They allowed us to hit about 10 fps (accelerating within a 1/4 of a second according to JVNs calculator) and still be traction limited. We also only used two stages of reduction (spur gears, then sprockets) as opposed to the more common three to increase efficiency.
Looks really nice.
About how much did those weigh? And what size wheel were they running? Were they direct driven in a 1:1 ratio with the chain, or was there further reduction?
(as I’m a gearbox nut, tons and tons of information would make me really happy, as I love the tiny size of this thing.)
He mentioned there was a two stage reduction, one with gears then one with sprockets.
And yes, they look very nice. How many times (if any) did you have to replace the FP motors?
Once… because someone pulled the power lead off the back. We never burned out a FP though, even though we were playing rather rough with them.
The spur gears are from andymark, so that is a 14:50 from the small CIm (28:50 for the big). The 10 tooth sprocket drives a 42 tooth on a 6" wheel. It was actually closer to 9 fps if i remember right.
As for the weight, it was about as low as it could get, I don’t have the official weight, but I know the mounting plate is about .4 lbs… So that, plus the three motors and gears makes up the weight. The other plate would be a frame member so that doesn’t count i guess. Without motors, they are about the lightest I have seen (the 50 tooth gears were later spoked and hogged out to save some weight there as well) besides Travis Covington’s amazing creation.
When I get home from work tonight I’ll check the CAD models and get a weight.
The transmissions look great. Our team is also working on something similar with the fisher price motor, and I’m wondering how well the AM planetary worked to match the speed of the fisher price with a cim. How close do the speeds of two motors have to be to use them together in a transmission?
I’ve heard within 90% of free speed is good.
the AM planetary has a reduction of 3.67:1 which works pretty well… the only issue is that the FP motor tends be different every year, and have different free speeds.
this year the FP had a free speed of 15,636, which is 4260.49 after the reduction. The small CIM was at 5310… So, you can see that the FP was well out of the 90% of the small CIM (80.24% to be exact). However, it ran just fine. Even after many tough (on the drive) matches through the elims (tough as in we were playing solely defense on good, fast offensive robots [968, 330]) and the FPs never became more than warm.
Iirc, this is one of the slowest FP motors I have seen over the years, so if anything, we’ll probably get a faster FP next year that would be a closer match. Or, if you’re not in a hurry like we were, you could put a different size pinion on the output of the planetary to account for the difference.
does the FP motor really put that much out. by that i mean is it worth having on a gearbox
Before this year 648 used the two FPs as our main drive motors in our three wheel design. They drove the rear wheels while we used a CIM to drive the fronts. They are that powerful.
At 387.5 Watts, they are the most powerful motor in the kit; The small and big CIMs are 337 and 270 watts respectively. The bad thing about FP’s is they don’t like being stalled very much. But since we already had another 600 watts of motor that don’t mind being stalled paired with it we thought it would be alright. Also, I remember the thunderchickens running a very similar setup in 04 (drill, CIM, FP), 05 (2x CIM, FP) (and 06?) without issue.
For future reference, page 8 on this .pdfhas some great data on the kit motors.
So, short answer; absolutely yes… they increased the power of the gearbox from 607 watts to 994.5 Watts.
That’s actually an error in the Guidelines, Tips and Good Practices document. FPs are about 170W, not 387.5W, making them the third most powerful motor in the kit, not the first. Still 170W is nothing to sneer at, especially in such a small and light package.
Darn, too late to edit…
well, I stand corrected. Thanks for letting me know that because I’ve been throwing that around for a while.
Well, at least I can still say it’s pound for pound the most powerful.
