Mindboards

That is correct, there is no way to control that type of ESC directly with the NXT (unless perhaps using custom NXT FW). However, you don't need a $50 servo controller interface for the NXT; a uC and a couple resistors could work just about as well.

Matt: Interesting, I'll have to try that on a re-visit. Going over my current options -I am opting out of the PWM control via the IR receiver, I already have too many combinations to test.

Taking time off from work is so great! I've finally made some progress on this. I've measured the inertia of each of the tires that I will use. And I have completed a chassis that will carry all of the electronics, has a quick change rear axle attachment, as well as front and rear cargo area to add weights.

Now I would like to ask for any ideas you may have for gear trains to test. If you have a link or a pic that you can post here that would be great. Or you can PM or email me. I would be happy to re-create anything that you have designed or come across. Thanks in advance!

Here's a pic of the current chassis. The extra wheel in the middle is to measure distance.

Link to larger picture:
http://jwiger.isa-geek.com/MBF/jwiger/DSCN1103lrg.JPG

Finished all of the test runs for the Motors vs. Tires combinations. I originally planned on making a 10 meter long track. But I didn’t want to work outside, and didn’t want to drag all of my stuff to a gymnasium and explain what I was doing to every random person that stopped by. Luck would have it that I have enough room in my house to set up a 3 meter track and thanks to the benefit of averages I could simply run each combination down this track say three times for a total effective length of 9 meters (pretty close to my original desire) and still get a good chunk of data. Now I have five different motors, and 17 different types of tires for this test. That results in 85 different motor/tire combinations, then I ran each test three times -that is 255 runs. Each run was three meters, so I drove my little LEGO vehicle 765 meters! That’s about 0.48 miles, which isn’t far to walk or drive, but is a long way to chase a little LEGO vehicle for sure.

I used the same axles and gear reduction (46.656:1) for all of these tests. The most power hungry motor/tire combination was burning about 38 Joules per meter (yeah about 114 watts for one 2 min. 30 sec. run), the best combo resulted approximately 1.5 J/m (covered the same distance in about 20 seconds), that's a 76:1 ratio! Again this is a very slow gear ratio, I'm expecting higher gears to turn the tables a bit.

Unfortunately I have to work tomorrow. But I have have Tuesday to Thursday off, so I will chart and graph everything out for you guys. I still need to know if there are any axle or gear trains you are interested in.

Gear ratio of 1:125

But seriously, if I were doing the tests I would start to go up in the gearing, then do direct drive, and then see how geared up you can get it. For axles, the standard types. Pendular, independent, solid-axle, that kind of stuff.

Well I can check off fixed live axle now. I will definitely build a independent set up but I don't think a pendular type would really matter. I don't need the suspension to flex for my tests. So even the independent style(s) will be locked out. I think my next test will explore gearing ratios and be limited to just three of the wheel/tire sets. I'm a little concerned about the speeds I will get, the previous test saw a max of about .25 meters per second. The stopping distance at that speed was about 40mm and that's with low gears and motors that were relatively hard to back drive. Faster gears will take longer to stop and it will be going much faster...

I need to get some pillows I guess.

Take a look here: http://jwiger.blogspot.com/2012/09/the- ... -test.html

There will be more (much more) to follow. All this test did was help identify some tires with relatively low rolling resistance. I've chosen one small, one medium, and one large diameter tire to base further research on. The next step is to find optimum gear ratios to minimize the Joules per meter used with each motor.

After finding each motor's optimum setup I will have a basis to compare all of the gear and axle configurations we have discussed earlier in this thread.

Keeping things organized; here are all of the usable gear ratios I can find with LEGO gears. I'm working on modifying my test vehicle to more quickly change the gearing for the next group of tests. The 3m wide differential has a 28t gear which opens up other ratios such as 2.333:1, 1.4:1 and 1:1.286 but those would all be perpendicular angles. Which I want to avoid for these tests. Thus I will not be using the worm gear yet.


Link to large image: http://jwiger.isa-geek.com/MBF/jwiger/E ... ratios.jpg

Of course this is not every possible gear configuration. It is just a display of usable ratios from 1:1 to 5:1. Also I must give credit to Sariel, his Gear Ratio Calculator made it much easier.