biggamehunter 127 Posted June 25, 2013 harder than a stone ehh ? trying to make a bullhead go straight !!!!!! , without having the tx trimmer move of centre line , OMG i just had about 3 hours of hairpulling trying this incredible feat ,i have terrible ocd with tx trimmer settings , they with out a doubt have to be set on zero or no more than 2 clicks either side of zero (tamiya ocd) but honestly the 4 wheel steer on the bullhead is a nightmare , it all started as i changed the steering rods to heavy duty lovely alloy ones , i set the new lengths exactly the same as the old rods , but i never run the truck before changing the rods , so whoever set it up originally had done a great job of getting the steering rods totaly wrong , i mean it was almost slew ! like an old mini with the subframe gone , pretty sorted now but any tips or tricks for doing this job guys , ............. it was like painting the firth of fourh bridge cheers shaun Share this post Link to post Share on other sites
TA-Mark 195 Posted June 25, 2013 Transmitter sub-trims are designed with the Tamiya OCD in mind. You get a perfect zero on the main trim everytime. 1 Share this post Link to post Share on other sites
MadInventor 3884 Posted June 26, 2013 I always start with getting the servo horn upright, regardless of the trim setting on the transmitter.If hornisn't upright, you won't equal throws in both directions, so although it might go straight, it won't turn equally left and right. I also set the toe in on the axles without the wheels fitted, as it's tricky judging this with the wheels on. I would also use a vernier to set both front and rear main axle track rods exactly the same. Then set the cantilevers on the gearboxes so they are perpendicular to the alignment of the gearbox. It's just then a matter of setting the servo to gearbox track rods so that everything is sensible. Failing that, bin the single servo option and fit a servo behind the axle guards front and rear. 1 Share this post Link to post Share on other sites
mongoose1983 3335 Posted June 26, 2013 I know I wouldn't go for mods on that exceptional 4x4x4 vehicle. Both poster above are correct. You have to disconnect the servo horn and place it correctly in the middle. Then you'll have all of the possibilities available with the trim controls. 1 Share this post Link to post Share on other sites
94eg! 834 Posted June 26, 2013 I always start with getting the servo horn upright, regardless of the trim setting on the transmitter.If hornisn't upright, you won't equal throws in both directions, so although it might go straight, it won't turn equally left and right.. This is close, but there is more to it than that. It's not so important that the servo horn is perfectly upright (perpendicular to the servo itself), but rather that the horn is perfectly perpendicular to the angle of the rod being connected to it. By having the horn perpendicular to the connected rod, you are making the initial steering rate as equal as possible in both directions. 1 Share this post Link to post Share on other sites
94eg! 834 Posted June 26, 2013 BTW: The only way to have truly equal steering left to right is if your servo bell cranks are all perfectly parallel (between connecting rods), exact same length, rotate in the same direction, and lie along the same plane (or parallel planes between different rods). Otherwise you will always have some variance or rate. And since most RC's have the servo laying on it's side, you will NEVER have perfectly equal steering. This is part of the reason expensive radios have so many adjustments like EPA and Expo. These can help to compensate for inherent differences built into the model geometry. Even the TRF417 isn't perfect. I know cause I modeled the steering system in the later 415 in Autocad. With a lay-down servo, there is no way to eliminate the inherent steering rate differences. You can only minimize them with drag-link setup and radio settings. 1 Share this post Link to post Share on other sites
berman 5315 Posted June 26, 2013 All the posts above me all make valid points in regards to steering and servo positioning with rc cars in general. The biggest problem is that it is 4x4x4, and basically you are fighting yourself doing this. The rear trailing wheels depending on whether you are going forward or backward ( 90% of the time forward) will drag and any play in the linkages servos or servo savers will amplify this. This is a common trait in all vehicles that steer from a rear axle, but more so on front and rear. Even the TXT-1 with a rear servo is hard to keep in a straight line, I actually think it is worse for this. Even if you managed to get every linkage, servo, servo saver, trim etc perfectly in line, once you start driving it (flat or uneven ground) will start wandering and you will be correcting it with steering input or trims. 2 Share this post Link to post Share on other sites
wolfdogstinkus 1893 Posted June 27, 2013 You guys drive in a straight line?, with Tamiya's? 1 Share this post Link to post Share on other sites
TA-Mark 195 Posted June 27, 2013 When your Grasshopper and Lunchbox does 35mph+ (60km/h) it needs to be able to go in a straight line 3 Share this post Link to post Share on other sites
MadInventor 3884 Posted June 27, 2013 All the posts above me all make valid points in regards to steering and servo positioning with rc cars in general. The biggest problem is that it is 4x4x4, and basically you are fighting yourself doing this. The rear trailing wheels depending on whether you are going forward or backward ( 90% of the time forward) will drag and any play in the linkages servos or servo savers will amplify this. This is a common trait in all vehicles that steer from a rear axle, but more so on front and rear. Even the TXT-1 with a rear servo is hard to keep in a straight line, I actually think it is worse for this. Even if you managed to get every linkage, servo, servo saver, trim etc perfectly in line, once you start driving it (flat or uneven ground) will start wandering and you will be correcting it with steering input or trims. And you have to take into account torque steering effects on the TXT-1 When your Grasshopper and Lunchbox does 35mph+ (60km/h) it needs to be able to go in a straight line If your grasshopper does 35mph+, it only goes in a straight line. Steering circle on my DF-02 at 50mph with the front diff locked (to get it to get power down off the line) is about 150metres. 1 Share this post Link to post Share on other sites
berman 5315 Posted June 27, 2013 When your Grasshopper and Lunchbox does 35mph+ (60km/h) it needs to be able to go in a straight line Mark, I dont think you have much option of anything else at 60kph in a lunchbox :lol: And you have to take into account torque steering effects on the TXT-1 Absolutely I forgot about that. And I also forgot about gearbox roll on a clod too. Because the servo is rigid mounted to chassis and the gearboxes pivot with the arms, this also moves the steering linkages when loading and unloading the motors, even with the anti rotational brackets. 1 Share this post Link to post Share on other sites
TA-Mark 195 Posted June 27, 2013 Mark, I dont think you have much option of anything else at 60kph in a lunchbox :lol: If it doesn't steer straight, you don't get to that 60km/h. Instead you get 'bounce once, bounce twice and then cartwheels'. :lol: 1 Share this post Link to post Share on other sites
biggamehunter 127 Posted June 27, 2013 All the posts above me all make valid points in regards to steering and servo positioning with rc cars in general. The biggest problem is that it is 4x4x4, and basically you are fighting yourself doing this. The rear trailing wheels depending on whether you are going forward or backward ( 90% of the time forward) will drag and any play in the linkages servos or servo savers will amplify this. This is a common trait in all vehicles that steer from a rear axle, but more so on front and rear. Even the TXT-1 with a rear servo is hard to keep in a straight line, I actually think it is worse for this. Even if you managed to get every linkage, servo, servo saver, trim etc perfectly in line, once you start driving it (flat or uneven ground) will start wandering and you will be correcting it with steering input or trims. perfect !!!!!!!!! Share this post Link to post Share on other sites
biggamehunter 127 Posted June 27, 2013 Steering circle on my DF-02 at 50mph with the front diff locked (to get it to get power down off the line) is about 150metres. Share this post Link to post Share on other sites
berman 5315 Posted June 28, 2013 If it doesn't steer straight, you don't get to that 60km/h. Instead you get 'bounce once, bounce twice and then cartwheels'. :lol: So true! Plus the fact the front wheels seem to be ineffective while in the air from 0-60 kph, ...might aswell put rudders on them hahaha 4 Share this post Link to post Share on other sites