Starting from scratch - MT conversion

[10kman]

Oh yeah, an 8 year old with a 13 pound truck is more than enough right there, throw in some speed and you have yourself some damage waiting to happen.

How many volts did you run on your 7xl setup?

[BrianG]

That's true, but nice if you have it. If not, the Y adaptor works well too - you just don't have all the seperate EPA/range/etc adjustments you would with the channel mixing.

Personally, I like locking the tranny into one gear and using the motor as the brake and reverse. A lot of times, you can remove components out of the tranny making it simpler and lighter (less rotating mass). Plus, less overall weight and complexity since there are no metals discs, servo, linkage. It is a little harder on the ESC though...

[10kman]

Yeah, the lighter weight is a nice feature of not having all of those parts, plus, like you said, it is simpler and less stuff can go wrong.

I'm wondering if locking it into 2nd gear would be too high for BL power? I'm thinking it would be fine with a big powerplant in there. There's so much room on the chassis on the MGT that you can run plenty of cells to suit your needs.

But, the ESC strain worries me as they are expensive. What ESC's can handle that kind of strain without causing any issues in the near and long term? Assume 14-16 cell voltage ranges for this project, so what is that, 4s/5s LiPo?

[BrianG]

What's the weight, final gear ratio, and tire size of the vehicle? If heavy, geared kinda high, and using larger tires, it does place a larger strain on the ESC. I think an ESC with a solid 120A+ rating should be OK...

[riceman]

Originally Posted by 10kman

Yeah, the lighter weight is a nice feature of not having all of those parts, plus, like you said, it is simpler and less stuff can go wrong.

I'm wondering if locking it into 2nd gear would be too high for BL power? I'm thinking it would be fine with a big powerplant in there. There's so much room on the chassis on the MGT that you can run plenty of cells to suit your needs.

Depends on your motor and batteries really. I went with stock second speed gearing on my LST2 and was still pulling wheelies. I recently went up three more pinion teeth on my LST2 and the MM didn't even blink.

Originally Posted by 10kman

But, the ESC strain worries me as they are expensive. What ESC's can handle that kind of strain without causing any issues in the near and long term? Assume 14-16 cell voltage ranges for this project, so what is that, 4s/5s LiPo?

Roughly figure 1.2 V/cell NiMH vs 3.7V/ cell Lipo. Set up with BEC the MM will handle 4S. I've put 5S on my BK 9920 in the MGT no problem. Did have to run a fan on it though

[10kman]

Drive ratios according to web searching yield this -

Transmission ratio: 8.132:1 (first) 5.624:1(second)
Final drive ratio: 28.22:1 (first) 19.51:1(second)

So, assume 2nd gear locked, and 13 pounds is probably reasonable for a weight guess. Tires I don't run super big ones, maybe 5" max.

[BrianG]

~19:1 is a fairly typical final ratio for a MT with those sized tires (which I think are 5.65" IIRC for standard MT tires). Shouldn't be bad at all even locked into second gear. Of course, I'm assuming your motor will be the typical XL size motor found in the RCM store. If it is an L size, the two speed might be better off.

:Off topic: If you know the gear tooth counts of the diff ring/pinion, and the tooth counts of the tranny gears, I'd appreciate those numbers to I can add them to the speed calculator presets.

[10kman]

I found this -

http://alumniblinds.com/MGT/MGTINFO.htm

I'm looking for actual numbers though, I don't think this stuff is in the manual to that level of detail.

[BrianG]

LOL, I've actually counted teeth from manual drawing before. If the manuals are done right in PDF form (using true vector drawings), you can resize them as big as needed with perfect resolution for counting. Also, sometimes you can get tooth counts from the parts list. If all else fails, I just go to the LHS and count the teeth in the package. :)

I'm running the MGT on 4S lipo. Nothing off the wall. As for the strain on the esc due to braking, I don't think it's a problem. I remember seeing my MGT running when it was in nitro form and owned by someone else and the braking wasn't "all that." When I converted to electric, I kept dialing down the brakes until the truck would brake without flipping over. Apparently, the motor braking was a lot better than the stock setup. I'm only running 30% on the brakes and it stops the truck pretty quickly without locking up the tires causing the truck to nose dive and flip.

10Kman, if you are looking for speed, perhaps keeping the two speed is the way to go, but you said that you are familiar with the MGT. As you know, the second gear setup doesn't look like it could take much without modification. All that's kicking it into second gear is that little arm that pops out on the rear disk of the second gear shaft and all that's holding that in place is a little set screw. I don't think it will hold up.

I suppose that you could lock first gear and use a low kv motor with lots of cells and use a large pinion to get it moving faster. I do have to say again though, going fast isn't the strong suit of the MGT with the large tires. This thing as I have it setup borders on having rock crawler status and is a hell of a basher in confined areas. It's the most fun RC vehicle that I have, although it is the slowest. The lack of speed also means much fewer broken parts. In over a month of thrashing, I've only had to replace one lower arm.

[10kman]

Update on the project to make it "officially started" -

Ordered up a brand new MGT. I was thinking about trying to get a used one and just giving it a going over, but then I realized that I am scrapping a lot of parts off of a new one, and will rekindle some money that way.

So, got a new MGT RTR, Forward Only Conversion, and some diff shims coming right now. Once I get it, I will tear it down anyway to do the shim/tranny conversion, and give it a once over with some loctite where necessary, shrink wrap the CVD's to keep the screws in place on the cups, and get it bulletproof.

I'm going to take the nitro parts right off and sell them as a kit, and probably the radio gear as I already have 2 JRXS3's sitting around with RS300 synthesized receivers as well, and a 958Z servo for steering. That will give me back plenty to get the Feigao 7XL motor that I am going to use, and probably enough for some aluminum from Lowe's and some small tools to hopefully get it cut how I need to mount up that motor. I wish there was a mount out there to do it already, it's simple enough really to just bolt to the chassis.

Then I'll just have to figure out which ESC I am going to use. I'm thinking I can save some cash if I use the mechanical brakes rather than the ESC's brakes, so I won't need as high of an AMP rating.

Any thoughts on ESC's for the application? I'm assuming I'll need a BEC as well, which I do not have experience with, I have always used a receiver pack but do not want to have another pack on the truck.

I also need battery packs and probably a new charger if I switch to LiPo, if not my MRC 969 will do fine up to 8-cell packs, but then I need a series harness.

Once I get by the mounting of the motor, I will be in a better situation.