Rapid React Shooter

This is a pick-up/shooter for the 2022 rapid react season. This device will both pick up and shoot the roughly 9.25 in diameter ball (cargo) of the game the files referenced below are located at https://grabcad.com/library/rapid-react-3/details?folder_id=11939286

Proper material to print this items include HIPS, ABS, PETG and possibly a hard Nylon for all structural parts. The “tire” referenced later is to be printed in TPU. All parts will fit on a printer with a build plate size of 300×300 or bigger. The biggest part – the housing – is 283×283. The parts printed below have been printed in HIPS and TPU on an anycubic Chiron with a .8 nozzle. 0.4mm layer height, 1mm outside perimeter width 1.25mm inside perimeters, 6 perimeters 100% infill. Except the tire – the TPU part that was printed 2 perimeters of .88mm and 10% infill.

For the body you will need to print 2 of the file ShooterHousing.stl and 1 of ShooterHousing_Center.stl. You then will connect them with 1/2 in square aluminum or steel tubing and M5 or 8/32 bolts of the proper length . The front and back square cut outs also get 1/2 in square tubing as reinforcement

Shooter Vertical
Shooter Body Vertical
Shooter Body Horizontal
Shooter body Horizontal

Then assemble each Shooter hub/wheel assembly. As they are getting most of the stress make sure they are printed with 100% infill (except the TPU tire

Motor Holder
Motor Holder

File Name: MotorHolder_small.stl. Mount CIM, miniCIM or NEO to the 3DP bracket as shown and press fit a 6805 bearing

Bearing Holder
Bearing Holder

Then Press fit the 6805 bearing into the Bottom Bearing holder

Next cuta 1/2 in square tube to fit flush With Hub_small.stl and Hub_smalltop.stl and drill the 2 holed. The bolt in Hub_small will not get a nut a M5-20mm will cut its own thread into the plastic and will be held in place by the tire

Hub_small with 1/2in square tube
Hub_small with 1/2in square tube

The top of Hub and Hub_small should make a tight fit in the 6805 bearing. In case you have some overprint use some sandpaper or other abrasive to make it a tight fit.

Hub and tire
Hub and tire

The Tires File is ShooterTire_small.stl. It is to be printed in TPU with about 2mm shell/wall/floor/Ceiling thickness. The whole assembly is slotted so it can be adjusted and shimmed to give the proper “squish” to the tire. After finding the proper “squish” 2 holes can be drilled through bracket, shim and square stock to properly fix it to the shooter housing

Shooter Wheel/Tire Assembly
Shooter Wheel/Tire Assembly

The whole Shooter Wheel/Tire assembly with motor and bering holder ready for assembly to the body. As both motors are to always spin in opposite directions the 2 motor wires could be connected red to black, black to red and then as the bottom of the “Y” to one motor controller

Next Mount the motor for the elevation. In this case either 1 or 2 PG-71 old style with 10mm round keyed shaft (we have a bunch and none of the newer kind) is used. The heads of the M4 bolts are recessed and should fit most machine or socket head screws. Press fit the 6805 Bearing(s) above that. Depending on where you mount the motor(s) you might need 1 or 2 PG-71 motor or less if you got a higher ratio gearbox. The nice thing of the PGs is that they have a quadrature encoder included that make elevation positioning possible in multiple positions

PG Motor with Pillowblock
PG Motor with Pillowblock
PG Motor with Pillowblock and 6805 Bearing
PG Motor with Pillowblock and 6805 Bearing

The Following is 2 of the 3 possible Mounting positions for the elevation Motor(s) in this case using one of the PG to square tube adapters. (Note from experience smaller then 1/2in HEX in HEX format skips easy in plastic under high torque. The plastic is quite capable to stall the motor on a 4mm key but not on a small hex)

Shooter Mount Center
Shooter Mount Center
Shooter Mount End
Shooter Mount End

There are multiple Dogleg assemblies/Motor Holders in the above folder. Which ones to select depends on how the shooter mechanism is going to be attached to the frame and what will fit without extending beyond the legal parameters. The sample holders in the folder are for the PG motors above and for Mini Limit switches like this one

They will mount to the hole pattern on the Shooter body.

Parts needed for the above assembly

less than 500g of TPU, about 3-4kg of HIPS,ABS or PETG, 15 to 20 ft of 1/2 in 16 gauge square tubing, Assortment of Nuts and bolts. preferably M4 and M5 with Nylock nuts and/or whatever the motors need.

The operation is as follows

To Shoot (ball assumed loaded and trigger dogleg in the back parallel to back plane of shooter body. )

1.) Spin up wheels (CIMs) takes about 1 sec to full speed

2.) asure proper elevation and aim (can happen simultaneously to 1)

3.) have intake dogleg out of the way in the “all up” position

4.) activate the trigger dogleg to feed the ball into the spinning wheels

To take in Ball

1.) have the trigger dogleg parallel to the back plane

2.) Spin up shooter motors to about 10-15 % max speed in reverse (oposite from shooting direction

3.) Aproach ball – drive into it and if necessary have an intake dogleg “help” the ball in

Depending on mount position and angle and driver skill from past years experience especially stronghold ball pickup is quite possible without a front dogleg with a good driver . Front doglegs no matter what they are made of often fall victim in collisions with other robots.

If the robot is used on a standard Andymark frame without a cutout then the only way to mount it is from the rear and the pick up angle becomes quite steep and a “dust pan” type ramp needs to be attached to the front or a front intake dogleg is advisable

The folder also contains the bigger 4 inch tires and hubs with motor mounts and an alternate shooter made out of 1/2in tube and 3dp Gussets. This shooter was not completed and is considered “work in progress”

4 in Wheel Shooter
4 in Wheel Shooter

Besides the stls the folder also includes all the inventor (.ipt) files

Dialing in the filament for accuracy

After getting the basic dial in done like temperature (usually the higher the better the layer adhesion – up to a point – but the more stringing) and retraction it is time to dial in for accuracy. In many cases it will be a compromise between mechanical strength and over/under extrusion.

This is done by using the Extrusion multiplier and NOT ESTEPs . Esteps are used to calibrate the extruder. I do that usually with no back pressure that means if possible either mathematically or by measuring how much filament is coming out the extruder without having to go through the hotend. As a side note if the amount of filament going through the extruder with lets say the Bowden tube disconnected compared to how much goes through with it connected and going through the nozzle differs then the extruder is slipping and any further tuning will be meaningless until that problem is corrected. That slipping can have many reasons like too low a temperature, too high a speed or the tension on the extruder adjusted improperly or a combination of such.

For the purpose of tuning the print we use a file “multiwall” that is created for

just that purpose and the STL for the file is here https://grabcad.com/library/frc1989-filament-dial-in-1

Here is an image of it sliced in Prusa Slicer

This is with the width option selected and you can see the walls are 1, 1.25, 1.5, 2 mm wide with a 3mm wall connecting them

From printing them with different extrusion multipliers and then measuring with a caliper you can get an idea as to the expected accuracy of your part. When you measure with a caliper make sure you measure in a way to not include the first couple of layers in case of elephants foot. So make sure the legs of the caliper end about 2 mm above the part that touched the build plate. For this post I printed the same file with an extrusion multiplier of .9, 1.0 and 1.1. Inspecting those prints you can gleam some additional slicer about your printer/slicer combo. Like for example the 2mm wall used to allow to be split if the perimeter thickness did not add up to a 2mm wall. This stl was designed to test when printing with a .8 so with an external perimeter <1mm there used to be a gap between the 2 lines making that print. You can also measure at the beginning, ending and middle of the wall and find how well you do in regards to things like linear advance issues.

In general the walls for that test should be in % 125, 156.25, 187.5,250 of the nozzle diameter. You can see how your external perimeter settings will influence slicer performance when it comes to splitting the print into perimeters. It will also give you information as to how the slicer places perimeters

We print with the option set to outside perimeters first as that is more consistent when it comes to accuracy as the slicer will place a perimeter of the selected “outside perimeter width” first and you can better predict the outcome when coming up with a slicing plan. This print also will demonstrate to you how your printer/slicer/filament option behaves when it comes to single vs multi perimeter sections of your print. In most cases the single perimeter walls will be wider in relation to the target thickness and the multi perimeter walls thinner in relation to the target width and that most likely has to do with how the filament flows.

Also the higher the flow rate – the more filament – the better the layer adhesion on the plus side – on the negative the most likely over extrusion will cause walls that are thicker than intended and at some point the nozzle will start to “plow” and the next layer will have a rough/bumpy ride and on many parts – especially with a lot of perimeters – a point may come where enough “bumps” build up for the nozzle to get stuck and you suffer a layer shift or knock the print of the print plate

After test printing this in HIPS at 255/105 Bed we came up with a wall thickness as follows

Wall (target).911.1
1 mm.981.051.18
1.25 mm1.141.291.42
1.5 mm1.411.591.77
2.0 mm1.861.972.09
3.0 mm2.812.953.20

All measurements were performed by taking 5 measurements at the middle in close proximity discarding the high and low and averaging the remaining 3 with a 2 digit accuracy. We can see that the 1 extrusion multiplier came closest to the target width. In practice this filament should extrude well with a multiplier close to 1. For most application we use .98 on this and for some gears as low as .94. At the 1.1 multiplier you can see the phenomen that – as its too high – it starts pushing the walls out due to the pressure from squeezing more filament into the middle. One in theory from the wall placement would expect a wall thickness around 3.1 yet get 3.2

If you examine the prints you will see that the higher the extrusion factor the more pronounced the layer lines.

In summary the higher the extrusion factor – the better the layer adhesion – the lower the extrusion factor the better the visual appearance and the more predictable the dimensional accuracy. Not going to an extend at which prints will fail.

So if within an organization like an FRC team you agree on an acceptable range of parameters. So for example we tune for precision fit parts like gears to 96-98% of target and for low precision high force use to 100-105% target – AND you tune all filaments no matter what make to those ranges. Then you can make a test print of a gear or bracket in lets say HIPS or PLA which is low cost and once it has gone to all the iterations necessary to have a working assembly you can reprint them in Nylon or PETG or whatever other higher cost material the final product will be in and expect it to fit.

Printing the Prusa Face Shield

This is to maybe help some printing them faster. To share what we learned. The mask is at the narrowest point 2.4mm thick that is why prusa recommends to do 3 perimeters (3*.4 = 1.2 and that *2 = 2.4) So with any nozzle you have up to 2x is width that you can relieably print so first establish your max extrusion rate as mike did in a recent video or I outline in my tutorial here https://grabcad.com/martin.pirringer-2/tutorials read the one on Volumetric E and the one on bigger nozzles if you have a choice of nozzles. If you use Prusa Slicer/Slic3r just enter that max Volumetric E in the apropriate fields and you are done. Next calculate the layer height apropriate for your printer with most it should be a multiple of .040mm and keep it between 40-60% of nozzle diameter. Then take a layer width where you can get to 1.2 mm so

.4/.5 nozzle Layerheight .24-.32 (tested on PLA) #perimeters 2 Perimeter width either .6 on all Perimeters or we got one running .48 outside perimeters, .72 inside perimeters. 0.8 on infill
.7/.8 nozzle layer height .4mm (tested HIPS) Perimeter width 1.2 on all. #perimeters 1.
we have no one with a .6 but I might be tempted to run the .8 profile with a .36 layer height

If you do not use prusa slicer take your max Vol E and divide by (perimeter width * layer height) And make sure it does not exceed what your printer can handle. Like if its 60 that your printer can handle then the max speed you set is 60 even if the above equation gives you 80 or 100.

One problem we ran into that as those parts are rather thin sometimes with some material one warped up a little at some point so we added a Brim – the brim is a pain especially on the pegs in the front so I broke out inventor and put “lillipads” at some locations. As you have camfers in the design and with printing with a .8 and 1.2mm layer width a lot of them just had 1 bead making contact with buildplate and on occasion the Nozzle left a little retraction tab and on layer 2 it pulled it off the plate the files are called FSChiron here https://grabcad.com/library/face-shield-11 The files are called FSChiron and the x2,x3,x6 is just how many I combined both print the top and bottom in one shot here is some pics
This is after 2 layers

And this is about 5ish hours later when finished 2
With the print popped off . Those 14mm liily pads are quite easy to remove.

If you want to Help check for details on how at www.vernonrobotics.com

Prushashlisha FRC team 1989 2020 build season pics

Our Season has ben canceled due to COVID-19 so I figured I make a post about our robot that we printed on our 2 Anycubic Chirons. But first some info. The team decided to name the robot Prushashlisha probably cause that is what it sounds like when I say Prusa Slicer which is the software we use to turn our inventor generated STL’s into gcode to print it. Our goal was to have our robot shoot and climb and we pretty much achieved those goals even though – unfortunately – not battle tested. And there are ongoing improvements. So without further ado…

First test with the shooter mounted to the robot
First climb test – at that time without limit switches
GT2 3d printed pulley next to aluminum one – 3DP so we can have custom sizes
Ball intake with 3DP 2.5in Mecanum wheels
View at the Electronics board through the conveyor
Look down the climber at the 3dp winch powered by a Cim and toughbox mini the winch is 50mm in diameter and so is the 78 tooth GT2 pulley part of it. The GT2 belt deploys the hook the rope does the lifting
Look at one of the climbing hooks on top of the robot. Also view of 1/2in conduit to protect the cabeling
Full view of robot before adding braces and extra stiffening in case we had to play D (as we had plenty of weight left to play with
Close up at conveyor and laser cut 1/8 in aluminum plate for added stiffness and lowering center of gravity
First test hook broken to get some data and to inspect the inside to verify the quality of us printing “solid” that means as close as possible as you can come with an FDM printer to injection molding. Nice clean break with a little trailing edge due to the camfer as it should. All in all an indication that the print has great layer adhesion both vertically and horizontally
Winch with 78 thooth GT2 pulley and ratchet teeth before cleanup bench tested to hold 300lb
View at the bare frame with wheel (skateboard) 3DP HIPS and aluminum (1/2in 3/32 wall square tube) composite We later replaced the rear wheels with omni wheels
Frame pieces before assembly
One of the toughbox mini axle holders being printed (about 30% done)

Overall there is about 14 kg of HIPS in the 3DP parts. All parts have been printed with a .8 nozzle. We used a little over 40 kg of HIPS so far this season some went into prior iterations and tests and some into spare parts. We have almost a 2nd robot in spare parts – at least regarding the plastic pieces. The whole robot without bumpers and battery currently weighs 116 lb. all the inventor files and STLs are at https://grabcad.com/library/frc1989-infinite-recharge-1 . Also check out the tutorials in regards to dialing in filaments and selecting nozzles at https://workbench.grabcad.com/martin.pirringer-2/tutorials

The Prusa slicer config file is in the root “infinite recharge” root at the above grabcad link

Temporary Harness fix

For now I cut the damaged kinked part out of the harness and used crimp connector splices to splice in some 16 gauge wire and placed the protective cover back over it. There will be some redesigning of the harness. I also for now used the drag chain as a support and extended it with some zip ties its now working for a day already so we are back to printing

Printing Bed leveling test with temporarily fixed x harness

Pulse PTFE tube popping out of Bondtech QR

One of the problems with the way the Bondtech extruder is mounted that on some occasions the PTFE tube will pop out and filament will feed all over the place. To avoid that print this

PTFE Tube Holder for Bondtech QR

Mount it instead of the “C” Clip and tighten with 2 m3 screws and lock nuts. Depending on your printer you might have to be careful to not crush the PTFE tube

PTFE tube holder mounted to Bondtech QR