Before MAR Champs in a week and a half, Team 5404 needs 3 20t aluminum gears with 1/2" hex bores for the 3rd stage of our VexPro ballshifter drive gearboxes.
We have already replaced one on our competition robot after it stripped, and the second on the competition robot as well as the two on our practice robot are all nearly stripped as well.
We would also like 2 775pro motors before the event. After we smoked our shooter motors at the Westtown district event we used our remaining spares.
Does anyone have any spares of these parts?
We can cover the costs for shipping from wherever you are, or pick them up if you are near us (we are in Lansdale, PA).
Perhaps. There is a lot of discussion about 3rd stage gearing wear for a Ball Shifters on this thread. I would contact some of the folks on there that have put these gearboxes through very, very tough trials.
The answer is probably yes depending on the hardness of the smaller steel gear and coatings on the aluminum gear.
Good news though. for the run times of a typical FRC robot, it wont matter much. The larger gear will almost always wear more slowly than the smaller gear because each tooth on the larger gear will see fewer cycles. With matches only a few minutes long and seeing a maximum of 21 at an event (except for replays) the aluminum gear should not be seeing much wear in the 40 minutes or so it is going to be running for.
However, in the future I would advise you to not use aluminum gears unless you are right up against the weight limit or are using very large gears (team 25, I am looking at you with those massive gears on your wheels…) Steel has better wear and fatigue properties in general. If you are really concerned about durability of the gears you can always have them case hardened. I did this to an old toughbox that I use for a 6000 watt motor (~15 CIM equivalent) to power a silly electric racing car and I have run under load for about 15hrs with almost no signs of wear.
Yes, but if you properly lubricate your gears they will not wear significantly within the runtime of an FRC robot, and this will not compromise performance. Aluminum gears like to wear a little until they run nicely and then that tapers off for a bit.
However, I would advise you to not use aluminum gears unless you are right up against the weight limit or are using very large gears (team 25, I am looking at you with those massive gears on your wheels…) Steel has better wear and fatigue properties in general.
There is nothing wrong with using aluminum gears in FRC - the weight savings is dramatic and for most applications the strength is just fine. The aluminum gears Vex produces are of higher quality than steel gears from AndyMark as well - better tooth profile, more consistent manufacturing, etc. Wear and fatigue properties are not really a concern with 100-200 hour run times.
On those 775Pros-
To keep brushes from smoking out like that, it is absolutely essential to have airflow past them. Lots of airflow, since you have to keep the brushes cool.
Also, avoid applying full power are low speeds.
We went to 3 regionals this year and wore through 5 20T VexPro gears with our 3rd stage of Ballshifters. We ended up switching to the Andymark steel gears (broached hex). At the end of our Idaho regional, our 64T VexPro gears were trashed, luckily we had replacements for those.
Some of our issues were due to the lack of securing the 3rd stage to the BallShifter. We were having a lot of binding when we tightened the 3rd stage too much, so we tried to find a happy medium between too loose and too tight, we think this caused some issues with gear tooth engagement when it experience shock loading.
For those of you that broached gears how did you align things?
I tried a rotary broach in a Bridgeport but found it difficult to get a good center. The existing keyway in the gear would end badly on a coaxial indicator. I tried a few times with a 0.2 edge finder and the DRO but still managed to be broached straight but slightly off center.
It is either I am off center or my back plate protecting my chuck face is not rigid enough. It is strange because I drill out the hole to 33/64" and chamfer before I go in. Center does not move. I have not tried this much lately…maybe just have not gotten the knack of it.
That is my Plan B. Kind of hoped to sort out where the weak points of Plan A were and if there where a good fix.
Seems a similar alignment issue. Gear is just a bit too big for a 5C collet. Plus the collet would not likely provide the support for the thrust involved. It is an even number of teeth so a 3 jaw chuck will not engage the teeth all the way around. My 4 jaw Chuck are all independent so then I need to center. The way I center I guess I would need to turn down a rod snug to the bore and use a dial test indicator.
Any other ideas cause my press is looking good right now