Custom Vs. COTS Transmissions
 

After some pretty serious discussion recently on our team and decent arguments made back and forth, I'm even more interested in the transmission discussion between making custom transmissions or going with COTS transmissions.

If some of you wouldn't mind, I would really appreciate some insight into your thought process when making this decision. It's no secret that some elite teams (254, 118, 1625) make custom transmissions. I don't think they are simply trying to make FRC harder on themselves. There must be a significant benefit to fabricating custom transmissions.

Teams that don't make custom transmissions, why don't you?

Teams that do make custom transmissions, why do you?

I look forward to the discussion.

Re: Custom Vs. COTS Transmissions
 

We don't have a ton of machining capability. We certainly don't have the ability to wire edm or hob gears. We don't have the money or time to build, fail, build, fail. So we use KOTS transmissions with thousands of hours of competition behind them.

If you have the time, money, and expertise to develop a transmission in the off season, refine it, build it, and test it to failure, you're a candidate to design and build your own transmission.

If you're asking the question now..... it's probably not a good idea for this build season (unless your mentors know a lot about transmission design).

Re: Custom Vs. COTS Transmissions
 

A lot of the teams who make custom transmissions or gearboxes also have design specifications for their desired reductions (obviously) to meet their speed requirements, torque requirements, as well as optimal acceleration. The well known teams who make their own gearboxes each year have really awesome ways of analyzing exactly what specs they want their drivetrain to have and specific requirements for the things I listed above.

Re: Custom Vs. COTS Transmissions
 

It really comes down to resources, knowledge, and money. I honestly don't know anything else that could really explain why teams do/do not make their own transmissions.

EDIT: Actually, come to think of it, anyone could make their own transmissions with a simple lathe and mill. That's pretty much all you need for it. However, the benefit of actually making one may not be positive in the long run.

Re: Custom Vs. COTS Transmissions
 

Speaking from experience having been on teams which made their own custom transmissions (with a manual mill and lathe) before the age of AndyMark and who have used COTS transmissions; the COTS solution is the way to go. The amount of hours invested in design and fabrication involved in the creation of a custom transmission simply aren't worth the minimal gains compared to the COTS solution for 99% of teams.

It's a good exercise to go through if you have the resources, time, and money. But in the condensed build season schedule, it's simply not worth the allocation of those resources.

Re: Custom Vs. COTS Transmissions
 

COTS is a really good way to save resources like everyone here says. Who wants to tie up half their season machining a few transmissions when you can get the same done for less by buying a few parts.

Last I checked AndyMark shifters are still cheaper than I can buy the parts to make one on the open market. I built them from Andy's whitepaper the year before he started selling them so I had pretty good info to justify switching my team over.

Another thing a lot of teams do is buy gears from AndyMark and package them in a custom housing to meet their packaging needs. Doing this you can buy gears, pre hex broached even and get the ratios that you want by combining various gears. This is what we have done several years and occasionally we swap in a custom gear that we have to hex broach ourselves.

Re: Custom Vs. COTS Transmissions
 

Many/most custom transmissions in FIRST seem to be repackagings of AndyMark ToughBox/Shifter guts into something that fits with a team's chassis. Banging out new sideplates is trivial if you have access to a laser cutter/water jet/CNC mill.

Re: Custom Vs. COTS Transmissions
 

We do not make custom drive gearboxes anymore because OTS solutions are great. Having a driving robot base 1-2 days (at most a week) after kickoff is fantastic.

Re: Custom Vs. COTS Transmissions
 

We've made custom gearboxes for our robot every year I've been on the team (06-present) and as far as I can tell just about every year prior to that (98-05).

We've tried several designs, and combinations all with various degrees of success. The main reason we continue to produce custom gearboxes is because we're good at it. We've gotten the process down quite solidly so we are able to tweak and modify our design each year without too much of an issue. We're able to dial into exact speeds and different wheel sizes/configurations. The custom factor allows us to take as much weight out of these designs as possible.

In my time on the team we've constructed 2 speed shifters using AM guts, 2 speed shifters using just the AM dog and custom gears, 2 speed shifters using a ball-lock style (fully custom), a few single speeds including a 6 motor single speed and even some drivetrains that build the gearbox into other aspects of the drive (eliminating the gearbox itself).

Our resources and support have allowed us to do this and we are quite grateful for it. We will continue to take this approach and continue to refine our designs as necessary.

-Brando

Re: Custom Vs. COTS Transmissions
 

Many of the teams who have "custom" gearboxes simply simply take COTS AndyMark gears and rearrange and/or repackage them into custom housings. Usually this is done to reduce weight, facilitate mounting and integration into chassis/mechanism, or to obtain custom gear ratios by swapping out gears. 228 has used this style of custom gearboxes for several years now, mostly in drivetrain applications. This is pretty easy to do, so long as you have accurate machining capability (CNC mill, laser, punch, etc).

Actually designing a fully custom gearbox and machining gears from raw gear stock isn't much more difficult, but is a lot more time and resource intensive. We did this last season on 228 for one reason, and that was that it was still faster to do this than wait for Banebots gearboxes to arrive.

Re: Custom Vs. COTS Transmissions
 

There is one more thing to add to these comments. Some teams not only use AM parts to make their own custom gearboxes, but they also spend much time to optimize AM parts before assembling the parts into their gearboxes. People have told me that before they put the AM parts into these gearboxes, they have their students go over each gear with a jeweler's file, clearing away any miniscule burr that may be on the edge of the gear. This attention to detail makes the gearbox slightly more efficient than it was before this final precision work is done. We could do this at AM, but it would increase our cost and price significantly.

Andy B.

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

We, like the majority of average teams, don't make our own transmissions. We've just never had the need to. A good old 1 speed (last year) Cimple box with 2 CIMs in each has given us the power we need. We MAY go into a shifting gearbox this year, pending on game and drive train. We've never really had the time, resources, or know how to do so, and even if we did make our own, the AndyMark ones (IMO) are better than anything we'd make in build season. Transmissions are something, like swerve drives, better left for the offseason, and even then, we like the AndyMark transmissions, and have no use for custom ones.

And just for fun, I'm gonna quote Karthik: "Build within your means".

Most teams don't have the means/need for custom transmissions. I'm saying most being the majority of teams in the world.

Re: Custom Vs. COTS Transmissions
 

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

Re: Custom Vs. COTS Transmissions
 

We use COTS for a few reasons -

1. We used to make our own. Without the precision machining capability, it is difficult to create the proper alignment for efficient running.

2. By purchasing, we can focus our time on the items we cannot buy as fabrications, such as lifts, arms, turrets, kickers, etc.

3. The purchased components work better than any we made ourselves.

From a business standpoint, purchase commodities and manufacture the custom, unique, "high value" items - especially if you only have 6 weeks.

Re: Custom Vs. COTS Transmissions
 

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.)"

Re: Custom Vs. COTS Transmissions
 

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?

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

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

Re: Custom Vs. COTS 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.

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

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

Re: Custom Vs. COTS Transmissions
 

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

Re: Custom Vs. COTS Transmissions
 

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?

Re: Custom Vs. COTS Transmissions
 

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

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

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.

Re: Custom Vs. COTS Transmissions
 

In my opinion, COTS are better overall until you want your drive to do special tricks. For example, the inclusion of P.T.O.s and neutral gears of 254s and 1114s gearboxes in 2010 to drive their hanger was brilliant. That is one of very few specail cases where I would value custom gearboxes over COTS. Just for the timing of the build season, I would still expect many of the individual parts in custom gearboxes like those to be COTS to save time.

Re: Custom Vs. COTS Transmissions
 

We need to be careful here... If you have actually "designed" the gearbox, you need to publish the design in a "public forum" in order to legally use it for the competition. (This is assuming that the same rules apply as last year... which may change, but probably not.)

The rule of not using custom designs over again is certainly the most violated in FRC. Many teams use the same designs over and over again without understanding that they are not following the rules.

The best part is that many teams have begun to publish their designs with complete drawings and specifications. This goes for both parts and software. THANK YOU to those teams who have been sharing their success!

- Mr. Van
Coach, Robodox

Re: Custom Vs. COTS Transmissions
 

I disagree. How many teams use the exact same design with zero changes? I would bet zero or very near to it. Plus the way you interpret the rule is very misleading. You can certainly use something designed outside of the build season without making a single change to it...you just have to redraw it all during build to technically satisfy the rule.

Maybe the casual observer would think it's exactly the same, but if you change anything, you alter it such that it's an acceptable usage.

Our bases often look nearly identical, but there are constantly small changes to gear ratios, sideplates, shaft lengths, wheelbase length, etc.

Re: Custom Vs. COTS Transmissions
 

This year, we're going to do a custom gearbox ... somewhere, but not on the drive train. We've been mucking around with 1-1/8" hole cutting for a few weeks now, getting them correctly positioned and straight. In the end, I think we'll use custom gearboxes for a small wrist, a conveyor, or roller intake of some sort.

These systems do have a good argument for attempting custom gearboxes:
Those types of robot systems seem to need the most compactness of any robotic system, and often modifying COTS to can be more difficult or time consuming than designing the gearbox from scratch. With a custom gearbox it's easy to control mounting points and which side of the gearbox the output shaft is on -- with COTS, modifications have to be made to get the same effects. If the manufacturing of the mods goes wrong, new parts have to be ordered -- eliminating any time/headache saved by modifying COTS to begin with.

On another note -- The black FP gearboxes come with very forgiving plastic gears that have giant teeth. While they're probably not great for high-precision or high-power systems, they do seen to find their way onto some very successful robots every year. Hopefully they'll be in the kit again this year so they're legal to use.

Re: Custom Vs. COTS Transmissions
 

If it's legal to use DeWalt gearboxes (not in the KoP) wouldn't it be legal to use the FP gearboxes even if they're not in the KoP?

Re: Custom Vs. COTS Transmissions
 

I would consider what the students will get out of a Custom vs COTS Transmission. If one were on a team that had all the resources available(time, materials, tools) and some team members looking for a new design/fabrication challenge, I think a custom transmission would be a great project even if there were a perfectly suitable COTS one available.

Re: Custom Vs. COTS Transmissions
 

These are an excellent choice for the Banebots RS-775 motors since they already have the appropriate mounting holes for a 700 sized motor and the plastic gears and mounting holes electrically isolate the motor from anything else a short in the 775 could could interfere with.