pic: 114 New Gearbox Design

[Cory]

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.

At any rate, the 40 amp breakers don't trip at 40A anyways--it's significantly higher for a short period of time, so the torque would increase as well.

[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.

[pakratt1991]

i would love to see these worked into the outbaack treads, and I'm sure Sam would also love to see this, were you planning on having 2 per side or just 1?
I know that running the two motors into 1 transmission actually cuts down on efficiency... thinking those treads could push any harder is sorta mind blowing,
awesome design :-)

[AdamHeard]

Originally Posted by pakratt1991

i would love to see these worked into the outbaack treads, and I'm sure Sam would also love to see this, were you planning on having 2 per side or just 1?
I know that running the two motors into 1 transmission actually cuts down on efficiency... thinking those treads could push any harder is sorta mind blowing,
awesome design :-)

Running two of the same motor has no inefficiency. Running two different motors (at matched speeds) have some, but it can be minimized by close matching.

Either way, two decent drive motors (small/big CIM, FP) will be more powerful than any single motor.

[Alex.Norton]

But when it comes to any 2 DC motors you can't get them to be exactly the same. Even if they are the same model so there will be some efficiency loss. However it is insignificant so it really doesn't matter.

[Qbranch]

uhm.... just wondering, but why are you calculating everything out based on one point along the motor's torque curve? Personally, I just find a spot that makes me happy (and the Victor drive happy) and use that as my torque numbers at that rated speed.... then i rate my top speed at just rolling friction, etc, watching what current i'm at, etc....

I RapidShare'd the torque specs for the 2.5" cim. I'll see if i can dig up my copy of the 3" cim torque curve. Post with ?'s or //s.

-q

[AdamHeard]

Originally Posted by Qbranch

uhm.... just wondering, but why are you calculating everything out based on one point along the motor's torque curve? Personally, I just find a spot that makes me happy (and the Victor drive happy) and use that as my torque numbers at that rated speed.... then i rate my top speed at just rolling friction, etc, watching what current i'm at, etc....

I RapidShare'd the torque specs for the 2.5" cim. I'll see if i can dig up my copy of the 3" cim torque curve. Post with ?'s or //s.

-q

Hmmm...

To make this whole process easier, I just use JVN's design calculator. Go under the simulator section, enter your motor specs and the robot stats (wheel size, friction, weight, etc...) and it will provide some wonderful graphs about the performance of your drivetrain.

It can also do a bunch of other cool things.

Check it out if you're ever designing ANYTHING on a FIRST robot that has a motor and reduction; it will help immensely.

Thanks JVN

[Qbranch]

Originally Posted by AdamHeard

Hmmm...

To make this whole process easier, I just use JVN's design calculator.
Thanks JVN

Neato, thanks! Now i have to figure out how to keep the guys in the robotics club (guys learining how to build robots) from finding this....

-q

[AdamHeard]

Originally Posted by Qbranch

Neato, thanks! Now i have to figure out how to keep the guys in the robotics club (guys learining how to build robots) from finding this....

-q

Don't thank me, Thank JVN.... I keep hearing around here that he's a dweeb... but he makes some cool stuff

[robostangs548]

nice!