Just this - why is our swerve bevel grease moving to the inside of the wheel after running? Shouldn’t it be centripetally moved outward?
We’re using red ‘n tacky grease and rev maxswerve. This was only an hour of running after greasing. The grease is all inside the bevel and the gear itself is bone dry.
Has anyone else had this happen? Really curious why this is, and if there’s any way to keep wheels greased for longer.
Calling all chief delphi grease experts!
Turns out that this instance was just because of improper greasing. I probably should’ve been more clear when I told a member to “grease the gears”
However, what greases do other teams use on their bevels? We’ve had to regrease our wheels about 5 times so far this season
This is not how centripetal acceleration works.
Centripetal acceleration causes moving things things to turn, not the other way around where the turning causes centripetal acceleration to appear out of nowhere. Something has to create centripetal acceleration for it to happen, and a rotating body won’t just create it on its own. In fact, the the linear momentum of a given point due to an objects rotation will create centrifugal “force” which would try to pull the grease outwards.
We use white lithium grease per Greg (REV’s) recommendation here:
We are using SDSSwerve Drive Specialties modules and not REV, but we use PTFE spray on lubricant on the bevels so it collects less carpet and dirt.
I am a strong believer in using redline assembly lube, it gets everywhere but its so smooth
You rang? I have expertise in both FRCFIRST Robotics Competition grease and non-Newtonian fluids!
(Bad dispensing aside, we see similar behavior in our wheels/gears.)
Grease is most often non-Newtonian in my experience. This means that its viscosity changes with stress, and most greases are thixotropic. But what does that mean? It means the grease gets thinner as it is sheared/squeezed/flows, and more viscid when it isn’t being deformed.
How does this explain what you see?
When the gear compresses the grease the grease is both displaced/pumped and made less viscous. Half-ish goes outwards and is slung away. Half-ish goes inwards, stops being deformed, and becomes firmer again. This grease can just kinda hang out on the inside lip of the bevel gear between its higher viscosity and lower acceleration. We will just wipe it away when it builds up.
Mobil XHP 222 is the recommendation since EP1 is out of stock at McMaster.
Also strongly recommend syringes and needles for application.
External grease should be attended to regularly. Minimum once per day if the robot is driven at all. I ask my students to regrease every 2-4 battery’s worth of driving. You don’t need a ton because excess grease is pumped away almost immediately, a little dab’ll do ya.
For engine and transmission assembly, absolutely. For FRCFIRST Robotics Competition robots it is wildly too expensive and not particularly appropriate.
Assembly lube is designed to work for initial startup only, then get dissolved into the engine/transmission/differential oil and flushed out after break in. It isn’t intended for more than momentary usage. XHP 222/EP2 is specifically designed for open gear lubrication and won’t get slung off quite so bad as assembly lube.
A real grease for open gears, like XHP 222/EP2, costs $5-6/14oz instead of $11/4oz of Redline assembly lube. The redline is thus 6x more expensive.
Hands down, one of the best recommendations made on CDChief Delphi in the last decade.
thanks for the reply!
we bought some syringes and needles a few days ago actually, super eager to get these in hand
I’m not sure if @siyeng made it clear, but the image posted was indeed a goof, and not a physics problem. One of our newer members didn’t realize that “grease the wheel” meant to put the grease on the gear teeth, and not the hub. 
that said, we do see the same behavior to a less striking extent on our properly greased wheels. I posted this picture because I was caught off guard by how seemingly fast it had happened - the grease wasn’t even dirty! It’s usually dark grey by the time it moves inward, so seeing a red ring was odd.
Will definitely keep these tips in mind when greasing in the future, though. Would it be okay to apply Mobil xhp 222 on top of the semi-red-lithium covered bevels, or is it best to clean them fully before switching?
Yes, and yes!
I believe both greases are mineral oil bases, thickened with lithium, and an NLGI viscosity rating of 2. They should play nicely.
It is good to clean out the gears on a regular basis so that grit doesn’t remain entrapped and damage the gears. A toothbrush is really handy for cleaning gear teeth like this.
Just curious - if they have such similar properties why does the xhp work better for y’all than the andymark standard Lucas red n tacky?
It doesn’t work any better/worse in the sling-off testing we did. But the red’n’tacky packets at $1/14g are relatively expensive and create more plastic waste than the larger grease containers that EP2* comes in, at $5-6/13.7oz.
FWIW we bought one tube of EP2 in 2022 and it’s looking like it will last through 2024 because we can use it so precisely with syringes. Whereas we used to crack open a redn’n’tacky packet, use half of it, then try to save it in a ziploc only to have the rest of the packet gets smooshed out everywhere. You could use red’n’tacky with a syringe of course, but I’d rather buy the big tube once every 2-4 years.
*McMaster is OOS on EP2 and suggests XHP 222 as a replacement, by the specs that is a totally reasonable call.
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