Bwaaatch 528 Posted July 19, 2020 Finally got everything together to finish my slammed comical buggy build today. The concept is simple: get the chassis low, the stance wide and the tyres big – turning the Comical Hornet into something more like a street racer. Yes, I know it's ridiculous. The wheels and tyres are the third party 'Monster Beetle' items found all over eBay. They look good and feel good, but I think they are causing some problems … In testing the electrics before it's first run, it was clear that there was a lot of vibration in the rear wheels. When running, I could see vibration in the fronts, too. For the rears, it kicks in even at slows speed if i spin the wheels in mid air, and gets worse as I get faster. At the front, it's most notable as the car struggles for traction when turning full lock at max speed. I can see the wheels wobbling around alarmingly. I'm prepared to be told that this is not fixable, but merely the result of sticking a heavy, wide, large diameter rotating mass at the end of shafts that are not really designed to withstand such forces. but then how exactly does it work on a Monster Beetle, or other car designed for this kind of size of wheel? I'm hoping there might be something I can do to mitigate it. Any thoughts? The only thing I've tried is adding an extra o-ring in the cups at the back to cut down the play in the axles. It does sit down the play, but doesn't stop the vibration. The other possible cause (at least at the back) is the crazy suspension set up, with arms sitting super high to allow dropping the chassis despite the huge wheels. It means the drive shafts sit at about a 20 degree upward slop by default. Finally, I hear lots of talk of 'shimming' to solve vibrations and slackness. Sorry for being an idiot, but I'm not sure exactly what this means. Is a shim what an English person might call a 'washer'? Could I 'shim' either side of the wheel bearings to cut vibration? How would I do that? Thanks for your expertise as ever, TamiyaClub! PS, the setup does the trick in many ways. Drove around for 20 mins on tarmac and didn't come close to turning over. Tried my 'normal' (17t brushed) hornet afterwards and could not keep it upright for more than 15 seconds! It was a festival of grip roll. 11 Share this post Link to post Share on other sites
Badcrumble 4204 Posted July 19, 2020 Love the stance! And those exhausts look so mean! How are the wheels without power applied? Any wobble? Would something like this help? https://www.modelsport.co.uk/tamiya-wheel-spacer-blue-/rc-car-products/391519 Share this post Link to post Share on other sites
Bwaaatch 528 Posted July 19, 2020 Thanks @Badcrumble, yes there is some play at rest. The rear has a bit of 'up/down/left/right' play, and the front has loads of 'in/out'. How much of either of these kinds of play is desirable? I always assumed it served some function, as most cars seem to have a bit by default. Should I be aiming to tighten then down to zero, with shims like this? Share this post Link to post Share on other sites
Bwaaatch 528 Posted July 19, 2020 Oh yeah, Yeah Racing exhausts … brrrmmmmm 1 Share this post Link to post Share on other sites
Juls1 1661 Posted July 19, 2020 If there is a lot of vibration that’s getting worse as you speed up I can’t help but feel your tyres are possibly so poorly made that there weight balance is completely shot. It is possible to balance the tyres using a prop balancer, although the fronts you can nearly do it on the car if the wheel/tyre seems to want to rest in a particular position meaning it’s heavier at the bottom. of course if there is slop this will make it worse but ultimately it’s the balance of the rotating parts that’s probably causing the issue. 4 Share this post Link to post Share on other sites
BattleTrak 61 Posted July 20, 2020 There probably is a minor balance issue with the tires but the rear is probably from the driveshafts being at such a sharp angle. Try raising the ride height and see if it improves. 2 Share this post Link to post Share on other sites
Bwaaatch 528 Posted July 23, 2020 Thanks for all the suggestions! I have shims on order. I replaced the YR universals at the back with the kit cups and dog bones, and this seems to have improved things. Perhaps the stock stock parts are a little longer? Following the suggestion from @Juls1, I had a look at teh tyres more carefully one of the readrs (on the side with most vibration) did seem a little worked when it span. Changed the left/right rear wheels and again saw a slight improvement. At this point, hopefully the shims can give me another small increment and I'll be happy :-) Share this post Link to post Share on other sites
Bwaaatch 528 Posted July 23, 2020 Also, I just tried @Juls1's suggestion of spinning the fronts to see how they settle. Indeed, they come to a standstill, then roll back the other way, suggestion a heavy spot at a certain point. Off to watch a wheel balancing vid … https://www.youtube.com/watch?v=RvJS13KsHtc Will report back! Don't have a stand, so will just do all four wheels off the from axle … 2 Share this post Link to post Share on other sites
ACCEL 2014 Posted July 23, 2020 Your Lil' Ride is Phat! dig those tires. Share this post Link to post Share on other sites