Were we ever limited on the amounts of non-CIM motor

[NyCityKId]

Okay, heres the deal: I'm in the midst of designing a continuously rotating swerve drive module, and I want all of th wheels to move independently of one-another. So basically I have 4 CIM motors and Four window, mabuchi or FP motors for a total of 8. The problem is I'm not a sure sure how many of the non-CIMs we are allowed to use. I looked through the motors and actuators section of the manual but I've only found specific info on the CIMs and servos. If anyone knows your help would be greatly appreciated. Also if anyone know the limits on theses motors in the past (2009 an back) that would also be helpful.

Thanks in advance
-Andre Dunkley

[EricH]

The limit on motors other than CIMs has always been, only what is in the KOP.

For a while, that included the CIMs--it was only expanded in 2005.

The rule in question is <R53-A>:<R53> Items specifically PROHIBITED from use on the ROBOT include:
A. Electric motors and/or servos different from, or in addition to, those in the KOP, with the exception of those specifically permitted by Rule <R52>.

[NyCityKId]

Okay. just to clarify, that means that if 2 mabuchi motors came in the kit of parts for 2011 then we would only be allowed to use 2 on the 2011 robot?

[jspatz1]

You may use only what was in the KOP: 2 left-hand Denso (window), 2 right-hand Denso, 2 FP, 2 Mabuchi (1 each of 2 different model numbers), and an unlimited number of qualifying servos. Check the KOP Checklist.

[EricH]

I understand that part but I want to know The amount of motors we are permitted to use.
You're going to facepalm when I tell you:

"in addition to" covers both type and quantity.

I can also point to the 2010 Inspection Checklist, page 2:Only KoP Motors – 5 CIM, 2 Denso Left, 2 Denso Right, 2 Fisher Price, and 2 Mabuchi. <R52.A,D,E>

By some funny coincidence, that matches up with both the KOP checklist and the rules mentioned in the checklist item.

[NyCityKId]

You're going to facepalm when I tell you:

"in addition to" covers both type and quantity.

I can also point to the 2010 Inspection Checklist, page 2:

By some funny coincidence, that matches up with both the KOP checklist and the rules mentioned in the checklist item.

Lol re-read your answer and i understood it the second time around::ouch::
in my defense, its past my bedtime.

[EricH]

Okay. just to clarify, that means that if 2 mabuchi motors came in the kit of parts for 2011 then we would only be allowed to use 2 on the 2011 robot?
That is correct.

Same for any other motor you can think of.

Unless, of course, the GDC specifically declared that you could use up to 10 Mabuchis or something like that.;)

[NyCityKId]

Okay well that clears everything up. I guess I'll have to design a few different models. Now to the next problem: Should i delete this thread? I feel a little stupid keeping it up since the answers are a bit obvious now that I think about it...

[Alex_Miller]

You are not the only person with that question. Many teams do not know that rule until an inspector comes around and tells them that their robot is illegal.

This is a common rule that is overlooked more often than realized.

[Al Skierkiewicz]

Andre,
Do not limit yourself to designing a drive system for next year by using this year's KOP. The motor list changes every year. A continuous rotation crab drive module will require slip rings if you plan on using motors in the modules or "on wheel" speed or distance sensors. Slip rings are illegal this year but may be legal next year. Globe motors were great for steering in the past but are not available/legal this year.

[PAR_WIG1350]

Andre,
Do not limit yourself to designing a drive system for next year by using this year's KOP. The motor list changes every year. A continuous rotation crab drive module will require slip rings if you plan on using motors in the modules or "on wheel" speed or distance sensors. Slip rings are illegal this year but may be legal next year. Globe motors were great for steering in the past but are not available/legal this year.

You don't need any sort of rotary electric contacts if you use co-axial swerve and bevel gears

[rsisk]

Should i delete this thread? I feel a little stupid keeping it up since the answers are a bit obvious now that I think about it...

Absolutely not! Threads like this are valuable for answering basic questions that someone else may have but be too timid to ask.

My third year team had this exact same question this year since it is the first time we really ventured beyond using CIM motors. We looked at the rules and interpreted them in our favor, planning to add several more FP motors. We later found a thread similar to this on CD that informed us we had to stick to the KOP motors period.

Just make sure you search for the answer first before starting a thread. If the answer is already out there use it, it is good to avoid duplication, otherwise ask away. Sometimes the most basic questions spark the best discussions, see "Drilling a hole in a magnet" thread as an example :D

[NyCityKId]

To Al and PAR_WIG1350
The module I'm designing will have have the main drive motors stationary and actually drive the wheels via a set of bevel gears. I'm trying to design it so it can be slightly reconfigurable to fit each years motor limitation. I actually did some research and looked through some manuals from past years to see if, and how much the motor rules changed. They all had the same wording and I was still unsure about the rule. I did do a search and I got like a million threads even after I narrowed it down. Needless to say I was a little flustered. So i posted this thread (somewhat arbitrarily, I will admit:o )

[Al Skierkiewicz]

Andre,
Make sure that you can live with the efficiency of the bevel gears.

Par,
Take a look at my post again, please.

[NyCityKId]

Andre,
Make sure that you can live with the efficiency of the bevel gears.

Now that you mention it I do remember reading something about bevel gears losing 5-10% efficiency,but I'm not sure how accurate that is, so don't quote me. Anyhow thanks for the advice Ill look into that.

[The Lucas]

If you are looking into designing a swerve drive with no prior experience, I recommend you check out the video of Team 118's crab drive presentation (http://thinktank.wpi.edu/article/152) from the '09 Robotics Conference. It should show you the basics.

[NyCityKId]

If you are looking into designing a swerve drive with no prior experience, I recommend you check out the video of Team 118's crab drive presentation (http://thinktank.wpi.edu/article/152) from the '09 Robotics Conference. It should show you the basics.

Thanks for the link Lucas. I'm watching the video right now. I'm only 8 minutes into it and they're pointing out some problems that I over looked.

-Andre

[PAR_WIG1350]

Andre,
Make sure that you can live with the efficiency of the bevel gears.

Par,
Take a look at my post again, please.

I understand that you were specifically referring to motors mounted on the module it self, I was just clarifying that point for others who might have less experience with swerve drive and wanted a way around the rotary electric contact ban while still maintaining the unique capabilities of continuous rotation swerve drive.

[Al Skierkiewicz]

I was also referring to sensors mounted on the wheels, a convenient method of tracking robot movement for auto mode. Slip rings were legal in the past and may be legal in the future. Although cool in some respects, continuous rotation is generally never needed nor does it supercede the need to use inefficient bevel gears. Although they look good on paper, mechanical guys can discuss the unique problems with alignment and power transfer better than I can.

[NyCityKId]

How inefficient are bevel gears? I've looked it up and I keep getting a pretty big range (around 1-45% efficiency loss typically). What makes them inefficient? is it the quality of workmanship (i.e. how well they fit together) or is it just a flaw of the design and cannot be circumvented? I'm no mechanical engineer but it seems to me that if a pair of bevel gears a custom machined so that the fit together near perfectly then there should be very little losses. If anyone can explain this it would be greatly appreciated.

-Andre

[Mike Betts]

Andre,

When you stop to investigate, many gear efficiencies (or inefficiencies) may surprise you. For example:

The Globe motor (KOP a few years ago) had a 77% gearbox efficiency (23% loss). Granted, it was multiple stage (117:1) but it was probably better designed, integrated and implemented than anything you will accomplish in your school's machine shop.

Another example: A Globe gearbox/motor I used in another robotic competition last year (65:1 gear ratio) sported a gearbox efficiency of 66% (34% loss).

Also note that these examples were manufacturer's numbers and likely optimistic...

When we learn physics, we almost always "ignore friction". The real world never does...

Regards,

Mike

[SteveJanesch]

NYCK,

It sounds to me like you're attempting a really cool and ambitious development, which is great. It's the off-season, so don't let yourself be restricted by what's allowed in a particular year's KOP - this would make an excellent demo-bot. For turning, you could use 2 LH and 2 RH window motors, or four old Globe motors, FP's with transmissions, or whatever you've got in inventory. Learn as much as you can and have fun with it. Do keep in the back of your mind what restrictions you'll face with next year's KOP, but for now don't worry about it.

Also, if you plan to actually build a demo chassis, start working with a programmer or two on what sort of driver inputs (in addition to drive module sensors) that can be used/will be needed to control eight independent motors. Let us know how it works out.

- Steve