paper: DIY 'encoder stage' for VersaPlanetary

[Joe Ross]

Originally Posted by AllenGregoryIV

As I'm still looking at this, does anyone know the max encoder rate for the roboRIO and Talon SRX? With 21 or 30 counts/rev at 20000+ RPM we may be coming pretty close to or surpassing that spec. For the cRIO I think we are over the spec. For lower speeds it would be fine and we could also possibly remove some teeth, but I'm not sure how easy that would be.

The RoboRIO samples faster and has much higher bandwidth then the cRIO. 30 cpr at 20,000 rpm is still well within the capabilities of the roboRIO.

[AdamHeard]

Originally Posted by Joe Ross

The RoboRIO samples faster and has much higher bandwidth then the cRIO. 30 cpr at 20,000 rpm is still well within the capabilities of the roboRIO.

What is the limit? Would 10000 cpr at 5krpm work?

[Gdeaver]

Great work. Inspired to look at this sensor for our swerve module. Question. How were the pull up resistor and caps added?

[Monochron]

Originally Posted by Nate Laverdure

All lathe operations were done on a machine that I picked up off Craigslist for $200.

What brand/model of lathe is that? We have been looking for a good one second hand but size is our limiting factor right now :/

[Nate Laverdure]

Originally Posted by Monochron

What brand/model of lathe is that? We have been looking for a good one second hand but size is our limiting factor right now :/

It's a Chinese 7x10 similar to Harbor Freight 93212. I've since rebuilt it as a 7x16 with a number of other modifications, but stock it would have been able to do this job just fine. They sell new for $550.

[asid61]

Originally Posted by Nate Laverdure

It's a Chinese 7x10 similar to Harbor Freight 93212. I've since rebuilt it as a 7x16 with a number of other modifications, but stock it would have been able to do this job just fine. They sell new for $550.

You can find Harbor Freight 20% off coupons online, and it's usually only $500 there, so it ends up being $400 for a 7x12. The Seig style chinese lathes are all made in the same place, so you still get the same thing as if you bought from Grizzly, with minor customizations.
mini-lathe.com is a good resource.
The 7x10 is actually only a 7x8 (7" diameter part, 8" max length to be simple) and the 7x12 is an actual 7x12, so it's a good deal to invest in the latter IMO.
Craigslist can sometime have good deals, but you should know what you're looking for to do that. Measuring the accuracy is critical.

EDIT: In general I would use a mill because of the versatility for FRC, so if it comes down to buying a tool a mill would be my first choice.

[AllenGregoryIV]

We just posted our version of this modification to our blog.

We haven't got to play around with it to much yet but we did hook it up and check that the system was getting good distance values from the encoder.

We made several substitutions to reduce the overall cost of this setup. Each additional gearbox modification for us should only be around $10.

[Ryan Dognaux]

Originally Posted by AllenGregoryIV

We just posted our version of this modification to our blog.

Getting a lot of broken images on the blog post. The read through part looks awesome though, can't wait to see all the pictures

[AllenGregoryIV]

Originally Posted by Ryan Dognaux

Getting a lot of broken images on the blog post. The read through part looks awesome though, can't wait to see all the pictures

Thanks for the heads up, I tired a new system for putting the pictures up from google photos but apparently it doesn't actually make them public. Should be fixed now.

[Nathan Streeter]

Excellent work!

I'd love to see someone (VexPro?!) sell one of these... it'd be really great to not need to make a part year-after-year just because it's not sold when it'd be so widely useful.

[Nate Laverdure]

Originally Posted by AllenGregoryIV

We just posted our version of this modification to our blog.

GREAT improvements! Thanks for the excellent documentation.

As far as epoxy vs RTV silicone:
We were going to use RTV at first, but after a short debate we chose a potting epoxy that my professional colleagues use. The internal magnet(s?) within the Allegro package are quite strong, and when the steel gear is nearby there is a significant attractive force between them. It's probably a dynamic force as the gear rotates. Had we suspended the sensor in a flexible potting compound like RTV, we were worried about the effects of the induced vibration.

[Monochron]

Originally Posted by Nate Laverdure

Had we suspended the sensor in a flexible potting compound like RTV, we were worried about the effects of the induced vibration.

Sorry I haven't had a chance to read the blog, but that would be a great point to mention in the blog. Many teams probably aren't familiar with the differences in those compounds and if that is an issue, it would be good for them to see it coming and avoid it.

[Monochron]

Originally Posted by Nate Laverdure

Had we suspended the sensor in a flexible potting compound like RTV, we were worried about the effects of the induced vibration.

Sorry I haven't had a chance to read the blog, but that would be a great point to mention in the blog. Many teams probably aren't familiar with the differences in those compounds and if that is an issue, it would be good for them to see it coming and avoid it.

[AllenGregoryIV]

Originally Posted by Nate Laverdure

GREAT improvements! Thanks for the excellent documentation.

As far as epoxy vs RTV silicone:
We were going to use RTV at first, but after a short debate we chose a potting epoxy that my professional colleagues use. The internal magnet(s?) within the Allegro package are quite strong, and when the steel gear is nearby there is a significant attractive force between them. It's probably a dynamic force as the gear rotates. Had we suspended the sensor in a flexible potting compound like RTV, we were worried about the effects of the induced vibration.

That makes sense, we'll test and see how it goes. We ran it for a while with out any ill effects.

Something like this may be a viable solution if that problem does arise.

[Ryan Dognaux]

This is great. I'm adding it to our projects to try in the off-season. We use VersaPlanetary gearboxes everywhere that we can for their small form factor, ease of use and ability to modify gear ratios as-needed. Integrating sensor feedback into that package would be absolutely huge for a team like ours.