# 12VDC motor specification question *Need Help!*

## Main Question or Discussion Point

Here is some basic information:

Part A requires 23.34lb.ft. (31.644 Nm) of torque @ 3600 RPM to function.

Part B is a slave motor, 12VDC(or BLDC).
This inquiry is specifically directed at Part B:

Is it possible to achieve the target required torque rating using Part B?
I have calculated 1/4 HP motor @450RPM, with an 8:1 G.R. to be 23.3416, which is right on target, but finding this motor has proven to be extremely challenging (custom built motor of this spec is over 10K USD *yikes*), so I wanted to reach out an see if there were any other options I can explore (and afford) to reach my target using this motor setup(i.e.-type, RPM, torque rating, G.R.)

Part A is fixed and cannot be changed, as is the power supply in Part B

Thanks for any help.

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russ_watters
Mentor
Welcome to PF.

I'm getting 16hp for your power requirement there, not 1/4. You might want to check your calc (I think you multiplied the torque instead of dividing it!). And I think the difficulty might be with the power supply: 12V is awfully low for such a horsepower (heck, it's low even for 1/4 hp). Why the 12V limit?

I should clarify:
Part A requires 16hp (23.34lb.ft.) @ 3600 Rpm.

16HP * 5252 / 3600 = 23.34222 lb.ft.

The calculations on Part B were using 1/4HP @ 450 RPM, 8:1 G.R.
Meaning:
.25 * 5252 / 450 = 2.91777lb.ft.
At an 8:1 G.R., that would mean 2.917 * 8 = 23.336lb.ft.
450 RPM * 8 = 3600 RPM final.

Also another question, am I correct on the assumption that torque travels through a set gear ratio?
Ex: 2.917lb.ft. for the above stated 1/4HP motor, at 8:1 gearing, would be the 2.917lb.ft. * 8 on the final drive, producing the required 23.336lb.ft.?

The 12v power source is part of how I have this device prepped to run, and although I may be able to use a 24v, it remains DC. The 12vdc is only used to run Part B, which in turn will link into rotating Part A.

It is Part B that I am having a major issue with finding a usable motor. I would be willing to consider another alternative, so long as the final requirements of Part A are met in entirety and Part B is powered from DC </=24V

Last edited:
russ_watters
Mentor
I should clarify:
Part A requires 16hp (23.34lb.ft.) @ 3600 Rpm.

16HP * 5252 / 3600 = 23.34222 lb.ft.
Ok, agreed.
The calculations on Part B were using 1/4HP @ 450 RPM, 8:1 G.R.
Meaning:
.25 * 5252 / 450 = 2.91777lb.ft.
At an 8:1 G.R., that would mean 2.917 * 8 = 23.336lb.ft.
450 RPM * 8 = 3600 RPM final.
An 8:1 gear ratio will multiply the torque and divide the rpm. You can't turn 1/4 hp into 16 hp with gears.

You should read the wiki on gearing: http://en.wikipedia.org/wiki/Gear
Also another question, am I correct on the assumption that torque travels through a set gear ratio?
Ex: 2.917lb.ft. for the above stated 1/4HP motor, at 8:1 gearing, would be the 2.917lb.ft. * 8 on the final drive, producing the required 23.336lb.ft.?
A 1:8 gear ratio will multiply the torque by 8 but an 8:1 will divide it by 8.
The 12v power source is part of how I have this device prepped to run, and although I may be able to use a 24v, it remains DC. The 12vdc is only used to run Part B, which in turn will link into rotating Part A.

It is Part B that I am having a major issue with finding a usable motor. I would be willing to consider another alternative, so long as the final requirements of Part A are met in entirety and Part B is powered from DC </=24V
Voltage is not difficult to change, so I don't understand why it would be such a hard constraint. You may not have any choice here - what you are trying to do may not be possible.