Specs:
Looks interesting. Why direct drive everything? That would mean that you would need to have encoders everywhere to ensure all the wheels are rotating at the same speeds, and a center drop means you lose 1/3 of your drivetrain at any time. Chain in tube would be good just to somewhat equalize everything.
That being said, I like this. It looks like it doesn’t use up too much space by basically spreading the volume out. Have you considered flipping the 775pros?
What’s the reasoning behind 14fps?
Belts and chains are a nice hassle to avoid if you can. In an ideal world I would direct drive everything, it’s one less thing to worry about.
But you’re right - depending on your weight distribution at any given time you will have some wheels off the ground, thus it may make sense to run at least one chain to one set of wheels and eliminate that gearbox. You could also maybe put an idler wheel with an encoder elsewhere to get your speed and not rely on running encoders off the driven shafts. Haven’t really thought about that yet.
Yep, flipped 775 is probably the next gearbox option I’ll CAD up to free up even more space.
I’ve ran drives in the 14 ft/s free or 11 ft/s adjusted space before and it seems like a really nice balance between speed and acceleration. If it’s a bit too slow you can always get rid of the 3" wheels and throw on some 3.25" or 3.5" ones in about 2 minutes.
While belts and chain are a bit of a hassle, using a center distance calculator for belts and add about 0.001 to 0.003 tolerance is easily done. Plus running all motors for a side in a single gearbox would be cheaper than 6 gearboxes.
Nothing about this drive would be cheap. Up to 12 775pro motors & speed controllers :ahh: This drive train will bleed your budget.
More realistically - probably run 8 motors and do 4 gearboxes, or just two 4 motor gearboxes which I also have designed. The 4 motor gearbox has to use a larger 1st stage gear to fit the 4 motors around it and so the overall gearbox gets bigger. These small 2 motor gearboxes can use a 60 tooth first stage gear reducing the overall size.
Could always skip the center drop and throw omnis in the corners (Vex has 3.25" omnis). This concept (direct driving with 775pros) also works really well for 2+2 drives, which there’s a ton of this season. I’m not sure flipping is really needed. You could flip CIMs or miniCIMs for most of the same saved space. You’re already saving a ton of space as it is.
This. Personally I would look at weight. While it is fun to design, you do not want to over design it.
One thing I would do is use plastic spacers (those small nylon ones from home depot/lowes) if your hex standoffs only exist for spacing.
Makes me interested in an 8 wheel variant where you are driving the front and back wheels with belts. Less total 775’s means less power but less cost, but you’ll still push around some 6 CIM folks.
Love that idea too - put a gearbox in the back direct driving a wheel and run a chain in tube up to the front omni wheel. Lots of exciting options with these 775pro motors.
How about 8WD with 8 16:1 VersaPlanetaries (direct drive from the VP)? Still cheaper than many COTS gearboxes. Not a huge amount of space savings, but it would be so fast to put together. (Also, not sure if VersaPlanetaries would like wheels being cantilevered, but that’s beside the point >_>).
Not necessarily, or at least not very much - you could have two inboard motors (as pictured) and two “flipped” outboard motors, possibly engaging a second large cluster gear of the same size located outboard of the small cluster gear. Depending on your approach, you might have to rotate things a bit so the pinions from opposite sides don’t interfere with each other, or you might just decide to use some long pinions run from shafts on both sides. In any case, you’d have to be careful to run the inboard and outboard motors in opposite directions.
Very nice concept, Ryan. However, I am concerned about the concentration of motor power, and wheel load, on the 14 tooth gear.
You can find several pictures illustrating what can happen in similar situations, by search CD threads for the word “stripped”.
Maybe consider using a steel gear?
Lots of wasted motor power.
When you start moving, (I presume you have center drop), you have (at least) two wheels off the ground. Bam, you’re already only using 4/6 motors per side. Get into a pushing match- this puts a moment on the drivetrain, putting more force on the rear wheels and less on the middle ones (and none on the front ones). You’re limited to at best, 4 motors, and worst, 2 motors of power per side.
Plus gearbox weight, “what encoder do I trust?”, the increased area protruding into the frame… I’ve never understood distributing gearboxes along your drivetrain in tank drive setups. It’s 2017, belt drives are cheap, fast, robust.
But…why?
Depending on what you are trying to do, you might only need the encoders during Auton. In that case, it would probably be sufficient to put one encoder on each of the middle gearboxes and ramped your motor power up so you don’t get wheel spin. It would probably not matter much if the motors on the front and back gearboxes are powered during Auton.
Where are you buying your pinion or 5mm gears from that attach to your 775 pros?
http://www.wcproducts.net/32-dp-gears
They are easy to press on if you have access to an arbor press.
Just an FYI Ryan, the little boss on the 12t pinion should be facing the motor bearing so you have the pinion on the wrong way( not an issue until assembly)
Good catch, I was wondering what that was all about.
In reality I don’t know that I would build this drive. With the reports of eight 775pro’s working just fine, you should probably just run chain in tube and do a 4 motor gearbox in the center or rear of the frame.
12 motor drive might be a fun off-season project though, just to see how fast you brownout (or don’t.)
1 gearbox for every wheel to make each wheel feel special.
100% yes. Use steel 14 tooth 3/8" hex gears unless you want gear confetti in your robot.
Nice Design.
I would like to use larger wheels and slow down the wheel speed a bit.
We typically get our pinion gears from Banebots and they list a 15 tooth pinion, but I can’t tell if its a 30 dp gear.
Where do you suggest getting the 30 dp gears that could do this?
Dave
Build Mentor
