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"Team Build" concept

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27 minutes ago, Juggular said:

How on earth could you manage to punch 288 holes so uniformly?  That seems like a superhuman feat.  

Hahahaha, thanks!  On each side of the chevron I started by punching holes down the middle, using the ridges as edges to position the punch and eyeballing the center line.  Then I would halve the half, so to speak, and run the punch along the inside line of holes, and finally run the punch on the outer line of holes.  I wouldn't do a group of six holes together; I'd do one hole in each of the 24 locations around the whole tread, then the next hole, next hole, and so forth.  Cutting distances in half and doing the whole tread one position at a time made it easier to do.  But, yes, each hole was punched by hand!

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Ball bearings for the rollers showed up this week. I haven't used them yet, but they're here.  I'm debating whether to use them or not, just because so much of the friction seems attributed to the rubber tread belt itself.

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All the chemicals showed up, too (2 liters of methyl salicylate, and 1 gallon of 99% isopropyl alcohol).

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I soaked the hole-punched rubber tread in a 1:3 mix of methyl salicylate to isopropyl alcohol in an aluminum pan for 24 hours, and a few interesting things happened.  First, the liquid itself turned a gold color.

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Second, the rubber tread actually swelled in size somewhat (maybe 10-15%?).  The belt swelled so much that it fit loosely on the rollers, and the drive gear wouldn't engage the belt.  So, I let the belt sit for another 24 hours, and over that time it shrunk back to nearly the original size (maybe just a few percent larger?).

I tested the friction torque with the gauge, and it measured just 0.7 in-lb.  Then I let the belt sit for another few days and tested it a second time, and it still measured 0.7 in-lb.  This is down from 1.1 in-lb with just holes punched in it, and down from the original 1.75 in-lb.  So, that's a pretty nice reduction overall.

At this point I'm thinking about punching holes in the other three original belts and soaking them.  Then I might get back into the rear axle and add some bushings/spacers to keep the gear mesh consistent under load.  Finally, I may install the HPI 35T Saturn motor to slow things down and generate some torque.  Dropping the total friction torque from 7 in-lb to 2.8 in-lb should help the model a fair amount.

 

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Ya,,know,,,there was this weird movie that came out in 1985 that kinda reminds me of this project !!!!!!!

 

 

weirdscience.jpg

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If you want to be a party animal, you've got to learn how to live in the jungle.

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Latest update...

The rubber belt I soaked in methyl salicylate actually shrunk to a size smaller than the untreated belts!  It also feels stiffer, and it's too small to install on the gears/wheels and test for friction.  So, ultimately I have given up on the belts and am working on a 3D-printed track set to replace them.  I did a quick design and ran a single piece print first, and it fits and feels pretty good, so I've kicked off a print of enough parts to build a full track.  We'll see how it goes.

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Latest update...

I printed a full set of parts a week or two ago, and finally today stainless button head screws arrived in the post.  Here's the first prototype using the original Team Raffee guts and my 3D printed tracks:

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I tested the friction torque with the same tool I used in the past, and it measures only 0.15 in-lb!  In comparison:

  • The original rubber belts each measured 1.7 in-lb of friction torque.
  • Punching holes in one of the original belts dropped the friction torque to 1.1 in-lb.
  • Soaking the original belt, the same one with the holes punched in it, dropped the torque to 0.7 in-lb.
  • Now with these 3D printed tracks replacing the rubber belt, the friction torque is 0.15 in-lb!

This first set of tracks is just a tad loose; I could afford to reduce the total length by about 5 mm.  If I shrink the hole-to-hole spacing for each track and link by 0.1 mm, that will reduce the total length by 3.7 mm, which should be enough.

So, the next step is to do a slight redesign shrinking the hole-to-hole spacing and try again.  For a first attempt I'm pretty pleased with the outcome.

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Incredible work, and knowledge applied to achieve this. I hope you upload some video of the truck when you get it running with those amazing tracks.

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It's back!  Here's a recap and status.

On the previous page Scollins installed lighting, installed electronics, and took it for a drive last winter.  He even has a showroom entry for it here.  The rubber tracks have been problematic from the beginning, so I asked him to send it back so I could experiment a bit and see what could be done.  The model has been sitting in the living room since February and I've done some testing with punching holes in the tracks, soaking them with chemicals, and then ultimately moving on to 3D printed tracks.  The first pass was good but just a little loose, and then we both got busy with work and life in general this spring and summer.

Well, winter is coming and I think it would be great if the tracks were done and we could put this model to rest.  I just updated the designs for the track parts and have been printing the links.  Next up is printing the treads themselves.  We're getting there!

IMG_3184.JPG

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 The first of the treads are coming out of the printer now...  Hopefully I'll have a finished track to show in a day or two.

IMG_3185.JPG

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This is awesome, just read the whole thread.

I realise you've probably (possibly) overcome the friction/drag issue with the tracks but if they still prove troublesome you could run it in a 2x2 setup with either normal wheels or even skis up front (such as: https://www.amainhobbies.com/team-integy-traxxas-2wd-front-sled-ski-conversion-set-sliver-intt8552s/p203745). Since you'll be travelling at relatively low speeds you'll only need basic steering and either should prove sufficient. I'd imagine that a set of rear tracks would provide more than sufficient forward traction.

Looking forward to seeing it running.

 

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I finished printing all the tread and link parts by Thursday morning, and it's a good thing because we lost power for two days due to bad weather.  I just assembled the first set of revised tracks, and it does work better than the previous version.  The track is slightly tighter and doesn't seem as prone to skipping on the main drive gear.  I think I'll finish assembling the other three sets and give them all a drive to see how they work together.  Worst case, I think slotting the screw hole in the main drive gear's support bracket will let me fine-tune tension later if necessary.

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Four tracks done.  The last steps are to install a 65T motor, install the tracks, and give it a quick test drive tomorrow!

IMG_3188.JPG

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All right folks, I think I'm ready to send this back to Scollins for any final touches he might want to add to it.

Mounting the rear tracks was no problem, but mounting the front tracks revealed a small issue I hadn't caught before.  If you look at the front track in the background above, you'll see two button head screws holding a plate in place.  The problem is the button head screws dig into the front uprights and cause some binding in the drive gear for the tracks.  I had to remove the plates, countersink them, and use countersunk screws to help the tracks not bind against the uprights.  I will say, with all four tracks mounted I had no problems with spinning the center prop shaft by hand.  This is a big improvement over the original rubber tracks; I couldn't turn that shaft by hand with those installed.

In addition to correcting the front track attachment, I also installed a 65T motor in place of the kit silver can.  Then I went back to the GPM steering kit and added a couple 0.3 mm thick shims under the servo arm to help the turnbuckles clear the bottom of the chassis a little better.

Final shot with the tracks installed:

IMG_20181016_125706.jpg

Also, two very short videos:

 

Maybe Scollins will add some snowboards, stretchers, or first aid kits to the bed of the truck...

 

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20 hours ago, speedy_w_beans said:

Maybe Scollins will add some snowboards, stretchers, or first aid kits to the bed of the truck...

 

After he's recessed it, obviously ;)

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