luke1983 Posted February 22, 2022 Share Posted February 22, 2022 Hi folks, I'm trying to get a 6x6 I've built running well but have come up against an odd problem. It steers very well in reverse but when driving forward seems to not have the power to turn? I'm perplexed by this. The model is quite heavy, about 18lbs/7.5 kg but well within the servo's torque settings. I've done a good bit of searching but can't find anything to suggest what the problem is so though I'd ask on here. Quote Link to comment Share on other sites More sharing options...
Kpowell911 Posted February 22, 2022 Share Posted February 22, 2022 What voltage are you giving the servo? Do you have an external BEC? Quote Link to comment Share on other sites More sharing options...
luke1983 Posted February 22, 2022 Author Share Posted February 22, 2022 (edited) I've got it running on a 2s, so 7.4v, LiPo, with Quicrun Fusion FOC. Just had a play and it has a built in BEC which I've set to 7.4, no change. I think I need a more powerful servo.. Edited February 22, 2022 by luke1983 Incorrect information supplied Quote Link to comment Share on other sites More sharing options...
JonnyUK Posted February 22, 2022 Share Posted February 22, 2022 If you fit the BEC mod you should see a big improvement, plus its safer for the stock electrics. Is it a TRX6? The Traxxas kit is quite simple to fit, I fit them to both of our TRX4's. Quote Link to comment Share on other sites More sharing options...
luke1983 Posted February 22, 2022 Author Share Posted February 22, 2022 Hi It's not a TRX6, it's an original Blackwell Beast with a fair few mods. I've been recommended to get a 5th scale servo on another forum but will look into fitting a BEC too. The original set up had one but that broke several years ago and I've replaced it with a Quicrun fusion which seems great so far. Quote Link to comment Share on other sites More sharing options...
Kpowell911 Posted February 22, 2022 Share Posted February 22, 2022 (edited) Im pretty sure the 1256 can only handle 6.0v? Edited February 22, 2022 by Kpowell911 Quote Link to comment Share on other sites More sharing options...
luke1983 Posted February 22, 2022 Author Share Posted February 22, 2022 OK, it was on 6 and didn't move them so I tried 7.4. I'll switch it back but basically I think the servo is underpowered. I've bought a Power HD 70kg servo, that ought to do it! Quote Link to comment Share on other sites More sharing options...
luke1983 Posted March 3, 2022 Author Share Posted March 3, 2022 I bought this in the end, at 7.4v it's 55 kg per cm, which has improved the steering but nowhere near as much as I would have liked. I think the full scale truck would have a smaller turning circle!As a result this evening I shortened the steering link, then the drag link to create some toe in hoping this would help. Again, there was improvement, but not enough going forward, again its good in reverse. Also, despite the high torque, the BEC being set to 7.4v, the servo doesn't seem to have the power to turn the wheels when stationary to full throw, it's not far off, but if I lift it they carry on to full throw, and occasionally it doesn't settle in the middle very well either. I don't think there are many servos out there for reasonable money that have much more power than this one though!I think it has to do with the geometry of the servo horn. The servo horn points to the rear of the model so in reverse the force from the direction of travel is helping the servo to push the front wheels round to full throw, obviously when moving forwards the force is fighting against the servo.I have room to move the servo mount and from studying pictures of the Cross RC 6x6s and 8x8s, I think mounting the servo on its side so that the movement of the servo horn is parallel with the drag link will help to overcome this problem. Quote Link to comment Share on other sites More sharing options...
Kpowell911 Posted March 4, 2022 Share Posted March 4, 2022 (edited) Are your end points set to 100%? With the servo Unattached can you manually turn the wheels to achieve full lock? Ive ran that new servo in an Xmaxx with 8" wheels. It turned them on Carpet stationary, so I think its a vehicle issue maybe? Edited March 4, 2022 by Kpowell911 Quote Link to comment Share on other sites More sharing options...
luke1983 Posted March 7, 2022 Author Share Posted March 7, 2022 On 04/03/2022 at 18:15, Kpowell911 said: Are your end points set to 100%? With the servo Unattached can you manually turn the wheels to achieve full lock? Ive ran that new servo in an Xmaxx with 8" wheels. It turned them on Carpet stationary, so I think its a vehicle issue maybe? I've played with the end points, even putting them up to 150%, no difference. Manually it moves no problem either. I have only tested on carpet which I presume will be very grippy, especially with sticky crawler tyres, and may effecting the throw, it is a heavy rig. I'm going to move the servo this week and see what that does for it, will report back here, hopefully as a success! Here it is showing off its flex... 1 Quote Link to comment Share on other sites More sharing options...
luke1983 Posted March 7, 2022 Author Share Posted March 7, 2022 I've tilted the steering servo by 90° which has gained me more throw going forwards. I also spent a while experimenting with different steering rod lengths and the steering settings on the Tx. I think I've got it as good as I'm going to get it now however it still steers more in reverse?? I'm wondering if it is something to do with it being 6wd? Maybe needs some OD at the front axle to help them pull, rather than being pushed by the rear axles? Quote Link to comment Share on other sites More sharing options...
luke1983 Posted March 9, 2022 Author Share Posted March 9, 2022 I'm looking into buying a Castle 15A BEC so I can boost the voltage to 8.4, which buys another 15kg per cm, bringing it to 70kg , which has got to be enough! Might couple it with a 3s battery too. Quote Link to comment Share on other sites More sharing options...
JonnyUK Posted March 22, 2022 Share Posted March 22, 2022 On 09/03/2022 at 22:16, luke1983 said: I'm looking into buying a Castle 15A BEC so I can boost the voltage to 8.4, which buys another 15kg per cm, bringing it to 70kg , which has got to be enough! Might couple it with a 3s battery too. If it going to take 70kg of servo effort to move that steering, surely that points to an issue somewhere?? 70kg is a huge amount!...or am I missing something 🤔 I'd be waiting for something to snap. Quote Link to comment Share on other sites More sharing options...
JonnyUK Posted March 22, 2022 Share Posted March 22, 2022 On 22/02/2022 at 20:41, luke1983 said: Hi folks, I'm trying to get a 6x6 I've built running well but have come up against an odd problem. It steers very well in reverse but when driving forward seems to not have the power to turn? I'm perplexed by this. The model is quite heavy, about 18lbs/7.5 kg but well within the servo's torque settings. I've done a good bit of searching but can't find anything to suggest what the problem is so though I'd ask on here. Have you had a voltmeter on the wires going to the servo to confirm its actually getting the voltage feed it should be? Quote Link to comment Share on other sites More sharing options...
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