How to use three (or any odd number) of motors on a mechanism

Any active intake can run with one motor (for cones that is). If your team wants to use all twelve motors, then one of your mechanisms (chassis, mogo lift, main lift, etc) is going to have an odd number of motors, unless you decide not to use it. However, it’s a waste of a motor that can be used to give a mechanism more power. But let’s say you want to use it on your two motor mogo lift (an example but really it applies to any mechanism using an even number of motors). You can’t use put it on one side, you’re giving one side more power than the other, creating unbalanced movement. What would you do? Maybe a bevel gear? Maybe (specifically for the mogo case), you add another ‘leg’, but then let’s say you’d rather put it on your lift. You can’t just add another ‘leg’ for that. In my opinion, the best solution would be the bevel gear one, but what do you guys think?

A lot of internally-stacking robots (such as my team’s) have a 1-motor chain bar or four bar on top of their dr4b or other lift of choice. Some teams also have a 1-motor mogo lift. The solution that most teams have come to is running the gearing in the center of the mechanism in order to distribute power as evenly as possible. On a four bar / chain bar for cones it’s not a big deal because load is minimal anyway, so most teams have opted to do that. However, teams with 1-motor mogo lifts have to run a 1:7 ratio in the center of their drivetrain, which takes a lot of extra support and adds a lot of weight to the robot (unfortunately). This is another reason most teams have decided to put their chain bar / four bars on one motor instead, since it requires much less weight to do so as opposed to a mogo lift.

I would say that if possible, this solution would be much more preferable to bevel gears.

Our team runs a 1 motor, 1:5 speed ratio on our four bar (on top of our DR4B). With rubber bands, it’s fast and reliable enough, so we can dedicate a full 2 extra motors to our drive for a 6 motor drive.

Our sister team, however, used 2 motors for their chain bar, for a total of 11 motors. As a first year team, they decided to add an H-drive wheel in the middle of their bot, powered by the extra motor and geared for torque. It’s worked decently for them, so that’s always another option you can explore.

I’ve opted for the one motor mobile goal lift, because a 1 motor chainbar is not the way to go.

Just curious, why do you think a 1 motor chain bar is not the way to go? Plenty of teams run it to plenty of success, and the teams that run a 1 motor four bar can do so at a 1:3 ratio, some even running their motors on a hi-speed internal ratio for essentially a 1:2 ratio overall. I’d think that’s much preferable to having to run a 1:7 mogo lift as opposed to 1:3 or 1:5.

Our middle school teams did a joint re-design and are both using a 1 motor mogo 4-bar. It is ridiculous to say that ads weight over a 2 motor 4 bar. These are 2 of the lightest robots I have seen. One of them just posted the 6th highest middle school skills score in the world with it, and it would have been higher had the programming skills not failed. With 7 motors they scored a 104 in driving skills.

Adding motors just for the sake of using all the motors is not a good idea. If you can accomplish the task with fewer motors then take that advantage. It is less weight and has less power consumption. Only add motors if those added motors actually help you.

These teams do plan on adding some motors as they finish adding more function to their robot, but every motor they add will add function that will actually help them.

Well, first, just because you have one motor on something doesn’t mean you have an odd number to use where you would otherwise use an even number. What if you have two spots that each use one motor? Then you have an even number remaining.

And, as @blatwell said, just because you could use another motor doesn’t mean you should. You can look all through the real world to see this.

Now, let’s say you really do want to go with an odd number of motors for an even number of arms. If they’re supposed to move in sync, you could give them a shared axles somewhere and drive that axle from three spots. For example: A-|–|--|-A, where the A’s are the arms, the -'s are the axle, and the |'s are where the motors drive the axle (gears, sprockets, etc.). This doesn’t take a lot more effort than putting in two motors, assuming the longer, shared axle doesn’t get in the way of something else. The shared axle also makes sure they move in sync.

It is not ridiculous to say that it adds weight. Because it has to be run in the center of the robot since it is one motor, more metal has to be used in order to brace and support that gearing properly. With a two motor mogo lift, the gearing can be done inside the drivetrain, using the existing metal as support for the gearing instead of having to use additional metal in the center.

I think the best strategy for motor management is to outline the minimum amount of motors necessary for each function and then add the extras to the functions that need or could use extra speed.

If using one motor to power a 4 bar for a mogo intake causes things to weigh more, you might be doing it wrong. We have 2 teams using 1 motor for the mogo and the way they constructed it, there is a net weight reduction. There is less metal being used and 1 less motor, and fewer screws.

Maybe you should look around at other robots that have 1 motor for their 4 bar and find someone that has done it efficiently and try copying it if you are stuck. You may also want to improve the design you find. Our teams found a design they liked, but modified it to use only 1 motor and made a few other changes. It works great for them.

You can take a look at 2915A Sack Attack.

Think it was a 5-motor lift.
But I must say that it is easier to put that odd motor on the lift than in the drive.

I’m not looking for other designs, as my team has a very well built 2-motor mogo lift, and it’s working great for us. I was simply trying to explain how a 1-motor mogo lift can add weight to your frame. No matter how you phras it, it’s always going to be more weight to have even a slight amount of extra metal in the center than to just run that gearing inside of each side of your drivetrain.

Thanks for your suggestions though, as I do look at other designs anyway just to see if they outperform my own (which I have not seen as of yet).

@Mystellianne if you are using more metal and that more metal weighs more than the extra motor and any gears you may be using then you are correct, it would weigh more. The point I was making is that if designed correctly, you can make a 1 motor mogo lift using the same amount or less metal and drop a motor and associated gears making the single motor mogo lift lighter. Also, with fewer motors dedicated to the mogo lift, you have a less complicated robot with fewer things to go wrong.

There are advantages to having 2 motors on the mogo lift but reduced weight is not one of them. Speed or capacity of cones on the mogo are likely the biggest advantages.

@Mystellianne I think what @blatwell is trying to say is that if your single motor mogo weighs as much or more than a 2 motor mogo lift, you simply need to GIT GUD.