Hello, I want to preface this post by saying that I want to give as much detail as possible on an issue that we’re still figuring out. If at any point, more detail is needed or clarification would be helpful, don’t hesitate to just ask. I am also not trying to throw Vex under the bus, we’re just curious if others have had similar issues.
CONTEXT OF ORDER: In early December of 2022, Purdue ACM SIGbots ordered 14 motors (in 2 purchases but on the same day). We had planned to do this earlier but were waiting for motors to come back into stock and for the rev10 issues to be resolved. By this time, we knew Vex was aware of the issues. Our package was delivered on January 5th, and we picked it up on January 9th from the Purdue mailroom. This was the beginning of our spring semester, and we were preparing for hosting our first VRC competition as well as CADing robot redesigns for all 3 teams, so the manufacturing dates were checked to see if they could be from the rev10 batch and everything was set aside until later.
ORIGINAL PROBLEM IDENTIFICATION: The motors were left unopened for 2 weeks until a bot was ready to use them. Knowing they were new motors, they were not tested for power draw(as we normally would) before they were placed in a drivetrain. Without giving information for robot leaks, the drive train consisted of low profile mounts, custom motor cartridges, custom gears (relatively standard for SIGBots and teams in VexU), and 6 motors. All 3D printed geometry was consistent with previously used bots, but immediately there were inconsistencies. We checked for build issues and we found none that would lead to these problems. A member grabbed one of the 8 remaining motors and tested its power pull which was 0.8W. For context, we don’t run motors that pull over 0.3W, especially not on a drivetrain.
On January 20th, when DROW posted the rev10 checker, we immediately checked, and they all passed the rev10 test.
TESTING SINCE: Today, we spent a few hours going through the 8 motors that aren’t attached to robots to try to figure out what is wrong. We’re limiting the motors that we work on as opening them voids them from competition use.
- Of the 8 motors, none pulled power below 0.7W, the highest was 1.2W, with an average of roughly 0.8-9W.
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- This was all done through the brain with the motors as they came out of the bag (with carts and caps on)(multiple brains and ports were tested with some to make sure it was not an issue there).
- We then took out the carts from all 8, and tested again where the change was greater than normal, but still WAY above average for our current set of motors in the club. Testing with older carts drew less power but was still above average than with other motors.
- We disassembled 4 of them (would like to do more but they’re now not competition legal) to look for issues and below were the key things we found. These are not in the order of when they were discovered.
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There is less grease than we normally see in the upper section of the motors. The grease is also poorly placed with most of it being on the motor casing, not the gears itself. The grease appears to be thicker than what we see as normal but all of our other motors are 2019 or earlier.
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The center white gear has a center hole that is tighter than older motors. for testing we had a hunch and tested by swapping between new and old gears on both new and old shafts
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The bushing that is on the inside of the middle casing at the drive gear is much tighter on these motors. It is to the point where it will freely fall out of the motor casing, but stay stuck to the drive shaft. This is the opposite of our older motors. (new on left, very tight is furthest left, and old is on the right)
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There are some thin overhangs on the center gear. This was first noticed on the center hole for the axle on 2, but also appeared on one of the tooth faces. (3 issues on 3 different motors)
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The quieter the rattle when shaking a motor, the higher the current draw is. We believe this is related to the torque of the casing screws as we noticed they were inconsistent (by hand) and tighter than we expected.
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The casing for the motors is MUCH tighter than our other motors when it is being slid on and off. This could be wear related, but for the older 4mmotors we compared against, we didn’t think they had been disassembled previously.
the following relate to the motor cartridges
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Immediately, the new cartridges had more friction than normal. I will try to attach videos later but at the current moment, I cannot. It felt like the carts were gummed up with grease, but it was to the extent that with 9 carts in a blind test, every person could find the new one. We did a test connecting an old cart and a new cart against each other, and with 8 new and 8 old all tested against each other, the new one was always so bad that it wouldn’t rotate (test setup shown below). Very plausibly could blame wear but the extent is way above that of wear.
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The grease on the inside was very sticky. Seeing the photo below, a gear could be placed in with no support, and shaken up and down without falling. (gear at the bottom shown below)
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The diameter of the posts for internal gears is inconsistent. With a video to come, a gear could spin freely on one, but struggle on another.
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Similarly, the gear center holes were all tighter than on newer carts. Our cart ages are unknown in the club, but with a random handful, the new gears acted differently than old ones on all posts. (so many tests were done that it is hard to summarize, and the scientific method fell through so this is just what we consistently found)
Finally, this issue was across both carts and motors, but there were other small defects that didn’t affect performance but just showed overall small issues in the manufacturing process. Mostly, it was lettering issues and small gaps. For example, a photo of one of the cart caps having a double-stamped 3.
We spent time cleaning the grease, regreasing, and doing some other things to two of the motors in an attempt to make them usable (again, not for competition) and without a cart we were able to get the power draw to around 0.4W which is much better than before, but still not what we would use on any part of our robot ideally.
We have discussed this with some people on VTOW in the VexU channel with people saying they have noticed similar things. As people do further testing we will update this post. Corey from GULLS said they noticed similar issues in their rev10 motors. Maxx from GHOST has 22325AGs and saw a similar 0.5W draw or higher across the board but will test more soon.
Final Details:
- We have 14 motors from December. 2 are 22282AG which are not perfect but much better, and 12 are 22325A. The second set is where we did our testing and noticed the QC issues.
- The testing was done by around 5 people in the club all with lots of experience so a lot of things were done qualitatively with what we know.
- We are aware that some differences could be due to the wear of our current motors which are all before 2020, but we don’t think that accounts for the difference.
- I am trying to get some videos we took attached, but have not done that yet.
Through this post, we are not trying to trash on Vex engineering or Vex as a company as a whole. We are well aware that Vex has done lots of work to make their products reliable as well as cost-effective and with complicated supply chains, high demand, and so many more difficulties, this is not an easy task. We are just curious if other people have noticed similar differences, and we want to bring this to the attention of Vex and IFI so it can be resolved in future batches.
