Jump to content
Bwaaatch

I made a monster! (please help me fix it)

Recommended Posts

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.

IMG_3133.JPG

IMG_3138.JPG

IMG_3121.JPG

IMG_3127.JPG

IMG_3137.JPG

  • Like 11

Share this post


Link to post
Share on other sites

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

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. 

  • Like 4

Share this post


Link to post
Share on other sites

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. 

  • Like 2

Share this post


Link to post
Share on other sites

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

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 …

  • Like 2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...