Puggie Posted December 15, 2015 Share Posted December 15, 2015 Noob here looking for some advice on scratch building essentially a drag car. This is part of a uni project so I have some distinct criteria to work with and some rules and regs which must be obeyed. The plan is with a £100 budget, to build a RC car to drag race a 120m long 2m wide asphalt track (may be uneven and contain bumps and cracks). The vehicle can be any configuration, no more than 10kg, minimum turning radius of 2m, minimum ground clearance of 25mm. Controlled remote shutdown system than kills power and operates a mechanical brake quickly slowing the vehicle to a halt, this must also operate when communication is lost. All propulsive and steering forces must be through the road (no rockets). The braking system must manually lock the drive. So my current thoughts are basically it is a budget RC tarmac car, so I'm immediately thinking Mardave V12 (partly as I have one here), but a bit bigger. To get my 25mm ground clearance I'm thinking 1/8th foam tyres they should be about 105mm tall so relatively easily getting me my ground clearance. Chassis will probably be a 3mm alu plate, looking at about 400mm long and say 250mm wide. The rear end I'm tempted to try and make a motor-solid axle pod, similar to the V12 and attach it to the chassis by a 4 bar linkage for suspension and watts linkage for lateral stability (basically as that is close to what a grown up drag car would run at the back and should give me some adjust-ability in the suspension for launching). Front end I'm tempted to copy the mardave as its very simple but it may make more sense to cut a double wishbone setup from delrin (I have a 100w CO2 laser cutter in my build arsenal). Power I'm thinking a aero outrunner, they seem cheaper watts per pound and gearing I can sort in the build, I'm also considering mechanically braking the motor can as part of my braking system (making a foam/rubber brake shoe to push against the outer can to brake the whole rear end). The rear will be a solid 1 piece axle and gears will be budget steel stuff probably from HPC. Motor I'm thinking Turnigy L5055b-600, NTM 50-60 380kv 2665W or similar, ESC will be a car unit probably for the electronic braking. Batteries will be as much lipo as I have budget for. I also need a cheapie radio set in budget too. So thoughts and crit' on my ideas please people? Quote Link to comment Share on other sites More sharing options...
Carpmart Posted December 15, 2015 Share Posted December 15, 2015 Cool project, far more interesting stuff than I ever studied! Few Q's How many cells can you run under the rules? any restriction on physical dimensions other than fitting the track? why a live axle approach? IRS will give you more scope to adjust the car by balancing each side? can you run 4wd? Big power motors, probably an in runner is the best approach? 380kv is very low for a speed project even with mahoosive gearing, why so low. Success is probably tied to the number of cells you can get and the biggest motor you can find? Youve stipulated £100, is that your own restriction or other project governance? Do you need to demonstrate fair market value on any bits you purchase? Lots of other questions but I shall leave it there for now! Quote Link to comment Share on other sites More sharing options...
Puggie Posted December 15, 2015 Author Share Posted December 15, 2015 20 minutes ago, Carpmart said: Cool project, far more interesting stuff than I ever studied! few Q's How many cells can you run under the rules? any restriction on physical dimensions other than fitting the track? why a live axle approach? IRS will give you more scope to adjust the car by balancing each side? can you run 4wd? Big power motors, probably an in runner is the best approach? 380kv is very low for a speed project even with mahoosive gearing, why so low. Success is probably tied to the number of cells you can get and the biggest motor you can find? Youve stipulated £100, is that your own restriction or other project governance? Do you need to demonstrate fair market value on any bits you purchase? Lots of other questions but I shall leave it there for now! How many cells can you run under the rules? No restriction, not even limited to electric power, but I figured it would be best for the purpose of simple acceleration in a limited size track. any restriction on physical dimensions other than fitting the track? nope, just the 10kg weight limit and 2m turning radius and that could possibly be achieved using power oversteer. why a live axle approach? IRS will give you more scope to adjust the car by balancing each side? Simplicity, a 4 bar would allow me to mount a 'dive pod' and maintain simple tyres parallel to the road. Something like this link http://i1177.photobucket.com/albums/x355/mikepage1942/Suspension/4barparallel.jpg can you run 4wd? Yes, I was assuming I could get enough power to the back to make front wheel traction of little relevance, and driven steering wheels is significantly more complex to realise on my budget Big power motors, probably an in runner is the best approach? 380kv is very low for a speed project even with mahoosive gearing, why so low. I'm looking purely at watts per pound and that is what I found, I'm here asking because I don't know if there is a better solution. I also thought of braking on the motor can which could be done on an outrunner. I'm budget limited as said below, the NTM is a lot of power for £30odd I though may do better buying the most power available and gearing to suit. Youve stipulated £100, is that your own restriction or other project governance? Do you need to demonstrate fair market value on any bits you purchase? £100 is the stipulated budget, this is new product market value, I have to provide receipts for all items and materials used, if second hand parts are used I still have to provide budget for new equivalents. for instance I have some 4 cell 2200mAh Turnigy nano Lipo Packs sat here, I may use them, but I still have to budget for the cost of new equivalent packs. Likewise I can buy suspension arms or a sheet of delrin and cut my own with the laser, this may mean I prefer building simple engineering designs to buying more complex solutions, I reckon a 250x400mm sheet of 3mm thick aluminium and 5-6mm thick delrin would go a long way to my chassis and suspension construction. Quote Link to comment Share on other sites More sharing options...
ajlovering Posted December 16, 2015 Share Posted December 16, 2015 Hi. I am interested in how the project came about. Can you answer a few questions? What university are you attending? Was the project also given to others so you will be racing against each other? Or was the project conceived by yourself? if so who would you be racing against? I am interested as I have proposed that ROSSA come up with a special class for schools and universities for a speed car where each group builds a car to the special rules and competes against each other at a ROSSA event. If you are able could you suggest possibly entering your car in the ROSSA UK RC Speed Championships? Cheers Quote Link to comment Share on other sites More sharing options...
Puggie Posted December 16, 2015 Author Share Posted December 16, 2015 1 hour ago, ajlovering said: Hi. I am interested in how the project came about. Can you answer a few questions? What university are you attending? Was the project also given to others so you will be racing against each other? Or was the project conceived by yourself? if so who would you be racing against? I am interested as I have proposed that ROSSA come up with a special class for schools and universities for a speed car where each group builds a car to the special rules and competes against each other at a ROSSA event. If you are able could you suggest possibly entering your car in the ROSSA UK RC Speed Championships? Cheers 1) University of Surrey 2) Yes a number of groups will be completing the project 3) Conceived by one of our Academics, its just a internal university competition. I've PM'd you a bit more info, off to look at these UK RC Speed Chamionships now! Our rules and regs are pretty open so not sure how we would qualify to enter, unless there is an anything goes for £100 propelled by wheels category. Quote Link to comment Share on other sites More sharing options...
ajlovering Posted December 16, 2015 Share Posted December 16, 2015 We had a £100 challenge last year but limited entry. Quote Link to comment Share on other sites More sharing options...
-BEZ- Posted December 31, 2015 Share Posted December 31, 2015 As Tony says we had a £100 build challenge in 2014 which was good fun but its very difficult to buy a donor car and electrics for that budget. I used Mardave donor bought off ebay and cheap Hobby king electronics (minus radio gear) It managed 85ish MPH (before going off track and hitting an immoveable object buried in the grass destroying the little car). It ran on 2s and weighed about 1.2kg give or take. The fail safe on the ESC was strong enough to lock the wheels pulling the foam off the rims so a mechanical break wasn't something I needed to worry about. Personally I think the best approach is if you are limited by budget is keep it simple and keep it light. Quote Link to comment Share on other sites More sharing options...
Puggie Posted January 12, 2016 Author Share Posted January 12, 2016 Thanks for all the info so far guys. I'm just starting roughing something out for this. I think I'm building something between a 1/8th Pan car and Mardaves big ugly brother of a banger. I have a 125 x 350mm 3mm alu plate for a chassis. I'm aiming for about 225-240mm track and 250-300mm wheelbase (subject to exact positioning of arms and rear pod). I'm cutting front arms from 6mm Delrin. Front suspension will be a mardave-esque springs over kingpin setup Wheels will be 1/8th foams to give me the 25mm ground clearance I need. Any suggestions for the rear end setup, I'd like a solid axle I think for simplicity? I could do something similar to the mardave or try and build a 4 link rear end off a motor and rear axle pod. Quote Link to comment Share on other sites More sharing options...
Puggie Posted January 23, 2016 Author Share Posted January 23, 2016 (edited) Right! I have built up a Mardave v12 from bits I had and added the following: Turnigy 6Ah 1s2p LiPo Trackstar 1cell 120a esc 'orion' 2.5t motor of stupidity! 18:48 gearing Trackstar TS4G radio Its impossible to keep straight and stupid fast, if I find a 600' long billiard table it may be successful. So I need some more suspension travel... I have got some 1/8th foam boots, I need some good value 1/8th uprights, hubs, axles and diff. Any suggestions? I will make arms from 6mm delrin to suit. Edited January 26, 2016 by Puggie added pic Quote Link to comment Share on other sites More sharing options...
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