Drawbar Pull: How it Affects your Manual Material Handlers

posted on: Friday March 6, 2015

s4If you’re trying to determine whether it’s safe for your employees to push or pull something, you’re dealing with drawbar pull. The term is more commonly referenced with vehicles like trucks and trains. However, it also applies to how much effort it takes for your employees to move a cart across the production floor.

Put simply, drawbar pull is the amount of horizontal energy in pounds required to get a cart to move forward or backwards. It is not the same as the weight of the cart or object. A number of variables factor into this. Rolling resistance greatly affects drawbar pull.  Floor surface, debris, thresholds, and inefficient wheels are all factors in rolling resistance.

It’s important to know this because the amount of force needed to push or pull an object changes from point A to point B. Initial force is different from sustained force; sustained force can change throughout a terrain; and stopping an object can take more energy than sustained force.

All of these forces determine the amount of strain your employees experience in a workday.  Furthermore, the longer and more frequently your production team has to push something, the more fatigued they become. The forces stay constant, but your team’s physical capabilities decline throughout the day.

There are equations that determine drawbar pull. To calculate the drawbar pull of a truck, for example, you would multiply the torque of the motor in inch pounds by the gear reduction. You would divide that number by the radius of the drive tire (in inches.) Finally, you would subtract rolling resistance from that number.

There is a much easier way for you to figure this out for your own needs. Peter Nelson, owner of Load Mover, Inc. helps his customers find drawbar pull so that he can fit them with the right power tugger. These tugs, or cart pushers, are used to assist in pushing/pulling tasks and improve productivity. He says,
“[Customers] should do a simple “people power” test as follows:  a person with good upper body strength (like a 200-pound production guy) can push about 100 pounds for a short period of time.  If a customer’s cart takes three guys to get the cart moving, then it takes about 300 lbs. of ‘Draw-bar pull.’”

While it isn’t exact, it is quick and useful, especially if you’re using safe pushing guidelines. (You can find Liberty Mutual’s full table of guidelines here.) Nelson says that his Load Mover units can typically offset 100-1000 pounds of drawbar pull, or up to ten people pushing a cart.

Overall, if you’re looking to help your workers push/pull more safely and efficiently, it’s drawbar pull, not weight, that you need to know. If you think a Load Mover might benefit your production team, contact 952-767-1720 or info@loadmoverinc.com. Load Mover Inc. will discuss the advantages of their equipment and determine what will best help your employees.