Quick napkin sketch of a drive system I figured I would share since everyone and their brother seems to be posting these new fangled west coast drives. Weight estimate ~27lbs (no electronics)
Direct drive the middle wheel (dropped 1/8") from the toughbox. The TB has the optional 40 tooth output and 24 tooth cluster gears for a total reduction of 5.97 and a rough top speed of 10fps when using 4" plaction wheels. The outer wheels are dead axle and chained to the center wheel. Chain will be tensioned via AM Chain Tensioners.
Ok, now that you read all that you get to read why I did this. You don’t need fancy renders, in fact, they are a crutch. In the time you spend figuring out how to make it render pretty you could have figured out the correct ratios to make the robot drive properly or how to route your chain. I think I speak for any mentor when I say that I would rather see that you guys figured out how to properly calculate what sort of reduction you need rather than see that you figured out how to click the “make it pretty” button.
(And yes, I did actually figure out a rough weight based on my materials!)
Snarky. Although I am a fan of what your showing. We need to stop relying so much on computers to do all the work for us, and knowing how to do it by hand is always a good skill. However, technology is the future. The reason we have these things is so that we don’t have to do it by hand anymore. We can have machines do stress analysis for us, saving us time of going though it by hand. However, the skill of calculating things by hand and sketching by hand is something that we should continue to teach the youth (until my netbook can run Inventor :D)
One of the HUGE things that I think the cad monkeys miss out on (and I’m one myself now), is the gut feel you develop of how this stuff works out and the talent of visualizing this stuff in multiple views in your head.
Being able to close your eyes and actually see the views, rotate the components, and then say “yep, that’ll work” rather than having to cad it is a talent that is only developed through use.
If you’re used to sitting down and drawing something every time, you’ll never develope the visualization skills to do it. Heck, I spend nights in bed when I’m falling asleep doing exactly this during first season. Especially with control board layouts.
This is a very good point. Since Ill be training a new CAD team over the summer, Ill try to emphasize visiualization before CADding.
I wouldn’t say they all are missing it though. Most of my friends in CAD are equally competent sketchers, they just prefer the completeness you get from CAD. Maybe this has somethig to do with the fact that my school mandates a year of hand drafting before CAD.
I do think visiualizing ideas first is becoming a last art though.
I have two thoughts on the value of being able to at least estimate without CAD.
It is very easy to make silly mistakes while using CAD that cause results to be way off. It is quite useful to be able to recognize when things don’t make sense.
It is also handy to be able to come up with sensible ideas quickly at the beginning of the build season or of a project at work when many decisions are made without the time to do the CAD.
The funny thing here is that while you’re preaching to us how doing the math is better than a pretty render, I think your drivetrain won’t perform adequately with the gearing you’ve outlined. 10 fps with 4 CIMs isn’t the best acceleration, and you are nowhere close to traction limited. Pushing matches will probably trip your breaker faster than I would be comfortable with. Your gearing would probably eat through batteries faster than I would want as well. You could increase your reduction a bit to become traction limited at much more feasible currents, while increasing your acceleration enough to virtually make up for the speed loss in a Breakaway like field.
This is assuming you bring your robot to full weight. At the 27 pounds pictured, I bet you would have zero problems.
Couldn’t or Shouldn’t? I know a lot of guys who are of the opinion that if you can’t explain the idea using a napkin and a pen you are probably over complicating it.
Specifically, what part of my math did I do wrong? (Remember folks, I am a programmer, I do this in my spare time) I worked out what the speed of the motor at 40 amps was and based the speed off that. Is a 5.97:1 reduction too little for a 4" wheel?
Well I suppose one probably could still design it, but like you said, it’s probably not an elegant solution.
I think your powertrain calcs are probably fine, and I wouldn’t worry too much about acceleration. My freshman year (2001) we ran 2 Bosch drill motors geared for 10ft/s and it worked wonderfully, 4 cims should have plenty of torque to get you by. You probably won’t win a pushing match against a hardcore pushing robot, but that’s what shifting transmissions are for if you chose to use them.
