Dravpnir tries to build something light

[Dravpnir]

My first real post here on rccrawler so here is a short introduction. I live in Sweden and I guess I am more of a builder than I driver. Although when spring/summer arrives and the snow disappears I plan on doing quite a lot of driving.

I started with crawlers last autumn when I bought a used Redcat RS10. I modded it quite a lot, but realized after a while that I should have bought something proper instead, so I picked up a Berg Tracer V3. After modding that one quite a lot, I started to wondering if one could build one from scratch instead. Those ideas lead to what I am going to present here. As the gears will be Berg gears I guess it can be classified as a Berg.

I have been very inspired by so many of talented builders on this forum. I have borrowed quite a lot of ideas from those people and I would just like to start with giving a big thanks to those people, thanks!!!

I started on the rear gear box and for the first version I more or copied the V3 gear box, but made the box from 3D printed ABS and carbon fibre.





Then Erik presented the Dlux gear boxes with the ingenious use of flange ball bearings. So I "borrowed" that part and was able to create a much more compact, 6 mm thinner and 12 g lighter gear box. I thought the ABS plastic was to easy to scratch so I milled the middle part from delrin instead. The complete gear box with screws and ball bearings weights 33 g.


Version 3 on the left and version 2 on the right.


Version 3 on the left and version 2 on the right.


Version 3 on the left and version 2 on the right.

I have to make some adjustments to the gear box, so there will be a version 4 soon. However it will almost be identical, the motor has a slightly different position and the upper link mount is slightly moved to clear the motor can.

For axle tubes I am going to use carbon fibre and delrin again. The outer ball bearing holder and the lower link mount is one whole piece. The 2 delrin parts will be glued to the carbon fibre. I am planning to use chassis protector sheet to protect the lower part of the carbon fibre tube from scratches. Both tubes weights 22 g together.



I will be using the Berg V3 axle style for the rear axle shaft. The original rear shaft weights 45 g and I have made a new one of solid aluminum and that weights 17 g. But first I am going to try using an aluminum tube instead. The tube only weights 9 g but I am a bit worried that it wont hold. Perhaps I have to reinforce the shaft where the pins are going through the shaft with some solid aluminum rods inside the tube. If I have to reinforce the shaft I guess its weight will increase to about 13 g.


Original shaft to the left, solid aluminum shaft in the middle and the aluminum tube on the right. Instead of using an E-clip in the middle I will use a thin aluminum tube to get the distance to the ball bearing in the gear box.

For wheels and tires I will use 1/10 front buggy wheels with delrin hubs and narrowed Rovers in the rear and narrowed Sedonas in the front. The front wheels with hubs, screws, tires and foam weights 115 g each and the rear ones weights 90 g each.





The complete rear axle with motor and wheels weights in total 422 g. This is with unmilled gears, so I guess I can loose a couple of more grams.



I am thinking of making some wider wheel hubs as the rear width is only 9.5" at the moment.

Now I am waiting on that my new front axle shaft and some more parts will arrive from dlux so I can start on the front axle. In the mean while I will be starting on the chassi.

Regarding electronics I wil be using a Hitec 7950 servo. The motors is at the moment some Jamara Cobalt 400/13 motors, which seems to be the same motor as the ones Holmes Hobbies sold as the Cobalt Puller 454. I hope to replace the motors with some of Holmes new 500 puller, or the 510 stubby.
The esc is a pairs of reflashed brushless escs. After the reflashing they can drive brushed motors and have instant reverse. For $11 each they will do until Holmes Hobbies starts to sell his new mini brxls.
The receiver will be the OrangeRx R410 4 channel micro receiver (weights 2.5 g, jummy).

[Tgreer]

Wow, nice work! Looking forward to seeing what you come up with on the rest!

[Jeepkid]

That's sooooooooooooo awsome. I was thinking of use the 3D plastic print at my work and making cases. I have been messing with solid works and trying to mess with super small cases sizes. I love those tubes bro.

[the kil]

What's this talk about Holmes's MINI BRXL's?

[Jeepkid]

Originally Posted by the kil

What's this talk about Holmes's MINI BRXL's?

Is been the talk of the town boss.

[Erik D_lux]

Looks great Tobias! Glad to see you on here.

[the kil]

Originally Posted by Jeepkid

Is been the talk of the town boss.

Are we talking a "new"speedo or the decased BRXL?
A mini mamba with a brxl brain?
Please explain

[Dravpnir]

Thanks for the positive comments so far. Right now the hobby room is occupied with another project, but I hope I can continue with the chassis soon.

I am a bit wondering if there will be to far between the lower link mounts. As it sits now it is 150 mm (5.9") between the mounts.

Regarding the BRXL mini, all information I have read is in Mr Holmes BRXL thread in the vendor section.

[Dravpnir]

Tonight I manage to get atleast some work done on the chassis. I made most of the cross braces, but when I was putting the saw to the aluminum tube it looked so boring... so instead I drilled out some short aluminum stand offs and cut some carbon fibre tube into suitable pieces. I have about 4 mm of m3 threads on each side to fasten it in the chassis.



I made 5 cross braces that was 46 mm in length and 1 with 73 mm length. The 5 small cross bracers weights 4 g together. If I should have made them with my normal 3/16" aluminum tube with 0.049" wall thickness those should have weight about 8 g. Much nicer looking and ligther, a nice combo

[marlboroman]

Wow Great work! I like those tubes.

[Dravpnir]

Today I got a little package from Dlux with lots of nifty stuff, so now I can start to manufacture the front axle



After reading the trouble Erik D_lux and stubs179 seems to have with finding the right foam for their light weight rigs I think I have to shelf my plastic wheels for a while. I will mill some glueable carbon fibre wheels instead so I can switch foams without debonding the CA glue. Luckily the wife will be away for a couple of days, so I will have plenty of time to work on the crawler

[stubs179]

Looking good!

Ya, do yourself a favor and get your foam situation figured out before gluing plastic wheels.

[filotr14lsdude]

What are these cvd's
What's the length and diameter of them?

[DickyT]

This an awesome build! Keep it up man, I can not wait to see the finished product

[Dravpnir]

Thanks

Regarding the CVDs they are made by Erik D_lux and I guess they are the same size as normal V1 axle shafts(?).

I draw some new wheels yesterday and was planning on cutting out 2 rear wheels and the some gear case sides, but me and my mill did not get along last night... so I have to correct the problems and I got a new spindle arriving today anyway so its was sort of a good timing...

I was able to cut out 1 wheel though. It is not good/useable, but should give a estimate of the weight and look of the coming wheels. The carbon version is a couple of grams heavier than the plastic wheels (22 g vs 19 g) but being able to change the foams makes it worth it, atleast in the beginning.





I used the cross braces I made for the chassis for the pictures, so I guess the weight will be slightly less for the real wheels when I am going to use shorter braces. I was planning on using 4 cross braces for the rear wheels and 6 for the front wheels. The width of the wheels will be the same as the plastic ones, 0.9".

[Erik D_lux]

Looks great as usual!

What type of glue/epoxy are you using for the AL to carbon? I tried to make the two hold awhile back and I didnt have any luck.

[Dravpnir]

I use some 4 h epoxy from Loctite and I am rugging up the surfaces on both the aluminum and carbon fibre with sand paper. After that some good cleaning with isopropyl alcohol. To quote the guy I asked for help to get the right glue for the delrin, the 3 most important things to keep in mind when glueing

1. Clean parts
2. Clean parts
3. Clean parts

[dezfan]

Wow that's awesome!

Seeing all these awesome hand built rigs reminds me of the early years of crawling, just on a whole different level!

[boosted4lyf]

That wheel face is dope!

[SkaldidDog]

Don't lose your rig in the wind! Not sure how tough she'll be but you will achieve your goal of low mass. Nice work.

J