Here’s a photo we grabbed of our drive train before its first test. The wiring is a bit messy since it was thrown together for a test. We’ve since cleaned everything up and will be mounting the rest of the robot to this chassis tomorrow. I thought a clear shot might be helpful since the video I posted allows just a quick glimpse of things.
We were aiming to have this completed in two build days’ time, but it took about 20 hours – or three build days.
Very nicely executed!
I was hoping to see the frame and wheel mounts you had up on CD earlier. That design really intrigued me. Either way, this looks really nice.
I must comment on the amount of chain wrap on the drive sprocket. With only this picture to judge by, I would say it looks a little suspect. I would be concerned about slippage under heavy load. If your testing proves otherwise, then you did a great job. Thanks for sharing.
We’re planning on bumpers sitting between 3.5" and 8.5" from the floor – and as such they land well above everything shown here except the wheels and motors. The bumpers, as a result, will be mounted to the super structure and spaced out beyond the wheels.
We’ll be adding an additional idler on the battery side of the motors to get a bit more chain wrap. Chain skips under high load using the default code, but not with our modified code that dampens the response during rapid input changes. Still, it’s better to be safe than sorry, and the new idlers will go in as soon as we finish work mounting the structure.
I like the simplicity and layout of your drivetrain. My question is, why are the front chains cantilevered so far inside? It seems to me that you could flip the gears 180 deg and move the chain out towards the rail, creating a slightly tighter package. Both of our #25 chain runs fit within an inch of the rails. Yours look to be hanging out much further than that. Overall, a great looking and performing drivetrain. Thanks,
The back chains run from the Dewalt to 24 tooth sprockets on each wheel. The front chains are running around 18 tooth sprockets for no reason in particular.
On the middle axle, the hub diameter on the 24 tooth sprocket approaches the outer diameter of the 18 tooth sprockets – so we had to turn them around to allow clearance for the chain. We could’ve ordered more 24 tooth sprockets, but I have about two dozen extra 18 tooth sprockets lying around from past projects, so we used those for convenience. As is typical of our robots, there’s really nothing else down there, so they’re not in the way of anything – but they’re also really easy to change if it becomes necessary.
Third gear (6:1) is somewhere above 12 ft/s without the rest of the machine sitting on top of it. We added 26 lbs. worth of stuff to the top this week and it hasn’t slowed appreciably, but I’m sure it will as we keep piling things on. Driving in this gear is considerably more like driving a race car than a robot. Cornering effectively requires a good feel for under and oversteer and it’s possible to get something that resembles a power over happening through the turns. It’s fun for me since I play a lot of racing video games, but maybe less so for folks who don’t.
Second gear (8:1) is about 8 ft/s or so. This is a good speed that allows better control, but hopefully we won’t use it too much.
First gear (24:1) is a monster. It’s slow and powerful and will allow us to politely escort robots and trackballs out of the way without a second thought – especially given how highly geared most robots will likely be. I think folks are considerably underestimating the frequency at which traffic jams will appear on the field.
We’re using one CIM per side after good experiences with that arrangement last season. We don’t typically play to push people off to a corner to begin with, so the extra power is better used elsewhere. A single CIM, coupled with the Dewalt, ought to give us plenty of versatility out on the field this season. The remaining two motors are used elsewhere to good effect.
Finally – switching the sprockets wouldn’t allow us to shorten the axles any since the hub would just be sitting on the opposite side. It’s not worth the work, anyhow, and it appears as if we’re doing just fine with weight this year.
Looks great. I have always wanted to try 6WD but we usually end up with 4WD. Please take a minute and try to put the MK Battery in your battery holder. Last year we had to ask a sponser to remake our battery holder because the MK Battery is slightly larger than prior years batteries. You may have enough room, I can not see exactly how it fits in and it would be easier to fix it now if you need to.
I am a Rookie coach here, so correct me if I am wrong please, but I thought the bumpers had to be 2.5" off the ground.
Your design is very inspiring. I have students who are making a catalog of pictures for various designs. They had made direct reference to yours as something they want to try and build during the off season in terms of the dewalts and 6 wheel drive.
The new batteries fit after a bit of gentle suggestion.
We’re really happy to have had a lot of time to practice driving with this and to let the students get a feel for it. It’ll be advantageous, we feel, and that’s why we worked very hard to get it done as quickly as possible.
We had similar adapters on our RC last season and were able to pass inspection at three events. We’re not expecting any difficulties this season, either, but you never can tell.
I don’t expect the chain will come off. The chain is aligned well and tensioned properly. It hasn’t yet come off in testing on this chassis or its predecessor.
Figure 8-2 in The Robot states “bumper must remain between 2.5 inches and 8.5 inches off the floor.” Since the bumper is 5" tall, there’s some play there for mounting things and so we’ll probably move it up as high as it can go as a result.
The Nothing But Dewalt white paper here on CD is a great resource for teams interested in trying a project like this out. We made a handful of very small changes – the sun gear pressfit, the servo mount and the overall mount – that we’ll probably detail later on in the year. Most of these changes were made to suit our capabilities better and so that we could feel like we put a little bit of thought into the design ;).