pic: FRC488 - 80/20 Drive Train

[Lowfategg]

Originally Posted by Madison

The bearing blocks are 80/20 pivot pieces. We're going to open the pivot hole from 1/4" to 1/2". They tie in to the 80/20 from the top using their existing mounting holes. They're part no. 4181.

We had some trouble shifting the Dewalts and made no use of 3rd gear last year, so we were a bit slower than I'd hoped. As always, the game may change what we put into the drive, but if we can avoid pushing matches again, we'll probably stick with 1 CIM per side. Similarly, it's shown with four traction wheels, but we may again use just two and put omniwheels back onto the corners.

We expect to have our hands full with the new cRio system, so anywhere else that we can remove complexity, we'll do it.

I would never mount bearing blocks to 80/20 using the T-slots. They slip way to easy under the strain that is being placed on them. Drill through the 80/20 and bolt them right into it.

Thats just my opinion.

[Madison]

Originally Posted by Lowfategg

I would never mount bearing blocks to 80/20 using the T-slots. They slip way to easy under the strain that is being placed on them. Drill through the 80/20 and bolt them right into it.

Thats just my opinion.

Well, the simplicity of this design is that 80/20's slot system substitutes for chain tensioning mechanisms. If we were to eliminate that advantage, we'd change the design entirely.

We haven't used 80/20 much, but have had success with it staying where we put it as long as the bolts are properly tightened.

[Lowfategg]

Originally Posted by Madison

Well, the simplicity of this design is that 80/20's slot system substitutes for chain tensioning mechanisms. If we were to eliminate that advantage, we'd change the design entirely.

We haven't used 80/20 much, but have had success with it staying where we put it as long as the bolts are properly tightened.

Well I guess then the T-slots are nice to have for that, but make sure to keep up with those screws. My experiences with 80/20 last year were not that great, but some people like it.

[AndyB]

Madison, this looks like a very simple, easy to put together design.

The only weaknesses are, in my eyes, angular clearance for ramps.

Assuming the wheels are centered at 3/4" above the 8020, and positioned about 3.5" back from the inside of the front rail, that only gives you about 17 degrees of angular clearance. But for a flat-field application, this looks like a very nice drive that you could easily modify at any point.

[qwertyuiop[]\]

Why do you need a six wheel robot if you are using omni's? also watch out, 8020 bots get heavy, fast. on our 2006 robot we essentially built our entire robot out of 8020. There is alot of un necessary weight in 8020. Do you really need all for slots in the metal? it is very strong and is very fast, so if your going for a fast build this is what you want. Also, what size 8020 are you using, the inch or half inch?

[Cory]

Originally Posted by qwertyuiop[]\

Why do you need a six wheel robot if you are using omni's? also watch out, 8020 bots get heavy, fast. on our 2006 robot we essentially built our entire robot out of 8020. There is alot of un necessary weight in 8020. Do you really need all for slots in the metal? it is very strong and is very fast, so if your going for a fast build this is what you want. Also, what size 8020 are you using, the inch or half inch?

8020 itself is not actually particularly heavy. A very long time ago I did the math to see for myself and the 1010 series is almost exactly the same weight as 1x1x0.125" Al tube. The weight difference comes from all the connectors, t-nuts, and fasteners.

[Madison]

Originally Posted by AndyB

Madison, this looks like a very simple, easy to put together design.

The only weaknesses are, in my eyes, angular clearance for ramps.

Assuming the wheels are centered at 3/4" above the 8020, and positioned about 3.5" back from the inside of the front rail, that only gives you about 17 degrees of angular clearance. But for a flat-field application, this looks like a very nice drive that you could easily modify at any point.

Yeah, this can clear a 17* angle, but nothing greater. If there's anything steeper, we'll figure out how to deal with it as a special circumstance -- or we'll turn the chassis upside down.

Originally Posted by qwertyuiop[]\

Why do you need a six wheel robot if you are using omni's? also watch out, 8020 bots get heavy, fast. on our 2006 robot we essentially built our entire robot out of 8020. There is alot of un necessary weight in 8020. Do you really need all for slots in the metal? it is very strong and is very fast, so if your going for a fast build this is what you want. Also, what size 8020 are you using, the inch or half inch?

6WD does a bit better at getting over obstacles -- whether those be field elements or game pieces. Again, the simplicity here is that we can swap in any sort of wheels we'd like easily -- and we can add or remove "drop" as necessary.

The profile shown is 1010 -- 1" square.

We have a good history of building reliable drive trains that are also very light. We've been working lately on minimizing manufacturing time, so we're conceding some of the features that make things light in favor of those that make them quick to build.

Originally Posted by Andy Baker

You are right, as the t-slots do allow for the t-slot nuts to slip. However, another thing to do besides drilling a hole is to just add another t-slot nut to back up the initial nut. If there are 2 in a row, and both are tightened well (and checked routinely), then the slippage does not happen.

Andy

That'll be Fred's job. Fred is the advocate for 80/20 on our team and even then we use it sparingly. If it breaks, it's his fault.

[Andy L]

Our base was almost exactly like this last year and we had a few problems because the middle wheel was more dragging than helping

We removed it for Cal Games this year and it made a noticeable change when driving, but other changes we made to the robot made it hard to actually compare.

[s_forbes]

Great design, you could build that whole thing in a day! Well, except for the transmissions... I like how you completely eliminated the need for any tensioning device with the use of 80/20, very clever. The only "problem" I can see with it is the lack of any diagonal bracing, but I suspect the electronics board or the top half of the robot will account for that. I doubt that you'd let anything like that slip by.

[Gdeaver]

Instead of the pivot blocks, you might look at the 10 s 2497 parts. They may handle the shock loads better and the 2 " and 2 T nuts grip better. The raw stock can also be purchased if you want to cut your own. Watch the 8020 garage on e-bay. Any reason for the 1/2" shaft? For a dead axle a 3/8" grade 8 bolt is enough and lighter.

[David Brinza]

Team 980 has used the 1010 size 80/20 extrusion in our robot chassis for years now. Our six-wheel drive with Andy Mark SuperShifters goes together very quickly and getting proper tension on the chains is easy. We use simply-machined phenolic bar stock as pillow blocks for the axles with fastener through-holes spaced at 2". Instead of the more expensive drop-in T-nuts, we use economy triple T-nuts. We haven't had problems with slippage of the fasteners, we put a bit of Lock-tite on the threads and torque them down.

I don't see us changing this approach for sometime to come.

Oh yeah, you can save some $$ if you buy from 8020 Inc Garage Sale on E-bay.

[M. Mellott]

Elegant in its simplicity--very nice.

Is this to be used as a test bed for trying new ideas, or do you think we could see Team Xbot using this in a future competition robot? I only ask this because of the additional weight of an 80/20 frame and fasteners, along with other issues with the potential of loosening fasteners.

[Alan Ing]

Hi Madison,

It was great meeting with your team at the Microsoft complex last year. I must say other than the competition itself, it was the highlight of our Oregon/Seattle trip.

I am sure you know what you are doing when it comes to your frame designs as we have seen your work and this is really directed at teams in general.

Anyway, our team has been using the Bosch Rexroth extruded profile system (similar to 8020) for 7 years and except for the fact that the profiles are a bit heavier than the equivalent size 1/8" wall square or rectangular tube, we have nothing but good things to say about it and have learned over the years how to exploit its features making some pretty spiffy lifts and robot frames.

One thing we really like about the Bosch system, is that the rotating T-nuts drop in from the side and have ribs that bite into the profiles making them less prone to slip which is a problem that was brought up in this thread. Slipping T-nuts have been a rare problem for us and our machines have taken a lot of hard hits over the years. Also you can premount the T-nuts and screws to the component itself, and drop it in along the extrusion at any point.

8020 has a much larger selection of accessories than the Bosch 1" system and in all fairness we have never tried them. 8020 also has a drop in nut but they are different and if I am not mistaken, they have to be rolled in unattached to the component you are trying to mount and cost something like $2.69 each compared to the $0.60 Bosch unit.

Not trying to knock 8020, it is a great product. Many teams use it with great success. If you are worried about the T-nuts slipping, you might want to give the Bosch units a once over. Hit them hard enough and they will move too, but I believe the ribbing really helps keep them in place.

Alan

[Ben Piecuch]

I'm posting to this a bit late, but we've used a similar 8020 setup to this for many years, so I thought I'd add some notes.

You may find that there's a lot of corner to corner twist in the frame alone. When you add any upper structure, it greatly stiffens it up. But, the 1010 extrusion, and especially connectors, leave a bit of stiffness behind compared to a welded 1" x 1" tube frame. (This is a similar problem with the kitbot chassis)

The bearing blocks, while convenient to use as tensioners, are always a nightmare to keep aligned. When you need to switch wheels, you'll need to un-tension the chain, remove the shaft, and reassemble after. It's not so simple. In our experience, even when you think you have an aligned wheel and axle, it's still not perfect. We've thrown more 35 pitch chains with a similar setup than I care to admit.

I've always found approach angles to be difficult (re: shallow) when you have a minimum of 1" of frame in front of the wheels. There aren't too many ways around this issue when using a frame like this.

Carefully plan out where you'll be adding extra mounting points, and pre-assemble some T-nuts into the rail. The drop-in's are a pain, especially when you need to line them up with the mating component. 8020 makes some T-nuts with a set screw, to hold them in position. I highly recommend those on any vertically oriented channel.

One last note, when cutting 8020, always square off the edges. Chop saws work well, as do milling machines. A band saw, however, does not.

Finally, for all those weight conscious folks... The 8020 brand, 1010 extrusion is within 2% of the weight of a 1"x1"x.125" aluminum tube. The bending stiffness is also withing 2%. Torsionally it's not quite as good, but a frame doesn't see the twist like an arm/appendage would. The connections are the key, and using the double-anchors on all corners are your best options (and lightest weight...) While the connectors do add weight, you're talking around 1-2lbs when done correctly. Using the proper material for your upper structure is the key to weight savings when using 8020.

Simplicity in design and manufacturing is always good, especially if you can make it as reliable as a highly machined and labor intensive chassis. I highly recommend building a practice bot and (literally) shaking out all the issues. Oh, since we only build one 8020 frame with the new bumper requirements... Figure out a way to mount the bumpers prior to week 6. Best of luck!

Bengineer

[Rich Kressly]

Originally Posted by Cory

8020 itself is not actually particularly heavy. A very long time ago I did the math to see for myself and the 1010 series is almost exactly the same weight as 1x1x0.125" Al tube. The weight difference comes from all the connectors, t-nuts, and fasteners.

Yep, no doubt about that one. We spend a little extra to save some fastener weight by using drop ins and the hidden corner connectors, but overall we choose the convenience that 80/20 brings and deal with the "extra" weight.