Winch re-design questions/sanity check.
Winch re-design questions/sanity check.
(OP)
I'm currently in the process of redesigning a winch system and wanted to go over some numbers and make sure I'm thinking about it correctly. The current design has been in place for about 10 years but probably wasn't used but once or twice a month for about 10 to 15 minutes each time. I've attached a picture of the current setup with gear ratios etc.
Here is the process I am following through the system:
1. 3/4 hp motor at 1725 rpm produces 27in-lb (36in-lb x .75)
2. 27in-lb x 5 x .9 (Assuming 10% friction loss) = 121.5in-lb
entering the gear box. (This is a 5:1 belt and pulley)
3. 121.5in-lb x 40 x .75 (25% friction loss for gear box) = 3,645in-lbs exiting gear box
4. 3,645in-lbs x 2.3 x .9 (Assume 10% loss) = 7545 in-lbs total torque for system (the last stage is a chain drive)
5. Compare 2000lbs x 2.75 (winch drum radius) = 5,500 to the 7,545 theoretical max and we should be good correct?
That being said here are some problems I am seeing with this design. The gearbox involved is a Boston Gear 721 40:1 with the following specs output torque 737in-lbs and input of 0.68hp. So am I correct in saying that the teeth on the gears should never feel more than 737in-lbs of torque? If so this system is seeing 3,645in-lbs which is 5 times larger than the manufacturers spec! It looks like the mistake was made by putting a pulley in front of the gearbox thus increasing the input torque beyond the rated spec. I'm throwing this all out there to do a bit of a sanity check and make sure my head is in the right place on this. Thanks in advance for any comments/feedback on this situation.
Here is the process I am following through the system:
1. 3/4 hp motor at 1725 rpm produces 27in-lb (36in-lb x .75)
2. 27in-lb x 5 x .9 (Assuming 10% friction loss) = 121.5in-lb
entering the gear box. (This is a 5:1 belt and pulley)
3. 121.5in-lb x 40 x .75 (25% friction loss for gear box) = 3,645in-lbs exiting gear box
4. 3,645in-lbs x 2.3 x .9 (Assume 10% loss) = 7545 in-lbs total torque for system (the last stage is a chain drive)
5. Compare 2000lbs x 2.75 (winch drum radius) = 5,500 to the 7,545 theoretical max and we should be good correct?
That being said here are some problems I am seeing with this design. The gearbox involved is a Boston Gear 721 40:1 with the following specs output torque 737in-lbs and input of 0.68hp. So am I correct in saying that the teeth on the gears should never feel more than 737in-lbs of torque? If so this system is seeing 3,645in-lbs which is 5 times larger than the manufacturers spec! It looks like the mistake was made by putting a pulley in front of the gearbox thus increasing the input torque beyond the rated spec. I'm throwing this all out there to do a bit of a sanity check and make sure my head is in the right place on this. Thanks in advance for any comments/feedback on this situation.





RE: Winch re-design questions/sanity check.
RE: Winch re-design questions/sanity check.
RE: Winch re-design questions/sanity check.
I have not sized a BG unit before, but perhaps the HP limit is a thermal rating. It would need to go well above 2-pole motor speed to have .68 hp and 737 in-lb output in the same application. Just a conjecture on that though.
David
RE: Winch re-design questions/sanity check.
Plus your motor can develop even higher torque than the full-load torque, at the pull-out load it might be closer to 200% of full-load. The reducers usually allow for brief excursions with higher torques.
Do you need all of the torque that was being developed, or was the motor-to-reducer-input reduction done in order to slow down the winch? If it was to slow down the winch, you could possibly run on a VFD at 1/5 of the synchronous hertz.