Big CIM Impressions

Well, I STFA and didn’t find exactly what I was looking for. My question goes out to teams that previously used the small CIM’s on their drive, and switched to the big CIM’s in 2006.

Specifically, did you notice any perceivable lack of power/torque? Did the motor exhibit any difference in electrical performance (current draw?) Looking at the specs, the Big CIM looses about 20% of power to the small CIM. But, when used in the kit gearbox with a small CIM, the gearbox should only loose about 10% of a dual small CIM setup.

Not knowing what the game will call for this year, I’m just hoping to see how flexible our motor usage can be. Any general, or specific, comments on the big CIM will be greatly appreciated.

Thanks,

BEN

Ben,

I know this isn’t exactly what you are looking for, but…

1712 used two small CIMs in each of the kit gearboxes in 2006 and was very pleased with motor performance once their sprocket and other issues were resolved. The team also used the large CIM to collect and deliver balls in the low goal which worked well, but seeing how relatively easy it was to stall the large CIM, I’d be really reluctant to put it in the drive by itself and I’d be hesitant to use one large and one small in a gearbox instead of two smalls (provided we are given that choice/option of 4 small CIMs again this year).

Rich, I find it quite difficult to believe that you were stalling the big CIM in a ball-pickup mode. Were you driving your impeller straight off the output shaft (ie. no gear reduction?) Also, what diameter was your impeller roller?

For general information, we have used the kit gearbox with 2 small CIM’s in the past. We did not use the big CIM at all last year.

BEN

I find the big CIMS beneficial to avoid if possible, simply because of how heavy they are. But then again, it depends on the application. You might get just as heavy by the time you gear down a small CIM or fisher price. Other than the weight and a little less power than would be great, I think they are nice motors.

I think I may have the answer you are looking for,

Back in 2005 we used a duel CIM per kit gear box setup for out drive, for that game we where happy with how it did. It was simply a pretty run-of-the-mill center wheel drive.

Last year (2006) we used a single big CIM drive that we put into a Kit transmission with a special joining plate on it. We where happy with this one as well.

Here is a link to out 2006 drive train:
http://www.chiefdelphi.com/media/photos/22991

When we where doing driver training our 2006 robot PUSHED out 2005 robot around the room when it needed to and seemed to be in the same ball park for speed. This year we seemed to be able to win or tie most pushing matches we went into against other single speed transmission robots that used the 2 small CIM method. I will say however that most pushing matches we encountered where when we where in scoring positions and out goal was to remain motionless not push the other robot across the field.

If you have any questions please feal free to ask, if i dont know the answer ill find some on who does. :slight_smile:

My team used the large CIM motors in the 2006 season. It was a big mistake. When one of the small CIM motors is geared to the same speed as the large motor it will produces a little bit more torque. we used the stock 4 small CIM setup in 2005 and I have driven both robots and will admit that our 2006 drive train was under powered compared with the 2005 robot. The two robot drive trains are very different from each other so it’s hard to make an accurate assessment. But having worked with both I would have to say that large CIM motors will work but 4 small CIM motors will out perform them.

our team used the big cim for our collector… and it stalled too. I don’t think we reduced it all that much, and we used maybe 1 inch compression with the balls. Whenever we tried to pick up more than 1 at a time, it would slow to a stop… then start up again, kinda jamming, but not really

Correct Ben, almost. No we didn’t run it directly off of the shaft, but as a rookie we used the nine tooth sprockets and little bit of chain we had available and when we got three balls in the correct configuration - either on the way in or out, we’d bog down significantly or occasionally stall. We realized with better gearing, we’d have gotten more out of the motor.
Our rollers were fabricated from PVC pinned through aluminum shaft and all three were driven by one large CIM motor. The two rollers that took the load were 1.25’ and 1.5" diameter respectively. The third roller was larger (don’t remember the size offhand maybe 3"?), but was above the intake area and only was there to keep the “popcorn popping” and prevent lodged balls elsewhere in the hopper.

We actually did just run right off the shaft (with 9 tooth sprockets and #35 chain connecting the 3 rollers). The balls would actually bind the roller system when in deployment mode (we would reverse the direction of the motor), stalling the Large CIM (pickup had no problems). And I believe that the roller diameters were 1 1/2", 2", 3".

http://www.chiefdelphi.com/media/photos/22727 picture to show what system looks like

On 395, we ran the 2006 Transmission Upgrade kit from Andy Mark and paired a big CIM with a small CIM. (http://www.andymark.biz/kit-tran-upgd.htm) We were very pleased with the performance. We found that as compared to our '05 bot with similar gearing and 2 small CIMS, we had comprable if not better pushing ability, though the latter possibly being more to an improvment in design and efficiency of the drivetrain. While its true that you have a higher power setup with the 2 small CIMs, there is definitely something to be said about the advantages of mass centralization and keeping weight as low as possible, decreased current draw, as well as the flexibility to have the small CIM motors available for use on mechanisms. I will definitely keep the big CIM motor as an option when considering powertrain options.
-wayne

So here’s a question that I have wanted to ask of the more technically advanced in the group.

It’s getting close to time to order the AM transmissions for the upcoming season (assuming no big changes in the game kit.) Should we order the first generation or the new trans that will take the two different motors? If we order the new style then we will also need to order the adapter kits for our older transmissions.

How can the two different motors (small cim and minibike) with different torque curves and RPM ranges work together on the same transmission? Won’t he two motors fight each other and be much less effective or do the two motors compliment each other?

Two years ago with the KOP trans we had a big problem when two cim motors weren’t well matched to work with each other won’t this problem be worse with such different motors?

Couple of things here…

  1. There is absolutely no benefit to order the original AM Shifter. It is a bit shorter, but that is it. The AM Shifter Gen. 2 can still accept 2 of the smaller CIM motors, just like the original AM Shifter. We try to make this clear on the site, but some teams still buy the original AM Shifter. The only reason we keep it available is to be nice to the teams who bought it in 2005 and they want to use it again as an unaltered purchased part (if the new year’s rules allow). If we discontinued the original AM Shifter, those teams would have to buy new shifters. Now, if I only looked at this venture in a short-term financial view, this would be a good decision. However, we think this is bad for long-term growth and maintaining loyalty and respect to customers.

If you are deciding between the two versions (original or Gen.2), I suggest the Gen.2. This gives you more freedome to deal with either the 2 small CIMs or 1 small and 1 large CIM or just one of either. Therefore, you have more flexibility to handle whatever motor combination FIRST gives to teams on Jan. 6th.

(plus… we have more inventory in Gen.2 side plates)

  1. Combining motors in a transmission or a geartrain is really not that big of a deal. As a rule of thumb, try to match the motors’ free speed. If you have more confidence in one motor than the other, make it turn at a rpm closer to it’s free speed than the other motor. The farther you get away from matching that exact free speed lessens your optimal power efficiency, but even if the match is out by 15-20%, there is still a power boost.

  2. In general, when you add in a motor, you are adding in power to the system, not drag.

Andy B.

Ben, as I’m sure you are familiar with our bot’s setup I’ll leave out some details but attach this pic.
http://www.chiefdelphi.com/media/photos/25671

Anyways, we used 2 of the big Cim’s on the shooter wheel mechanism for the sole purpose to get the wheel to have less time before it was back up to speed.

It worked out great, and we blew one motor at Battlecry, and you could definitely tell the difference when we went up one match with only one.

The time in between going from post-shoot speed to gaining full momentum in the shooter wheel was dramatically reduced with both motors.

As far as drive, we used the regular Cim’s this year so I’m not sure how the new larger mini-bike motor Cim’s would have worked.

Let me just take this opportunity to repeat an earlier comment. I would strongly recommend that teams do not go out on any big spending sprees, purchasing lots of mechanisms, stockpiling stuff in anticipation of some expected use in their 2007 robots (from ANY source - this is NOT a targeted comment about AndyMark or any other particular vendor). Wait until after kick-off and until you know the challenge, constraints, and limitations that may be included in the rules. Teams do not yet know what may be included in the 2007 rules that may constrain sources for additional (non-KOP) parts, limit purchased components to a given level of complexity, restrict the cost or size of additional elements, proscribe the permissibility of pre-ordering parts and components, or define the timing under which materials for the competition robots may be purchased. It would be a shame if a team were to commit a significant portion of a limited budget on a component pre-ordered before the 2007 kick-off, only to find once they read the rules that the component was not permitted in the 2007 FRC competition.

Just a word to the wise…

-dave

Not sure how relevant this is… but team 85used two small CIMS and one big in their drivetrain. Maybe contact them.

Thanks for your concern; your words are good for all to hear.

By “getting close” I meant after kickoff.

I would also bet you a lot of money that Andy wouldn’t be making those fancy new wheels if he didn’t know some inside info… :wink :wink

I don’t think any member of FIRST with inside information would use it to their, or anyone’s advantage; Atleast I hope not.

Dave is on team 116, but I doubt he lets them know the game before kickoff.

Wheels have been allowed from any source for quite some time now. While it’s not a sure bet, it’s a pretty good possibility that this rule will remain the same.

I don’t know the game. We are only supplying these wheels because the demand is there (teams are showing much interest).
AB

As always, those are very wise words from Dave. Teams tend to forget that FIRST is a non-profit organization and has to rely heavily on donations from private industry. Most of the motors in the KoP are donated and thus subject to change from year to year. All those window motors, seat motors, van-door motors, and Globe motors are donations from our friends in Detroit. The FP motors are for those FP kids cars. All of these donations were probably because of production changes or overruns. I doubt very much that anyone in Detroit said let’s make a few thousand extra motors for FIRST. AFAIK, the only motor made specifically for FIRST is the small CIM. Now this in no way guarantees it to stay the same from year to year since even it has changed some over the years. It may not even be in the kit at all. I would bet that the same is true with the big CIM motor and that some manufacturer ordered a bunch of those big CIM motors for a scooter product and then either canceled the order or changed the specs after CIM made a bunch of them so FIRST somehow got them. I wouldn’t be surprised at all if they weren’t in the KoP at all this year. One way (in addition to changing the rules) FIRST has of keeping us on our toes is to change the contents of the KoP each year. That IS THE challenge. Give us a pile of stuff, a task, and some rules and see what we can do with it in 6 weeks. Personally, I can’t wait to see what new surprises they have in store for us on January 6th.