Trying to use 3 stages with an encoder but I am struggling to find the correct screws to hold it together I have 2.75 inch screws for 3 stages but need help sourcing longer screws or ideas.
I do not need the reduction for load, but to stop backdrive with out straining the motor.
U can buy longer screws of McMaster
Bolt Depot is my go-to for all manner of bolts and fasteners.
Alternatively if nothing else works you can get some threaded rod, double-nut and lock-tight one end, cut it to whatever length you need and kinda works as a bolt. They never work as well as a bolt, but when someone says they need a 12" 8-32 or some such, they’re in for a bit of pain and creativity.
As others have said, you can buy longer screws from normal fastener sources.
My team did something similar with a versaplanetary last year and we had a lot of gearbox trouble because of how weak the plastic encoder stage housing is at bearing load. I’d be very careful whenever you are using a reduction that is not recommended on Vex’s load table document. Consider mounting the encoder elsewhere or at least putting the encoder stage closer to the motor to reduce the amount of torque it will see.
Each stage (including the encoder and ratchet slices) adds .50" length to the gearbox, so if you use 2.75" screws for 3 stages, you’ll use 3.25" screws for 4 stages.
side note what is the diameter and pitch of these screws?
Keep in mind that you should NOT make a 4 stage VersaPlanetary otherwise you risk breaking either the gears within or planet carrier, regardless of motor input.
Would an encoder be considered a stage?
Yes, from what I remember a encoder is the same thickness as any other gearbox stage. In doubt, get a pair of calipers and measure it.
8-32 bolt
Wait… why? It doesn’t sound like he’s making the mother of all gearboxes with 10000:1 gearing. I read it as two normal stages, a ratcheting stage, and an encoder stage. I assume only 2 actual gearbox stages and 2 accessory stages.
Why would putting 1:1 stages on a gearbox risk destroying it?
I misinterpreted. I understood it as having 4 gear stages, which is a big no-no. I would still be careful with that long of a gearbox, make sure it is mounted securely to avoid any unexpected forces or moments on it.
It’s 490 overall reduction, using two 7:1 stages and a 10:1. No Ratcheting stage, and a Talon SRX encoder stage
Have you consulted this document to make sure that the gear ratio you are making with the motor you have selected is safe?
What motor are you using? That’s in the danger zone for more powerful motors. If you haven’t already, I would take a look at VEX’s documentation on their gearboxes:
Also be sure to put the largest reductions closest to the motor side. This put less stress on them as they are more fragile and prone to failure.
Using a bag motor, it is in the danger zone according to that graph, so far we’ve had no problems, we could end up changing the gearing if it becomes an issue, it looks like it’s only just barely in the red zone with a 10-7-7 configuration
Really we only want that much reduction for the backdriving issue.
It had plenty of force with 2 stages stage.
Are you feeding that into a sprockets or are you direct driving? You can offload some of the stresses on the gear box by having a sprocket reduction after the gearbox reduction. I am setting up a gear reduction with the duel 775 input box, 2 10:1 VPs(with encoder), and then 15:60 sprockets after the VPs.
sprockets close to the gear box