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.

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).

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.

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.

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.

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.

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.

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.

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.


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.

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.

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.

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.

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

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.

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.)”

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 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.

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.

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.