HPI MT2 Brushless conversion

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orcusomega
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HPI MT2 Brushless conversion

Post by orcusomega » Tue May 18, 2010 3:37 pm

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After running nitro for a while, I have to admit, some of the nuances are getting annoying. It is a pain to tune, keep tuned, replace glow plugs, yada yada yada. Not to mention fuel (nitromethane) is $40/gallon!

So I was running the MT2 a few weeks ago, and the motor lets go. OS .18 motor, the truck was a SCREAMER. Unfortunately, even if I had a new motor to put into it, it takes forever to break them in in order to be able to run them...<!--more-->

So I was at the local hobby store looking at possible motors, and they had a Dynamite Fuze electronic speed controller and 5800kv brushless electronics set on sale for 2/3 the price of a replacement engine - so it came home with me :)
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To start the process off, I removed all the stock turnbuckles and steering rods and replaced them with Traxxas units. There are a lot of aftermarket turnbuckles, for like $25 for the rods PLUS $20 for the ends - but they are not as good as, or as easy to get ahold of, as Traxxas units - nearly every hobby store carries Traxxas gear! So for the record, the proper Traxxas part is #3644, and they run about $6.50 a pair, and you need 3 pair (front and rear camber links and 1 pair for the steering links).

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With that taken care of, it is time to strip down the chassis. I removed everything except the front and rear bulkheads. Since the battery is so large (3S LiPo muahahah) I need to move the transmission over to the right and forward. So I flipped the front and rear dogbones around to move the trans forward, and moved the trans to the right using a custom aluminum plate. It was pretty easy, actually, and made a TON of extra room.

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Once the trans was relocated, I moved the motor mount back in line using a custom motor mount I made out of 2"x2" aluminum angle.

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An important note: the MT2 uses the same spur gear as the Savage, and it needs a Mod-1 pinion to properly mesh, which has a 5mm motor shaft. In order to put the needed pinion onto the 1/10 motor, which has a 3mm shaft, you need an adapter, available from MyAtomic (among others). I started with an 11 tooth pinion and a 53 tooth spur - mostly because I don't know how much torque the Fuze motor has.

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Once the motor was in, and the motor mount in place, it was time to reinforce the chassis - and this was initially a head-scratcher. The original MT2 used a radio tray that tied in the front bulkhead to the center trans to the rear diff - but I can't use that anymore since I need the space for the electrical components. So, instead I used turnbuckles :) From the rear bulkhead to the trans, I used the turnbuckles from the HPI Savage - they worked like a dream. From the front bulkhead, I used Traxxas 3744 turnbuckles. One of the nice things about using turnbuckles is that you can set them to be the exact length you need, without all the measuring and drilling, etc :)

With the center trans in place, and tied into the front and rear bulkheads, and with the motor in place, it is time to mount the steering servo and receiver box. For the steering servo, I used aluminum uprights to move the servo in closer to the front driveshaft and forwards from its original location. I had to do this for 2 reasons - #1 I am still trying to make room for a large battery tray, so the servo needs to be as far forward as possible and #2 the original angle of the steering rod to the actual bellcrank is gradual in the original manufacturer's configuration, but with all the moving around, it becomes quite steep, and a lot of throw was lost to vertical angle between the servo saver and the bellcrank. To somewhat compensate, I used a M3x20mm screw to go through the rod end, then a M3 locknut on the other side before going into the bellcrank - this elevates the mount level and make the steering more crisp. For a servo, I used an HPI SF-2 I had lying around on the workbench, and trimmed off the rear most post from the front steering support plate. If you look (right-most picture), the servo is VERY close to the driveshaft - this was inevitable in order to make the steering functional :)

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Now that the steering was setup, it was time to get the receiver in place and figure out how to make it as weather resistant as possible. So I used an RPM radio box that is typically used in Savage Mid-Tank conversions, and dropped it in right in front of the motor. This worked out well, since the motor bracket extended forwards, and the RPM box has a leg underneath that I was able to shave off to make everything level. Only problem was an antenna mount, which I made out of 5/16" aluminum square stock and bolted to the top of the box. I don't like the way it looks compared to everything else, but I can certainly revisit that later if it bothers me enough :)

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Right behind the motor, I installed the ESC. I did not use the foam tape they supplied, though. Since I am forever tinkering with my RC's I needed something that would hold tight and still be removable. I used, instead, high-strength fastening tape from Grainger, similar to the stuff they use to attach EZ-Pass'es to the car window - works like a CHARM! I zip-tied the wires in place to make sure that there was no way they would get into the rear drive-shaft, and ran the wire to the receiver.

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Last but not least was the battery tray - the whole reason why the chassis had to be revamped. Using more of the 2"x2" aluminum angle, I fab'ed up a 3-sided box that will hold the battery in place. I did not add the 4th side, or the top, since I am going to use a Velcro-strap to hold the battery in the box onto foam padding. I had to do it this way to accommodate many different sized batteries. This will work for now, I am waiting for my Flux battery boxes to arrive.

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So how does it run? In a word- AWESOME! It needs some tinkering to get the balance and suspension tweaked but all in all it is a blast! The gear mesh ended up spot-on (not sure how LOL), and the ESC combo works great. I may put in a 3500kv motor to get some more torque out of the setup and put the 5800 into a street RS4 Evo, but that's another project for another day!

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Comments, as always, welcome!

Bob

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132NHAF
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Re: HPI MT2 Brushless conversion

Post by 132NHAF » Tue May 18, 2010 4:11 pm

Wow, what a conversion. I have an original MT and have run several gallons through it. Never thought of this conversion. Did you by chance look into buying a roller electric before starting this project?
Scott T

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orcusomega
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Re: HPI MT2 Brushless conversion

Post by orcusomega » Tue May 18, 2010 4:43 pm

I Did, actually, but decided against it. A replacement motor was $120 or so, and I got the esc/motor combo for $100 at the local hobby shop while i was looking at motors. I enjoy the fabrication and figuring out problems so this was right up my alley.

In my case it was economical because I had most of the raw materials on hand (I have quite a little RC workshop going). I only needed the esc/motor and pinion - the rest I already had. Truth be told, i had already replaced the camber mand steering links well before this build, but thought it worthwhile to cover, so i added it to this write up. I did not have a battery or charger (well, not LiPo at least) but those are items i can use on other vehicles.

Now that I have one project under my belt, I am going to do a few more I think. I have two Clod projects underway, one Jugg, and will be starting another BL conversion on a Hellfire. I pick my projects basef on 1) what would be fun to do and 2) what parts I can get my hands on cheaply. I have found the worst thing for me is the ebay app on tje iPhone :)

Bob

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Budhatrain
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Re: HPI MT2 Brushless conversion

Post by Budhatrain » Tue May 18, 2010 5:52 pm

well one and good job on the conversion. You definitely have skills going from conception to reality. I totally feel the same way about nitro- I like the trucks and all but they are messy, a pain to keep tuned and my gallon of fuel always goes bad before I use it all.
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vonclod
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Re: HPI MT2 Brushless conversion

Post by vonclod » Wed May 19, 2010 1:53 am

welcome to the world of brushless conversions..nothing like plug and play, good job 8) ..i did my first conversion to a thinder tiger 1/8th buggy ..same deal..mtr mount out of angle..at that time there werent any 1/8th brushless esc,s so we used mamba maxs with a bec,,good enough for 4s and for motors fiegao,s were pretty cheap and lots of power..nice job 8)
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