We are excited to have Molly Dugan, a high school student and president of team 1218, for a short time working at Vulcan Spring to complete her senior project. As sponsors of the FIRST Robotics, we are thrilled to have the chance to work with her and asked her to give us her unique perspective on the FIRST Robotics Competition...
Vulcan Spring has just introduced a line of stock constant torque springs. We call this our Contorque® spring. In this blog I will give some details on how to use these springs in your design. Contorque® springs have been discussed in previous blogs, so this blog will focus on the installation and use of the spring once it has been received.
A constant torque spring is a specially stressed constant force spring traveling between two spools. The spring is stored on a storage spool and reverse wound onto an output spool. When released, torque is obtained from the output spool as the spring returns to its natural curvature on the storage spool.
When a project calls for the use of a Power Spring, or a Pre-Stressed Power Spring, the design discussion should address initial winding on the arbor. This initial winding is often referred to as pre-winding the spring.
When designing a Constant Force Spring one must begin by taking a hard look at life cycle requirements. This decision will have an affect on every other decision made and ultimately could lead the design down the wrong path. If done correctly, the design can fall into place and allow for a successful project. First, let’s discuss the definition of life cycles as it applies to the Constant Force Spring.
Vulcan Spring has produced flat steel constant force springs since 1967. Vulcan has also produced power springs, twin springs and constant torque springs, all made from the same flat steel. Vulcan is now able to produce two new products: Spiral Torsion Springs and Wire Forms.
Power Springs are formed by winding strip material on an arbor and into a case or retaining ring. Power springs store and release torque through a central arbor or through the case that it is retained in. Pre-stressed power springs (Conpower®) undergoe additional processing to yield a slightly flatter torque curve and increase the available turns.
One of the most common questions about Constant Force Springs concerns the mounting of the spring on a spool. For starters, the spring doesn’t have to be mounted on a spool; it can be placed in a cavity or on an undersized bushing or pin. There are differences in the performance of each design so let’s take a look at the advantages and disadvantages.
A common practice for mounting Constant Force Springs is to utilize two or more springs to gain more force in a small space. This might be required if the diameter or width of a single spring exceeds the allotted space but there is room to add multiple smaller springs. A much smaller spring design may be used when engaging multiple springs. The total force is the sum of the individual spring forces. When combining springs it is recommended that the same spring is utilized for multiple mounting. It is more economical and the design will be much more simplified using this method as compared to using two or more totally different springs to achieve a load. Since the force is the sum of the springs, the total required force should be divided equally between the number of springs used. We will discuss three different mounting methods used with multiple springs.
A frequently asked question concerns the life cycle rating of a Variable Force “V” Spring. In this blog we will focus on this discussion and how the life cycles are analyzed. Let’s first give a brief description of what a variable force spring is and what it looks like.