We’re experimenting with using Andy Mark 6" wheels on the push end of our robot and using 6 inch 3D printed stars on the front. Seems to work but we don’t have any hubs that will allow us to use Tetrix motors with the larger Andy Mark wheels. Does anyone know or have a reference to which hub to buy or will this need to be a custom item from a machine shop? Any help would be appreciated.
what we have been doing is making adapters to 1/2 hex shafts using setscrews. (1/2 hex shaft center drilled 6mm, and then 2 tapped setscrew holes are added).
That adapter allows you to use any of the hex based FRC products.
are you looking for something like this? http://www.andymark.com/product-p/am-2609.htm
That’s what our FTC teams use to adapt from FTC hubs to the FRC 6 hole bolt pattern.
Our team has also successfully used this conversion plate.
Thanks to all. I’ve ordered a dozen (most of the team are newbies, we’ll mess up half of them…not really) of the adapter plates and proper screws. Now we can push our 8" star wheels up the mountain.
I suggest you consider using the FREE program Sprocketeer 2.0 to design your “star” wheels’ shape to get a star tooth shape that matches how the curve of a chain sprocket tooth profile engages and disengages with the chain rollers.
You can plug in the tooth pitch dimension that gives best results with the variable churror spacing and number of teeth plus star wheel diameter, and then you get data for the shape star wheel that is in G-code for CNC.
This could hopefully be used by a 3D printer too.
We were close to doing this star “wheel” design concept but our more unique idea of using 4 pairs of 6" “diameter” excentric wheels, with each pair chain driven by one AM NeverRest 60:1 motor, and a 1:2 step down with the sprockets for the motor-to-wheels, seems to be climbing onto the high zone finally, and allowing us to reach a height where a single joint, ~180º swing arm can deploy with a far enough outward reach to engage with the hang bar.
Consistent climbing performance and ending up within a specific targeted location zone on the mountain, however, remains as the bigger challenge.
Getting the star wheel teeth to let go of the churro as the axle moves further up slope past it can be an issue that locks the wheel up in between two churros and stalls the motor too We were looking at maybe laser cutting star wheels out of 1/4" thick firmer & denser urethane foam sheet, material and then sandwiching a few layers to make the star wheels. This would give some tooth flex against the churros to help both grip on mountain plastic and initial churro engagement, and also allow some tooth squishing slip on churro disengagement.
The firm urethane foam would reduce the likelyhood of the star teeth tips damaging the field tiles as well. Finding a firm foam that still has a good enough coefficient of friction to give adequate grip on the plastic sheet of the ltwo lower mountain zones may now be so easy though.
-Dick Ledford
We 3D printed several sets of 6’ star wheels and tested them on our practice field. They work as advertised consistently, we’re able to deploy a hanging arm from the top section without touching the bottom ot the hanging rack and get back down without incident. We used 3M VHB tape we got during FRC to put a gripping "tread onto the star “tips” to not tear up the field. We experimented with using Plasi-Dip on our smaller wheels. It works ok but the size of the wheels makes up the difference. We experimented with several types of “tip covers”. Right now the VHB tape works the best, does not scuff the smooth floor and not tear up the soft foam tile. We also went to a smaller rear wheel with the larger star on the front. We’ll see how things work out when we get our hubs, larger wheels and 60 motors.