pic: 114 New Gearbox Design

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[Cory]

Looks good.

Just as a heads up, to save yourself some effort, you really don't need to harden the shafts. 7075 or 7068 both work fine as shafting, in an unhardened state.

[Nuttyman54]

Where are you getting the gears from, or are you having them custom made?

Also, why the decision to move to one large CIM instead of the dual small CIMs like in most of your previous designs?

and lastly, I'm assuming the lower speeds are for use with the tracks? (IIRC, you had 15fps and 5fps this past year)

Originally Posted by Cory

Looks good.

Just as a heads up, to save yourself some effort, you really don't need to harden the shafts. 7075 or 7068 both work fine as shafting, in an unhardened state.

Thanks, didn't know that. That should save some time and cost.

Originally Posted by Nuttyman54

Where are you getting the gears from, or are you having them custom made?

Also, why the decision to move to one large CIM instead of the dual small CIMs like in most of your previous designs?

and lastly, I'm assuming the lower speeds are for use with the tracks? (IIRC, you had 15fps and 5fps this past year)

The gears will be custom made. I'm still looking into where, who, and how much, but it doesn't look like it will be that bad.

One large CIM ends up being more efficient, and when coupled with tank tracks, is plenty to shove just about anything around. That also leave 4 high power motors for a beastly manipulator.

Yes, the lower speeds help make this gearbox nice for the Outback track system, with the higher gear set as default. Then, when you need to get into a pushing match, you downshift and "politely escort the other bot across the field."

[AdamHeard]

The small CIM is a good deal more powerful than a the large CIM, at half the weight as well. Why not change the design to use one? You'd still have two small CIMs left for manipulators (I can't imagine needing more than that).

Can you show me the numbers that prove that statement? All of the numbers I've seen (the ones FIRST gives us for the small CIM are at 100amps of draw) point to the Large CIM being more powerful. Plus, with only one motor, there's no torque fighting or loss form having two motors.

[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.