We have a rule to mostly use true and tried and mostly kids designed so we are most likely going to climb to the mid rung using an iteration of the instant recharge/anything since 2007 climber. Now I am retired and thought how about a simple climber - I think there was a thread on that way back and inexpensive - as I said I am retired and I am building that.
First simple - how do you define simple? Well I thought if I can do the cad and math in a day it probably qualifies. And well the below is - except the 43:1 gear boxes (worm) driving it which we did last spring so why reinvent the wheel?
Inexpensive - well that is relative to your bank account. So here is the list for the parts
8 6805 bearings about $15
64 608 bearings - I bought 100 for $30 on aliexpress so lets say 50 if you don't want to wait
About 30-40 feet of 1/2in square 16 gauge aluminum or steel tubing (About 30-$40
Aprox 3 kg of HIPS or PETG I am trying both as I want to see how they compare at those tasks. I buy HIPS for $7-$10/kg and PETG currently for $9/kg so lets say $30
So totalling less than $ 150. I can do that especially as after the build/test the bearings and some of the squarestock will find their way into other projects.
So now the design. I opted for the above mentioned double worm gear 43:1 reducer I also could use a 43:1 conventional gearbox but I am leaning towards the worm as robot climb is judged 5 sec after timer goes to 0 (power off) and gear boxes that back drive might sink too much. Even though some kind of mechanical stop could take care of that
Robot will have a 2 hooks - one on each side of the robot that are fixed. A rack and pinion setup on the end furthest away from the “center” hook where center will be defined the line that goes close to the center of G of the robot. The one rack and pinion setup on each side of the robot lets call it RP-Vertical will extend and retract Vertical and the 2nd rack and pinion will be mounted horizontally as close as possible to push RP-Vertical in and out RP-Vertical will be hinged on the bottom of the robot end (5/16 bolt with 608 set of bearings.).Initially RP horizontal and vertical are positioned “retracted” to allign the climbing hook with the stationary hook
Climbing will be done by both RP extending until rp-vertical with the hook can hook the next rung (or first - middle to get started) then the retract to the point that the hand the rung to the fixed hooks and keep reaching for the next one
Rack. I opted for 1.840 mm modulus double rack - Why? As I said 1 day cad and math and it was the first one that was > 1.5mm (I know will lift a robot) and all the numbers worked out nicely.
I opted for a double rack. The Reasons: For one you don’t have to deal with deflection, And then you transfer the power from a gear on the top and one on the bottom which helps with things like tooth load, smoothness, wear, material creep etc.
Gear stack. Herring bone - involute. The gear interfacing with the rack of course also 1.84mm pitch 30 deg helix 14.5 pressure angle the gear on the bottom is 3.121mm pitch - that what math dictates to make the center distance proper to span the rack and transfer power to the “other side”
so they mesh below the rack14 teeth above the rack there will be another set of 2 stacks and between them a split double helical that is the power input which is a 2.129 mm modulus (again that s the math)
The 2nd set and the first plate is printing right now
![20220219_1930521|281x500]
(upload://a0HTcGLzXcAKCjqEU5a2XqkrW4s.jpeg)
The plate is about 225x200 mm So should fil on most printers even most low cost ones. you probably can loos 10-12mm if you are creative with the mounting in both the x an y axis.
Racks can be concatenated
And I designed 4 rack length ranging from about 150 to 400 mm. With the thought in mind not every one has a 400x400 printer. To join racks I print 2 short sections of single sided racks and clamp them over the intersection and then drill a couple holes in the printed places - preferably using a drill press - and bolt the plastic double rack to the inserted 1/2 in square tubing
On the power input we use 1/2 square either solid or tube - I went square as sometimes hex does nasty things to plastics and sometimes scips and square does not - at least so far I have not had any case where it did.
All prints are designed in a manner that - at least in theory - each section should survive repeatedly being subjected to push/pull of 250 lb minimum without counting on the additional support from the aluminum/steel tubing. The nuts are captured by the plastic the hex openings start of at 8.6mm nominal which is a snug fit - at least the way I print and as the hex hole has a 3 deg taper the snug fit becomes a press fit. The bolts to use are 25mm m5 machine screws and the head lies below the surface of the rack that makes it easier to mount rollers /wheels to help guide the rack and even though the herringbone setup is self aligning we don’t want to put too much lateral force on it. The clearances of gears not touching the rack like the drive gear of the section is 1.6mm - a little close but then I only gave myself 1 day to figure all that out. in the worst case we might have to resort to some filing.
IDK when all will be done - Some of the kids announced they will task me with some remote meetings over the weekend to “fix some things” so depending on how much printing time that will take - that comes first obviously. And then also depending on if there is any interest here. The intent is that I - when stuff works - will post it on my blog and grabcad and here and share. If you want some “preview” PM me and I can send what I have - don’t want to post publicly something I have not seen working properly and reliably first. If you ask and get a “preview” - well use at your own risk/judgement.
Just an old retired dude trying to contribute to the community… And yeah having some fun giving my old gray cells a workout