Re: Team 2526 - Propeller Propulsion Prototype.
 

Your shaft power is first limited by the maximum continuous current. Over 40 amps, the breakers will pop after some period of time. IIRC At 60 amps, they will pop after about 2 seconds. Until they cool down, they will pop - pop - pop if the overload remains.

Your voltage will be something less than 12V, depending on the condition of your battery and the losses in the speed controller and wiring. The reduced voltage will reduce your RPM (and torque at stall) proportionally. 10V plus or minus 1 is probably a reasonable design number.

Maximum power occurs at 1/2 the free load RPM with a torque load equal to half the stall torque. At 11V this would be about 2400 RPM and 158 Oz-In. However, your efficiency is only about 40% at this point so that 60% of your input power is going to heat. At 40 amps continuous and 10 volts your input power is about 400w and at 60% efficiency your output power would be limited to about 240w. Given the load from your 12.75 x 3.75 prop and ignoring drive losses you would have an RPM of about 7500 (2140 at the motor). Static thrust would be about 4.5 lbs.

You will have friction losses in the drive. The best you can do will be about 97%. You will also have inertia in the gears. This will limit how fast you can change the speed of the props.

You might find the FP motors to be a better match, albeit at lower maximum power, because their no load RPM at 12V is 15,600. Assuming these motors are spec'd similar to last year, the load of an 11x3 prop would give you about 3 - 3.5 lbs thrust at 8-9000 RPM with about 30 amps continuous input power. The airflow could keep the motors cool which is important for the smaller motor frames. You would need to be careful about adding a thrust bearing to limit the axial force on the motor shaft because they are probably not designed for axial loads this high.

Remember the trailer mass. You'll be dragging it around.

To hit the theoretical numbers you need to insure that the props don't stall and that the airflow is not turbulent. You also have to consider the airflow into the prop.

You will have to protect from the prop going forward and in other directions as well. This means a full shroud around the prop back some screening in the front. (Those who have seen a model prop spin off will be familiar with the hazard).

I haven't yet seen convincing numbers that thrusters are practical for primary drive with a trailer in tow. But 4 - 8 lbs from a pair of thrusters may add a considerable edge on top of a friction limited drive.

Above all take additional safety precautions, especially during testing. Make sure the front and sides of your test stand are clear and have everyone well back. Discard any prop with the slightest damage.

Re: Team 2526 - Propeller Propulsion Prototype.
 

It's primary purpose is propulsion, any other effects it may have on other bots or the balls are just extra perks ;D

Re: Team 2526 - Propeller Propulsion Prototype.
 

Where do I find these? Link please? =)

We think we might experience problems with the trailer because all of that air power may be pushing directly on it.. and since it's attached to the bot.. it's like pushing off of yourself.

And stalling may be a problem too, that's why we've gotten the smallest possible pitch on our fan.. although it still ideally runs at like 30 mph.


Yeah, we just got the housing off of standard fans from like offices are such. Those will surely do fine.

Re: Team 2526 - Propeller Propulsion Prototype.
 

Re: Team 2526 - Propeller Propulsion Prototype.
 

Now I'm confused. I thought that Fisher Price were the people that made/sold the CIM motors? These are different ones? Are they legal?

~Thanks.

Re: Team 2526 - Propeller Propulsion Prototype.
 

The small fisher price motors are the ones attached (this year) to the powerwheels transmission. There are actually made by Mabuchi if IIRC.

The CIM's are made by China Industrial Motor (IIRC).

The so-called pimp-CIM's from 2007 were also called Fisher Price motors IIRC because they were used in one of their products.

The small FP are great motors but because they are small they can't be operated at high power levels for as long as the CIM's. The internal fan bearings seem to melt after which the cooling is even less. The CIM's are much more rugged.

If you have a lot of air-flow, however, the FP motors should do well. In a drive train, they tend to burn out quickly without elaborate means to keep them cool.

Re: Team 2526 - Propeller Propulsion Prototype.
 

Those don't seem to fit into any one of the categories there. =/

Re: Team 2526 - Propeller Propulsion Prototype.
 

The Fisher Price motors come in the kit; they're the ones that have the huge funky plastic gearbox attached to them.

Re: Team 2526 - Propeller Propulsion Prototype.
 

When people talk about the FP or Fisher-Price motors, they mean the ones that came in the kit of parts, and that are attatched to the funky plastic gearboxes.

\

edit--yeah, like he said!

Re: Team 2526 - Propeller Propulsion Prototype.
 

2009 Kip of Parts, Page 14, PN: 00968-2910. Motor/Gearbox assembly.

This has the -9015 motor. This year it is installed in the gearbox so you have to remove it. (Last year it was separate). The rules as I understand them let you use these motors with or without the gearbox. You can use 2 at most. I also believe that you can use prior year 9015 as spares.

Re: Team 2526 - Propeller Propulsion Prototype.
 

Very cool, 2526. We are considering using prop thrust as well to augment wheel drive. We are in the process of building a test rig and hope to have a test soon with a few variations on theme. Will be interested to share performance data with you once we've done a few tests.

ONE NOTE OF CAUTION: I winced when I saw your video!! Please anchor the test rig to the table with something OTHER THAN A HUMAN C-CLAMP . . . I'd hate to see someone get hurt. Respect those high velocities. :)

Re: Team 2526 - Propeller Propulsion Prototype.
 

But those FP motors are really small then. I don't think that'd be enough power or torque to spin 12.26-in props.

Re: Team 2526 - Propeller Propulsion Prototype.
 

Oh and I did suggest bolting it down. But my dad (the guy holding) was like nah, i'll just hold it, let's not waste drilling holes in wood. XD

Re: Team 2526 - Propeller Propulsion Prototype.
 

Don't let size deceive you, those little FP motors are about as powerful as the CIMs you are using. They spin MUCH faster (15,500 rpm free speed, approx.), and are air cooled so they do not like to stall. Many teams have used them for applications everywhere from driving arms to winches to drivetrains. They are very well suited to your application.

Re: Team 2526 - Propeller Propulsion Prototype.
 

Maybe I'm thinking too fair inside of the box but I don't see any point in this. What advantage would a propeller propulsion system give you in this years game. It seems as if it wouldn't give you much of an advantage and controlling it would be very difficult - more difficult than a robot sliding on the floor. I would put a bit more thought into this before I made the commitment to a propeller propulsion system.

Btw, I forget who said it but, There's no Air on the moon.