Chief Delphi - Rookie team drive tream idea

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Re: Rookie team drive tream idea

Quote:

Originally Posted by maxlobovsky

Team 1257 (Parallel Universe or something like that.... don't ask me, I just build the thing :D ) is a rookie team this year without too much mentor support. We have started to settle on drive train idea but i have a few questions that no calculation or estimate could answer us well. We plan to use one Chiaphua per side (in a tank type steering system) in a four wheel drive with identical wheels front and back. We want to use a worm gear to gear it down about 15 times then a sprocket system for an additional 1.8 or so for a total of about 27. Assuming the the Chiaphua can give us 4000 rpm while driving the robot, that should give us a max speed of something like 8 ft/s.

One other things to note about worm gears: they have horrible efficiencies. A typical spur gear drive or chain and sprocket drive probably has efficiency around 95% or better. A typical worm gear drive may have efficiencies in the 60% - 80% range, and some worm gear drives can be even worse. Sometimes this is an acceptable trade off for the other desirable properties of a worm gear (typically impossible to back drive, large reduction in a small space), but for FIRST I don't think it's worth it.

BTW, I am of course talking about typical values above. There are very good spur gears with efficiencies over 99%, and there are very good worm gears with efficiencies over 90%, but I doubt that many FIRST teams have the money, time, or expertise required to get that kind of performance. And, there are also worm gears which can be backdriven (e.g. this year's van door motor).

Re: Rookie team drive tream idea

Quote:

Originally Posted by Solace

Ok, here goes

The two chips are not quite as powerful as the drills. I think that the drills give you a little under 350 watts and the chips give a bit over 250 watts. The next highest motor in power capabilities is I think the fischer price motors, with something like 200 watts. (don't quote me on the numbers).

The only problem with the Bosch's is they tend to be (at least with the prefab gears) a little more shall we say finnicky? When you pull them out of the box you immediately have to watch out for the leads to the motor (electrically) they are very very prone to breaking (we ended up sticking wire nuts on the ends during one match in GA and having all three of us electrical people working on it in the line for queing...) so you have to keep them from being pulled on or just resolder them. Secondly you have to watch the gear box it at some points will actually pop open (a mentor of mine noticed this on his team last year) so in short when using the Bosch's be careful and design it so that they have enough room that they are actually accessible in case you need to get them (another problem with my team's design last year). Meanwhile the CIM motors are very sturdy (good grief they are practically bricks) and they haven't failed us yet. If your a rookie team though I would probably use the Bosch's if your looking for the most "bang for your buck". They without the preassemble reduction give you .51 hp and with it give you .30 hp, whereas the CIM motors give you .46 or .41 ish power. I would say over all though either is a safe bet for a rookie team, but Bosch's will win out in power. :]

Re: Rookie team drive tream idea

If there are any other Rookies out there following this, here is a very pertinent paper about being able to turn with tank style turning:

http://www.chiefdelphi.com/forums/pa...le&paperid=222

Based on this paper, I think maybe some friction tests (in both directions) of these 12 inch wheels are in order

Re: Rookie team drive tream idea

As for using a gearbox, my suggestion would be to use the one that comes in the kit. I haven't seen the one from this year, but I know the one from last year could be retrofitted for use with chips.

I'm not saying that making a gearbox is totally out of the question. You can surely do it with a drill press if you had to. I would get a good idea of what you think you are capable of and work from there.

My suggestion to you is to find a veteran team who would be willing sit down with you for a day and help you work out some plans for a gear box, maybe even help you machine it. It looks like team 25 is only about 15 miles away from you, I'm sure they would be willing to help.