Hot swappable motor modules?

My team is having a very hard time deciding between using and not using a lift. So… why decide? What is your guys’ take on using little 2 motor modules that can be moved around between matches. Think something like the hot swappable drive bays in a server. There could be three columns: one for the drive, one for the lift, and one for the dumper/catapult/etc. Of course we would have 2-4 motors hard wired into the drive and 0-4 in the dumper/catapult, but that leaves 8-10 motors left to do whatever. If our partner has no lift, we plug in a module to the lift section. If they do, we use that module to drive faster. If our team is using a hoarding strategy, we take motors off of the drive and put them onto the catapult/dumper for extra firing speed at the end of the match when we need it. Or, if the opposing team have bots that are designed to shoot the stars all over our side of the field, we increase our drive speed to grab all of them. Or, of course, we can balance things out. On top of this we could have a jumper clip on each of the modules to tell the cortex where each modules are plugged in.

But there are a few problems.
1) How to safely connect the wires. This could be solved by making the modules on a very sturdy sled so the motors and jumper plug in very precisely.
2) How to take power from the motors. You can’t simply run an axle extender because the axle may be turned a different amount between the module and the slot. A gear may work, but the same problem arises.
3) How to transfer power. Modules would be rather awkward to fit into a bot because of everything in the way. Also, friction would be a problem with so many extra gears and axles.
4) Locking the modules in. This one would be fairly simple to solve, but still it’s a interesting challenge. You wouldn’t want motors falling out in the middle of a match.
5) Would it even be worth it?

That is a really complicated strategy but a cool one!

Honestly, I would say that overall, a transmission would be your best bet if you really want the ability to mix and match. While this might look cool, I think the efficiency loss from items 2) and 3) above would negate the benefits.

Also, if a referee was a little bit of a stickler, you could get called on <R1>:

The motors being swapped out might get considered as a separate Subsystem 2, meaning this technique would be illegal (I’m not a referee so don’t quote me on this :P).

Overall, I think this might be something cool to do on the side or as a potential add on to a future iteration of your robot, but I feel that it isn’t worth the time and effort that could be spent getting the more essential parts of your robot to the next level.

I too have thought of a similar solution, and I toyed with it for awhile before deciding that it probably wouldn’t be worth it. Let’s look specifically at motors for a hanging mechanism since that would be the most likely system to get benefits from swapping motors. Let’s say that your alliance partner has a lift that is reliable, and they are similarly equipped to your robot, so you decide to detach your lift motors and attach them to your drive to make it extra fast. You go through the match, and at 30 seconds left your partner is stuck on the opposite side of the field from the pole, with you right next to it, and with some stars and a cube between them and the pole. Now they cannot get to the pole easily, and you end up with only a low hang at the end of the match. Or, their hanging mech breaks because they get hit by a couple of stars. Now they can’t even pull off a low hang. Now I realize that neither of these situations are overly likely, especially if your alliance is good and all that, but it is a possibility because stuff likes to go wrong. IMO, it is better to have a functional lift that has motors, even if you end up not needing it, because that allows you to account for every possibility. Plus, if you go through after your initial build and optimize your motor usage, you should find yourself with enough power to run all your systems well.

Given the rule, you would still be able to switch between hang and catapult/dump (I think). They are part of Subsystem 3.

More power for systems is usually better.

Yes but usually you can find a good point where it works well and consistent enough without needing more power. For example, with optimization and good gear ratios, you could pull off a quality 4 motor flywheel last season, and you don’t really need more than that. What I’m trying to say is that IMO, you can usually find a sweet spot for how much power you need.

Well, if you had 2 extra motors last year, you could have used it on the drive, which is more important.

Yes, however last year my team worked with a 6 motor drive (the max to do easily on our 6 wheel tank), 4 motor flywheel and 1 motor intake. A second motor wouldn’t have made a significant difference on the intake, so we instead made a passive release elevation mechanism. This motor distribution worked quite well for us, and I thought it was quite optimal, at least for our design. Depending on the way you build your bot, there could be some discrepancies. For instance, if you had an X drive and you wanted more drive power you would need 8 motors (to do it easily anyway) which would limit your motor usage in other areas.

There have been two types I have seen but mainly on the drive train.

One was a wheel pod. The downside to this is the extra weight. Two screws hold the pod on and swap the whole thing.


The other has two motors connected with 36 tooth gears with one shaft connecting through. This is easily replaceable if you can get to the pod.

Does that base fit within 18"x18"? I’m looking to use something like it for my robot design.

Actually, it says

The motors are not an entire part of the subsystem, so just swapping the motors should be fine.

Yes. Some corners needed a slight trim though. I would try with the middle size wheels as this had some real torque problems once the rest of the robot was placed on top.

There was also a lot of dremel cutting to fit the motors, and the amount of screws/nuts made each wheel pod much heavier than anticipated.

I have been working with my teams on modularity which is a tough concept to get through to a group of kids that want to quickly build a robot. I finally had some success after one team struggled with a group of flywheel motors in NBN. If you look at the photo they have four motors linked by 36 tooth gears on a plate. That whole assembly has one (highlighted in yellow) axle that connects to the flywheel gearing.

By mounting the motors this way the team could remove the whole assembly with four screws (on standoffs) and one shaft collar. This allowed them to easily test and replace each motor, it’s scalable, and they even had backup assemblies that could be quickly switched out between matches.

While it does take up more space, this may be one way that a team could easily move a motor module to different areas of the robot.
One thing to note is that we had teams try with 12 tooth gears but the motors were right next to each other and ended up overheating (this was running a flywheel). The 36’s allow for some spacing and heat dissipation.

Exactly. The 36 tooth gear version that I saw had another layer to make the motor module easily removable without disturbing the gears and what not. This way, the 36 tooth gears were not completely exposed when you undid the standoffs.

Yes we had the 12 tooth variety too and that adds a bunch more friction. It worked but lithium grease was their friend.

For nbn, we had an identical setup as @Pete. After practicing for hours just before nationals, we noticed there was much more friction than before. After investigating, we noticed that the flat plate that held all the motors and 36 tooth gears had warped. It was not too difficult to switch the plate to a c-channel, since it was a removable module, but if you have the space and are planning on making a removable module, I would recommend using a c-channel instead of a flat piece.

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