All,
Thank you to
the Ginger for starting this thread. During this past weekend, we have received emails from three teams concerned about the same issue. I won't list the team names, as they may consider it confidential information.
This post is a review what we are doing. I will post updates in this thread regarding how things are progressing.
Customer Service:
If anyone has cracked hubs for these Rhino Track Drive modules, please send a note to
sales@andymark.com. We will send out* replacement pulley halves. It will help us if you take pictures of the pulley fracture and tell us which pulley it is. Please refer to the pulleys numbered as such in this picture:
In house testing:
We have a test mule here at AndyMark that has been tested many times. Our initial tests (before kickoff) did not show cracking. We drove this mule over the wooden defenses after kickoff and it seemed to do fine. As it drove more last week, seemed to have more resistance to driving the tread. Today, when we drove it, the 120a breaker tripped. We took it apart and found that there were pulley fractures on both sides, on pulleys 1 and 4. Pulleys 2 and 3 did not have fractures. They had a few hairline cracks, but nothing was wrong with pulleys 2 and 3 to affect performance. Here is a picture of our pulleys we took off today:
This picture shows that the front (#1) and back (#4) pulleys were fractured. Since the middle two pulleys fared much better, we think this fracturing is due to the higher forces on the front and back pulleys with regard to belt tension. We are building up the test mule with new pulleys in order to make a test today. We will be testing the chassis with a slightly looser belt tension to see if we can find a belt tension sweet spot between the belt not falling and the pulleys breaking.
Pulley improvements:
The bearing fit is good, in our opinion. It's a light press fit with no taper. The radius at the bottom of the bearing hole is smaller than the radius on the bearing. Since we are able to recreate this failure here, I don't suspect that a customer was inadvertently using thread locking material (which is always a no-no with polycarbonate).
Material: This material is black polycarbonate with no filler. We have tried fiberglass fill years ago with omni wheels, and we learned that while strength is increased with fiberglass, impact resistance is significantly reduced. We could try to make this part out of some sort of Nylon or a co-polymer using Nylon, but that would require an entirely new mold and would take much time to try.
Mold tool improvements: We can take away metal from the mold to add plastic to the pulley. We will look at improving the mold in 3 ways:
- Adding a rib in the pocket between the mounting holes
- Raising the counter-bored level for the screw head so that the top of the head is slightly under the face of the pulley (we believe that we can do this without changing the screw length)
- Increase the radius on the ribs supporting the inner circle bigger
Corrective Action:
There is enough evidence here to justify that we need to improve this mold. Once we get a new part designed, I'll post a pic of it on this thread with the additions highlighted. Since our molder is here in Kokomo and works with us very closely, I am confident that we can make a mold improvement and have parts available within 8-10 days. Thank heavens this part wasn't made overseas.
* - While you may need cracked pulleys sent to you very soon, you may also wish to wait until we get this mold changed and have new, stronger pulleys. Please stay tuned for timing regarding when we can do this.
I am warning our ops and customer service folks that we may be sending out many replacement pulleys soon.
It will be an interesting week. Please stay patient with us as we solve this issue.
Sincerely,
Andy B.