27-12-2007 12:18

=Martin=Taylor=

Re: pic: 499_Toltech_drivetrain

How exactly will the outer wheels be powered? Will you mount sprockets on the outer sides of the 80/20?

What kind of wheels will you use? Be warned about the preformance wheels... They are really expensive. $354 for six

Also, is it just me or does the 80/20 have three slots? Is it 1x2 or 1x3?

Nice job all around!

27-12-2007 13:11

Andrew Schuetze

Re: pic: 499_Toltech_drivetrain

Yes, Al sprockets and #35 chain. What is missing is the stand-offs for mounting the bumpers.

Will use AM / FIRST Wheels (On Sale before the season)

thanks for the kudos, I am a bit worried as weight estimates come in at 45 pounds once chain & sprockets, Dual Cims, front and rear bumpers are added to this design. I like the adjustability of the 8020 but is sure adds on the pounds.

27-12-2007 13:24

Alex Cormier

Re: pic: 499_Toltech_drivetrain

35 chain all the way around? Save some money and weight and go with 25, numerous team go with that without any issues if you tension it properly. I say 35 from transmission to one sprocket is good enough.

27-12-2007 16:07

=Martin=Taylor=

Re: pic: 499_Toltech_drivetrain

According to Inventor 1 foot of 8020-1020 is 0.9289 lbs. and 1 foot of 1x2 1/8" wall extrusion is 0.8077 lbs. In otherwords if you replaced your two 8020 rails with boxed extrusion you would save 0.748 lbs. Big deal.

#35 chain and sprockets are however a major source of weight. In a system with such easy tensioning there is no reason to not use #25. #35 should only be used when you don't want to have a tensioning system, or when (like on arms) there is a significant amount of twisting and the length of the chain has to be very long.

27-12-2007 17:07

Kevin Sevcik

Re: pic: 499_Toltech_drivetrain

Ah, but he's using 1530-Lite which, despite the name, weighs in at a whopping 2.012 lbs/ft. 1/8" wall 1.5x3" would run 1.339. I'm questioning the necessity of a 1530 profile here, unless you're planning for your robot to be rammed by a small car. I think 1020 with a cross brace or two would be plenty strong and would save you at least 6 lbs. If you're really hankering for that 3" height, then 1030 weighs in at 1.350 lbs/ft and would still save a few pounds.

27-12-2007 17:55

Cory

Re: pic: 499_Toltech_drivetrain

1010 works just fine on FRC robots, when used properly. Even with violent collisions.

27-12-2007 19:01

chris31

Re: pic: 499_Toltech_drivetrain

If you use 1010 with the correct support braces and bumpers you wount have any problems with it.

28-12-2007 09:42

Andrew Schuetze

Re: pic: 499_Toltech_drivetrain

1530 lite verses 1030 That is the trouble with ordering materials in advance due to the slow process at the school district. I had not checked the per foot weight of 1030 verses 1530 before ordering. The lite part not being lite threw me off. Seems odd that although it is a half-inch wider profile that light comes in heavier than the 1030. I suppose I could have gone with 1020. New at this design with 8020 thing, I wasn't certain how much structural strength would be lost by milling slots into the profile for the adjustable front/rear wheels. I now have two 8 foot lengths of the 1530 in the shop so either I don't go with this system this year and keep that around for some beefy vertical members or try and reduce weight on the other components. We still may not be able to go this route as I haven't heard back from the machine shop if they want to be an official team sponsor and help us with this project. Thanks for all the input.

28-12-2007 10:41

Kevin Sevcik

Re: pic: 499_Toltech_drivetrain

The strength lost would be negligible in even a 1020 profile, provided we're talking about something like a 1/2" x 1" slot or so. You could further reduce the effects if you could move the T-nuts from the top of your bracket to the sides so the side walls could carry a bit of the load. Realistically, though, in that profile, any strength you lose there isn't likely to hurt you. We've only used extruded aluminum once for a rather poorly executed robot that we let a sponsor have too much say in... But as I understand it, unless you have a few internal braces, your weak points will inevitably be the joints of your frame. A brace straight across the middle of your robot reduces the moment applied on the joins by 1/2.

28-12-2007 22:30

Andrew Schuetze

latest numbers

4 Front / Rear dead axle saddle 0.28402 = 1.13608
2 1530 lite rail 33 inches 5.51536 = 11.03072
2 AndyMark Supershifter mount / saddle 0.38186 = 0.76372
2 AndyMark Supershifter 4.6 = 9.2
4 CIM motors 2.1 = 8.4
6 1" Angle Aluminum 26 /w 1.5 cut-outs 0.564 = 3.384
8 #25 Aluminum sprocket 30 tooth 0.125 = 1
12 #25 rollerchain per foot 0.09 = 1.08
6 AM FIRST wheels /w bearings 0.8 = 4.8
4 0.50 inch Aluminum shaft 4" 0.077 = 0.308

Total = 41.10252

This minus all the fasteners which include corner gussets for the 8020. I'll try and post an assembly drawing in a few (hours...days)

Comments welcome on weight reasonableness

28-12-2007 23:05

artdutra04

Re: latest numbers

Are you using 1" aluminum angle to connect the two sides of the drive train? I personally wouldn't go any less than 1" box with 0.125" wall thickness (or equivalent 1010 extrusion).

Also, the 1530 Lite extrusion is overkill for practically everything in FIRST. 1020 extrusion should work just fine, and would save you a lot of weight (about 5 pounds!) in the process.

29-12-2007 00:30

Kevin Sevcik

Re: latest numbers

I'll answer for him. He's using 3 aluminum angles across the front and back. It certainly doesn't really match up with the strength of his side walls, but I don't think it's really that flimsy assuming you have bumpers to spread the load. A corner hitting a single angle would definitely be bad, but with a bumper the load would be better spread over several angles and a larger area laterally.

29-12-2007 03:59

artdutra04

Re: latest numbers

Will the three pieces of angle be perpendicular to the side rails, or will two of them be perpendicular with the other four bring used they connect from a point from along the front and rear members to the side walls to triangulate the chassis and better spread the load of a impact front/rear back into the chassis? Or will it be something entirely different?


I ask this, because last year during the mentor matches at Beantown Blitz, an impact to the rear of our robot bent the rear member of our frame in by about 0.5 to 0.75 of an inch through the bumper. The wood inside the bumper absorbed most of the impact by splintering slightly upon the impact.

After this, I've been a little cautious about the actual impact capacity of bumpers. I haven't seen lots of traffic here on Delphi about teams splintering their bumpers, so it is possible that there was just a void from a knot in one of the interior plys that formed a weak spot. Your mileage may vary.


A top view of the damage on the rear chassis member. (To put this in context, it's the rear chassis member in this photo of the robot, sans bumpers.)

29-12-2007 13:10

Andrew Schuetze

Re: pic: 499_Toltech_drivetrain

Thanks Kevin for clarifying my design intent. My idea is to have six lateral braces. Two on the front (top & bottom) to not only provide support but bumper attachments. Similar for the rear. May or may not include two, but definately one in the center to provide support and place to build from for electronics / battery.

Any thoughts as to the weight of my design? Almost half of the weight comes from the AM supershifters /w 2 CIM motors 9.2 plus 8.4 = 17.6 lbs 43% total weight of drivetrain. Add in 10 plus pounds for electronics and fasteners and that leaves approximately 60 pounds for any mechanisms plus pneumatics.

Psuedo-poll
Half of the wieght in drive system plus electronics is:
okay
could be better
way over the line

Thanks for all the input and suggestions and if I had not already purchased the 1530 (lite) I would be using 1020 based upon input and information provided in this thread,

Just a week from now this will all be academic

29-12-2007 13:26

=Martin=Taylor=

Re: pic: 499_Toltech_drivetrain

It really depends on how much weight you need for your scoring device. If your scoring device this year consisted of two lightweight plastic ramps, and you had 80 lbs. available for a monster drive train, it probably paid off to put extra motors and reinforcement in the drive system.

The same could be said for triple play, where all you needed to play the game successfully was a simple one-jointed arm without a manipulator.

But in general: drivetrain + electronics < 60 lbs. so... um... I'd vote:

30-12-2007 13:17

Andrew Schuetze

Re: pic: 499_Toltech_drivetrain

Latest version here with both sides connected by 1" angle.