0RBlT Posted March 2, 2014 Posted March 2, 2014 You did a great job, and now you have reached a very close result to reality. Thank you for sharing your ideas with us, so that we can learn from chemuto you. Most of all I liked the idea of how you could implement to achieve Custer, it is very realistic and believable! You added , аnd with its help you there was a place for the suspension, it is a very compact. Quote
Hrafn Posted March 3, 2014 Author Posted March 3, 2014 You did a great job, and now you have reached a very close result to reality. Thank you for sharing your ideas with us, so that we can learn from chemuto you. Most of all I liked the idea of how you could implement to achieve Custer, it is very realistic and believable! You added , аnd with its help you there was a place for the suspension, it is a very compact. Thank you! I'm glad to hear it's useful. I think I'm going to abandon the rack and pinion, and instead do the steering with a bell crank system. It's not true to how the real vehicle works, but it does seem more robust for this application. Now the trick is going to be making everything very robust and rigid so the wheels don't wobble. Quote
Hrafn Posted March 3, 2014 Author Posted March 3, 2014 Most real rc cars use bell cranks :) I was surprised to discover that after I improvised a crank-based steering method on my own and then googled to see if any real cars used anything like it. It's good to know it's not a crazy approach to take! Quote
MrNumbskull13 Posted March 3, 2014 Posted March 3, 2014 My rc truggy has 3 bell cranks in the steering system and my buggy uses 2. it works very well if there is no slack in the system Quote
Hrafn Posted March 3, 2014 Author Posted March 3, 2014 My rc truggy has 3 bell cranks in the steering system and my buggy uses 2. it works very well if there is no slack in the system Do you have any photos of your setup in either vehicle? I was looking at a single crank system (well, two parallel ones connected as a four-bar linkage) but haven't yet figured out how I want to connect them to a steering motor. Quote
MrNumbskull13 Posted March 3, 2014 Posted March 3, 2014 (edited) Here are some (terrible) photos I took in my iPod. There would b another crank on the one in the photo that would be connected to the servo but this is just a chassis for now... Position 1 http://m.flickr.com/#/photos/92293857@N05/12912680634/ Position 2 http://m.flickr.com/#/photos/92293857@N05/12912260315/ Edited March 3, 2014 by MrNumbskull13 Quote
Hrafn Posted March 3, 2014 Author Posted March 3, 2014 Here are some (terrible) photos I took in my iPod. There would b another crank on the one in the photo that would be connected to the servo but this is just a chassis for now... Position 1 http://m.flickr.com/...05/12912680634/ Position 2 http://m.flickr.com/...05/12912260315/ Thanks! I'm having a little trouble making out what's going on in those photos. I also misunderstood you - I thought they were Lego vehicles. The concepts behind bellcrank steering I think I get pretty well; implementing them in Technic in a way that's rigid and robust is what's tricky for me. Quote
MrNumbskull13 Posted March 3, 2014 Posted March 3, 2014 With lego you shouldn't need all the ball joints, just lift arms. But I think you will need ball joints where the rack connects to the hub Quote
Hrafn Posted March 6, 2014 Author Posted March 6, 2014 (edited) OK, I have made some good progress. Steering is currently done with a combination crank and rack-and-pinion setup which is sort of hard to explain; I will eventually post photos but there's so much stuff crammed into the front axle assembly that it's hard to see what's going on. Meanwhile the front and rear suspension modules are now very robust, and (with a dummy chassis) I've got a turning circle of about 4 feet (~120 cm). I'd like it to be tighter, and could probably squeeze a few more degrees of steering lock out of the current design, but right now the effort required to do that redesign doesn't seem worthwhile. 4 feet is still reasonable for a model of this size, I think, though in this scale the turning circle should be more like 100 cm. For comparison the wheelbase is 30 studs (24 cm) and the width including wheels is 21 studs. For steering, I'm probably going to use a geared-down PF-M motor, possibly with return to center. The train remote just introduces too much lag when using the servo. My initial plan was to use 2 buggy motors for propulsion, with an AA battery box for power. It sounds like the current limiting circuits on the battery box and the receivers will be an issue in getting as much power as I'd like, though. I'd rather not modify the battery box, but the RC control unit is so large it would really impact the design of the vehicle if I used it. 4 L motors (with no gearing) or 2 XL (geared up) are also options, but it looks like getting enough current to them could still be an issue. Edited March 6, 2014 by Hrafn Quote
MrNumbskull13 Posted March 6, 2014 Posted March 6, 2014 (edited) Modifying an AA battery box is actually really easy! I thing the problem is getting current from the receivers. If you use a v2 receiver you should be fine. Edited March 6, 2014 by MrNumbskull13 Quote
Hrafn Posted March 9, 2014 Author Posted March 9, 2014 Modifying an AA battery box is actually really easy! I thing the problem is getting current from the receivers. If you use a v2 receiver you should be fine. Thanks! I'll definitely have to use an AA battery box, as the rechargeable one gets overwhelmed after a while. I don't know if the car will demand enough current for me to need to modify the AA box. Right now, the test chassis performs amazingly well (and drives incredibly fast) with either the rechargeable or (unmodified) AA box, but I expect to add another 400-500g of weight before I'm done. Quote
MrNumbskull13 Posted March 9, 2014 Posted March 9, 2014 Sounds great! Your front suspension is great, what kind of suspension have you built on the rear? Quote
Hrafn Posted March 9, 2014 Author Posted March 9, 2014 Sounds great! Your front suspension is great, what kind of suspension have you built on the rear? Thanks! The rear suspension is a variant of Thirdwigg's floating differential double-wishbone setup for narrow vehicles, widened to 21 studs and using to hold the differential. Thirdwigg's original design was good but not quite up to handling the power of 2 RC motors; the L-liftarms slid on the 5L axle and the 20t gear started skipping. Like the front suspension, it's a short / long arm suspension, but with less travel and a stiffer spring configuration. I'm hoping that I can keep the current performance when I add weight. Right now the turning circle is 105cm, which is good for 1:10 scale. Moreover, right now I can do really tight handbrake turns (by using engine braking)! Front steering is with a servo, driven by a bang-bang remote, which gives fast steering and a maximum steering lock of more than 45 degrees. Quote
MrNumbskull13 Posted March 9, 2014 Posted March 9, 2014 Wow this is a really cool project. I can't wait to see a video. ;) I need to get the snowmobile for the new suspension parts before I can start my project, for now I'm just experimenting & planning... Hopefully your performance shouldn't decrease too much, I think the steering radius won't change but you might notice a difference in speed... Quote
Hrafn Posted March 10, 2014 Author Posted March 10, 2014 Wow this is a really cool project. I can't wait to see a video. ;) I need to get the snowmobile for the new suspension parts before I can start my project, for now I'm just experimenting & planning... Hopefully your performance shouldn't decrease too much, I think the steering radius won't change but you might notice a difference in speed... Thanks! I definitely want to do a video, but it'll be a while since there's a lot to get done - fully integrate the motors and battery, finish building the chassis so it's strong enough to endure crashes, do the bodywork, and figure out how to do decent videos. Right now I can just about squeeze in the motors and battery with some effort, but that leaves no room for any gearbox. Initially I wasn't planning on a gearbox, but I might want at least a manual 2-speed one since the high speed is so fast and hard to control. The chassis also needs to be very robust to withstand the inevitable crashes - my test chassis splintered every time I hit a wall, and the lack of a bumper meant that glancing blows to the tires tended to tear the tires off or detach the steering links. I'm concerned that in order for the bodywork to hold together in crashes, I'll have to make the model pretty heavy. I got the snowmobile parts straight from Lego, since the set isn't available in the US yet, and they're really nice to have. With some modifications, though, I could probably have done this model with just the old 6L ones. I got some 5L axles with stop in the same order, and those have also come in really handy. Quote
MrNumbskull13 Posted March 10, 2014 Posted March 10, 2014 If you build stong enough bumpers you might not need to make the chassis as strong? Also have you seen sariel's 2 speed gear box for RC motors? The one that switches between the fast and slower output? Thanks for the info about lego.com too! Quote
Marcel1980 Posted March 10, 2014 Posted March 10, 2014 Sariel buggy motors high/low gear is pretty good. I used it too in a model. Easy to fit in too. Quote
Hrafn Posted March 10, 2014 Author Posted March 10, 2014 Thanks guys! Sariel's gearbox is definitely one I'm going to test out. I may put a spring-loaded bumper on the front to help with crashes, but the chassis still needs reinforcement. Right now it's a basic double-rail system with some 5x11 plates between the rails; I'll need another set of longitudinal beams higher up and some sideways and torsional stiffing. It's definitely doable. After the amount of effort that went into the endless redesigns of the front suspension, everything else seems relatively easy! Quote
Thirdwigg Posted March 10, 2014 Posted March 10, 2014 I would like to see the progress you have made. Some pictures? Quote
Hrafn Posted March 10, 2014 Author Posted March 10, 2014 (edited) I would like to see the progress you have made. Some pictures? Ask and ye shall receive! Here's a top view with the wheels at maximum steering lock: The front axle structure is totally different than before in order to make it really robust, but the basic geometry is the same. The shock tower tops are not properly connected yet because I plan to integrate them into more reinforcements for the area in front of the front axle. I'd like to have a fake steering wheel connected to the servo and geared up, but I'm having trouble finding a way to route the connection without having the front axle assembly get too tall. The hood will be no more than a stud or so above the current axle assembly, so I don't know if there will end up being enough room for the steering wheel to be connected properly. EDIT: Or I could do the simple thing by moving the servo back 2 studs and gearing the steering wheel from there. EDIT 2: I just moved the servo forward of the front axle, which freed up a lot of space in the middle of the car for a transmission. Two cranks form the long sides in a parallelogram four bar linkage; one of the short sides is driven by a rack. The steering tie rods attach to ball joints on the long sides of the parallelogram. The Ackerman effect is actually exaggerated in this vehicle - when turning, the lines of the front axles intersect well in front of the car's rear axle. This was driven by a number of considerations when constructing the front axle (overall size, avoiding wobble in the tie rods, etc.) but ends up having a beneficial side effect: at high speeds, if the rear wheels are suddenly stopped, the car loses rear traction and goes into a sort of handbrake turn. Well, it did with a lighter-weight dummy chassis; hopefully that will still happen when the car is complete. The same area, from below: The rear axle, again, is your design with only small changes: The motor locations are tentative at this point. On the plus side, having them here opens up a space for a gearbox (if an odd-shaped space) and uses the rigidity of the motors to strengthen the chassis. On the negative side, I'll have to do a 90 degree connection with gears or knob wheels to get drive to the rear wheels. My hope is to have a low-profile gearbox in the space between the motors, and then put the battery box on top of the gearbox towards the rear axle, to keep the center of gravity low. EDIT: after moving the servo I will probably reconfigure the motor setup, turning them 90 degrees, putting them near the rear axle, and hard-coupling them. The driveshaft could then go forward to a transmission, then up and over the motors to the rear axle. Hopefully that will work. The car itself will end up very low-slung so I'm trying to keep everything as low as possible. Right now the front of the car is up too high, but with the added weight of the bodywork etc. it should drop down so that it's even with the rear, with 2-3 studs' ground clearance. Edited March 10, 2014 by Hrafn Quote
flyboy01 Posted January 5, 2016 Posted January 5, 2016 sooooooooo.... did you give up? or.... just forgot? or what happened? Quote
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