pic: Kit Transmission Upgrade kit
 

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

Jay

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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

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(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.

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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?

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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.

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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.

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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

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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!

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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.

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


Andy Baker

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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

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

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I am for one very disappointed with the upgrade part that is "supposed" to allow for the mini bike motor to be linked with the standard cim in the kit. one the instructions call for a 8mm id 3x8" long washer and a 1/4" long washer, both of which where not present in the box when the shipment finally arrived. second the 28-toothed MB gear can barley if any slide down on our mini-bike output shaft. i know this seems to be a little over the edge but to me when you purchase a upgrade for a certain part or object the upgrade should one, be of little ease to install and second have all of the parts that are needed for the completion of the upgrade. i know Andy mark is a good guy, but my team has no time to waste as i well know every FRC team has no time to waste to try to install an upgrade and not have it work. i have purchased his products before and they always have been of high precision and quality, but this current product is by far our worst product. instead of getting the motors installed in a few hours we have wasted two days trying to make parts for a "part" that is supposed to already work and fit on the mini-bike motor. if Andy mark does read this reply then i highly ask and urge him to look over every product that he sends and makes sure that all of the parts are in the box when it is shipped. :mad: to every one else who has already purchased one of these upgrades i hope and wish that you have better luck than we have.

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If you had read the assembly directions before you bought the kit, you would have been able to see that Andy clearly lists the parts you mention as not being provided in the upgrade kit. You should be able to buy some washers and nuts. It's a waste of Andy/Mark's time to go and buy a whole boatload of washers to include in their kits when you can just as easily drive down to OSH/Lowes/Home Depot/any other local hardware store.

Im sorry, but this statement COMPLETELY baffles me. Correct me if I'm wrong, but didn't you buy the upgrade kit so that you wouldn't have to make all these parts yourself? Andy provided you a fantastic service, at a fantastic price, since as you've already said, you don't have the time to waste by making all these pieces yourself. That being said, I'd be a hell of a lot happier to have spent $28 and another what, $2.50 on washers and be able to adapt my motors than to be stuck in a position where I was unable to use the motors due to the belt drive. Any amount of time you spend trying to get the upgrade put together is going to be a whole lot less than if you had to make everything yourself.

Andy and Mark are providing FIRST with fantastic, competitively priced products. Just because you buy something from them does not mean that it's going to magically assemble itself and bolt to your robot. Nowhere do they tell you that it will require no work on your own part. In the future, if you think their products are of marginal quality, I suggest you design your own adaptor, and machine it to your own specifications. Perhaps then you'd appreciate the value of their services.

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Thanks for the advice.

It's true that we listed a plastic spacer on our instructions, while sending washers as a replacement. We have changed our documentation being sent with these upgrade kits to reflect this change, as we have received 1 email about this issue also. I apologize that our documentation had this error.

The one thing I would like to have better with this kit is the tightness of the "D" holed, 28-tooth gear. These gears are being broached to be a very snug fit on the D shaft of the Mini-Bike motor. If the motor's shaft is marred slightly (by beating on the shaft to get the manufacturers' gear off... or by the manufacturer's gear set screw), then our 28-tooth gear needs to be pressed on firmly.

I suggest 2 things to help this situation:

1. Use a scotch-brite pad or a very light sandpaper piece to clean up the Mini-Bike motor shaft before adding on the 28-tooth gear.

2. Heat up the gear to expand its hole before putting it onto the motor shaft.

These two steps should help facilitate this installation. I will add these to our documentation also.

Andy B.

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ahh..this might be random. but nonetheless important.

for the large cim motor, aka: bike motor, are we allowed to take out the gears and the springs that are already attached? b/c we are planning on using the output shaft directly connected to a coupling...and so on...

so again...are we allowed to take out the springs and the black gear thing..??
if so..HOW CAN I? i tried to pull it out..it's pretty much impossible.

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Yes, you can remove them. If you look at the rule about modifying the motors, it allows you to modify the output shaft/mounting points.

Do a search for the thread about removing the pulley. The short answer is you need some sort of gear pulling device, and a heat gun/blowtorch with which to heat up the gear (due to the adhesive used on the shaft).