pic: 114 New Gearbox Design

[sanddrag]

On page 8 of the Guidelines, Tips, and Good Practices document you will see that the peak power of the small CIM motor is significantly greater than that of the large CIM motor.

Interesting. I'm still seeing higher torque on the 3 inch CIM... However, I'm emailing the source for the numbers I've been using, as to find out where they came from. Here they are, in case anyone cares:

----------------FP801-005 3.0" CIM---------FP801-001 2.5" CIM
Torque---------200in-oz--------------------100in-oz
Power----------245 W----------------------250 W
Efficiency-------59%------------------------45%
Current Draw----34A------------------------37A
Shaft speed-----1650 rpm-------------------3800 rpm


Again, not sure where this comes from, but I'm investigating that right now.

[Cory]

Originally Posted by 114ManualLabor

Interesting. I'm still seeing higher torque on the 3 inch CIM... However, I'm emailing the source for the numbers I've been using, as to find out where they came from. Here they are, in case anyone cares:

----------------FP801-005 3.0" CIM---------FP801-001 2.5" CIM
Torque---------200in-oz--------------------100in-oz
Power----------245 W----------------------250 W
Efficiency-------59%------------------------45%
Current Draw----34A------------------------37A
Shaft speed-----1650 rpm-------------------3800 rpm


Again, not sure where this comes from, but I'm investigating that right now.

Those numbers are totally wrong. The document Dave mentioned has the correct specs. I've never seen these before.

[AdamHeard]

Originally Posted by Cory

Those numbers are totally wrong. The document Dave mentioned has the correct specs. I've never seen these before.

Yup.

Also, of course the big CIM has more torque at the posted speed.... but that speed is half the small CIM. If you were to match the speed, the small CIM has more torque.

Also, the small CIM draws 133 amps at stall... further confusing me about the numbers you have.

[Gabe]

To reliably shift a ball-lock mechanism you need to apply quite a bit of force and apply it very quickly (speaking from experience). Too little force and the plunger won't push the balls into their slots. Too slow and ball bearings skip out of their slots. This is why every ball-lock shifter I have seen (including ours) uses pneumatics, and I can't see how a servo would work.

My suggestion is to make the gearbox have a mounting that can work with both servo and pneumatics. This interchangibility will be very good, as well as making your design more appealing to other people.

[Gabe]

(Deleted: duplicate post)

[Madison]

Originally Posted by Cory

Those numbers are totally wrong. The document Dave mentioned has the correct specs. I've never seen these before.

These are the performance statistics for the motors at or near 40A, not at stall or at free speed.

Also, though at 40A the larger CIM is producing more torque, it's moving much slower while doing so, as others have mentioned. A better indication of which motor is "more powerful" is to look at, as you might guess, the power. The smaller CIM has a power of 250W -- more than that of its larger cousin.

Originally Posted by M. Krass

These are the performance statistics for the motors at or near 40A, not at stall or at free speed.

Also, though at 40A the larger CIM is producing more torque, it's moving much slower while doing so, as others have mentioned. A better indication of which motor is "more powerful" is to look at, as you might guess, the power. The smaller CIM has a power of 250W -- more than that of its larger cousin.

That's what I was thinking. These numbers (I recently found out) came from some IEEE phD who was asked to find all the specs on these motors when running in between 30 and 40 amps.

From my basic knowledge, wouldn't the higher torque at lower speeds mean that my gearbox will end up smaller, less weight, and will still push just as much as an equivalent box with a CIM?

Also, only having one motor eliminates the issue of torque fighting when there are two motors on a gearbox.

[lukevanoort]

Originally Posted by 114ManualLabor

From my basic knowledge, wouldn't the higher torque at lower speeds mean that my gearbox will end up smaller, less weight

I'd be surprised if the weight difference would be that major, and it might even go in the other direction. Since the big chip weighs ~2lbs more than the little one, and you're using aluminum gears/shafts it would seem to me that the weight of another gear reduction or just a larger reduction on the first and/or second reductions isn't that different than the weight difference of the motors.

EDIT: I plugged the numbers into JVN's spreadsheet, and I got the following for the big chip @ 40 A puts out 276W, and the lil chip 275.7W so the difference is barely noticeable. And, yes, I realized the big chip is putting out more power than the peak power rating FIRST supplies, so I ran a quick power calc on the FIRST supplied NLS and stall torque numbers and came up with 285W being the max power of the big cim. So, something is amiss in either FIRSTs numbers or my calcs. I suspect FIRST's numbers are the culprit because using the same calc I got the right peak power for the lil chip.

[Pavan Dave]

Originally Posted by 114ManualLabor

Also, only having one motor eliminates the issue of torque fighting when there are two motors on a gearbox.

I am slowly trying to learn something other than controls, and I am having trouble understanding this "torque fighting" you are speaking of. Could somebody explain this phenomena to me?

Thanks,
Pavan.

[sanddrag]

Originally Posted by Pavan

I am slowly trying to learn something other than controls, and I am having trouble understanding this "torque fighting" you are speaking of. Could somebody explain this phenomena to me?

Thanks,
Pavan.

Motor "fighting" can be explained in one word: nonexistent. It comes up a lot in FIRST, I don't know why. It simply is not true. As long as the motors are spinning in the same direction, they are both contributing useful torque to the cause. Now, if you have two different motors geared together, their load sharing may vary over a range of speed, but they will easily strike a happy medium. While you will not end up with the full torque of each motor added, you will have significantly more torque than just one of the motors. The efficiency of the system is likely to drop a bit though.

[Jeff K.]

Looks a lot like our gearboxes from this year for our mecanum drive. haha. Spur gears were 20.5PA 24Pitch and so they're hiding behind.



Are you using big cim to save money on gears? If it's for weight, it wouldn't really help. The weight for a gearbox using a small cim motor and same final speeds will end up probably in the same ball park. But using two big cims in the whole drive, heaviest motors nice and down low, would allow the small cims to be used elsewhere up higher. But running at equal speeds, the small cim is more powerful than the big cim. I can't find the spreadsheet I used, but I remember that it was a decent loss, around 20-30 ftlbs, although when it really came down to it, it was traction limited. How much torque will the gearboxes be outputting before stall?

[AdamHeard]

Are you still intent on using just the Big CIM?

Also, you mention Outback manufacturing. Is this THE gearbox they will sell? If it is, it definately needs to support 2 motors and be able to use small CIMs to stay competitive on the market.

I'm still baffled by the choice though.... One small CIM is more power for half the weight (remember, the motor can draw 133 amps [at stall] and the electrical system WILL supply it for a short time. It doesn't just hit 40 and stop), two small CIMs is double the power for the same weight.

Also, One big CIM geared to 9 fps takes a little over 1.5 seconds to reach top speed... For 9 fps, that acceleration is rather slow.

Why not design it for One Small CIM and one Large? That leaves open two small CIMs for manipulators like you desired, and still provides a competitive level of power.

[Jeff K.]

Originally Posted by AdamHeard

Why not design it for One Small CIM and one Large? That leaves open two small CIMs for manipulators like you desired, and still provides a competitive level of power.

That'd be pretty interesting, if you could get one gearbox on either end. Probably break a lot of belts though. Having both on one end would need some decent displacing by a battery.

Originally Posted by AdamHeard

Are you still intent on using just the Big CIM?

Also, you mention Outback manufacturing. Is this THE gearbox they will sell? If it is, it definately needs to support 2 motors and be able to use small CIMs to stay competitive on the market.

I'm still baffled by the choice though.... One small CIM is more power for half the weight (remember, the motor can draw 133 amps [at stall] and the electrical system WILL supply it for a short time. It doesn't just hit 40 and stop), two small CIMs is double the power for the same weight.

Also, One big CIM geared to 9 fps takes a little over 1.5 seconds to reach top speed... For 9 fps, that acceleration is rather slow.

Why not design it for One Small CIM and one Large? That leaves open two small CIMs for manipulators like you desired, and still provides a competitive level of power.

This isn't THE gearbox, it's simply one of maybe three designs we're looking at. I was asked to design a single Big CIM gearbox, and so it was designed. An upcoming field test between two drive systems with equal speed but different motor choice should reveal which motor will end up better.