Thought I would share a lesson learned the hard way. All of the posts and videos relating to prototype testing of wheel shooters being hand fed has prompted me to share the results of tread connection failure on an AndyMark custom wheel with traction tread attached in standard way by rivets…please, please consider the possible separation of tread that is not rated for some of the high speed tests many of us have been running…the result- I have a broken thumb and am going to lose my thumbnail. At least use a stick or other device to load your shooter when using wheels with attached treads!
Edit: I have contacted Team Support and asked them to pass the warning along. Hopefully we see it in the next blog or team blast since most exposure is occurring now during the development stage…
You got lucky. We had a very similar injury last season, except it was a custom 10" wheel at about 5k RPM and when the tread came off, it shot straight through 1/4" plywood and broke the student’s finger. Lesson learned.
My thumb was probably 6 inches away and a flap of more than 6 inches of tread separated from the 6 inch wheel…that’s my point-normal safety procedure might not protect you given the nature of many of these shooter wheels.
same thing happened to me yesterday we were testing with a placation wheel and the mount vibrated to much and as it was falling off a table i went to catch it but my finger went into the wheel cracking the nail in my pointer finger in half the wheel was spinning at 6k rpm by the way
The lesson that should be learned is a lot of these parts from andymark are not designed for high RPM use. take for example the axle we are using on our shooter mechanism it sticks up about 6 inches past the mounted wheel and the vibration effect at 5000 RPM causes it to wobble a quarter to a half inch.
We had a similar issue a few days ago while testing a prototype. The tread was attached using aluminum rivets. We will be switching to steel rivets for high speed wheels as well as adding a guard.
Another point to add: If you are using a motor on a direct drive, use ball bearing assemblies RATED for greater than the RPM you will be seeing. Do not use a bushing at these RPMs. Main drive wheels can get away with less engineering due to the typically lower rpm.
There is no excuse for lack of proper thought when working with rotating assemblies. If your shaft is vibrating under load by itself, you are doing something wrong. Assess what you have and redesign. Rotating assemblies simply should not wobble or be out of balance freely spinning.
On last year’s robot, we also added a safety cage in the unlikely event of a shooter wheel separation.
Thanks for posting the picture to remind us all that safety is not to be taken lightly.
I’d be worried about any wheel tread that’s not designed for high speed use. The riveted ones are prime suspects, but I also suspect that the foam wheels may disintegrate. Granted, foam is safer than rivets, but still…
We have been preparing to run a shooter with the 8 inch AndyMark pneumatic wheelchair tires. I noticed that they are highly unbalanced due to the valve stem, so I’ll be taking some time to correct that before firing it up. I’m not too worried about the tires themselves holding up to a couple thousand RPM, as they appear to use standard pneumatic tire construction. I am worried about someone’s hand getting in the mechanism.
We’ll also work on ensuring that nobody’s in the line of spinning stuff.
here is a picture of me after the 6 hour bus ride home from last years regional in Duluth, I got a little friendly with our shooter wheel whilst testing auton in the pit… it was spinning 2500 RPM. It happened all of a sudden and I calmly disabled the robot and said “THAT HURT LIKE A SON OF A B****” My head mentor turned around to tell me to watch my language when he realized my hand was covered in blood. I put my other hand on the table to brace myself and said “I think I’m gonna pass out” I looked down, saw blood squirt from the tip of my finger and woke up in another mentors lap. As I awoke seconds later, the AWESOME medical staff at the regional was there tending to my finger, I signaled for a freshman to grab my phone and I promptly update my Status “Ouch!” lol I hopped up, ran out to queue with a wrapped up finger, and we won our last qual. Got back home, the wound had been opened too long to stitch and it was broken in like 3 places. Its healed now, but there is still some scaring and my nail is weird. I will now have a reminder of my time with FRC FOREVER! lol
Nasty job on your finger, but you’ll always have that memory of FIRST. My team has been fortunate enough to avoid major injuries. I got hit in the head with a soccer ball at high speed during Breakaway when we were practicing with our bot, and the turning control was brushed as someone moved their arm. But otherwise we have avoided anything huge.
The other day we were testing our shooter that was direct drive to a CIM motor. Apparently we had forgotten to tighten the set screw all the way, and the wheel literally came flying off and almost hit a builder’s face. It then continued to spin around on the floor like a Beyblade for a couple of minutes. Where safety glasses when testing things!
Eek! We will keep this in mind while prototyping shooters.
Reminds me of our original shooter design last year. We had two CIMulators driving a chain with a two to one gear ratio, and we got our shooter spinning at over 8,000, and then the chain broke and flew forward…
… luckily, we had used C-channel to make an enclosure to make sure the chain couldn’t go forward more than an inch I can’t imagine what would have happened to whomever was in front of it if we hadn’t had a chain guard.
Perhaps a further warning, be careful with chain!
One of our prototypes threw a chain at less than half of max RPM. Thankfully, we had been running tests inside a makeshift lexan box and nobody was hurt.
For the rest of the season we will be testing in a lexan cage, and run everything up to max speed and go through max acceleration/deceleration before removing the lexan.
I can’t imagine what would have happened to whomever was in front of it if we hadn’t had a chain guard.