Is my modded gold tub too heavy with too much torque?

[susko]

I started off wanting a mostly aluminum car that would be a good driver (possibly a contradiction). Weight became an immediate issue for every component of the car. I beefed up the steering because the original set up had a terrible radius and couldn't change the trajectory of the heavy car (this took some time to get fully functioning and still had a traction issue). My motor also didn't seem to have enough power to get the car going. So, I went with a 1/8th scale motor instead. I actually had purchased a 1/8th speed control by mistake anyway. After some reading, I discovered that the battery I purchased was not good enough for the speed control/motor combo in the first place. After all that was sorted out, I had a really heavy car with slow acceleration that couldn’t turn and had a decent top speed relative to what I had driven before. I was used to a b3 and a t3 with some stock brushed setups from modern Losi and Traxxas kits (which I never had any issues setting up).

Unfortunately, I ended up melting my ball diff gear twice. The first time I am sure that it was too loose. The second time I was at top speed and went into full brake. This may have been too much torque on the diff. I know I was supposed to set the slipper as a safety, but it kept slipping (probably saving the diff like it was intended to). I just cranked it down until it would just barely slip. I probably had it adjusted wrong again. Being frustrated with my learning experience and at the same time having to deal with engineering school, I put the car on a shelf and forgot about it. I never really got to run the car.

I picked up the car today and thought maybe I could buy a couple of diff gears and try once more to get it going.

My question is, should I just strip the engine/esp out of the car, put the shiny stuff on a mint gold tub and, buy a 1/8th scale to put the electronics in? I would rather get the gold tub running the way it is if that’s even possible.

specs:
tekkin T8 2650kv
hobbywing xerun 150A
Vicious Tek 4s 6500mah 60c
Stealth diff
Kimbrough Spur Gear 32P 62T(I think)
18t 1/8th scale pinion
brass gear steering servo
carbon fiber shock towers
and lots of aluminum
5.5 pounds according to the bathroom scale

Here are some pics of the car in its current state.



jk

[RC104ever]

The problem here is gearing. If you really have a 32P 62t spur and 18t pinion, you need to redo your gearing. Even with the big motor, you should be gearing up I think.

On the other hand, it would likely be simpler to just go with a smaller engine and change the gearing that way.

[susko]

I knew that was probably an issue as well. It was something I didn't really give much thought. I need to read up on it.

Are you saying that the ratio with the pinion and spur is too large or too small? Also, I originally bought a Tekin 4.5t Redline gen1(http://www.teamtekin.com/redline_gen1.html) for this car if that's a better fit. I only have the hobbywing esc.

BTW: I don't want to go the easier way but the better way to get the best performance.

[bully]

You can get excellent performance from a 8.5t 540,1/10 size motor and a 2s battery and it will handle alot better.. 1/8 motors and batteries are only good in a 1/10 for speed runs not much else,sometimes hobby shop's will or people will tell you need this and that but they just want a sale.. What do you use it for mate, for track racing I run a 10.5 in my RC10 and it is plenty of motor.. You might have been geared badly or had some other problem.. Yours is the first RC10 I have seen with 1/8 running gear fitted.. Lipos and brushless have given performance that has been reserved for only the top racers with the best gear available in the recent past. Check youtube videos and check the speed of 1/10 buggies in race conditions,they are quick.. The 4.5 turn motor is only good for on road or speed run cars mate

[bully]

That steering is not for the RC10 also mate,might be some of your turning problem.. Look at the re release worlds steering or the jconcepts steering or even the a+l steering will give you excellent results..

[RC104ever]

Keep in mind that your steering (understeer in your case it sounds like) can also be a factor of rubber compound. Hard to see what tires you have on the aluminum rims but that might be an issue.

You might also want to consider rigging a sway bar in the back - that will help rotate the car around a bit more.

As for the gearing, you'd want to consider going to a different gear ratio but I'm not an expert here. I run an 81T spur and a 21T pinion. This gives me tons of speed and it doesn't wheelie.

[susko]

So my steering setup is far better than stock. It is a custom setup using parts from a newer car plus some custom fabricated stuff. I have gotten rid of bump steer(mostly) and the radius has improved greatly. It is understeering though. I believe the issue has to do with the weight of the car (basically momentum), the way the weight is distributed (towards the back), and the tire type (not knobby enough). It's from not having enough traction on the front wheels to change the momentum of the car. I was exaggerating a bit about it not being able to turn. It just doesn't handle as well as I would like. I'm not sure about the sway bar. The car seems pretty rigid from being mostly AL.

I am not planning on racing professionally or anything. I just want to have some fun with the car. I also don't want to dump anymore money into it. I looked into gearing and basically learned nothing. I already knew what different ratios would do (how the mechanics of it work anyway). The problem is I have no idea where to start(pinion spur motor combo for a specific application). I mean there are so many things to consider like wheel base and track, tire size, weight, suspension, course conditions, etc.. I just don't have any experience with gearing an rc.

On that note I don't see how the gearing would be causing my diff gear to melt. It would just affect top speed, acceleration, and motor performance(i.e. electronics heat/failure). If that was the case then the diff would not be able to transfer the power from the motor or handle the weight of the car. If I can't get either of those motors to work with this car then I might as well just redo the whole car. I can put the al stuff on another car for display and stick a cheap brushed in it for bashing.

I was just debating if I should buy another diff gear and try to get the brushed system to work with what I already have. If I had to buy a few spurs and pinions that would be ok too. I don't want to buy anymore escs, batteries, or motors right now because I don't have the funds for it.

Also, thanks for the input. I do appreciate it.

[bully]

Most of the time a stealth diff will only melt down if it's allowed to slip or built incorrectly,with a properly adjusted diff first then slipper you should be ok with most 540 size motors.. Understeer is partly because they were never meant to have that much weight over the rear or such a heavy battery and possibly if that doesn't fix it which I think it will could be your cobbled together steering.. If you want to do it right use only 1/10 540 motor and a 2s battery and see what its like,if you have poor performance with that ballistic 4.5t motor and a 2s battery either your gearing is way off or you have some other problem.. Just a warning even with everything done right you might still have transmission problems with that 4.5t motor,usually a 2wd buggy doesn't need any more motor than a 6.5 and that is crazy fast and the 4.5 would be a test for any transmission... There was a steel diff gear made bitd but I don't know what or how much someone else who has used one could tell you..

[DMAT]

Id say to preserve your car better. drop your battery down to a 3S. Thats about the equivalent of running 2S on higher Kv motor. Id think dropping down to a 2S battery would just be too little voltage and your wont get enough top end speed.

Your probably better off converting to a b4 topshaft setup with a vts slipper to manage the torque your getting from the motor.

Like bully said, there are some metal diff gears that will handle heat a lot better. I dont know of a steel one but HG did make a titanium one and dhawk racing makes an aluminum one that is sold through ebay.

As to your pinion/spur gears, a 20-30 spur on an 81 pinion seems to be a good combo. its just going to take some playing around to find a good balance With the added weight of your alloy part.

understeer is definitely a problem I have too and its prebably heavily due to my car having most of its weight in the back. I was able to fix that with a little bit more grippy tires but trying to turn at any decent speed usually results in the flipping from a traction roll.

The only other thing I could think to do here is to reconfigure your electronics layout. You could use a square 3s battery or series (2) 2s shorty lipos moved right behind the servo and put your esc and reciever closer to the rear of the car.

[susko]

I have looked into the al diff gear. I even had a thread about getting dhawk to make some steel ones a while back, but nobody wanted one. Like you guys said, I probably had it too loose. Metal diff gears require more maintenance too. Everyone seems to like the nylon ones. Though, either motor plus the weight of the car are probably pushing the limits of that diff. The ti diff gear sounds very cool. I'm pretty sure it is impossible to find one though. I don't have b/s/t access anymore so it may be like a month before I could even look. I'll look into the b4 ts and slipper as well.

I would rather have more acceleration than top speed. The t8 should get better acceleration compared to the redline 4.5t. The question is does the excess weight of the 4s battery even the scale. The excess weight of the t8 is going to cause bad handling. Also, what are the advantages in changing to a 3s other than weight reduction/distribution?

It is probably best to buy a 2s for the 4.5t and compare the two. I think the exrun can be set up for a 2s. I'll have to look at the manual. For the 4.5t redline a 21t pinion and a 81t spur is what I will start out with. I don't think the t8 should be geared the same though. It's hard to say what I should use with it, but I'm thinking the ratio needs to be smaller to account for the higher torque. Maybe a 20t pinion and 60t spur? The nylon diff gears are much cheaper so I'm going to try one more time with getting it right. If I don't adjust the al one properly it will probably cause even more damage. I might look into another motor later on. The thing is most of my extra funds are going towards my 3d printer project right now.

Again, thanks for the help.

[Lonestar]

It's an interesting setup for sure... the weight balance is likely way off (to the back) which certainly doesn't help.

I think I can also see a "light" servo arm... that doesn't help either as it flexes under load, especially with the leverage created by that custom steering bellcrank system and the angle between the servo link and the mounting point on the bellcrank. I also have doubts about that steering, but I'd have to see it in the flesh to be able to make a proper assessment

Last Q: what servo are you using (other than the brass gears part)?

Paul

[bully]

Check the manufacturers recommendations for the gearing and the maximum cell count the 4.5t motor can handle.. From my experience with low turn motors is limited but I definitely would recommend 87/17 or similar,depends on the recommendation of the manufacturer but to get the speed and acceleration out of a low turn motor it needs to rev and be close to the recommended ratio for a buggy.. And I think that much motor would be a 2s only motor...

[Lonestar]

4.5T on a 2wd will be about as undriveable as it gets. It will go so fast that turn-in will feel even crappier than before

[susko]

The servo's a cheap Chinese one. It does have some torque though. Its a Tower Pro MG995. It's not going to be as crisp as a $90 servo but it does the job. I did see that the wiring was not secured well so, I will have to crack it open and hit it with some hot glue.

You were right about the flimsy arm having some flex . I just grabbed a random one out of my parts box. I'll have to get a few heavy ones. I ended up placing the servo as close to the front as possible while still keeping it functional. I don't know if I could reduce the stress on the servo/linkage if I was to change the position. The link goes parallel with the servo during a turn so it's not always at a weird angle. I still believe the understeer is mostly due to the weight. When I get the 4.5t setup instead of the 1/8th motor I think it will steer a lot better. When I initially ran the 4.5t I had it set up with a really low c rated 4s. Luckily the hobbywing kept cutting the voltage or it would have fried. I initially though(like years ago) it was cutting out because it didn't have the torque. That's why I bought that t8 (I know, ridiculous logic). I think it should be fine if I get the right battery for the 4.5t. I am just trying to salvage the disaster. Maybe I should try to sell all of the electronics and do it right. I know I wouldn't get nearly what I paid into them and I only ran them once each. I will try to find out what tekin recommends for both those motors for now.

[Lonestar]

The servo's a cheap Chinese one. It does have some torque though. Its a Tower Pro MG995. I

When you said "brass gears" I knew this would be the one

They are utter crap. I am talking from experience, I have bought some myself for bashers, as the torque spec was appealing. That very spec for the price is what makes it hard not to try! The hard truth is, they don't deliver even 25% of their promise. (I'm not even talking about the crazy overshoot...). They are truly, truly a POS (sorry if I'm offending anyone here).

Ditch the MG995, use a proper servo from a known brand : anything 10kg.cm and 0.12s/60deg on 6V will do, that should set you back about $40. You will discover a brand new car in your gold tub.

Paul