[FW] Tracked 4WD Lifter: Aegis

[maddox10]

I can't make head nor tails from your description of the gears you meassured.

It's the Imperial DP (how many teeth on pitch of 1" diameter.) or DIN standard module.

[R9000]

Ok, sorry let me try to be clearer. I measured the diameter of a 50-tooth gear (excluding the teeth) to be approximately 1 and 1/8th of an inch. So to find out how many teeth on one inch, I divided 50 by 1 and 1/8. This gave me around 44 for the pitch. Is that correct? Sorry if I sound clueless, this is the first time I've worked with this kind of mechanical engineering.

[maddox10]

I'm baffled how expertly you can convey confusion in this.

Lets start.
You need a gear with 50 teeth, and with an outside diameter of about 29mm .

The 2 common "types" of gears are Imperial DP or Metric Module.

if I use the WAG methode, I get these results.

Metric
Mod 0.5 Z50= OD of 26mm
Mod 0.6 Z50= OD of 31mm


DP 44, that's a non excisting size. It jumps from 32 to 48.

2 possibilities.
1) meassure again to get better values.
2) it's a custom size gear.

[daveimi]

Is it not just easier to buy a bigger lin ac?

[R9000]

Daveimi:
No. Way back when I was searching for linacs, I couldn't find one that gave enough force and moved fast enough. So I bought the one I have now, which can lift about 20 kg, but is slow, and then I built the robot around that. The distances between the end of the arm and the brackets I had cut are all set to fit the linac I have.

Maddox:
I was using this to calculate DP: http://www.robotpark.com/academy/LR/..._ROBOTPARK.png
I'll try measuring again, honestly the most important piece of information there is that DP 44 doesn't exist. But if I'm working out the pitch correctly, I don't understand why I seem confused to you. A 'yes' or a 'no' to that would've been most helpful. :P

Edit-
I measure approximately 29mm/50 = 0.6 metric module (rounding here) for the gear. This sounds more likely. I suppose I'll try buying a cheap 0.6 mod gear to see if it meshes, just to make sure.

[Will]

Hi Rory, just reading up on your build to get some ideas for mine (which even start until after xmas at this rate) and its good stuff.

For your linac problems - I'm not sure I understand the whole situation but, and shoot me down if I've got the wrong stick here, could you not employ a simple lever mechanism on the flipper/lift to give the desired speed/strength ratio instead of mesing with different gears motor side? It's a lot easier and cheaper to make some levers and pivots than it is to change gearbox ratios.

[R9000]

Hi Will, cheers. It's a fair idea to use some sort of leverage mechanism, but the problem is that I'm past that point. The whole design has been based around this linear actuator, and redesigning would be difficult and costly at this point, especially since I have basically all my parts ready. The other thing is that using a lever to increase the speed of the lifter would put extra force on the linac. Not only will a new motor increase the speed of the linac, it will also give increased torque (and thus force), so there doesn't have to be a tradeoff between the two. I've been looking into brushless motors with a similar diameter (and shaft diameter) to the current one today, if I could get sufficient speed and power from one of those then I'd just be able to straight-up replace the old brushed motor, no custom gearbox required. It's just a little difficult finding a brushless motor of the right dimensions that will run on a 5s lipo.

[daveimi]

I re read your thread n I get now that it's speed your after not so much push.

[Will]

Fair enough if you're that far down the line. I was suggesting not messing with the gearbox and just coupling the new motor directly to the one you have and using a lever linkage to get the speed right, much simpler if all you need is a 1:1 connection for the motor, could be done with a simple coupler.

[R9000]

Progress has been made! The linear actuator fiasco has finally been solved (or at least, most of it). I have upgraded the linac with a Leopard LBH3650 with a KV of 1185 (that's a measure of RPM per volt supplied in case anyone who doesn't know reads this - not kilovolts. I was originally going to get the original helical pinion off the old brushed motor and somehow 'cabbage' it onto the new motor's shaft, but it really didn't want to come off. I'm sort of glad too, because I think that would've been a lot more work. Instead, I removed the old motor AND another two gears in the train, because I'd ordered a mod 0.6, 25-tooth gear for testing anyway that happened to line up almost perfectly with the next gear in the chain and the shaft-hole. You can see what I mean in the pics linked below. All I had to do then was drill some new holes to match the motor's mounting holes, which are closer together than the old one's. I messed this up a bit the first time as you can see in the pictures, but it's not really a problem and when I basically drilled holes in-line with the existing ones, it just took a little bit of adjustment to get the gears to mesh. The result is a faster linac. Much faster than before, though I'm not sure about the power since I've dropped a part of the gearbox. However, I purposely ordered a higher-power, low KV motor, so it should hold up. Here's hoping it works when I test it in anger! Next step is to finish making the limit switches with the Arduino (which I think is mostly a matter of software) and then finally do a bit of metalworking to make the Hardox parts fit into the chassis.

Little imgur album of the linac images:
http://imgur.com/a/4VD9X

Test video:
https://youtu.be/W_P-0U14Q4U

[dotDominic]

Looking good, man! Glad to see you've managed to find a solution!

[R9000]

Looking good, man! Glad to see you've managed to find a solution!

Thanks! I was pretty lucky the gear I bought was just the right size. It's definitely very gratifying now to see it running so fast after the speed it crawled at before.

[maddox10]

Good to know that most of those industrial standard thingies use Mod 0.6

One reason more to buy a set of gear-cutters of that size.

[R9000]

Yo yo yo, it's update time. I've been working hard, and I finally got the linac limit switches working. More to come, but for now I'll leave you with this video explaining how it works:
https://youtu.be/KXR07KbvTKc

[RogueTwoRobots]

Nicely done
Any worries about the brushless being too powerful for the actuator? Having destroyed a few of these that had the stock brushed motor replaced with an RS-550 one fitted without limit switches, and hearing how quickly the actuator nut moves from top to bottom in yours, that would be my concern, primarily either gears stripping or the plastic nut inside failing. They're of a pretty lightweight construction, even for feathers, though as long as it's not overstressed (i.e used as a crusher or a lifter trying to lift excessive weight) it should survive. Either way, good work and thanks for the info video.