Custom Vs. COTS Transmissions

[Nemo]

Originally Posted by sst.thad

If you look at the big blue box under R22 this year, it says that if designs are posted publicly they are allowed to be reused because they are considered cots parts

This has been said repeatedly, but it is false. You are thinking of the following section, which only refers to software:

"Example: A different team develops a similar solution during the fall, and plans to use the developed software on their competition ROBOT. After completing the software, they post it in a generally accessible public forum and make the code available to all teams. Because they have made their software generally available (per the Blue Box in the definition of COTS, it is considered COTS software and they can use it on their ROBOT."

Edit: Maybe I'm wrong. I looked up the COTS definition and found this:

"Example 3: a team obtains openly available design drawings from a professional publication during the pre-season, and uses them to fabricate a gearbox for their ROBOT during the build period following kick-off. The design drawings would be considered a COTS item, and may be used as “raw material” to fabricate the gearbox. The finished gearbox itself would be a FABRICATED ITEM, and not a COTS item.)"

[Justin Montois]

Thanks everyone for the input. It seems that the general consensus is that custom transmissions can help great teams dial in their designs more efficiently, but for the most part it's not giving them a significant advantage.

Now, most of the comments on here seem to be based around transmissions for drive bases. Does everyone have they same outlook for custom transmissions for arms, conveyors, elevators ETC? Still not worth it?

[Nemo]

A custom transmission could allow the gearbox to mount in some specific convenient way onto a custom frame, which could save a bit of space or make it easier to fit other components around it. This seems particularly relevant for a directly driven wheel on a robot where the real estate around that wheel is crowded for some reason.

[Nemo]

Originally Posted by Justin Montois

Thanks everyone for the input. It seems that the general consensus is that custom transmissions can help great teams dial in their designs more efficiently, but for the most part it's not giving them a significant advantage.

Now, most of the comments on here seem to be based around transmissions for drive bases. Does everyone have they same outlook for custom transmissions for arms, conveyors, elevators ETC? Still not worth it?

A team need not be super elite to build custom side plates for a gearbox that uses AndyMark parts. Our team will consider it next year now that we've learned how to do it over the offseason. If we do go with that type of custom box, the goal will be to trade a small amount of time for some weight savings and some of the little niceties that come along with putting things where we want them instead of where they are on the one size fits all model.

[Andrew Schreiber]

I think, for me, the question of "roll my own or pull it from the shelf" has always been answered by a couple things:

Resources Available - What do I have access to?
Opportunity Cost - What does using my limited resources to custom make this mean I can't do?
Need - Is there a real need?
Overall Benefit - What do I get out of building custom?
Available Options Fit - How well do the COTS things meet my goals?

Admittedly, I'm coming at it from the software perspective but I feel the decision process is similar.

[thefro526]

Originally Posted by Justin Montois

Now, most of the comments on here seem to be based around transmissions for drive bases. Does everyone have they same outlook for custom transmissions for arms, conveyors, elevators ETC? Still not worth it?

This really depends on the game and mechanism.

We learned the hard way in 2011 that there's no 'easy' COTS solution for an arm transmission that requires a relatively high reduction. If we were to do it over again, we'd definitely build a custom box just so that we can avoid blowing half a dozen $70+ transmissions.

For conveyor games, Banebot P60's aren't a bad solution, neither are some of the AM gearbox combinations that have popped up recently. That being said, with a bit of know-how and a decent gear calculator, you can build a solid 20-ish to one transmission using some COTS gears from AM for half the cost of anything on the market, or so it seems.

Btw, for anyone looking into designing a custom or semi-custom gearbox, this is an excellent resource: http://team1323.com/resources/manafa...alculator.html

[Peter Matteson]

Originally Posted by thefro526

We learned the hard way in 2011 that there's no 'easy' COTS solution for an arm transmission that requires a relatively high reduction. If we were to do it over again, we'd definitely build a custom box just so that we can avoid blowing half a dozen $70+ transmissions.

Really? We went completly COTS by putting AM fischer-to-Cim planetery into a 3 stage AM stacker box with a single sprocket reduction on the output. This solution was quicker and easier than building a custom gearbox to get the same redction. The use of the planeteries also gave use a more compact footprint than we would have ever had with a spur gear based transmission.

[thefro526]

Originally Posted by Peter Matteson

Really? We went completly COTS by putting AM fischer-to-Cim planetery into a 3 stage AM stacker box with a single sprocket reduction on the output. This solution was quicker and easier than building a custom gearbox to get the same redction. The use of the planeteries also gave use a more compact footprint than we would have ever had with a spur gear based transmission.

Our overall reduction was ~1228:1, so using a similar solution to yours would've required a 4th Stackerbox or a ~7:1 Reduction off of the Third Stacker Box. We also ran two 775's on our arm which made playing with COTS stuff a little difficult.

[Peter Matteson]

Originally Posted by thefro526

Our overall reduction was ~1228:1, so using a similar solution to yours would've required a 4th Stackerbox or a ~7:1 Reduction off of the Third Stacker Box. We also ran two 775's on our arm which made playing with COTS stuff a little difficult.

I just looked at your robot from this year again. I forgot how long that arm was, so I can see why you needed the extra reduction. This is one of the reasons why we, the team that was known for making 12+ foot telescoping arms from 97-03, stopped making such long arms.

[Frenchie461]

Personally (note: I've never built a custom gearbox) I'd think that it would only make sense if the COTS solution wouldn't fit with an idea, and changing the idea to fit a COTS would make the design worse.


Since there's only 1080 hours in build season (45 days*24 hours a day) you have to make the most of it, and if you spend 10 hours working on a gearbox, that's 10 hours you didn't spend working on something that could give higher returns. By that I mean the final 1% of perfection on the drive train doesn't do as much for how competitive you are as the first 50% of perfection on an arm that could be done in the same time.

TL;DR version: If you need it and have the time for it, go for it, else wise, spend the time elsewhere.

-Frenchie

[joek]

Originally Posted by Wayne TenBrink

This subject touches on my biggest pet peeve about FIRST rules: the prohibition, without exception, on re-use of fabricated components, existing designs, or modified COTS items. Transmissions are a great example, but the same principle applies to any number of other components & assemblies.

If we were to go to the effort and expense of developing and building our own transmission (a good thing), it would glorified scrap at the end of the season (bummer). If we just bought a COTS transmission and didn't modify it (normal business practice, but not as much of a learning experience), we would be free to re-use it in the future. This is a big disincentive against making anything you can buy. Perhaps FIRST could set some allowance for "legacy" fabricated parts - by weight, parts count, dollar value, etc.

If we were to invest in a pair of COTS shifting transmissions and then we drilled one new mounting hole in each (heaven forbid we deburred or lightened the gears) they would be unusable for future games. Perhaps FIRST could set some standards for minimum allowable modifications for re-use of COTS items - i.e., drilling holes, shortening motor shafts, etc.

I know that its easy to recycle a design by making some meaninglessly trivial modification, but that just encourages "gaming the system". Perhaps FIRST could allow re-use of designs that had been publicly posted.

I like the FRC supplier base that has developed in recent years, and we take advantage of it. However, when combined with existing FIRST rules, it creates some negative and unintended incentives. I hope FIRST will consider allowing limited re-use of legacy designs & hardware that teams creat or enhance with their own brains & hands.

Besides, the unique requirements for each game put a natural limit on the number and type of items that are worth re-cycling.

as of 2011, they do allow re-use of custom designs that are publicly available, as they are then considered cots

[Wayne TenBrink]

I re-re-read the 2011 rules, and I concur that FIRST has approved the re-use of a publicly-posted design. That is certainly a good incentive to develop our own designs, and provides another resource for teams looking for new technical solutions.

PS - I have spent a lot of time over the past couple of weeks trying to design a gearbox. The experience has given me a deeper appreciation for the AM super shifter. The more you study it, the more you realize the elegance of the design.

Related comment and questions: All the gears in the super shifter transmit power to their respective shafts via a hex shaft (directly or indirectly via the shift dog) with the exception of the pinion on the intermediate shaft, which drives the larger gear on the final output shaft. It uses a square key. Has anybody had a problem with that key? One of the designs I am considering would require a square key on the input gear (that meshes with the pinions on the CIMs). Do you think that would work, or would it get loose over time/reversal of direction?

[Cory]

Originally Posted by Wayne TenBrink

I re-re-read the 2011 rules, and I concur that FIRST has approved the re-use of a publicly-posted design. That is certainly a good incentive to develop our own designs, and provides another resource for teams looking for new technical solutions.

PS - I have spent a lot of time over the past couple of weeks trying to design a gearbox. The experience has given me a deeper appreciation for the AM super shifter. The more you study it, the more you realize the elegance of the design.

Related comment and questions: All the gears in the super shifter transmit power to their respective shafts via a hex shaft (directly or indirectly via the shift dog) with the exception of the pinion on the intermediate shaft, which drives the larger gear on the final output shaft. It uses a square key. Has anybody had a problem with that key? One of the designs I am considering would require a square key on the input gear (that meshes with the pinions on the CIMs). Do you think that would work, or would it get loose over time/reversal of direction?

keys work just fine. They just are a pain compared to hexes.

[ajlapp]

It uses a square key. Has anybody had a problem with that key?

No. The AM Supershifter is rock solid in my opinion. After years of building completely custom transmissions we made the switch to all AM transmissions and we couldn't be happier.

On the topic of custom gearboxes....

Making a few custom plates and using COTS gears, dogs and shafts is a relatively easy endeavor that can shave critical weight and allow for improved mounting/servicing options.

Below is my take on the 254 shifter layout using AM internals and custom plates. The standoffs have a piloting feature that help keep the gearbox components aligned.

[Mk.32]

I just designed custom gearboxes for a WCD we are hopefully going to build. Based on the 221 "Super Light Toughbox Transmission". BTW thank you Anthony for posting CAD on all your stuff.

The reason being I needed something that would easily be able to be bolted on frame rails and it turned out it was was easier to just CNC out two side plates, then try to come up with some kinda of mounting system for the COTS ToughBox. It also is cheaper for us cause we already have the gears and shafts.

For me and our team, if I can I would use a COTS gearbox, but when trying to integrate a COTS gearbox takes up more time/work then just doing a custom gearbox, I will just design something custom that fits nicely.