I teach a high school robotics class and coach an after school club. We have 6 V-5 claw bots and a competition kit. I keep having the same hardware issue. Several times, almost on a weekly basis, students report that drive shaft on their drive trains keeping popping out of the motor’s seating resulting in the claw bot usually going in circles because only one wheel is turning. 9 times out 10, it’s typically the front right driveshaft on the clawbots.
I have double-checked the build plans for the claw bot several times and I’m rather confident that I have all the necessary shaft collars and spacers where they should be. Does anyone else have similar issues? I have trained my students to re-insert the drive shafts by now when it happens but it’s rather annoying. Have I overlooked something or is this a potential design flaw? Any solutions to keep the driveshafts in the motors during use would be helpful.
While its possible there may be some other issue with the way your students are mounting the shafts, a trick my students have been using is to drop in a gear insert whenever using a standard shaft since there is so little in the cartridge to hold the shaft.
The problem is that the clawbot kits come with rubber shaft collars, rather than the metal ones that most competition teams use. If you replace the rubber ones with these, I am 99% sure your problem will be fixed.
… and those useless plastic rivets. I’m all in favor of cost reducing product materials, but I’m doubtful that the difference between the rubber collars and a bag of screws is worth it. It’s 1% on the cost of the kit. When I order these for my schools/teams, I order the screws and collars and make them give me the other parts. The collars go to the IQ teams and the rivets go into the trash.
So my issue is they are not reusable many times before they start coming apart. Plastic drive rivet fasteners operate by pushing the stem of the fastener through a hole in a panel or other surface. One advantage of this type of fastener is that it can be fitted blind from one side of the panel. But to get them apart, you need to get to the other side to push the pins out.
I’ve used plastic rivets for projects, but they are mostly a once and done assembly. ForVEX kits, there is a lot of together / apart / together / rebuild / etc.
It’s not welding. Using Pop rivets to do metal assembly is awesome. Lots of the top FRC teams use them. Drill the holes, put the rivet in, use the gun and it’s together. If done properly, it’s not coming apart without drilling the rivet out.
Which isn’t an option with VEX. There is lots of iteration going on, so parts need to go together and come apart.
Google Pop-Rivets and you’ll see them in action. Pop rivets come in different lengths, you need to have the right length so the backs fold over correctly. You can also get them in plastic, but I like the push pin version, they tend to look nicer. I use the ones with the decorative caps, so it looks like a button when done. An inexpensive pop rivet gun and some rivets can be purchased at Harbor Freight for ~5. (https://www.harborfreight.com/hand-riveter-set-38353.html) Grab one and put some stuff together.
To return to the OP’s issue, anytime you cantilever the wheels you run into those issues. Even putting in the inserts as firegnome suggested is not a cure. When cantilevering the wheels, there is nothing really holding the axles in the motors except friction. Several things can help. One, use omni wheels so that turning doesn’t cause a large lateral force on the wheels. Particularly on the outer wheels in a turn (left side wheels in a right turn), Two, and what we do with our competition robots, DON’T cantilever wheels. Build a box around the wheels so that the shaft collars can be placed in a way that resists the movement of the axles out of the motor