pic: Final 2011 Drivetrain

It looks really small. Really small…


No gearboxes?


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Each CIM is about 4.3" long. Seeing as that model looks can it hold 4-5 CIMs end to end, I don’t think that thing is more than 20" long.

  • Sunny
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You think that’s small? If those are CIMs, that thing is pushing right up to the edge of 28" wide, actually. I’ll grant you it’s not the full 28"x38", but I’d never call that a small robot.

Hey comrads!

Here’s our team’s final design for our first drivetrain ever and its pretty innovative if i say so myself :smiley:

-the body is milled from a solid block of 7071 aluminum (with our sponsor’s five axis mill) to retain the maximum structural strength.
-the wheels are decagons instead of circles. NOW can we squeeze in more than tangential contact every tenth of a rotation, therefore we get more traction.
-the wheel formation allows for no “getting pushed around” and great defense. We might be the rookies, but thanks to our ingenuity, we’re not going to get bullied on the field :stuck_out_tongue:
-these four wheels are directly driven by CIMs so we can zip across the field at 154 fps according to JVN Design Calculator (great tool by the way guys).
-the bot fits in a 26x26 square. its octagonal shape allows for surface area for electronics.

I know its pretty good, but what are some design tips you veteran teams might want to bestow upon us?

P.S. The manipulator is coming soon with just as much innovation as you see here. Watch out for team 3815!!! :cool:

P.S.S. We would like to thank our professional mentors for their wisdom and guidance in designing this beastly beauty.


Welcome to CD, that is a pretty good first post if I have ever seen one. I thought 15.4 fps was going to be fast this year but you guys are taking this to whole different place (value).

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-Frame milled from solid…um…wow! How long is that operation going to take, and how much does that block of aluminum cost?? :eek:
(seriously, check this, if the block is over $400 market value, you may run into trouble)

-Has the wheels/wheel formation been prototyped? I’m intrigued, yet skeptical of how well it will work. Do the corners of the wheels have low-traction material? This formation typically uses omniwheels for multi-directional motion, and I’m not sure how it will work with traction wheels.

-Again, you may want to prototype and see just how much traction you gain from decagon-shaped wheels, and whether it’s worth the bumpy ride.

-Direct drive from CIMs…That’s not quite how it works. Gear reductions add torque, and a free-spinning CIM does not have close to enough to move a robot effectively. You may want to look at JVN’s calculator again, and see how much torque it will take for a 6-8" wheel to effectively acccelerate 150-ish pounds of robot. The fastest I’ve ever heard of a robot moving is 18-ish feet per second. Also, consider the drivers. Do they have the reaction time to effectively control a speedy robot? Might slowing it down, in some ways, speed you up?

Wow…just…wow. I thought fast would be good but, at those speeds you should be able to use the Lorentz Contraction to get away with a larger manipulator into the 84" cylinder (the refs will never be able to tell!). This is sheer brilliance! Have you considered the possibility of using the Picard Maneuver in match play?


woah, that means it will cross the field in 1/3 of a second, if you can effectively make a frame like that i like it. also without gearboxes you will be pushed around quite a bit.

actually this would work, you just need to control it with a melty brain.


um… wow… where to begin…

Brace yourself, this post is going to be extremely critical, but you will thank me for it later. Take it from a four-year FRC team member and a design/strategy specialist, there are like nine thousand and one problems with this drive train that will make it all but unusable on the field. I’ll start with your bullet points.

This is almost definitely outside of the budget allowed within the rules and is also a huge waste of money and resources. Frankly, I am a bit dumbstruck that your sponsor is willing to commit their five-axis mill to this kind of project.

I have no concrete criticism of this one, but suffice it to say that I am extremely skeptical. Wheels are circular for a reason, if decagons worked better, some automotive specialist would have noticed in the last hundred years or so. Of course, robots are not cars, so if you really think you’ve hit on something here, I would create a prototype to see what happens, but I am 99% certain that this will not be effective. I think the most likely result is your motor does not have enough torque to turn the wheel.

Are you referring to the 45 degree angle “holomonic” wheel configuration? Every year we see a team try this. Traditionally it’s done with omni wheels, but I’ve seen it done with regular traction wheels. It never works. The traction from the “front” and “back” wheels gets in the way of the “side” wheels, and all you can do is spin. You can use omnis to fix this, but you end up with no traction. If you want omnidirectional steering, take four hundred bucks you would spend on that aluminum block and invest them in a good set of mecanum wheels instead. Better yet, if you have access to the kind of machine shop that lets you use a five-axis mill, you probably have the ability to make a legitimate swerve drive. Or, since you’re a rookie team, you could go with a traditional four-wheel or six-wheel drive. Anything but this mess.

Either you missed a decimal point (or two?) or you’re doing something very wrong. This number is completely ridiculous, throw it out (btw, I rolled on the floor laughing when I read the comment about the Picard maneuver). Seriously. The most likely result is your motors stall from not being able to rotate your (decagonal) wheels. Particularly without gearboxes. Seriously, get some gearboxes.

No problem here, moving on.

Here’s a tip: don’t try anything crazy in your first year. Innovation rocks, but if there’s a traditional way of doing something, the reason “everyone else is doing it” is because it works. Learn from historical teams’ mistakes, not your own. One should never be afraid to depart from the norm, but should never do it without careful thought (which clearly wasn’t given here). You have to really understand the rules before you know how to break them.

Of course, there’s a chance that you’ll just ignore me, in which case I hope I don’t end up on an alliance with you. Just remember that Dolan from 2374 warned you.

Anyway, that whole post was very rude (inb4 “you’re trampling creativity”), but you really needed to hear that before you wasted all of that time and money. Now you’re out a third of your build season, it’s time to think about reprioritizing.


Wow. I don’t know if this is a joke, in which case I just wasted my time typing up the following post. In the rare event that it isn’t a joke, I’ll describe some motor loading for you. If nothing else this post is a good summary of what goes on when a robot accelerates (or catches fire, whichever comes first).

Short version:
If you build this thing, it won’t work at all. My spreadsheet should have some kind of “are you serious?” warning built into it…

Please review this presentation immediately:

JVN’s “in a nutshell” description of motor loading and acceleration:
Motors have limited power, this means for a given amount of load they can only move so fast. The less load they have on them, the faster they move. At some load they won’t move at all (stall), and at no load they have a maximum speed they spin at (free speed). They draw current from the battery depending on how high the applied load is. If the current drawn is too high, the breakers will trip (or the motors will catch fire, whichever comes first).

When a robot is accelerating, at the instant it starts moving, it isn’t moving – the motors output their stall torque. Drivetrains typically increase this torque with a speed reducer/torque increase geartrain. This torque is then applied on the ground as a force which is used to accelerate the robot. As the robot accelerates the robot starts moving which means the motor spins faster which means the torque output decreases (the motors speed & torque are linear, remember?). So why does this matter?

With CIM motors, the stall current is much higher than the capacity of the 40amp circuit breakers. If you try to accelerate with too little gear reduction (i.e. the drive is too fast) or with NO gear reduction as you show, the output force of the wheel on the ground will cause the robot to accelerate very slowly. If this acceleration is too slow, the motor will be very high on the torque curve for a long period of time, which means it will be drawing lots of current for a long period of time, which means it will catch fire (or pop the breakers, whichever comes first).

The moral of the story… your robot would take approximately the length of an airfield to accelerate to top speed, which it never would because it would pop the breakers or catch fire (whichever comes first).

Ohh… not to mention that if you ever try to get into a pushing match the wheels act as brakes on the motor and if your gearing doesn’t reduce the torque load enough it will also cause the motor to draw too much current and cause the robot to catch fire or pop the breakers (whichever comes first).

Ohh… not to mention that you have traction wheels opposed at 90-degrees from each other. So in order for the robot to move in any given direction it needs to slide a set of high traction wheels sideways across the carpet… which of course it needs torque to do, but since it has no gearing it will probably just catch fire, or pop the breakers (whichever comes first).

Physics is such a pain in the butt when it gets in the way of innovation, isn’t it? I guess true innovation is when you can actually harness physics to do what you want. Heck – that sounds suspiciously like engineering.


PS - Expert tip: robots work much better if they are 9-sided. 100% of 9-sided robots have won World Championships. Add an extra side, quick! True story.


This has to be a joke. Conservatively, that would be a NINE HUNDRED POUND block of aluminum. 7075 is about $7-10 per pound. That’s a $6000-9000 block of aluminum. No sponsor is stupid enough to waste that kind of material. This also ignores the fact that there is no such thing as 7071 aluminum. The frame would also be substantially weaker than a properly constructed welded tube or sheet-metal chassis.

Basically…obvious troll is obvious.


In that case, I must leave a well-deserved,


Decagon wheels mounted directly the cims will be the drive train of the future.


Very nice design! Robotics is supposed to be fun…this is definitely fun :slight_smile:

I agree that this is good fun - most likely this is someone’s practical joke on CD. If not, one consolation is that you learn more from failure than success.

Consider the following: his name is poohbear, this was his first post, his location is “the dirty south”, and he claims his robot can go 105 miles per hour… this all sounds pretty legitamate to me.


I have to agree with this one. You all will see!

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