Doing a feasability study with a local team as to how inexpensive you can do a custom frame based robot. The robot will hopefully be part of an off season competition or 2 - That is if we can locate a set of FRC legal electronics to run it. If not it will be arduino/ESP32/BTS7960 run.
Of course as its me there is a lot of 3DP I have been busy 3 weeks now with that (I am retired). The bottle neck is cad. I probably can print it in less than a week with what I have - If all the cad is done. I had designs to mount some toughbox minis but no toughbox minis and the budget is allready strained. I got 10 CIMs though so everything will be run by CIMS. Ideally some should be PG71 but hey - its a build out of what you have project
The dimension of the robot is 29.5 x 29.5 so about 118 circumference. The 1/2 in in each direction is to allow for Fiber Glass reinforcement if we decide on that.
So the composite in the frame will be plastic (HIPS and PETG) probably in some places wrapped in 10 oz cloth 1-3 layers. the square holes take 1/2 in square tubing 16 gauge either aluminum or steel. The decision has not been made yet if we go for a light weight (just shy of 100 lb) or if we shoot to get close to the 125 max.
Here some pics
Overview of all parts cadded and printed so far. Its a revamp of the 1989 2019 frame with some upgrades and (hopefully) improvements so the next iteration if you so want.
This is a focus of the rear which will have the battery and electronics
The frame will have to 6.31 in bumpers in the front and an almost 17 in cutout for the recessed shooter/ball pickup.
The robot will have the shooter/pickup (next iteration) I posted of earlier and have on my website Rapid React Shooter – Martin's 3D Printing Blog
It will also sport a CIM powered with custom 40ish:1 reduction for climbing and a 2nd CIM with 20ish:1 for helping out and moving the arm to grab the next rung.
Here is some pics of the front wheel tank drive setup. It was desided to put the main wheels in the front (the opening) as it will make ball pickup and aiming in general easier for the driver. So the back where the climber is mounted will have powered omnis. The first stage is 41:19 on a bevel setup to save space so the whole drive module is 6.3 x 8.4 in thereabout. Allowing for a wide intake opening
Some pics of the tank drive module
The rear will have the 2 in wide omnis with also a planetary inside and a bevel gear input. It was quite difficult to stuff the existing planetary from the front into a custom omni but looks like it happened (proof will be in it running and not breaking. The rim/omni setup might be a candidate for Nylon but for now its HIPS and PETG.
The prior tests have indicated that PETG and HIPS with a dab of silicone grease will way outlast a season. Now we will see if they survive the abuse of driving it.
As I get (in quantity) both hips and petg for about $9-$11/kg I will for the guess use $10/kg as filament cost.
The whole thing should use less than 20kg of filament (you are looking at 11 on the table) so $200. I pick up the 1/2 in square aluminum for $1/kg if I get full length (no cutting fee) and the steel for about the same. The robot should need less than 100 feet so about $100 for aluminum/steel. I get HTD 5 belts from aliexpress for $2-$5 each and also openended (10m) which I will use for the climber setups so all in all $30 in belts. I get 608 and 688 bearings for about 30c each and use about 60 of them on the robot so $18 and mostly M5 bolts and about $30 and 8mm (5/16) and 5mm shafts so probably about $50. So right now we are at $400. Plus CIMs which are reusable as they are COTS and so are bearings and fasteners.
If we can’t get the FRC legal electronics - maybe a relatively local team (NJ) might want to put theirs on and test it at an off season event. If not after some tests the parts will wind up in my next project.
The frame is based on 26.7mm section so a 28x28 section makes roughly 29.5 x 29.5 mm section allowing to be legar with reinforcement either fg or even 1/8 in AL plate. which would bring it to 29.75 x 29.75. (hence that odd measure
The square holes are 14x14mm allowing even with slight print imperfections and some slight possible warping to insert a 1/2x1/2 in square tube with minimal cleanup
there are 2 layers to allow to “double up” in critical sections and to mate the 1/2 in bars at corners
At the corners where 2 bars meet holes are placed to allow to drill through both bars (5.5mm drill bit) and fasten them with an M5 bolt. The size was also determined to its current dimensions to allow to countersink or place the bolt in one of the squares to mount other things without having the head to protrude. It also allows bolt selection and Nylock locknuts with minimum protrusion. As bolts come in 5mm increment in pretty much any case there is less than 3mm sticking out of the nut when the proper bolt is selected
608 and 688 bearings have been selected as they are cheap and use an 8mm shaft. 8mm is about the biggest hole that can reliably be drilled (clearance hole) in a 1/2 in 16 gauge metal square tube. A 688 is rated at about 128 lb and a 608 at 313 both static. So well enough for robot applications.
1/2 in square tubing will also be used as drive shafts. Plastic likes square better than hex
6805 bearings (25x37x8 (work quite well for that)
So all is based on a 26.7 x 26.7 cube with 14mm square hole and you can concatenate and combine them in cad to make pieces of your desire and complexity. In some cases a vertical mount is inserted to tie everything even together stronger
So you could say the plastic defines the location of the 1/2 in square tubes and guides the holes that mount the tubes together so the strength is a combination of the plastic and the steel or aluminum. The weight of the tube for steel is .39 lb/foot or about 0.15/ft for aluminum. The whole can be wrapped in epoxy soaked 10oz or so FG tape (or CF if you have the $$) up to 5mm thick if you want to. And the bumpers mount flush as this is intended to not have heads of fasteners stick out. so the plywood adds to the structural integrity and evenly distributes the hit over at least 6 in of the composite structure.
Some files are already available on my grabcad all will be at the completion of the project when its sure everything fits as intended