Do you need bearing flats where the motor is attached?

Im building a test base right now and I’m wondering: do you need to put a bearing flat on the side of a drive axle where to motor is? Does it help at all with the alignment? Obviously you need one on the other side of the axle.

no, the motor acts like a bearing. you can drill out the hole slightly if you wish, but it’s not necessary.


Make sure you nest the tiny metal extensions on the motors into the c-channel holes


imagine having motors that haven’t had those things torn off.

if you don’t like me might want to use a bearing just in case.


RoboSource has shoulder screws that are designed to correctly position the motor when the “tiny metal extensions” are missing. It has an #8-32 thread and a .182 diameter shoulder.


I usually put bearing flats on both sides of an axle to decrease the likelihood of axles bending, rlly depends how much you think it’s worth, and for what task you are implementing it in.


Vex sells replacements

It’s under the “threaded inserts” product name

While the journal bearings inside the old 393 motors looked strong enough for the job of handling the force to support the robot’s weight, the jury is still out on whether it is a good idea with V5 motors.

Planetary gear system in the output stage of V5 is very good for producing high torque and symmetrically distributing wear and tear around the ring.

However, it may not hold as well with asymmetric high force that keeps pushing into the same area of the ring all the time.

The best way to determine if this is an acceptable practice would be for someone to run a robot weighting around 20 lbs for about 100 hrs of practice and game play, including transportation to and from competitions, and then open up cartridges and see if one spot of the plastic ring has more wear and tear than the rest.

On the other hand, if you have setup your motors for quick swap, you could mark your cartridges and regularly rotate them to distribute any wear and tear more uniformly.

If somebody wants to research this - it would be a great topic for an engineering notebook and will significantly improve your chances at getting a design or excellence award.


Yes. The more bearing flats the better, until you get over 25 flats. You are supporting square shafts in a round hole.

When you get to the 25th flat you should ask, what am I doing here.

Plastic to metal friction is minor, your real concern is how do the holes line up?


Yeah, I have to disagree with @Xenon27. While the motor will probably still work even if you use only one bearing, it’s much better to use two bearings, with one on the side of the motor. Like @technik3k said, it may contribute to wear on the planetary gearbox, but you can do this if you want.


I would disagree. for most applications, 2 bearings is plenty to hold the load of the shaft, and any more bearings will cause friction because vex holes don’t line up perfectly.

a motor when mounted properly will act like a bearing, supporting the shaft well enough that the shaft never touches the metal hole, so no bearing needed on the motor.

if you’re unsure about the load on the shaft, like in a drive, you can use a bearing on the motor just to be safe. but you should never use more than 2 or 3 bearing max, it will just cause friction.


How would the bearing be positioned though? The metal parts that stick out of the motor dont fit inside the bearing holes

you’d put the bearing on the other side of the metal.

please never screw a motor on top of a bearing…


I’ve personally used a motor-side bearing for high torque applications where I need the shaft to have little to no bending potential (a Tower Takeover Tilter for example). Otherwise, you shouldn’t have to use a motor-side bearing.

A good example of using just enough bearings would be a majority of Turning Point flywheels where the topmost 12t pinion would have its shaft only supported by the main vertical channels holding the wheel up. To reduce friction the shaft would not reach across into the gearbox channel.


If your worried about a shaft bending use a HS shaft my guy

There shouldn’t be any need for a High Strength Shaft unless you have a large enough gap to the point where the shaft is able to bend outwards from movement. Otherwise, simply doubling up on shaft support for a LS shaft is more than fine enough.

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That’s kind of a janky fix tho, if you think the shaft will bend you should use a HS shaft, cuz you don’t want to find out in the middle of a comp that you didn’t add enough support

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I used HS shafts for my tilter in TT and my catapult in TP. they’re a pain to work with, but really make building quality high load gearboxes much easier.

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You will rarely need more than low strength on the input shaft of a torque oriented gearbox.


Its not really considered a “janky fix” given that the same concept applies to screw joints on many lifts. These can vary from adding two bearings (one per side of the channel) to utilizing a boxed C-channel coupler joint with bearings on the inside to increase the surface area the screw is bolted into. All the “bearing on motor in high torque application” is doing is translating the same concept over to shafts.