I don't need the extra load when muscling the head up/down nor the extra wear on that gear train.

The sprocket required is the same as the on that already exists, but needs to be changed from idler to drive. The gears I'm adding are to allow the motor to be disconnected from the mast. Power drive will only be available when at the very front of the mill and I'm fine with that. One gear is attached to the same shaft as the replaced sprocket, larger in diameter than the drive gear on the motor. In this arrangement I get a method to disconnect and gear reduction at the same time.

I will see if I can get some pics and sketch my plan.

Thank you all for the input, suggestions, and sources.

[ljohnsaw]

From your description, I take it the crank is on the saw head trolley, not the actual saw frame.  How about a spoke pulley on the gear train or the crank itself and on the motor, a fork-like end on the shaft?  The fork will easily mesh with the spokes when you back into it.  Very little alignment necessary (like a spline).  Just need the center of rotation on both part to be reasonably close.

[Kbeitz]

Again this is why I use wheel chair gear box motors...

 

 

[AnthonyW]

Again this is why I use wheel chair gear box motors...

 

 (Image hidden from quote, click to view.)

I was thinking the disconnect lever was to remove the motor from the gear box. I take it the lever is to "put it in neutral"? I wonder how much back drag there is in the gear box when disconnected from the motor. I will need to look for a 12V version.

[Kbeitz]

You can turn the output shaft with your fingers when disconnected.
Remember that you can use a 24v motor on your unit. But it will only run around 1/2 speed.
But there is 12 volt wheelchair motors out there.
You could also just buy the gearbox off a wheelchair and put a 12v c-face motor on it.

[69bronco]

Anthony, have you figured the torque to raise the 25 yet?

[Kbeitz]

Anthony, have you figured the torque to raise the 25 yet?

The torque depends on your speed....

[69bronco]

So to figure how many in.lbs you will need in a motor, you have to know the speed? You lost me there, but that's not hard to do sometimes!

[Kbeitz]

You lost me....

You need more torque to move the mill head fast. A watch motor could move it if you move it slow enough.
It takes more Hp to make more torque to make more speed.

Wheel chair motors come in all sizes,...

[AnthonyW]

You lost me....

You need more torque to move the mill head fast. A watch motor could move it if you move it slow enough.
It takes more Hp to make more torque to make more speed.

Wheel chair motors come in all sizes,...

Torque is inch-pounds. No dependency on time. Horsepower is torque per time. More horsepower means the torque can be applied for a longer time (think of the power a horse can provide...before it gets tired).

[jmouton]

is that one horse power then



                                                                                                   jim

[AnthonyW]

Anthony, have you figured the torque to raise the 25 yet?

I think some disassembly and clean-up may be in order.

I followed http://www.forestryforum.com/board/index.php/topic,16775.20.html reply #22.

The center to center distance from the drive sprocket to the crank handle is 5.5" and took 2 1/2 gallons of water to move the handle from the 1:00 to the 5:00 position. At 8.34 lbs/gal and 5.5", it required 115 inch-pounds to move the handle. To raise the head 30 inches in 30 seconds (or 1" per second which is about the rate I can crank it) would require a 1/2HP motor when connected in direct drive. Adding a gear box or gear reduction to the system will decrease the HP requirement. Adding a 4:1 gear box to the 1/2HP would provide a 4x safety margin. The next factor is the current draw. Slower motor rotation requires more current. Increasing the gear ratio will allow the motor to run proportionally faster while decreasing the current requirement.

I think it would be most effective to pull the sprockets off the mast and check and clean the bearings.

[AnthonyW]

is that one horse power then



                                                                                                   jim

Nothing to laugh at. That's where the term horsepower came from; the amount of work a horse can do in a given amount of time before it got tired.

[69bronco]

Thanks for clearing that up, thought I was losing it there for awhile!

[ljohnsaw]

Horsepower:
A unit that is used to measure the power of engines and motors. One unit of horsepower is equal to the power needed to lift 550 pounds one foot in one second. This unit has been widely replaced by the watt in scientific usage; one horsepower is equal to 745.7 watts.

And:
This term was coined by James Watt, who invented a new type of steam engine in the eighteenth century. Watt found that the horse could do a certain amount of work per second; when he sold his steam engines, this measurement allowed him to estimate the worth of an engine in terms of the number of horses it would replace. Therefore, a six-horsepower engine was capable of replacing six horses.

However:
1806, established by Watt as the power needed to lift 33,000 pounds one foot in one minute, which is actually about 1.5 times the power of a strong horse.