775pro .5" Hex Output Shaft

So I am trying to figure out the best way to integrate the 775pro into a custom gearbox. I see that the VEXpro ThunderHex has a 5.10mm hole through it, and the 775pro has a 5mm shaft. Would it be possible and or be a good idea to convert the 775pro output shaft to .5" hex by pushing it into the thunderhex and adding a small set screw?

I do not know a lot about tolerances, but maybe someone with some machinist knowledge can tell me what the 5mm shaft will fit like in the 5.10mm hole.

Thank you in advance!

0.1mm is a total of 0.004" of wobble; that’s far more than you want on a shaft. Also, thunderhex central holes are not guaranteed to be concentric with the shaft.
Instead, try using WCP 32 pitch gears for your first stage. They have a pinion that presses right onto a 775 shaft.

I would recommend taking 1/2" hex and drilling a .190-.192 hole in it. Then ream the hole with a .195" reamer. This should result in a press fit 1/2" hex adapter, it should “never” come off.

One easy way would be to use gears like these that are designed to press onto the output shaft of the motor, and use 32DP gears to handle that first reduction. In my aspiring-to-be-a-professional opinion, I would not do what you mentioned doing for interfacing with the 775pro, or really any motor, especially if I didn’t machine it myself to exactly fit. In any case, you’ll probably have more luck just pressing on a gear that was designed to attach to the motor. Also, since this is a custom gearbox, make sure you cut away space in your gearbox plate to accommodate the vents on the front of the motor. What are you trying to do with the gearbox?

WCP sells 32DP pinion gears with a press fit bore for 775 sized motors. SDP-SI also has 5mm HTD pulleys with a 5mm bore.

What is the best method to press a gear onto the 775?

Thanks for the input! It looks like I should either drill better holes in hex shaft, or use the 32DP gears. Does anyone know of a 5mm bore 5mm HTD pulley?

The reason I am doing this instead of a versaplanetary gearbox is because last year we had issues with shredding the weak little gears in the versaplanetary. Will the 12 tooth 32DP pinion gear from WCD hold up to high pressure is there are a few other stages after it in the gearbox? Or if it is a high stress mechanism, should I try to use the hex shaft adapter method instead?

We took a tube and machined a holder for the 775pro. Then just used an arbor press to push the pinion on.

You can 3d print a mount/holder as well. Probably can skip the holder, we’ve pressed them on free hand before as well. But we got to a point where we were pushing on 30+ pinions a season and didn’t wanna bend any output shafts.

The pinion itself should have no issue, we have some pinions on our 2012 robot… That look brand new. The gears on the VP are different from the WCP gears. They are used in different applications all together. So its not an apples to apples comparison.

We will have stock of all of the 32dp gears and belt pinions sometime next week.

Because the 775pro is a high-speed low-torque motor, even when stalled it shouldn’t break a 32 pitch gear. I calculated an approximate tooth force of 17lbs, and a tooth strength of 72lbs according to this calculator: http://www.botlanta.org/converters/dale-calc/gear.html so you have a pretty large factor of safety there.

Of all the failure modes I have seen from a VP, shredding gears is not one of them. That doesn’t mean it’s never happened, but you should make sure you used the correct planet and sun gears on the right carrier plate.

SDP-SI has those pulleys.

A 6Z25M0xxDF0905 is the part number, where xx is the number of teeth (11-14)

Do you happen to have any pictures of this machined holder? We have been pressing on pinions free-handed for the most part, I am curious to see how your mount helps with the process.

Why not just use a 1/2" Hex versa-planetary with no reduction? The tolerances will be much better and you’ll have the added bonus of standard mounting holes.

True that you could definitely do this, but if you are going through the trouble of building a custom gearbox, why add extra parts when you could just put a gear on the motor shaft and skip the extra weight/space/added friction (friction is minimal) of a 1:1 COTS gearbox?