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Unread 06-05-2018, 08:15 PM
jcpeng jcpeng is offline
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Question about the Robonauts' 2017 drivetrain

Hi! I had a question about Team 118's drivetrain from 2017 (Steamworks) and I was wondering if anyone here could help me figure this out.

From looking at their CAD files (https://ccisdrobonauts.org/?p=robots) it looks like they're using chain (or belt?) in tube with a 2x1 tube, but the exact drive method isn't modeled in CAD. I also can't figure out how you could fit two chains/belts next to each other in such a tight space (unless they're only driving the rear omniwheels?)

Any information is much appreciated!

Thanks,
-Jing-Chen
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Unread 06-05-2018, 09:07 PM
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Re: Question about the Robonauts' 2017 drivetrain

Looking at their CAD, like you said, they dont have it modeled. My team, 3735, in this PowerUp season took on the challenge of creating a chain in tube drivetrain configuration similar to that of 118's 2017 robot. We found that using double sprockets simply doesnt give enough room for the chain to sit inside the tube. (also the fact that VexPro only sells double sprockets for #35 chain where we wanted to use #25H) To get around this issue, we basically used two single sprockets (16T) from VexPro which we lathed off part of one side giving just barely enough clearance to fit the chain in the tube. Then on each other side, we were able to use normal single sprockets just making sure that we had proper spacing between the inside walls of the 2X1.

Just a warning, I wouldnt try this for the first time during the season. It would be best to test it out sometime during the offseason so you have time to iterate if need be. Its a tedious process that requires patience and a steady hand.

Nathan Ion
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Unread 06-05-2018, 09:12 PM
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Re: Question about the Robonauts' 2017 drivetrain

I'm not in a position to look at CAD easily, but I could hypothesize it's some version of the now-unavailable 221 17T double sprocket, which was great for tucking into 2x1 tubing. Anthony Lapp from 221 has worked closely with Robonauts in the past, so it's certainly convenient.
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Unread 06-06-2018, 03:21 AM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by Billfred View Post
I'm not in a position to look at CAD easily, but I could hypothesize it's some version of the now-unavailable 221 17T double sprocket, which was great for tucking into 2x1 tubing. Anthony Lapp from 221 has worked closely with Robonauts in the past, so it's certainly convenient.
Anthony was with the Robonauts in the past, not sure about now. A great one of the many that they have had over the years.

*Nvm, I just read a post that he’s moving.
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Unread 06-06-2018, 10:05 AM
Justin Ridley Justin Ridley is offline
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Re: Question about the Robonauts' 2017 drivetrain

Yeah, we've used Anthony's 221 double sprockets in the past (which he's no longer making). We've also made them ourselves by waterjetting blanks and then turning down the middle on a lathe.

We've been doing chain in tube using double #25 sprockets like this since 2013 and have really been happy with it.
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Unread 06-06-2018, 10:07 AM
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Re: Question about the Robonauts' 2017 drivetrain

Since the 221 sprockets are no longer available, another alternative that teams have shifted towards is using 2x1.5 tube instead. This allows 2 unmodified vex sprockets to fit in the tube side by side.
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Unread 06-06-2018, 01:39 PM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by Justin Ridley View Post
Yeah, we've used Anthony's 221 double sprockets in the past (which he's no longer making). We've also made them ourselves by waterjetting blanks and then turning down the middle on a lathe.

We've been doing chain in tube using double #25 sprockets like this since 2013 and have really been happy with it.
How do you chuck that in the lathe?

softjaws?
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Unread 06-06-2018, 02:05 PM
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Re: Question about the Robonauts' 2017 drivetrain

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Originally Posted by Michael Hill View Post
How do you chuck that in the lathe?

softjaws?

If the shaft is a hex shaft, you can just put it on a hex shaft, drill and tap a hole at the end of the hex shaft and use a washer and bolt to hold it on.
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Unread 06-06-2018, 02:46 PM
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Re: Question about the Robonauts' 2017 drivetrain

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Originally Posted by Chadfrom308 View Post
If the shaft is a hex shaft, you can just put it on a hex shaft, drill and tap a hole at the end of the hex shaft and use a washer and bolt to hold it on.
This is a great method, we've used it for several different things each of the past few years.
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Unread 06-06-2018, 03:56 PM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by Michael Hill View Post
How do you chuck that in the lathe?

softjaws?
Behold the power of the mandrel!

An expanding arbor is always nice. I have made many expanding hex shafts by drilling and tapping the end followed by a very aggressive countersink, then sawing grooves on the same end so when you tighten a CS bolt it forces the hex to expand.
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Unread 06-07-2018, 11:46 AM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by Justin Ridley View Post
Yeah, we've used Anthony's 221 double sprockets in the past (which he's no longer making). We've also made them ourselves by waterjetting blanks and then turning down the middle on a lathe.

We've been doing chain in tube using double #25 sprockets like this since 2013 and have really been happy with it.
I guess I'm just confused how two chains can even fit in the .75" gap. According to VexPro, the #25 master links are .381" across each, and you'd have to fit two of them (? unless I'm missing something)

I've also heard that you can just press chain links back together but never tried it myself...
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Unread 06-07-2018, 11:47 AM
jcpeng jcpeng is offline
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by n.ion View Post
Looking at their CAD, like you said, they dont have it modeled. My team, 3735, in this PowerUp season took on the challenge of creating a chain in tube drivetrain configuration similar to that of 118's 2017 robot. We found that using double sprockets simply doesnt give enough room for the chain to sit inside the tube. (also the fact that VexPro only sells double sprockets for #35 chain where we wanted to use #25H) To get around this issue, we basically used two single sprockets (16T) from VexPro which we lathed off part of one side giving just barely enough clearance to fit the chain in the tube. Then on each other side, we were able to use normal single sprockets just making sure that we had proper spacing between the inside walls of the 2X1.

Just a warning, I wouldnt try this for the first time during the season. It would be best to test it out sometime during the offseason so you have time to iterate if need be. Its a tedious process that requires patience and a steady hand.

Nathan Ion
Robot Captain
VorTX 3735
Our team (846, Funky Monkeys) has experience doing chain in tube (for the past three years now), but we've always had to use larger tube. I was just wondering how they got everything to fit in a 2x1.
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Unread 06-07-2018, 12:27 PM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by jcpeng View Post
Our team (846, Funky Monkeys) has experience doing chain in tube (for the past three years now), but we've always had to use larger tube. I was just wondering how they got everything to fit in a 2x1.
While I'm not the robonauts, what many teams do with chain in tube is use #25 chain and just stack two sprockets for the middle axle. In order to get everything to fit, you want to machine out a pocket in the 2x1 in the middle so you can fit the two sprockets, the hex hub part will be sticking out towards the inside
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Unread 06-07-2018, 12:32 PM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by deltafief View Post
While I'm not the robonauts, what many teams do with chain in tube is use #25 chain and just stack two sprockets for the middle axle. In order to get everything to fit, you want to machine out a pocket in the 2x1 in the middle so you can fit the two sprockets, the hex hub part will be sticking out towards the inside
I think more teams used a double sprocket that team221 used to sell like the one pictured below, but for #25 chain.

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Unread 06-07-2018, 02:28 PM
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Re: Question about the Robonauts' 2017 drivetrain

Quote:
Originally Posted by notmattlythgoe View Post
I think more teams used a double sprocket that team221 used to sell like the one pictured below, but for #25 chain.

(image snipped)
That's what 4901 did in 2016. The 221 sprocket was set up to fit two chain runs within the 1" wide tubing, as long as there weren't any odd clippy things on your chain run (like a half link with the wire you bend around). It would've fit in 2x1, though 4901 ran 3x1 so they could get a bigger-than-usually-desirable drop on the center wheel to account for the pneumatic wheels. The result didn't make playoffs, but for my money it was the coolest robot I've had a hand in over the last 15 years.
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