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They killed both the Dune racer....UPDATE.

Posted: Mon Jul 30, 2018 4:53 am
by Ron_J
Well, the kids managed to kill both toys over the weekend. The one drive wheel on the dune racer had been slipping, and them riding double really did it in, but the kicker is now it will only run in high gear...no low or reverse. I'm guessing that those 2 speeds run off the same motor?

The 4 wheeler must have burned up a switch or controller, because it won't do anything. I haven't had time to investigate yet, but given all I paid for them, I might just keep my eyes open for a couple more and use these fro parts.

Re: They killed both the Dune racer and the 4 wheeler....

Posted: Mon Jul 30, 2018 7:58 am
by Hammer-fm
The Dune Racer sounds like it's just stripped the teeth off a gear in the gearbox, likely 1st gear (the one that connects to the motor). When that happens, the motor in that gearbox will go full speed in the 1st and reverse (series) modes, but won't go anywhere, and the other (working) gearbox will get no voltage. 1st and reverse operate in series and is similar to how an open diff on a car will send all the power to the tire with the least resistance (traction). When the gear is stripped, it has "no" resistance.

In high mode, both gearboxes are in parallel and get the same voltage, so the working one will still work -- but now it has to do all the work of pushing the car.

New gearboxes are relatively cheap, and yes ... if you can find a cheap working 'anything' on craigslist, you can probably salvage some usable parts.

Were either of these modded?

Re: They killed both the Dune racer and the 4 wheeler....

Posted: Mon Jul 30, 2018 9:16 am
by Ron_J
They were both bumped to 18v. The dune racer had been like that for a while without issue, the 4 wheeler not too long, so that may have been what killed it.

Re: They killed both the Dune racer and the 4 wheeler....

Posted: Thu Aug 02, 2018 6:03 pm
by Ron_J
Turns out the left rear motor is bad (I assume it's the one that runs low and reverse), and a couple teeth missing off a gear on the other side. the numbers on the gear box is 00968-0502-01 A. I have found a few gearboxes, but they are stamped with a "C". Anyone tell me what the difference is?

Re: They killed both the Dune racer....UPDATE.

Posted: Fri Aug 03, 2018 7:21 am
by Ron_J
The bad gear

Re: They killed both the Dune racer....UPDATE.

Posted: Sat Aug 04, 2018 2:27 am
by Hammer-fm
Hmmm... I haven't broken one of those yet. Three options (out of many more :lol: ):

(A) Replace just the bad motor and the bad gear. Individual gears are $12 on somewhere like this on ebay. A motor is another $17 or so when bought standalone.

(B) Get a whole new gearbox + motor for a model with the same # of teeth as the bad motor. Use the new gearbox in place of the one with the broken gear, and use the old motor (from the gearbox with the broken gear) in the gearbox with the busted motor. I think the DUne Racer is 16T (should be printed on the gear on the motor), which is the same as the F150, so a gearbox like this would work. Biggest advantage with this is you'd have some spare parts, since you'd have an almost-complete gearbox sitting around, in case one of the other gears breaks.

(C) Get two new 23T (Corvette) gearboxes w/o motor, drill out the axle hole, and put in 775 motors with 22T gears. You can go with the super-cheap Nichibo 7013F ($16 for 4, shipped), which have about 30% more torque than stock motors, basically the same speed, and pull only about 10% more stall current. They should last quite a long time at 18V. But I recommend you only run them in a 21/22/23T gearbox or with an ESC, because otherwise they put too much stress on the gears at startup (22T vs. 16T means about 40% less stress on the teeth, but also 40% more speed; since the 775 motors are 30% higher torque, that means overall about 10% less stress than the old stock motors put on the current gearboxes you have). It may end up being faster than you want though. You'd have lots of spare parts, but it's substantially more work.

Re: They killed both the Dune racer....UPDATE.

Posted: Sat Aug 04, 2018 11:34 am
by Ron_J
I think I screwed up. I punched in the numbers from the gearbox and it brought up one that is for that machine, but after I ordered it, I saw it had 16t motor. Mine are 15t. Not sure if I can swap the gears on the motors or not. If not, I'll have to order either another 15t, or 16t motor.

Re: They killed both the Dune racer....UPDATE.

Posted: Sat Aug 04, 2018 11:51 am
by Hammer-fm
Gears aren't too hard to swap if you have a vise and a good punch. I've done 8 motors this way to swap for faster motors.

Re: They killed both the Dune racer....UPDATE.

Posted: Thu Aug 09, 2018 4:56 am
by Ron_J
I got it back together last night and all is well in the world again. Thanks for all the help.

I ended up making a little puller for the gear. I guess I was bored. :) It worked like a charm.

Re: They killed both the Dune racer....UPDATE.

Posted: Thu Aug 09, 2018 7:22 am
by Hammer-fm
Nice solution -- always good to have a welder and a bit of tubing lying around!

Re: They killed both the Dune racer....UPDATE.

Posted: Sun Aug 12, 2018 6:55 pm
by Ron_J
Yes it is. I don't throw anything away, and as luck would have it, I had a 2" piece or 3/4" square tube in the bin.

I found the problem with the 4 wheeler as well. The quick disconnect I put on the battery wasn't heavy enough and it got melted under the 18v. Oops.

Re: They killed both the Dune racer....UPDATE.

Posted: Mon Oct 15, 2018 11:55 pm
by emolatur
Just want to chime in on your understanding of "that one must run reverse" (or however you worded it) since nobody else has.

In low speed, or reverse, the motors are in series, like christmas lights: "if one goes out they all go out," except "they all" is both. If one motor burns out and goes open-circuit, neither motor runs.

In high speed, they are in parallel, so the non-fried motor will continue to work.