Motors Vs Motors

so this year, for our shooter mech, we used a cim motor, belt gears, and a belt to power the shooter.

but in the queing area, i noticed some teams used a FP motor or smaller motor to power their shooter…

when would you suggest to use a CIM motor, or FP motor, or bane motor
in what scenarios?

our team has only been experienced with CIM motors and the denzo motor
so we dont know how we would set up the motor with the sprockets and all…

help on what parts we could pick up?

What motor do you specifically want info on?

For a shooter/dumper, you want both speed and torque. (Or speed and power, which can be translated into torque.)

A CIM is good for driving because it’s VERY hard to smoke one accidentally. It also is pretty heavy, so you want it low, and it’s got pretty good power and speed.

FPs are typically used to supplement the CIMs or power arms, lifts, and shooters. Depending on the application, you can use their own tranny, a Banebots tranny, or an AM Planetary to get your desired characteristics. At it’s lighter than a CIM, it can be mounted higher.

Banebots are typically used mainly for light-duty FP-type work with their own trannies.

Note: all height references are with respect to the CG in a game that involves climbing or sudden acceleration.

To set up a motor with a sprocket, you need a gearbox of some form, at least for the FP and the Banebots. While each has its own, others are available from AndyMark or Banebots.

Generally, use fp’s and banebots in low friction applications. As soon as you build up a bit of friction and try to run it at a high rpm, your going to smoke the motor. FP/banebots’s are good for intake systems if everything is very rigid and built with high precision. I can’t tell you how many fp’s we’ve smokes because of improper use. The motor specs are misleading on the fp and banebot. They can do what they say, but not for very long under a big load. I’ve seen several teams use the fp/banebots’s very effectively (1625, 254/968, 71, 111) for intake systems. Gearing on these is of utmost importance. You want to have the least load on the motors as you can. So if you know you can only move your ball conveyer at say 60 rmps, then gear the fp for 60 rpms, not a little more and hope that it goes faster. Its better to start slow and gradually increase instead of pick a relatively high number and hope it works, thats when you smoke em.

My rule of thumb is use a cim if you can help it. Cim
s are great because they can take on big loads and are pretty hard to smoke. I miss the minibike cims =

Which motor to use really depends on a couple factors:

Weight - Obviously if you want a lightweight arm you don’t drive your manipulator with a CIM.

Torque/Speed requirements - This is dependent on the application, obviously for a shooter you want a a decent mix of both torque (to get up to speed quickly) and speed. Obviously, this is a tradeoff unless you can put two motors to the application but this increases weight.

Size - Obviously if I have only a 4 x 1 x 1 space to put a motor and transmission into I am NOT going to use a CIM motor.

Thermal Mass - For the most part this is not an issue in FIRST but occasionally it causes a team a problem. Running a motor near stall generates a lot of heat in the motor (running any motor generates heat) You have to take this into consideration. A motor getting two hot can cause problems, you could demagnetize the magnets inside it, you can melt the internal components. Or it can become a safety hazard to anyone working on your robot, someone smarter than I can tell you numbers but motors can quickly become too hot to touch. This is one of the reasons CIM motors are often used in the drive train, the larger mass of the motors allows them to handle more heat.

Electrical requirements - Along the same lines as Thermal Mass, most teams dont take this into consideration. If you have 4 Cim motors, and 2 FP in your drive train and you get into a pushing match you will be running those motors near their stall points, this will suck your battery dry. What this means is that when you try to turn, or raise an arm, your motors will not be able to draw nearly as much current to do so. Keep this in mind.

My suggestion on what to use motors for? Look to the past, check out the successful teams and how they did what they did. The motors may not be the same but chances are you could look up data for those motors and see if you have a motor with similar characteristics. There is NO reason to reinvent the wheel.

Just my $.02 (not adjusted for inflation) Sorry for the book but I hope it helped.

A good comparison between the FP and the CIM might be like the difference between a turbocharged four cylinder engine in Cobalt SS and the turbo diesel in a Mack truck. They are both rated for about the same horsepower, but the SS needs to run at an extremely high rpm to get that kind of power… the mack truck can churn it out day after day after day.

So I tend to use the CIM in “mack truck” applications, where low rpm and continuous hard pulling are common, while I tend to use the FP’s in high RPM applications for shorter periods of time… race car applications.

I have found that while CIM’s can handle pretty much all the current you can throw at them for a two minute match (and will pop the 40A* breaker before you damage the motor) that an FP is happiest at about 10A or less. Sure, they CAN draw more… but for a very short period of time unless there is some truly awesome cooling going on.

So if you are going to use an FP in any kind of torquey application, make sure you have it massively geared down (the Banebots gearboxes work great for this, you just need to press a new pinion gear on to the FP) and don’t run it near stall (for instance, holding an arm in one place). When you stall it you keep pumping current through it (generating heat), but lose all the cooling from the fan mounted inside the motor. You might also want to consider strapping on an auxilliary cooling fan, a heat sink, or… (and I haven’t done this, or seen it done, but it might work) having a small pneumatic line set up to blow a bit of compressed air into one end of the motor. It may also be legal to attach a bit of dry ice to the FP right before a match…

Jason

  • when dealing with a short time frame… continuous current draw of even “moderate” (for an FRC application) current will heat up the motor without even coming close to tripping the breaker… we almost got into trouble in Seattle this year when we were able to play four practice matches in a row. GREAT for the drive team to get practice, but the motors were very warm to touch when we got back to the pits… and if the motor is warm on the outside, that means it is HOT on the inside, and the heat just hasn’t made it out yet.

One thing that I haven’t seen mentioned here that I think is important is ease of interface.

Some motors are naturally more suited for work in different speed ranges than others. For example it is easier to gear a Globe Motor for a low speed high torque application than an RS 545 motor. (There are some products such as the Banebots gearboxes that make the task of gearing down the RS 545 and Fisher Price motors easier, but I found the old models gearboxes unsuited for really high reductions, and I haven’t had any experience with the new models)

Additionally the physical characteristics of a motors output shaft may make them more difficult to use. Personally I wouldn’t use the window motors for anything unless it is really necessary, because they have an odd output shaft that may be difficult to connect stuff to.

May I suggest reviewing the following white papers…
Motor Selection & Drivetrain Sizing posted by Paul Copioli
http://www.chiefdelphi.com/media/papers/1378
and Advanced Drivetrain Seminar posted by JVN
http://www.chiefdelphi.com/media/papers/1676

Both of these gentlemen are typically willing to answer questions.

For motor selection, you have to consider the space you have and how much power you need to perform your task. Some teams used the Mabuchi motors to power 25 rollers for their shooting system. If you adjust the gearboxes on the motors, it could do the trick!

One interesting thing of note is that the AM Planetary Gearbox (with a FP motor) can be substituted (mechanically) for the CIM. The gearbox is designed with the same output shaft and the same mounting screw positions. I am not indicating that it is a POWER substitute for the CIM … I am just saying that the form factor and RPM end up similar…)

The planetary is also geared in such a way that you get approximately the same RPM out of it that you do with a CIM (but of course spinning the FP at its normal high rate…)

If, in the off season, you might like to do some testing … this makes it very easy to try the FP or even the 545 motor without changing your setup that you were using with a CIM previously.

This is some really good planning on the part of AndyMark… they really do have some well thought out products.

The FP’s are my personal favorite. I recommend the CIM’s because they have gearboxes already available and are hard to smoke. Often, it’s the gearing that isn’t right rather than the motor not having enough oomph.

-Vivek

The FP and other can motors have a fan blade inside them. they rely on the fan moving air through the motor for cooling. Because of this they perform best when run at high rpms. Put them under heavy load and the rpm’s drop the fan effieciency drops and heat builds. Also note that allot of can motors have ventilation holes on the mounting face. Attach the motor tight to a mounting plate and the fan does not work. I’ve seen the paint cooked off a cim and they kept on going.