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Jul 31, 2020, 11:28 AM
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Tonka Sawback


I've been tinkering with an FPV Tonka Summit for years but I saw a thread on RCCrawlers.com where someone mounted a Tonka to a more scale-looking GMade Sawback chassis and it looked really cool. I've been wanting to copy his build for a while and finally got around to it. I'm still waiting on the actual Sawback kit to arrive but a few parts came in so I started the build yesterday. Here's my parts list:

Gmade Sawback 52000 kit

Gmade Sawback GS01 Powder Coated Black Steel Ladder Frame (total splurge but might blend in better with the Tonka)

20KG Steering Servo

Hobby Wing Quicrun WP1080 ESC

Axial AX24007 55T Motor

Flysky FS-GT2B Transmitter and FS-GR3E Receiver

RC4WD MICKEY THOMPSON 1.9" BAJA MTZ SCALE TIRES

Crazy Crawler LaserFoam "WP Magic" 1.9 Foam Crawler Tire Insert (2) (101x35mm) (stiffest foams I could find)

1.9 Aluminium Beadlock Wheels

Hitec HS-81 Servo (steering wheel servo)

24T C1 Spline Servo to 1/4" Shaft Coupler (for mating the servo to the steering wheel)

Gmade Stainless Steel Hex Bolts Kit

RC Screwz Stainless Steel Screw Kit for GMade Sawback (wasn't sure if the Gmade hex kit was comprehensive enough)

Gmade Metal Spacers for GS01 Sawback Leaf Spring Kit

Gmade 30003 Aluminum Zero Ackerman Knuckle Arms (to raise the steering linkage above the leaf springs)

Gmade 30004 Bent Zero Ackerman Steering Rods

Gmade GS01 Aluminum C-Hub Carrier

Gmade GS01 Aluminum Rear Axle Adapters

I've already cut the metal bottom off the Tonka and assembled the tires. The tires are grippy and the WP Magic foams are nice and stiff. The circumference of the foams was dead on but were a little too wide so I used a table saw to shave off a few millimeters. The picture looks like I'm pushing the foam through the saw but I was really just turning it in place lol. I'll post more as I go.













Last edited by replayreb; Aug 10, 2020 at 10:26 AM.
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Aug 05, 2020, 07:58 PM
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Well, I've committed now lol. I cut the frame in half and now fashioning a plate to hold the two ends together.











Aug 06, 2020, 09:29 AM
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Looking good, I like the choice for tires and wheels. You going to make it FPV?
Aug 06, 2020, 09:44 AM
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Hey, thanks! I'm not going to FPV with it. I prefer driving rock crawlers from a 3rd person perspective. I'll keep FPV'ing with the Summit since there is a very low chance of a rollover with that platform.
Aug 06, 2020, 10:00 AM
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I was just going to fashion some sort of straight brackets to connect the two ends of the frame together but I was thinking of a making an aluminum skid plate anyway and then realized I could just bolt the ends directly to the plate and also mount the transmission and motor directly to it and by mounting them flush with the bottom of the frame it gives me a little more clearance so I won't have to cut out as much of the Tonka's interior. I had to bend the ends of the ends of the aluminum slightly to fit the shape of the Tonka's rocker panels but I think it turned out perfect. I'll probably have to cut some notches for the drive shafts.









Last edited by replayreb; Aug 06, 2020 at 10:06 AM.
Aug 06, 2020, 10:24 AM
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BTW, one caveat about leaf spring setups I didn't know is that the wheel position shifts slightly forwards and backwards within the wheelwell depending on how compressed the springs are because of the hinged hanger on one end of each spring. That made it more difficult to determine how long I needed to make the frame because the wheels would be in perfect position with no weight on the suspension then be slightly off center when I pressed down on the truck so I had to find a happy medium. Like in that last picture above the wheels might look a little too close together with no weight on the springs but when I get everything installed the extra weight will compress the springs and the wheels will be perfectly centered within the wheelwells.
Last edited by replayreb; Aug 06, 2020 at 10:52 AM.
Aug 07, 2020, 01:38 AM
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I got the transmission and motor mounted. I shortened the front drive shaft a lot; Down to less than an inch. I was surprised how steep an angle the Gmade U-joints would work without binding so I was able to mount the transmission as far forward as I wanted which is good so I don't have to cut into the seats of the Tonka's interior too much. I had to make cutouts in the aluminum skid plate to give the driveshafts enough clearance and used one of my wife's emery boards for the template.







Aug 07, 2020, 08:57 AM
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Quote:
Originally Posted by replayreb
Hey, thanks! I'm not going to FPV with it. I prefer driving rock crawlers from a 3rd person perspective. I'll keep FPV'ing with the Summit since there is a very low chance of a rollover with that platform.
I tried crawling FPV to me is was just to weird and the lines are hard to follow. The Summit is a much better crawling experience.

Tonka/Sawback is looking good.
Aug 10, 2020, 10:04 AM
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Well, I got on a wild tear and finished it over the weekend but I got behind posting updates obviously so I'll try to explain what I did over the next several posts. Anyway, after I got the chassis finished I bolted on the Tonka body. I could get away with using little screws on the frame ends since the skid plate will also be fastened to the body.





Last edited by replayreb; Aug 10, 2020 at 10:19 AM.
Aug 10, 2020, 10:09 AM
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I started cutting the interior very conservatively but ultimately had to cut out a lot to make room for the frame, steering servo and front wheel clearance when turning.





Aug 10, 2020, 10:14 AM
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They don't make a chassis servo mount for the Sawback anymore and I could have 3D-printed one but I decided to make a simple one out of leftover aluminum plate. I also made some L-brackets brackets for the steering wheel servo. They're just held on by velcro and a cable tie.



Last edited by replayreb; Aug 10, 2020 at 02:05 PM.
Aug 10, 2020, 10:18 AM
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I had to cut out the plastic floor pan and make grooves in the seats to accommodate the frame.





Last edited by replayreb; Aug 10, 2020 at 02:46 PM.
Aug 10, 2020, 10:29 AM
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I had to move the rear shock tower supports forward about a half inch so they would fit inside the hollow seat backs. I hated using those zip ties on the springs because they slid off too easily so I removed them and placed the smaller springs under the main spring. I would up using all three springs with the small one on the bottom and the medium one between it and the main spring. You'll see some pictures with Gmade's anti-wrap bars installed but I wound up taking them off because they made the suspension too stiff and inconsistent.





Last edited by replayreb; Aug 10, 2020 at 11:56 AM.
Aug 10, 2020, 10:34 AM
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I installed the ESC and receiver in the rear and a heavy battery in the front. It's one of two SPC 2C 8200 mah batteries I use in my Tonka Summit. I suspect I can drive all day with that thing lol.





Last edited by replayreb; Aug 10, 2020 at 11:17 AM.
Aug 10, 2020, 10:36 AM
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Shot of the steering linkage. And I need to get some boots for my GI Joe lol.



Last edited by replayreb; Aug 12, 2020 at 09:58 AM.


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