what type of motor do I need???

Hello...new to the forum and have little knowledge on the subject of electric motors. I am working on a project where we have a 12v wiper motor mounted to a verticle stand. The motor is connected to a horizontal bar with a rod which then is going to move the horizontal bar up and down like a seesaw or oil rig pump. When we have objects on the end of the rod that are identical weights this system works great. However, we would also like to be able to have objects on opposite ends of the horizontal bar that are of different weights. With our current setup, with a 4-pound object on one end and a 5-pound object on the other, as the heavier end goes down the weight is causing that end to fall faster. Is there a better type of motor that will control the fall with the torque and durability of a wiper motor? Also, for what we are doing we are trying to build this at a reasonable price. Looking for a motor less than $50 if at all possible.
Thanks in advance,

All motors will have a characteristic and will run at different speeds depending on the load -
You need to look at some form of speed feedback to try and control it , reducing/increasing the power input

If you have all that stuff look also at worm drive gearing ,disability scooter motors

Post a drawing of your mechanical setup.

Post a drawing of what circuit you are using to control the motor.

Wiper motors are worm drive arrangement and normally cannot be "back driven".
There are exceptions with worm drives but not in this instance.

I would suspect you will need to adjust your mechanical setup however this is just speculation at this stage as, without any drawing, we have no idea really.

A see-saw has onone connection point
You might need to have a pair of shafts that move the platform

A pencil sketch of what you have would clarify things greatly.

Thank you for the info...I will try to get a drawing put together in the next day or 2.