RC Controls For RC Lawn mower

I know i'm not building a battlebot per say but if i can get this thing to work I will definitely make a battlebot. I figure understanding the controls RC / Rx / Tx / Speed controls are more difficult than the mechanical side of things. SO here are my questions:

I have a RC Helicopter that i destroyed so I am going to use the Transmitter from my destroyed Heli. Its a ESKY Tx (EK2-0404) 72 mHz

I want to use the Tx and buy a new Receiver / motors / battery / ESC's

I'm still in the very early stages of design but would love to get all the components together for a bench test.

I bought 2 motors with gear box (Fisher Price Powerwheels) The battery that comes with them is a 12v 9.5a battery

I've been calling around for 4 channel receivers but I keep getting different answers from different online stores. Can I use any 72 mHz receiver with my Tx?

Next issue: From my receiver i want to connect 2 electronic speed controls to power and control the motors. I need the ESC to be 12v. What i was told is if i connect more than one speed control to my receiver i will more than likely fry it since the speed control delivers power for the receiver to power up. I thought that some speed controls have a BEC connector to power the receiver and the cables that connect to the reciever are just signal cables (no Power)

I will give it a rest for now till I here back from someone.... Thanks

I'm not sure about the specifics of your radio setup, as I've only ever used Spektrum stuff, but as far as receivers / ESCs go, the only thing connecting the ESC to the receiver is a PWM cable. The PWM cable is three leads, ground, positive (+5V or so with a built-in BEC, otherwise it draws from the receiver's power) and a signal lead. You will never fry a receiver by connecting two ESCs to it, unless they run on some totally weird system that I've never heard of, and are totally incompatible.

A really great resource for all your R/C needs is Robotmarketplace (.com). Jim, the owner, is very helpful, and the people there for the most part know what they're doing. You can buy everything you need to make this project work from them.

There are plenty of people on this forum who can tell you a lot more about everything than I can, but that's my two cents.

Technically, 72mhz is for air and 75 is for ground. It will work but it will be illegal.

Many escs exist that do not have Battery Eliminator Circuts. Also you can easily disable the bec function by breaking the positive lead in the PWM cable.

I would recommend shelling out $125 for a DX5e and a BR6000. That is a great rx/tx combo. It mixes, failsafes, and is proven. Edit: Also it's legal for both air and ground incase you want to use a heli again.

Do you have any idea about what weightclass you would possibly build a battlebot in? This would affect my ESC recommendation. escs are something that last longer than robots. I have a pair of 885's that have been in 4 different bots. They are not something to skimp on.

I'm not sure what kind of lawnmower you can push effectively with those motors. A really great way to go for a rc lawnmower would be to get an electric wheelchair and either scrap it for parts or cut it down and use it as a base. Those npc style motors are bulletproof in a non combat robot and still pretty stout in combat. Those frames come with batteries, charger, motors, hubs, tires, and maybe some cheesy joystick esc. Get a sidewinder, some 883s, or maybe a big sexy old vantec and you'll be happy.


Basically, read this

http://www.riobotz.com.br/riobotz_combot_tutorial.pdf

I was told the same thing about the 72 MHz being illegal for ground RC. It’s just going to be in my yard so I hope I don't get caught.

Thanks for the advice guys, I’m new to the RC side of things. I have a AOS in Mechanical Design so building the mower chassis is fine it’s getting it to move that is the hard part. But After reading tons of websites and forums I think I have a decent idea of how it all works. Once I get this RC Mower up and running I will post some pics and then move onto a Battlebot. I wish they had a place in Mass for competitions but will more than likely have to travel to battle.

Like I said before I have a design degree not an Engineering degree so I am having a little trouble picking out the right motor incase my Fisher Price power wheels motors don’t work. Maybe one of you guys can help me along.

My mower after modifications will weight about 75 lbs. The fastest I want it to go is maybe 5-8 mph. Rear wheel Diameter is 8”. A few guys I work with have been telling me a few different ways to calculate it. I guess I need to find out what the Torque and RPMs will be for the motor but I’ve hit a wall.

I was told to use the 2lbs of torque at the ground for every pound of robot. Then once I know the Radius of the wheel I can figure out what the torque will be at the center of the wheel then that’s where I get lost. If I remove any friction blah blah blah and just take the weight times the 2lbs torque I get 140lbs * 4” = 560 in-lbs at the center of the wheel. Then I add in 2 pulleys or gears from my wheel shaft to the motor… That’s when I fall apart. Lol… Any help?

Thanks in advance…

Shawn

RemoteContact wrote:

Technically, 72mhz is for air and 75 is for ground. It will work but it will be illegal.

I don't think it's illegal, just frowned upon. the reason for it is that the aircraft guys don't want some dude with an RC car to crash their several thousand dollar balsa plane into the ground.

I agree on the Riobotz manual. It's got EVERYTHING in it that you could ever want to know.

One really cheap way to do your electronics would include some servos and the triggers from a power drill. Go to Harbor Freight, or something like it, and get 2 of the cheapest drills you can find. Take them apart. Now, you can either use the motors inside of the gearboxes, which are probably more powerful than the one's you've got, or use the Fisher-Price ones you already have. Whichever you chose, wire the motor up so that when you pull the trigger, the motor runs. the way that you control your motors is with some servos. Set up the servos so that when you activate them, they push on the triggers. if you do that, you can also use the batteries that they came with, and the chargers too.

It might be more time-consuming than buying some ESC's and some batteries, but it sure is a lot cheaper! 40 bucks in drills, 40 bucks in servos. that's not even enough to buy 1 of the Victor ESC's mentioned above.

Just a thought..

And as far as Battlebots in MA goes... NERC has an sort-of annual competition in Winchendon. It's gone by several names, and they seem to have skipped a 2007 competition and a 2009, but there was one in July 2008.

The NERC site seems to be down (North East Robotics Club, Inc - http://www.robotconflict.com/ or http://www.nerc.us/) so I don't know what the status of future competitions is... The economic downturn has certainly thinned out the number of competitions out there, but with the return of televised battlebots this december, things should perk up again.

What weight class are you considering? Battlebots (the official competition) only has a 220 lb class for "professional" builders, but there are competitions out there for many different classes (150g, 1 lb, 3 lb, 12 lb, 15 lb, 30 lb, 60 lb, 120 lb, 220 lb...). There used to be super-heavyweight competitions for 340 lb bots, but these proved much too expensive to maintain in a not-so-booming economy. Who knows? maybe we'll see a glorious return of robot combat...

-Dan