Specs:
Weight- 34lbs
Frame is welded 6061-T4 1x1x1/8 tubing, wheels are 6in plaction, standard toughboxes
We have just recently learned CAD and this is our first attempt at a drivetrain.
What do you think? All input is welcome!
Sorry for re-posting this (though it would be easier to see as a pic instead of an attachment)
Great job.
Just a few questions.
-Is there any reason you don’t have any axles?
-I don’t see any sprockets. How do you plan on driving the wheels?
-Is there a specific reason you chose the toughboxes over the supershifters? (My guess is cost)
-Is the center wheel dropped? If not, you might want to change the front or rear wheels to omnis because it will be a nightmare to turn.
Joe, the OP seems to be a beginner, cut him some slack on missing parts. He probably knows they need to be there. Its just unfinished CAD.
Excellent start!
Essentially what Joe is getting at is to continue adding detail. You will find that the biggest benefit of CAD is having everything planned out before hand so that when construction rolls around there are no questions and it just flies together. You can make sure everything fits exactly how you need it to before cutting anything. So you’re off to a great start, just make sure to pay attention to all the detail. Since this is just practice it’s not as crucial but when build season rolls around it will be.
One suggestion: I assume you are using dead axles, given the bearing blocks you have chosen. In that case, you might want to consider putting the wheel axles straight through the lower frame rails. This will give you some freedom in the vertical direction to get a drop on the center wheel, which you will need if you want to turn, and cuts out extra components.
For axles I was planning on using 1/2" bolts so I didn’t bother to CAD them, and there’s no sprockets yet because I don’t have any 25 sprocket CAD files.
I chose the toughboxes over supershifters for cost and the simplicity.
The center wheel is dropped 1/8"
Here are some 25 sprocket files. http://team1323.com/cad/pages/sprockets.html RC has done some great CAD and has put most of his stuff online for download.
I chose the toughboxes over supershifters for cost and the simplicity.
Thats the exact reason that I thought. Whats the reduction that you are running?
The center wheel is dropped 1/8"
Perfect. You might be able to go a little less but 1/8" is perfectl.
Great start on CADDING. I hope to see some of your work in the future.
Just a tip:
McMaster has CAD models of many of the products they sell, including bolts and sprockets. It’s great to help build up a BOM when you eventually build the robot. There’s hardly an excuse to not have those bits modeled because it’s a simple download if they have the parts you want.
It is a 12.7:1 reduction, just the standard reduction they come with. I’ll update the CAD tonight or tomorrow and repost it.
http://i.imgur.com/RKhyZ.jpg](http://imgur.com/RKhyZ)
Update! I’ve added axles from Mcmaster carr and sprockets from team 1323’s cad library. Right now I have a 22 tooth sprocket on the toughbox and a 36 tooth sprocket on the wheels. Also the top support for the toughbox I changed from 1/8" wall to 1/16". Thanks everyone for your help so far!
How are the chains for the two back wheels set up? Specifically, are the wheels lined up (with the sprockets spaced out to line up with the drive sprocket) or are the wheels out of line (with both sprockets mounted flush with the wheel)?
Great Job! My First CADed Chassis didn’t look this nice. (i have now made 7 chassis). Make a couple more chassis and you will then definitely have a feel for the CAD you are using. This will also give you a chance to choose a basic chassis design when designing this season. Try making a sheet Metal one, mucanum/omni, West Coast Drive, Swerve (maybe). Experiment a little with wheels and gear boxes.
I have to say that I do not like how the bearing block’s are set up though. Because they are sitting on the top of the lower Brace all your wight from your robot will be on two bolts. If you had them on top then the weight would be on the brace. Another option is to make plates to put on either side of the wheel. Bolt the plates to the top and bottom braces and the axles bolted to the plates.
Good Luck!!
Edit: Here is a pic of what i was talking about before.
It’d be more like ten bolts, each of which could easily hold the ~15 pounds of force on them (based on a 150lb robot with even weight distribution).
The sprockets are mounted flush to the wheels and the wheels are out of line. The back wheels have a slightly shorter base, but the middle and front wheels are in the center of the axle.
There’s 24 bolts total that hold the axle mounts in place. If the robot is 150lbs that’s 6.25lbs per bolt. Right now the axle mounts are designed to use 1/4"-20 bolts, but I might change that to 10-32 to save weight.
When designing a chassis i’ve always tried to line the wheels up. I dont know if it makes a difference at all though. Im not saying you should line them up, but does anybody know if lining the wheels up vs letting them be off make a difference in performance, or efficiency?? Thanks 
Consider that the working tensile load of a Grade 2 1/4-20 bolt is around 1,700lbf. That is to say you could hang 10-11 robots from a single Grade 2 1/4-20. I do not think the four bolts on what I assume is a dropped-center 6wd middle axle will have any issues at all.
Your design is structurally superior, and your suggestions to improve strength is sound, but I believe the design is already strong enough. More reinforcement will only add weight.
179 and 234 have both used offset wheel 6wd several times with good success. I don’t know that it necessarily provides any advantage (the tapered ends do, but the wheel placement itself I can’t comment on), but it certainly didn’t seem to have any negative effects.
Beautiful first model. Keep up the good work.
If you want a real challenge, then add chain runs (depending on the program this can either be a nightmare or a few simple clicks). Adding the chain runs will let you know how your wheels and sprockets are going to be lined up.
I’d like to use a one or two piece bumper on it, is there a specific way anybody would recommend mounting that?
Also I CADed a belly pan for the drivetrain. It is .05" aluminum with no lightening holes. Will that be strong enough to hold the electronics without flexing or should I use 1/16" or 1/8" maybe with lightening holes?
This is how i was gonna mount our bumpers. They aren’t two piece bumpers but could easily become a two piece bumper. I have a slot that the bumper would be mounted to, it is slotted so you can easily adjust them to the proper hieght, and then tighten it so it is always be that hieght. They are gonna have a quick release, most likely a pin (like on a trailer that would go on the tongue), that goes through the top hole. the bumper brace is detatched and stays on the bumper, not onto the robot.
I would be scared to use .05". Talk to whoever is going to make it for you if they have a lot experience with sheet metal. .125" is nice and strong if you secure it well, but it can easily bend and flex on its own. I can’t imagine how weak .05" would be attached, let alone just by itself. I think ours is about 4.3lbs, but it’s full of holes. Without holes, Inventor quotes about 10.5lbs.
