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nowinaminute

New build Hotshot pulls to the left *sometimes* under *heavy* acceleration

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I almost feel stupid asking if any kind of handling issue is unusual for a buggy that has "on the fly" toe adjustment but I thought I would ask.

I've put in a 3000KV brushless motor so it's packing a fair bit more punch than Tamiya intended. It's "only" one of those finned out 390 jobs but we all know those things punch above their weight.

The issue I'm having basically is that sometimes under heavy throttle the car wants to pull to the left a little. It's not drastic and it's very easy to keep it in check with a tiny bit of corrective steering but I just wondered if it was normal?

This has been happening on smooth tarmac, it's a non issue on dirt because you're struggling for control anyway but I noticed it doing some test runs up and down the street. It doesn't happen every time and it seems to happen more depending on how violently you accelerate.

I seem to remember my Boomerang was prone to it too but I might just be misremembering.

This is a list of things I've checked:

All wheel bearings and diff output bearings (all clear)

Diffs for binding (all clear)

Dog bones for binding (all clear)

Droop (equal at each corner)

Toe-in (well it's symmetrical, that's as much as I can say.)

Any kind of assembly error causing chassis twist/tweak (all clear)

Servo (I thought it might be the cheapo towerpro clone I recently got a load of but when I replaced it with a hitec it was worse if anything because the Hitec apparently has lower resolution so I couldn't correct the veering without going the opposite direction) then I tried another servo and it was no better or worse than the first one.

The only issue I could see is one front wheel is a little warped but it's not severe at all and I've driven Tamiyas with way worse wheels and not had this issue.

The only thing I haven't done yet is glue the tyres, they are on there so tight anyway I didn't envision them slipping but I guess maybe with the brushless motor it's possible, it only takes one to slip slightly I suppose.

Anyone else have any experiences like this? Could it even be something like torque steer perhaps?

That minor issue aside, I have to say I had a real blast driving it. I know it's not the most high tech chassis in the ultimate sense but jeez, you can see why it was a big deal at the time. It might not be the last word in sophistication but it makes a Grasshopper or Hornet seem like a shopping trolley! I honestly didn't think it would be so close to my Boomerang for handling. It has flaws of course like bump steer and it nose dives so hard on breaking that the bumper scrapes the ground but even so, I could really chuck it around and it took the brushless power well, even cornering fast on-road. It understeers like crazy but that at least keeps the dreading traction rolling at bay and it's quite easy to use the throttle and full lock to make your way around corners.

I find it a really good balance between being a handful but being able to be thrown around and not flip over or spin out. It's sort of planted but lively at the same time. Good stuff! And thanks to it being a re-re, it's supple young plastic can take a bashing without bits falling off every single run like what was happening with my Boomer! It's a credit to Tamiya that it can deal with a brushless and lipo when they were decades off when this car was designed!




 



 

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9 minutes ago, nowinaminute said:

Could it even be something like torque steer perhaps

Sorry didn't read that bit before I answered ;)

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1 minute ago, KEV THE REV said:

Do you think it might be pulling under motor torque?

 

10 minutes ago, nowinaminute said:

Could it even be something like torque steer perhaps?

Yes lol! I think it's certainly a possibility. 

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Just now, KEV THE REV said:

Sorry didn't read that bit before I answered ;)

:lol:

Sorry didn't read your correction before I said that!

 

  • Haha 1

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Try applying some grease to the servo saver, I've found that sometimes they can stick and not stay central. Or try a hi torque servo saver......

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Yeah, I think you're just running into some torque-steer. That front end has so much bump-steer as it is, that if you're getting any amount of twist from the driveshaft, it's going to load up one front wheel more than the other, and pull the front end off-course.

I never was supremely happy with my Hotshot re-re, and ended up selling it. Kind of a "don't meet your heroes" situation, I think. I have an old/new mongrel Boomerang now that I like a lot more. But it sure sounds like you're getting your money's worth out of it...

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12 hours ago, markbt73 said:

Yeah, I think you're just running into some torque-steer. That front end has so much bump-steer as it is, that if you're getting any amount of twist from the driveshaft, it's going to load up one front wheel more than the other, and pull the front end off-course.

I never was supremely happy with my Hotshot re-re, and ended up selling it. Kind of a "don't meet your heroes" situation, I think. I have an old/new mongrel Boomerang now that I like a lot more. But it sure sounds like you're getting your money's worth out of it...

Early days yet but I enjoyed it's maiden drive for the most part. It's definitely not finely honed, you have to kind of wrestle it around corners because of the understeer but at least it doesn't come out of the corner on its roof lol.

I thought I had busted a gear within 10 seconds of driving it too but it was just the bumper scraping the ground where it nose dives under breaking so much :lol:

Time will tell but I'm quite enjoying it so far. It wouldn't get anywhere near a modern 4x4 buggy, even an lowly HSP or FTX but I like the way it's just about controllable at speed despite all the "quirks" 

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Have you glued the tyres on?

Sometimes once you start running decent power, one of the tyres can slip on one of the wheels, driving the car left or right.

Try swapping the wheels over (left hand to right hand side) and see if it goes the other way.

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Hi,

I'm pretty sure it's torque steer like other members already posted. Had this on other cars too, when I put in a motor with "extreme" torque. How about using a gyro in the steering servo line? Used this when I ran my Tamiya Humvee with a Novak SS BL kit.

Cheers, Martin

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On 8/8/2019 at 12:26 PM, Wooders28 said:

Have you glued the tyres on?

Sometimes once you start running decent power, one of the tyres can slip on one of the wheels, driving the car left or right.

Try swapping the wheels over (left hand to right hand side) and see if it goes the other way.

I tried swapping them around but it made no difference here.

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2 hours ago, urban warrior said:

Hi,

I'm pretty sure it's torque steer like other members already posted. Had this on other cars too, when I put in a motor with "extreme" torque. How about using a gyro in the steering servo line? Used this when I ran my Tamiya Humvee with a Novak SS BL kit.

Cheers, Martin

It definitely feels like it when I drive it.

I will definitely try my gyro in there at some point but it will have to get in line behind all the other vehicles I'm curious to try it in!

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My money would be on bump-steer.  Normally bump-steer wouldn't cause this problem under acceleration but the Hot Shot's unequal length tie rods cause different toe-in/out on either side when the front end lifts & dives.  Under acceleration it lifts.

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