optical shaft encoder

Whenever I use the encoder it puts a lot of friction on my axel and the motors won’t rotate. I can barely rotate the axel with my hand. Did I do something wrong? Any suggestions?


On one of our encoders sometimes the red cap unsnaps and partially blocks off the hole that the shaft goes through, check that first. Make sure that the shaft isn’t bent. Next try taking the encoder off of your robot and just put an axel into the encoder and spin it by hand, see if it is spinning tightly. If the encoder isn’t spinning tightly when you spin it by hand then its just a matter of mounting it properly.

Make sure that the encoder is mounted so that it isn’t being pushed sideways by any other part on the robot. Next when you put the bolts into the encoder leave them a little bit loose and turn the shaft that is in the encoder a few times to center the encoder. After it is spinning nicely with the bolts loose tighten the bolts and you should be good to go.

Good Luck,


Is the encoder on the same axle as the motor?
Is the axle bent?
Is everything lined up and are you using bearing flats?

Sometimes I have to make the screws that hold the encoder to the structure slightly loose (use lock nuts) to make them work well.

perhaps post a photo so we can see what you are doing.

Kelton and jpearman have both given good advice; I would follow that. However, and this is important, is your encoder on the same shaft as your flywheel?

If you put the optical shaft encoder on your flywheel axle, you’ll just get higher and more accurate values of your flywheel’s rotation than if you put the axle on a gear(depending where that gear is) you’ll get lower values but for programming you shouldn’t have any problem inserting your optical shaft encoder in a specific location.

That’s theoretically true, but the red encoders have a tendency to destroy themselves if run at a high speed.

This is not true. The optical shaft encoders can only measure up to 1133 rpm accurately. (See the encoder information sheet for more information.) Properly designed flywheels, both single and double, spin faster than this. If you attach your encoder directly to your flywheel, the encoder readings will be wrong. This is why I mentioned the encoder placement. To get accurate readings, you should attach the encoder to an axle in your gearbox that spins below 1133 rpm, and then multiply the calculated speed by an appropriate adjustment factor.

Please don’t jump to conclusions without looking up relevant information. You may mislead others.

They can (again theoretically) go higher than 1133rpm, that number may be from the PIC days. We did some tests few weeks ago and determined the limit was probably somewhere around 1500 rpm (which I guess is not much higher than 1133) but it’s really mechanical limitations that determine the maximum speed.
How fast can a quad encoder detect movement? Post #10

Ah, I didn’t know that. You say the mechanical limitations determine the maximum speed–do you mean that the mechanical limitation on speed is lower than 1500 rpm?

I think the tower was twisting a little bit so I reinforced it. But now, I’m having vexnet issues. I’m getting a single blinking red light. I will try and replied the firmware or retether tomorrow.


Sorry for all the questions. I feel like the curriculum doesnt cover a lot of the info that i need. Does anyone have vexnet issues? Did i do something wrong?


Which LED?
Are the batteries good?

Have a look in the cortex user guide, perhaps that will help.

It’s on the cortex.

I would download and update the cortex, joystick, and the keys to the newest. This is usually the problem (at least for our teams). Then, link the cortex and joystick with the USB cable, and finally test out the keys.

It’s been I really long time since I’ve debugged VEXnet issues. I seem to remember that reloading firmware was not the answer; usually a VEXnet key had broken and needed to be replaced. This was with the old (black) VEXnet keys. The new ones may be more durable.

Ok. Thanks for the tips. I remember upgrading the firmware on the cortex and the joystick, but I can’t remember if I did the keys.

If the cortex and joystick are on the latest V4.25 firmware, then the new white VEXnet keys must be updated also to V1.46.

ok, so the cortex, the controller and the wireless key are all updated. It works when I tether it, but the connection gets lost when I use the joystick. The only other thing that I can think of is buying a nine volt battery and plugging it into the backup battery power. Does having a nine volt battery make that much difference?

Are you sure that all your batteries are charged? I know that bad AAAs in the joystick and robot batteries tend to create unstable connection.

Make sure the batteries are charged and that your controller and cortex are synched tovether because the vex nets wont communicate if they arent. If that doesn’t work put your vex nets into your computer and update the firmware on those through RobotC