1/6 Losi Hummer (CC1717) Build

[brian015]

1/6 Losi Hummer (CC1717) Build

With Castle selling their 1717’s for a bargain recently, I decided to plan a build that would make the most of one of these motors:




Since the 1717 is almost as large (20oz) as my Neu 1527 (21.8oz), I figured I could plan another larger-scale build in the 16-20lb range. I again will make use of the Losi LST2/Muggy platform because I have seen that it is quite capable in a truck this size. If you haven’t seen it, here’s my previous large-scale build:

http://www.rc-monster.com/forum/showthread.php?t=26979

The first thing I had to consider with the 1717 is that it has a relatively high kv and a larger diameter than the 15-series. For both of these reasons, I looked for a center diff with a larger spur gear and decided on the AE RC8T that comes with a 54t spur. I want to have gearing options for 6s-8s and for both MT and 1/5 scale tires. Playing with the top-speed estimator, I was happy with the gearing options available with the 54t spur. For example, with 1/5 scale tires and running on 8s, I could use a 12t pinion and get a top speed around 51mph (I’ll be running 45/11 Muggy diffs):

Differential Ratio: 4.090909090909091
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 54
Pinion Tooth Count: 12
Total Voltage: 29.60
Motor KV: 1580
Tire Diameter (inches): 6.8
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 4.5 : 1
Total Ratio: 18.40909 : 1
Tire Circumference (inches): 21.36 inches (542.62 mm)
Rollout: 1.16:1
Total Motor Speed: 46768 RPM
Vehicle Speed: 51.39 mph (82.56 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...


Or, with MT Badlands on 6s, I could use a 19t pinion and get a top speed of 52mph:

Differential Ratio: 4.090909090909091
Transmission Ratio: 1
Other Ratio: 1
Spur Tooth Count: 54
Pinion Tooth Count: 19
Total Voltage: 22.20
Motor KV: 1580
Tire Diameter (inches): 5.84
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor Coil Resistance: 0
Spur/Pinion Ratio: 2.84 : 1
Total Ratio: 11.62679 : 1
Tire Circumference (inches): 18.35 inches (466.01 mm)
Rollout: 1.58:1
Total Motor Speed: 35076 RPM
Vehicle Speed: 52.41 mph (84.2 km/h)
Effective KV Value: 1580
KT constant: 0.86 oz-in/A
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...
Final Power: Amperage not specified...

And therefore, any setup I’d want to use with this would be possible with pinions in the range 12-20t. I know that 8s puts the 1717 slightly over its max rpm of 45,000 – but others have been doing it, so I’ll possibly give it a try.

I’d like to have reverse and esc braking, so I’ll either run 6s through a MMM or pick up a Mamba XL to run either 6s or 8s.


Next, I looked into various bodies for this and found myself looking at extra large 1/8 scale or 1/6 scale bodies with wheelbases from 16-18 inches. I don’t want to go as large as 1/5 scale with this because it would likely become too heavy for the 1717. I really liked the FG Jeep body, but found that it is currently unavailable in the US. Since I wanted to do something a little different than a pick-up body, I settled on the FG Hummer body. I like the size and the look of it. It has a wheelbase of 17.5 inches, so that’s the wheelbase I’ll build my truck to have:



The FG truck itself with the Hummer body definitely has the monster truck look with very large tires and a wide stance:



I’m thinking right now of setting mine up initially at least with a more scale-size tire look. I’ve mocked it up with MT Badlands:




I might end up going with larger tires, but we’ll see.

Anyway, that’s the start of this project – I’m in no hurry with it, but hopefully will have it done sometime this summer to be able to run it in the nice weather.

[Overdriven]

I think it'll look great with the somewhat smaller tires, definitely gives it a more scale look. I'm curious to see how wide the body is in relation to the chassis and its track width, so measurements please?!? Either way, subscribed. Cool to see you starting another large scale.

[v8hatch]

This is going to be a very cool build, going by Brian's previous build.

Be very interesting to see how the 1717 handles the 8s, i have thought about running it higher myself.

Great now your giving me idea's...............

[brainanator]

niiiiice, should be a very fun and cool looking truck :D

[bdebde]

Sounds cool! May look more scale (and true to life) rolling on some phaltlines.

[JERRY2KONE]

Nice project. This looks like a similar setup to what I hope to do once all of my R/C gear arrives here at our new home. I have two of those Hummer bodies as well. They are nice and big so they cover extended projects like this one very well. I like the idea of having a few options for the tires, because they can have very different effects for top speed and better handling depending on what you end up trying to do with the project. For just fun bashing the smaller tires will be a great choice. For high speed runs the larger tires give you more runout to get your speeds up. This should be fun to watch. I have been wondering how peoples drivetrains are holding up using these 1717's, because I picked up three of them before leaving Korea. I have not gotten to play with mine at all, but the mere size of these motors is intimidatingly emense when mounting them into a 1/8th scale vehicle.

[brian015]

I've been thinking that since I'm leaning toward the smaller tires I can start out with a slightly smaller spur gear, and use one of these new Maximizer aluminum diff cups I just picked up:



One "unique" feature they have is that they take a larger ID bearing (10mm) because they are made a bit beefier than stock:



I'm using an 8ight-T 50t spur gear and Sportwerks internals - so I shimmed everything inside properly and it fits nicely.
The 50t spur gear gives me almost as much flexibility as the 54 RC8T spur, and this way, I can either sell the RC8T diff if I don't use it, or drop it in later if I need it - only if I run 1/5 scale tires on 8s.

Here's what the CD looks like assembled:





I'm just waiting for new 100k diff fluid to arrive in the mail to fill this up (I used up the last of my old 100k fluid in my other large-scale CD).

[Jahay]

looks very shiny and would be strong...

BUT i moved heaven and earth to remove that rubbish, weak 10x16x5mm bearing on the savage cups as it fails prematurely compared to the 8x16x5mm bearing.

So im using a vorza cup now with HD internal diffs... Just a heads up when your 10mm ID bearing fails.

Otherwise.. very shiny indeed :)

[brian015]

Or I could turn it down so the 8mm bearing fits!

[Jahay]

Yea you could brian, thats what i wantedt to do with the IRC Cups... but they told me the alloy quality means that it has to be that diameter for a reason or it could crack and fail.

So turn it down but at a risk?

I wouldnt risk it as a lot of strain is put on those areas with brushless setups... especially that 1717!

[brian015]

I'll see how long the bearing lasts and go from there, I guess.

Edit: I could always enlarge the opening in the CD mount for one of these:

10x19x5 bearing

[mothman]

Brian, i was wondering why the inner surface of the cup doesn't look shining like the outer surface. Are they anodized or hard coated?

[brian015]

Originally Posted by mothman

Brian, i was wondering why the inner surface of the cup doesn't look shining like the outer surface. Are they anodized or hard coated?

I wondered the same thing, but I'm not sure what it is - some type of rougher finish on the inside, though.

[Jahay]

maybe just polished on the outside?

do you know the quality of the alloy? if it isnt a high grade, it could be very dull if not polished?

[mothman]

Jahay, they are 7075-t6.. and I believe that they put some layer of coating/anodizing on the inner to make it harder..