Chassis weight

Thanks for the info, our group has been working on a direct drive mecanum system. The frame, gearboxes, motors and wheels weigh 47 lbs with a perimeter of 108 inches. I am not sure we want to cheese out the frame any more than it is. At this point it only exists in SolidWorks.

[treffk]

That's okay! Ours only consists in to scale drawings and a 1/3 scale cardboard cutout.

[pmangels17]

Our drive generally averages around 30-40 pounds. However, in 2011 we built a crab drive (with freshman builders and one sophomore, might I add) that weighed approximately 50 pounds. However, you could easily make a lighter custom one or a lighter one using the kitbot. It all depends on your goals.

[Donut]

I think the average is in the 30-40 lb range. We did Mecanum last year with very large standoffs and full size Toughboxes for each wheel (read: overkill) that weighed in at a whopping 60 lbs for the frame, wheels, gearboxes, and motors. This year we're trying out the Nanotubes from Andymark and the new Mecanums from VexPro, I think it should weigh in at around 30 lbs for it all.

Mecanum systems will tend to be a little on the heavier side due to significantly heavier wheels and an extra pair of transmissions. Direct drive should help keep the weight down some without chain or belt needed. Are you using stock gearboxes from Andymark or VexPro, or are these custom? There are quite a few low weight transmissions out there now that can save you some weight.

[akoscielski3]

My Chassis' on average weigh about 40lbs. Try to keep it under that.

[pmangels17]

The shifter transmissions we ordered this year were around 8 pounds with a motor and shifting cylinder installed. However, we took off the side plates and replaced it with the star shaft that comes in the kitbot, and dropped a pund already between the two. THere are also some extraneous mounting brackets that could be cut, and some holes in the side plate (or thinned out areas) that could be taken out for more savings, but we will probably keep the plates stock. We are only using to drive transmissions this year, so we should be okay. Transmissions make up a huge part of your weight, so consider your power distirbution wisely.

[Chris is me]

Originally Posted by pmangels17

However, we took off the side plates and replaced it with the star shaft that comes in the kitbot, and dropped a pund already between the two.

I think this is a really bad idea. Those hex shafts are designed to be used as spacers, not as drive axles. That part could easily fail when you need it the most.

Spend your weight where it matters. The drivetrain matters.

[pmangels17]

Originally Posted by Chris is me

I think this is a really bad idea. Those hex shafts are designed to be used as spacers, not as drive axles. That part could easily fail when you need it the most.

Spend your weight where it matters. The drivetrain matters.

I think I misspoke, or you misunderstood me. http://www.andymark.com/product-p/am-superoptions.htm
The black plates seen in the image on this page serve as a spacer. We replaced those with this:
http://www.andymark.com/product-p/am-2241.htm
We didn't skimp on anything like a shaft. I misspoke when I called it shaft material. We did use it as a spacer. By using it, we saved a lot of weight.
When I referred to side plates, I didn't mean the main plates, I mean the other four sides, which I replaced with spacers. I apologize for saying it wrong.

[Chris is me]

Oh, I'm sorry, I assumed you were using the cross hex to drive a shaft. Only reason I jumped on it is because I've actually seen teams try to do that on a robot before.

[pmangels17]

Oh, no. I just shuddered at the thought. But we will be machining some custom shafts for direct drive, instead of paying for the AM ones. We have two great students (I'd like to think that I'm one of them) that are good at the lathe. I am more the mill guy, and he is more the lathe guy, as we call each other. We also have a tool and dye machinist who works with us as a mentor, and he can practically make anything.

[bardd]

Originally Posted by DMike

Thanks for the info, our group has been working on a direct drive mecanum system. The frame, gearboxes, motors and wheels weigh 47 lbs with a perimeter of 108 inches. I am not sure we want to cheese out the frame any more than it is. At this point it only exists in SolidWorks.

47lbs is quite heavy, though you should avoid cheesing it out just yet. First finish CADDing the whole robot and see whether you pass the weight limit or not. If you don't, it'll be better keeping the chassis heavy than cheesing it out and losing structural strength.