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speedy_w_beans

Speedy's TRF801XT Build Thread

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I spotted that yesterday, congrats. I tried to find the price for UK postage but their website wasn't playing ball ?

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Price for UK postage is 13,90 €.

Thanks - so ca £180 to the UK. Not bad for what you get.

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Well, after a lot of measuring and calculating, here's a motor mount design I think I'm going to try to fabricate:

7h6a.png

The L-channel is 3 mm thick. I plan to secure it to the chassis with four M4 countersunk screws, and also secure it to one of the center diff mounts using the brake caliper mounting holes. The motor will have a 1 mm thick foam pad underneath it. Torque from the motor shouldn't spread the gears apart since the mount will be secured to the brake caliper holes and chassis. I plan to use four M3 cap head screws to secure the motor to the mount. With the motor connected to the mount like that, the whole structure should be quite stiff. I'm not expecting any jumps or landing to bend the mount. The weakest possible orientation is if the truck lands upside down on its body, but I would expect the body and mounts to absorb some of the energy. Normal jumping and landing, and side to side forces, should be constrained well.

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After a few hours of work, I now have a motor mount. See pics below. It fits fine in the chassis; I just need to mark a few holes in the chassis and drill them to complete this installation.

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That's great work Paul. Good that you managed to tie it in to the centre diff housing as well as bolting down to the chassis plate. Are you going to double up and have a bracket under the motor too ?

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Originally I thought I might do a back-to-back design with two L-channel sections facing each other; this would make the motor mounting surface 6 mm thick and provide up to 8 mounting points to the chassis. While I was working on the design I found a few things:

1) The thickness of an extra L-section directly under the motor was going to raise some of the motor adjustment slots uncomfortably close to the top edge of the material.

2) Just a single bracket 3 mm thick seems plenty stiff on its own.

3) The face of the motor itself, in combination with the L-section, provides additional stiffness when all four adjustment screws are torqued down.

4) Tying into the center diff mount as well as the chassis really constrains movement.

So this isn't quite the design I originally considered, but it seems very robust. I'm confident using it.

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I was able to finish installing the motor mount tonight. I wasn't happy with the square outer corner, so I ground, filed, and sanded it down to more closely match my drawing. I installed the center diff and motor mount together as a single assembly, then used the bottom pilot holes to mark the chassis and drill those as well. I had purchased some metric drill/tap/deburr bits from the local Harbor Freight store, and the M4-0.70 was perfect for tapping new holes in the bottom of the mount. Then I drilled out the chassis for the screws and countersunk the bottom of the chassis so the screw heads are flush. I put it all back together and used blue thread lock on the bottom screws (reused from the nitro motor plates), added the foam cushion on the chassis, and installed the motor.

The mount is amazingly stiff; when I try to pinch the motor against the rear chassis brace, the brace flexes more than the motor does. The motor sits on the foam pad and will not bounce up or down. The motor doesn't want to budge whether I'm pushing or pulling on it in any direction, even with considerable force. I'm pretty happy with the design overall. The only downside I see right now is the lower inner motor screw is difficult to reach; it takes some patience to get it started. A few ball end metric hex drivers would make installation easier.

I'm expecting a Tekno V4 battery tray to show up soon, so that will be the last major component to install. I chose this battery tray because it's a minimalist design with countersunk holes molded into it. It ships with six M4x6 countersunk screws that thread into chassis holes. It should be pretty straightforward to locate the battery tray, mark all the holes, drill and tap them, and then bolt the tray in place.

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Thanks man! I wish I could move a little faster on this; when I got back from my extended business trip I was just dying to get into a build and the regular box build went by quickly (almost too quickly). Converting this to brushless has taken some extra time to think about the options and come up with some ideas, and work has been getting busy again lately. *cough cough* I feel a sick day coming... (just kidding)

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Finally, the batteries have a place to go!

I tried the Associated e-conversion battery tray and didn't like how the batteries hung way out over the chassis guards. The batteries are in line with each other and the bullet connectors exit opposite sides of the tray, but with the batteries so near the edge of the guards I just didn't like the impact on chassis balance.

I also tried the Tekno V4 battery tray and found several of the screw holes were already over existing large chassis holes, so there was no material to drill and tap for installation. Also, the battery tray interfered a little with the chassis guard and one corner extended a little past the chassis near the rear gearbox. It was going to be a tight fit, and I didn't have a good way to wire the batteries with it since the packs are in line with each other and the inner battery is very close to the rear prop shaft.

So, I just decided to make my own battery mount to get exactly what I was looking for. Things important to me:

1) Batteries are offset from each other a little so all bullet connectors exit the same direction (out).

2) Weight is closer to the center line of the chassis to minimize the imbalance with the motor.

3) Batteries stay truly vertical and never rock side to side; there must never be interference with the rear prop shaft.

4) Ideally the chassis guard is left intact and doesn't need trimming or modification.

5) It would be great to leverage existing holes in the chassis if possible.

I started with some aluminum L-channel, the same material I used for the motor mount, and came up with this:

IMG_1272.JPG

The bottom of the L-channel has been cut at a slight angle to mate perfectly with the chassis guards and hold the inner battery parallel to the rear prop shaft. There are two pairs of countersunk screws, each pair exiting in the opposite direction in the vertical section of the mount. The screws are held in place with leftover ball connectors covered with nitro fuel tubing. The purpose of the ball connectors/fuel tubing is to prevent the batteries from sliding forwards or backwards in the chassis. The bottom of the mount has two M4-0.7 tapped holes and one M3-0.5 tapped hole that align with the nitro motor mount and gas tank holes in the chassis.

Here's a view from the other side.

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The bottom of the L-channel has been ground to create passages for the battery straps...

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Here are the batteries in the mount. The inner battery is staggered backwards a little relative to the outer battery, and this reveals all of the bullet connectors on one side. I cut some of the mount to make the inner battery's lower bullet connector accessible.

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Batteries from the other side...

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Straps installed. These are Associated e-conversion battery straps; most Associated e-conversion parts are about half the cost of Tekno. I also like how these straps don't have any branding on them.

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Other side...

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Here you can see the straps passing underneath the mount in the cut channels.

9pzl.jpg

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Placement of the battery mount in the chassis...

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Everything installed...

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Top view. This provides a good perspective on how the batteries are placed relative to other parts. The ESC will go behind the motor.

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Bottom view. This should be the end of the drilling, tapping, and custom fab work.

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The batteries and mount feel very solid in the chassis. I'm happy with the end result. All that's left is electronics installation now, and it will be ready for a test run! I'm glad the body is already done!

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Tremendous work there. Very impressive and absolutely one of a kind. Looks great too. From a purely aesthetic, non-functional point of view... looks beautiful.

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Great idea with the batteries, well done. This build have turned out excellent. Looking forward to see it RTR, and hear your thoughts about its performance. Can't wait till I get mine.

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Allllllll right, this build is now over. I installed the electronics today and wired everything up, and it all works great. I'll let the pics do the talking. I did some driving up and down the street to dial in the steering and check the ESC settings, and it's in a good state now. It's a little slower than my NEXX8 (as expected due to the motor rating), but everything was running cool and glitch free. I need to raise the ride height a little bit; the chassis is sitting low with all the weight in it now. I ran out of daylight, but I will post one final pic with a different rear wing (black instead of white, a few decals applied) tomorrow and I think we can call this one good! :)

"If you have the means, I highly recommend picking one up." -- Ferris Bueller

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VERY impressive Paul

Great layout, well thought out and excellent execution - bravo !!

:D : D

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Just noticed you've gone with a sensored 2100kv motor, which pinion are you using ? 14T?

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Hi Percymon -- Thanks for the comments! The motor is sensored, but I'm running it sensorless because that's what the speed control supports. I'm running a 13T pinion.

Final pic. For the color scheme I'm using on the body, a black wing for $5 looks better than the white wing that ships with the kit.

uwar.jpg

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You have to put a video up man! I want to see it moving! Looks great! Is that a 350Z in the pic?

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Yes. I agree with JeepnMike. This thread won't be complete till we get a video and then a review of your custom 811XT, how it handles and what not.

Anyway, great job! Wish I had a truggy.

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I will put some video together and post up some thoughts sometime in the next few weeks. Right now I'm on business travel, and when I get home I have a bunch of yard, house, and 1:1 car work to do before I can play again... This is slowing down my CR-01 build thread as well...

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