Pump Motor Sizing 1

[jeffc0987]

My company is looking to power a pushrod through the use of an eccentric disc. I have tested two motors and have also been trying to find an equation to somehow relate the amount of motor torque to the amount of force on the pushrod, but there seems to be huge gaps between the theoretical numbers I am getting and actual test numbers.

For now I am simply trying to get a simple statics idea of how the force is transmitted from torque onto the pushrod. From testing I have been able to determine the maximum force (at phi=90 degrees).

For a 1/9 HP, up to 64 RPM, 84lb*in torque motor I found the maximum force was ~160 lb.

For a 3/16 HP, up to 120 RPM, 157 lb*in torque motor the maximum force was ~186 lb.

It doesn't seem to make much sense that a motor with nearly twice the torque hardly puts out any more force on the pushrod than the other motor. I am trying to avoid turning this into a dynamics equation involving angular acceleration, speed, moments of inertia, etc..., but I was wondering if I would really need to to get answers even close to this.

I attached a JPG file with the basic setup of how the cam and pushrod work with dimensions.

Any help would be appreciated.

 

[BigInch]

Do you have any idea of what torque is?

100 lbs * 5 ft radius = 500 ft-lbs torque, but 500 ft-lbs torque / 2.5 ft radius equals 200 lbs

When you can explain that, we'll move on to how the motor's speed enters into this problem.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[desertfox]

hi jeffc0987

The torque of a motor is related to its speed by the formula:-

power = 2*pi* RPM * Torque/60

Now if you transpose the formula you can see that the faster the RPM of the motor for a given power the torque is reduced.
Now the torque delivered by the motor is determined by the external load its driving.

I am used to metric so 1hp= 746watts therefore 1/9hp = 83watt

torque = power * 60/(2*pi*RPM)= 12.367Nm or 9.134lbsft

similiarly the 3/16 hp 120rpm motor has a torque at that speed
of 11.13Nm or 8.21 lbsft

So you can see the more powerful motor actually produces less torque in your case.

Without dimensions of the pushrod and the radius that the pin driving the pushrod acts we can't help further.

desertfox

 

[desertfox]

Hi jeff

Sorry the dimensions are there, they were faint and I couldn't see them at first.
Well your first motor 1/9hp delivers 194lbf running at 64rpm at .563"radius
The second delivers 175lbf at the same radius.

desertfox