Practical Parts LLC Product Release: Worm Gearbox


#1

Practical Parts LLC is excited to release our newest product: The Worm Gearbox.

We recognized a lack of options for high reduction lightweight gearboxes. There were also no easy-to-implement options for non-backdrivable gearboxes. This gearbox is perfect for actuating large arms requiring precise control that will be common in this year’s competition.

Practical Parts LLC was founded by two alumni from team 2169, KING TeC, with the purpose of providing unique products that are easy and cost effective to implement for all levels of FRC teams. While working on KING TeC we had lots of “I wish we could buy this off the shelf” moments. Practical Parts is here to make those ideas a reality.

The Worm Gearbox was one of those ideas. While designing arms to actuate the defense in FIRST Stronghold, we were forced to use expensive and hard to control pneumatic pistons. A much better solution would have been to use a motor and a gearbox to achieve more flexibility and better control. However, window motors were very difficult to design a quality coupling for and couldn’t deliver the force required. A setup using traditional gearboxes would have required lots of reduction and thus too much weight and too much cost. The Practical Parts Worm Gearbox would have allowed us to have a lightweight, cost-efficient, well controlled, and powerful arm that wouldn’t stall and burn up motors because, by nature, the worm gears can only be driven by the motor, not the other way around.

Other industrial worm gearboxes regularly exceed hundreds or even thousands of dollars, we are offering our worm gearbox for only $79.99. First units will be shipping out early this week.

Click here to order


#2

Have you built this and tested it under real loads on the output shaft?

How is the worm retained on the shaft? Is there a thrust bearing between the worm and the gearbox? What about in the other direction–assuming the worm is attached to the shaft securely, is there support within the gearbox to prevent pull-out and/or a thrust bearing to avoid excessive friction between the shaft retention in the gearbox and the gearbox housing?


#3

Using your Stronghold example, we used the Andymark RAWBox to actuate our (3184’s) arm that year. We ended up snapping this going over a defense at week zero.

What kind of loads have you tested this on?

Why the choice of 3/8th hex?

What’s the torque rating?


#4

We are currently developing our test fixtures and testing procedures. We should have hard numbers within a few days. We saw it as more important to release now so teams can consider this as part of their design process. However some of our less scientific tests indicate the nylon gears are much stronger than anticipated.

There is an additional support brace running in front of the worm gear, this is just an older render. Our render guy will have some updated renders made Monday morning. We’ll probably get some actual pictures out too.


#5

Thanks for the data. It is important for teams to consider shock loading such as what was seen when going over defenses in 2016. 2016 shock loading was truly on another level and it caught many teams off guard. We will be publishing max loading data soon (hopefully later today) so teams can design for this. Fortunately, the nature of the 2019 field means there will not be as much shock loading from traversing the field.

We chose 3/8" hex because 1/2" hex would have added a small amount of unnecessary cost and weight. The new 3/8" to 1/2" adapter from Vex allows teams to use existing 1/2" hex hardware if they choose. Any miscalculated implementation that manages to break the 3/8" shaft (especially if teams choose to add their own steel shaft) would likely break something in the Worm Gearbox or the VersaPlanetary first.


#6

… and I thought Swyft released their product line late.

Color me concerned that this will stand up to the stresses of competition. Personally, I’d need to see a significant amount of both bench testing and on-robot testing with well-documented setups and video proof before considering this. And given that you (based on your rookie year) are likely still in college, I’d want some confirmation from some more senior mentors/engineers that all of the testing was done correctly. I’d also need something to guarantee that you can manufacture and ship the parts within a reasonable time and that your business is big enough to qualify as a COTS vendor under the rules.

It’s nothing personal, but seeing a new company announced during the build season with a product that still has yet to be tested doesn’t inspire confidence that the product was designed with the time and care needed to ensure that it can withstand the stresses of a FIRST robot. I’ve designed and approved designs for plenty of things I thought looked good but ended up breaking on the robot. I’d hate to see that happen to a COTS product and have all of the teams using it affected.


#7

Load Testing Update:

Apologies this came later than I had hoped, we have been quite busy with manufacturing and fulfilling orders.

We performed load testing and found it able to hold 17 ft-lbs of static torque load before reaching the elastic limit and then having total failure occur a few seconds afterward at the worm gear (the large black gear). This confirmed our hypothesis that this gearbox is suited for low to medium load applications such as driving intakes or an arm wrist. In fact, we have customers that are planning to use our gearboxes for these exact applications.

A few design tips:

  • We offer custom mounting holes and custom output shafts. Contact us on our website for more details. for example, one of our customers requested their shafts be made less than the width of the gearbox so they could easily push the stock shaft out with their own shaft.

  • Driving intakes wasn’t a huge part of our design requirements, but customers are showing us that this gearbox is an absolutely perfect solution. The geometry of the gearbox allows for easy perpendicular mounting, eliminating frame perimeter concerns. The user-swappable shaft means no coupling is required. The gearbox also provides a high amount of reduction while keeping weight low.

  • The lightweight and low-cost nature of this gearbox mean using 2 to power a single mechanism is quite practical and will get you roughly double the strength as well as the added benefit of having support on both ends of the drive shaft.