pic: Kit Transmission Upgrade kit

[Andy Baker]

loading photo ...

[Jay Trzaskos]

AndyMark is right on top of things once again. Great job guys... So where did the black battery plug go?

Jay

[ryan_f]

do you know if we're allowed to cut off that part protruding from the from of the CIM? (the threaded part that sticks out). I don't see why not since it doesn't really change the characteristics of the motor but i just want to be on the safe side

[sciencenerd]

Originally Posted by ryan_f

do you know if we're allowed to cut off that part protruding from the from of the CIM? (the threaded part that sticks out). I don't see why not since it doesn't really change the characteristics of the motor but i just want to be on the safe side

Originally Posted by FIRST manual 2006: The Robot

<R36> So that every robot’s maximum power level is the same, the motors in the kit may not be modified in any
way, except as follows:
• The mounting brackets and/or output shaft/interface of the motors may be modified to facilitate the physical connection of the motor to the robot and actuated part.
• The gearboxes for the Fisher-Price, and Globe motors are not considered “integral” and may be separated
from the motors. FIRST will not provide replacements for parts that fail due to modification.
• The electrical input leads on the motors may be trimmed to length as necessary.

(bolding added)

The intent of this rule is to make sure "every robot’s maximum power level is the same", and of course not allow any dangerous modification of the motor that may lead to safety concerns. I believe that the bolt that sticks out would fall under the category of "the mounting brackets and/or output shaft/interface of the motors", and thus may be modified. And it certainly does not change the maximum power output and isn't dangerous, so I don't know why it wouldn't be allowed.

[Travis Covington]

Question...

How would one calculate the velocity of the robot when using one large and one small CIM motor given that the 40amp RPM's are nearly identical, yet they are geared 2:1?

[sanddrag]

I can't provide a good answer to that, but I can present another question.

If you have the large CIM and the small CIM geared together (at the ratio of your choice) who/what says one will be pulling 40 amps when the other is?

I have a feeling this issue is either much more complex than many of us hope, or far more trivial than any of us know.

[Travis Covington]

Agreed. At 40 amps, it appears that the Large CIM provides nearly 70% more torque. I am no motor expert, and am sure Joe, Paul, Andy or many others could help here.

[Paul Copioli]

Guys,

The fact that the torques are different than each other at 40 amps doesn't matter at all.

Think of it this way, as Dr. Joe always says: The two motors are combined to act as one motor. The motors force each other to run the same speed. If the motors are matched at free speed, then each motor contributes 0 N-m of torque at the combined gearbox free speed. If the motors are matched at a lower speed than free speed, then the slower motor has the possibility of being overrun by the faster motor and will contribute negative torque (a generator). The faster motor will contribute a positive torque equal to the slower motor's negative torque, thus having 0 torque at free speed. The motors will find equilibrium, but each motor may draw different current values ... who cares?

All of this can be calculated from the torque vs. speed and current vs. speed curves. Don't get hung up on the different current draws from each motor.

I match free speed ... why? Because it is easy to do, but you can match at any speed you want to. Remember, though, the small CIM has more power (notice I didn't say torque) than the larger one.

-Paul

[Travis Covington]

What happens with RPM? If we were to match the free speed of the large and small CIM motors, how would I determine the RPM to use when calculating the gear reduction to give me the desired robot velocity. I am trying to estimate a true robot velocity but am getting confused with the varying RPM's under load.

Thanks so far though Paul!

[Biff]

Originally Posted by Travis Covington

What happens with RPM? If we were to match the free speed of the large and small CIM motors, how would I determine the RPM to use when calculating the gear reduction to give me the desired robot velocity. I am trying to estimate a true robot velocity but am getting confused with the varying RPM's under load.

Thanks so far though Paul!

The quick answer is to use about 4300 from the smaller Cim, Friction keeps the drive trains from making free speed (5200 approx) the other quick method is to guess that you will make between 75 and 85 percent of the motors free speed if you don't have too much friction in your drive train. As you add parts to the drive line you get less, and you get more friction. Last method it to build it and measure it. Hope this helps

[Validius]

So how much better is it to have a hybred gearbox then a standard gearbox with 2 small CIMs?

[Rick Wagner]

Originally Posted by Andy Baker

Thread created automatically to discuss this image in the Picture Gallery.

I'd like to see how the motor mounts to the interface plate. Do you replace the long screws holding the motor together with longer ones? Thanks.

[Andy Baker]

Originally Posted by Rick Wagner

I'd like to see how the motor mounts to the interface plate. Do you replace the long screws holding the motor together with longer ones? Thanks.

On this page there is a link for very detailed assembly instructions with more pictures included.


Andy Baker