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pic: Its twins - prototype drives
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Re: pic: Its twins - prototype drives
Are both the 4in and 6in wheels powered? If so, how are you planning to account for the differences in circumference between the two wheel sizes?
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Re: pic: Its twins - prototype drives
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Re: pic: Its twins - prototype drives
How do you plan on connecting the two sides? We had a somewhat similar design this year and we needed a lot of reinforcement to keep the chassis from flexing.
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Re: pic: Its twins - prototype drives
Will you be sharing CAD?
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Re: pic: Its twins - prototype drives
Just curious, what sort of efficiency loss do you get with using the right angle gears? Is the loss in efficiency/power worth the savings in space?
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Re: pic: Its twins - prototype drives
Do you have a drop center on this? Just looking at the picture it appears all wheels make contact so I would say no. Doesn't seem it would turn well.
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Re: pic: Its twins - prototype drives
I know it's prototype but how thick are those side rails, and those are 1/2" bolts? How's the frame work here? Anything to try and stiffen things up in sideways flexure?
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Re: pic: Its twins - prototype drives
What is the weight of one pod as configured in the picture?
It hard to tell, but it appears you only have a few degrees of chain wrap powering the outside set of 4" wheels - definitely less than 90 degrees. You'll get bad wear on that sprocket. As others have stated, your 6" wheels are touching the ground. Turning on carpet will give you trouble. Keep working on the prototype and let us know how it performs. David |
Re: pic: Its twins - prototype drives
Between the bumpers and mechanisms installed this should stiffen up the frame. If I get a chance (it won't be soon) I will post the CAD drawings of the plates. We actually used the Andymark CAD to find the distances. Far as efficiency loss, I am not concerned, its small and our mechanisms are geared correctly with low power use so if we have loss at the match it will be over before it is a problem. We will just recharge the battery a little more. Between the front wheels, center and rear wheels their is a difference of .375 inch. The side plates are 3/16 thick. We do plan on cutting the bolts shorter or go with aluminum with C clips but we have had problems with the C clips coming off. The chain wrap is a problem, but we do not plan on using the center 4 inch wheels on future designs. We wanted to put double sprockets on that wheel but we only have 2 inches between the side plates and the chains barely clear now. One unit weighs 20 pounds.
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Re: pic: Its twins - prototype drives
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What exactly are you guys trying to get out of this drivetrain that could not be done with a standard 4 or 6 cim versa drive or even a kitbot? This is a 50lb drivetrain while people have made 25-35lb drivetrains out of 2x1 tube for years now. They are simpler, cheaper, have less custom parts, are stronger, easier to assemble and maintain, have more reliability can push harder, accelerate quicker, and weigh 20-50% less than this. the only advantage I see in this is that it gets the Cims out of the way and frees up some bellypan space. if thats your sole goal then i highly recomend checking out designs for gearboxes that put the cims over the top of the drive wheels. its a simpler and more proven concept than this and has many more upsides with none of the downsides i listed in this post. |
Re: pic: Its twins - prototype drives
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We used 3/8" drop due to the AM pneumatic wheels, and found that was a good number for us.For an 8WD, having a bit of extra drop doesn't hurt a lot as long as your CoG is near the center. 4WD is definitely not a good idea, agreed. This drivetrain seems to save a ton of space compared to "normal" WCD setups, and doesn't take too many extra custom parts. They weigh less, but with a slight redesign this drivetrain too could be pretty light (maybe 40lbs for the whole deal). For this year, a 40-50lb drivetrain isn't usually a big problem because of the lightweight robots people ran in general, although the rest of the robot could be as overbuilt as this and cause you to hit 120lbs. Flipped CIM gearboxes don't save nearly as much space as this design. |
Re: pic: Its twins - prototype drives
If I remove the four 4 inch wheels in the center of each quarter I will still have 8 wheel drive. Far as weight this is a PROTOTYPE. We need to test it and find out how we can improve it.
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Re: pic: Its twins - prototype drives
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1 Spur 1:1 to 6:1 94-98% Efficient 2 Straight Bevel 3:2 to 5:1 93-97% Efficient reference: "Comparison of Gear Efficiencies." MEADinfo.org . N.p., n.d. Web. 11 Aug. 2016. <http://www.meadinfo.org/2008/11/gear-efficiency-spur-helical-bevel-worm.html>. |
Re: pic: Its twins - prototype drives
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Looking at that page, I realized the OP could probably switch to spiral bevel gears without much increase in price, depending on the supplier they're using, but since they already have the straight bevel gears they need, it probably doesn't matter. |
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The quoted numbers have no context, but I would assume most FRC bots will get less efficiency. |
Re: pic: Its twins - prototype drives
I like the wide open interior space - it would have relived a number of constraints on manipulators this year.
With those long chain runs close to the carpet, I would be worried about snagging threads and other debris, especially as the chains get loose. Is there some reason you decided to route the idler offsets to pull the top chain down rather than lift the bottom chain up? My initial understanding of the small wheels inboard was to have the ability for more contact points with the floor. If you reduced this from 6 wheels per module to 4, would you make the wheels of equal/closer size, or did you do this for some other reason? |
Re: pic: Its twins - prototype drives
I like what you are trying to do. Four of the last five years the GRT drive trains have been working on increasing the free space in the robot. With the three motor drivers the loss of a few percentage points of power is compensated by the increase in space for interesting mechanisms.
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Re: pic: Its twins - prototype drives
Nit-picking at best, but I can't help but notice a lack of fillets on both interior and exterior vertices. The sharp corners will introduce stress concentrations that could be avoided by including even small radius fillets (albeit larger than the inherent radius left but whatever cutting tool you are using). If you are going to continue using 3/16th material during competition I would urge you to reevaluate your truss pattern. I think that you can be much more aggressive on material removal.
I appreciate trying to free up space inside the frame, but I have to wonder what is the acceptable cost. Max hits the nail on the head with this question IMO. Quote:
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Re: pic: Its twins - prototype drives
This is cool. I definitely like the idea of trying to save interior space in the robot for mechanisms. It sure can make moving multiple or large game pieces through a robot easier.
Only one thought - other than wheel bolts, are there any standoffs inside the frame connecting the inside and outside plates of the pods together? I would be a little bit worried about a significant impact to the plates - even 3/16" thick. Some carefully arranged standoffs could help mitigate this, especially near the corners. Please keep working on this drivetrain, offseason projects are a great way to try new designs that push the limits of "should I really do this?" -Nick |
Re: pic: Its twins - prototype drives
Looks like motorized roller blades LOL
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