So, my team has recently acquired two competition super kits with the intent of participating in a VEXU Nothing But Net competition in February. Some of you may have noticed my sporadic appearances here and there around these forums asking for help.
Last week, my team and I got together to begin practicing fabrication and we decided to try and put together a double flywheel design. Admittedly a silly mistake, we tried doing so with only one motor. Naturally, anything we came up with was fairly fragile and came under extreme loads when we tried putting a ball through the flywheels.
We learned a lot – especially that we knew very little. I recall reading a thread around here stating that most teams used approximately 4 motors for their double flywheel contraption. However, I’m not particularly sure how that is achieved. Sure, I could just mount 4 motors such that they are all driving a common gear (or common set of gears), but wouldn’t that open up the possibility of the motors not turning perfectly in synchronization? How do you eliminate that issue when you go to interface more than one motor together in a sort of “gear box”?
Also, are there any good sources that anyone has posted (especially in regards to VEX) that I can go over with my teammates to become more familiar with gears and gear ratios?
Also, our super kit appears to have only came with 7 motors. That seems to be silly considering the limit is a combination of 12 servos/motors. Also, it did not come with any servos. Is that going to be a problem? Do most teams utilize the full 12? I guess I expected to get everything we could possibly need with the amount of money that went into purchasing the kits.
When powering a mechanism with more than 1 motor, coupling them using the same size gears (for the same common ratio) works just fine and is how you are supposed to do it. Small differences in each motor’s rpm won’t have an effect that you have to worry about. Another method is having two motors share an axle (one motor on each end) and then have a gear on that axle mesh with a copy of the later.
In order to be competitive against other teams, you will need to max out the 12 motor limit. Servos are very, very rarely used, in fact I have not seen one on a competition robot for years. It is much more effective to use a 393 motor and use a sensor rather than a servo since 393’s are way more powerful and durable, and are continuous rotation compared to those small plastic geared modules.
Assuming that you are new to vex, in order to be on par with the majority of other competing teams you are going to need to spend hundreds on new parts that super kits just simply do not provide you with.
It is possible to be competitive, but your potential won’t be as high as if you had 12 motors on each robot.
For example the 15" robot could have a 4 motor drive, 2 motor intake, 2 motor LP and still score at 1.6 balls per second full field using match loads.
the 24" robot could have a 2 motor intake, 4 motor speed drive, and a 2 motor flywheel and be a good mid field robot.
However, the mid field robot in that video had an 8 motor drive and thus was extremely fast.
The full field robot had 2 launchers(2x2=4 motors), although only one was used so effectively it was an 8 motor robot.
Additionaly the full field robot had pneumatics,and the mid field robot used 12 motors in total. Without these resources (maxed motor limit) they could not have performed how they did.
When you combine multiple motors to the same load they inherently “balance things out”. Even if you gear them differently, they’re still going to find their “happy place” (although it won’t be as happy as if they’re all geared the same).
This allows you to combine motors with slightly different specifications, or even entirely different motors (not in this competition).
Yeah, the different internal gearings in a gear train will make it go to about the slowest one. So open them up and make them the same. You will be much happier this way.
On a drive train, if this happens, the robot will list to one direction as one side is not quite up to speed.
Robots, like race cars, can get expensive quickly in buying stuff. So you may want to budget for some more parts. And expect about 10% of your motors to have some failure within a competition season. (busted wires, busted connectors, internal gears strip, just does not run as well as the others, etc). So buy a spare motor or two at a minimum.
(Nice avatar JVN! I liked the new Vex worlds branding you guys did)
So yes, most competitive teams use as many motors as possible in order to have the fastest lift, cleanest intake, best launcher, smoothest drive base, and so on. However, my current robot only uses 9 motors and no pneumatics -mostly due to a very, very limited amount of school support- and is very competitive with some of the “maxed out” robots. Honestly, we could probably improve it with more motors, and we will need pneumatics for elevation once we get that figured out, but at this point, we are right up there with teams that are using more motors than us. Interestingly, I have not seen many teams try to put 6 or 7 motors on a launching mechanism to get an absurd fire rate. Most teams with the full 12 motors use the extra ones for an inefficient elevation mechanism (no offense) or an 8 motor drive. An 8 motor drive is probably better for an outfield bot in which mobility is of more importance than fire rate, while a 6-7 motor shooter is better for a robot that shoots preloads as quickly as possible. But many preload-bots just have 4 motors on the shooter and are still able to achieve a very high fire rate with phenomenal accuracy. For maximal synergy in VEX U, you might want one of each. Elevation is another thing, which can be accomplished with motors if you want an active lift or pneumatics if you want a passive ramp. Or you might choose not to worry about elevation, as you will be competitive with many teams even if you don’t have it.