Help on electric skateboard

[julia1]

Hi.
I want to build an electric skateboard (like those you see on the market) out of a regular skateboard.
The chassis would be basically the skateboard itself, I suppose I can leave the two front wheels and their axis, right? So I`d just have to take off the back axis because that`s where the motor should be.
I have almost no experience on RC, I`ve only built that $50 dollar bot until the part where he tests it with a remote control (so I`ve build a simple RC vehicle, not an actual bot).
I only want the electric skateboard to move forward, no differential drive or anything like that.
Can I by any chance do that without a microcontroller? I though perhaps I could do that with high torque servos such as the
 "Hitec Ultra Torque, Titanium Gear Digital Robot Servo"
Specs->Voltage: 6.0 - 7.4V
Torque: 333 oz/in @ 6.0V, (417 oz/in @ 7.4V)
Operating speed: .17 sec/60° @ 6.0V
The skateboard doesn`t have to be very fast but I want it to work for a teenager/young adult. I also want it to be as simple as possible.
If I can`t use servos, and if I must use DC Motors, is there a simple way to do this (something plug and play like it happens with servos)?
I`d rather have a button on the skateboard that you step on than a wireless remote control.
Also, how do I attach the servos / motors to the back wheels (regular skateboard wheels)? I suppose I need a specific hardware to do this, and I can`t use the regular back axis on the skateboard. Where can I find that hardware? I`d also like to know about the batteries and about the motor control (button or wireless remote control).

Here are some pictures to show what I want to do-->
http://i13.ebayimg.com/01/i/07/cd/6e/34_1.JPG (this shows that the front axis is regular, the batteries are in the middle and the back axis has a build in motor. this specific skateboard works with a wireless remote control, but I`d rather use a button.)
http://i1.ebayimg.com/03/i/000/c6/39/e195_1.JPG (here you can see on a different skate pretty much the same as in the first skate. the hardware is a bit different.)
http://www.dotme.ws/ebay/ebaypics/liquidation/skateBRD/skbrd7.jpg (here you can see the button I`m talking about to control the motor. You step on it, the skate moves forward, you let go, the skate stops. but this is a three-wheeled skate, and that`s not what I want, I just wanted to show the button).

Just so you know, I`m from Brazil so any store suggestions such as Wal Mart doesn`t really work for me because they don`t ship to my country. I buy from stores like Tower Hobbies, RobotMarketPlace, etc. But if you just say a product`s name I can probably find a store that will sell it to my country.

Well, so I have a basic idea of what I want to do but don`t know really where to start.
Any help will be very much appreciated.  Thanks in advance, Julia.

[Admin]

Its really simple actually.

You need four things:
DC motor
battery
on/off switch
method to connect the DC motor to your wheels/board (the hardest part)

(no microcontrollers or motor drivers or anything else needed)

Connect the on/off switch to your battery and your motor, and your electronics are done.

more reading to help you out:

To understand batteries
http://www.societyofrobots.com/batteries.shtml

Use this calculator to select a motor that is strong/fast enough:
http://www.societyofrobots.com/RMF_calculator.shtml

To understand gears and belts:
http://www.societyofrobots.com/mechanics_gears.shtml

And a potentially useful way for you to connect stuff:
http://www.societyofrobots.com/mechanics_brazing.shtml
http://www.societyofrobots.com/mechanics_chassisconstruction.shtml

[cooldog]

i been wanting to do this to for a while

i found these motors
http://cgi.ebay.ca/Powerful-High-Torque-DC-12V-160RPM-Gear-Motor-buySAFE_W0QQitemZ280177467119QQihZ018QQcategoryZ71400QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

but i am trying to find a gear and belt that will attach to the shaft to make the wheels spin

any help???

edit: are these strong engh to push 200 pounds

person+motors+batterys+chasi

batterys
http://www.onlybatterypacks.com/showitem.asp?ItemID=11552.37

[Admin]

edit: are these strong engh to push 200 pounds

person+motors+batterys+chasi

this has been asked a million times

Use this calculator to select a motor that is strong/fast enough:
http://www.societyofrobots.com/RMF_calculator.shtml

[julia1]

Hi.
Thank you for your answers.
I`m having a hard time findind the parts.
Usually the switches are those sliding switches that in one position are turned on and in the opposite position are turned off. But I need one of the switches that will be on while you`re pushing them and off when you let go. After doing some research, I think they`re called "Momentary Push-Button Switches".
For example, I found this-->
http://i110.photobucket.com/albums/n97/clinia/pushbutton_1.jpgIt says --> Normally Open Contacts close when the red actuator button is pressed, and open on release.
Mounts in a 1/4” hole, with Solder tabs. Rated 3 Amps @ 125VAC.
I`m not quite sure what these "3 Amps at 125V AC" mean, will that work? I think I`d need to do some soldering, right? How would I connect batteries with a Rx connector to that pushbutton? (if that`s possible).
And should I use two DC motors (one on each back wheel) or just one motor connected to both wheels somehow? If I use two they have to be half as powerful than if I use just one, right?
Also, the size of the hole in a stakeboard wheel is very big. What`s the easiest way to attatch the wheel to the motor shaft?

[Admin]

I`m having a hard time findind the parts.

http://www.societyofrobots.com/robot_parts_list.shtml

I think they`re called "Momentary Push-Button Switches".
For example, I found this-->
http://i110.photobucket.com/albums/n97/clinia/pushbutton_1.jpgIt says --> Normally Open Contacts close when the red actuator button is pressed, and open on release.
Mounts in a 1/4” hole, with Solder tabs. Rated 3 Amps @ 125VAC.
I`m not quite sure what these "3 Amps at 125V AC" mean, will that work?

yeap thats what you want.

So 3 Amps at 125V AC is the rating for AC current - exceed that rating and it melts. I don't remember how to convert an AC rating to DC (someone know offhand?) . . .

I'd guess 6A at 12V is a reasonable rating. I'd get a nice and big button anyway, since its easier to hold/push.

And should I use two DC motors (one on each back wheel) or just one motor connected to both wheels somehow? If I use two they have to be half as powerful than if I use just one, right?

depends on many factors . . .
- sometimes two half strength motors are much cheaper than one full strength motor
- two motors require twice as much mounting/gearing/belts/screws/wiring
- one big motor might not fit, forcing you to use two smaller ones

as long as you do the math, you won't waste money buying a motor that isn't strong enough . . .

What`s the easiest way to attatch the wheel to the motor shaft?

look around for a wheelhub

[julia1]

The RMF result I got was 182 kg*m*rps. Is that reasonable?
I can`t find a DC motor that will be anywhere near 91 kg*m*rps (half of 182, if I used two motors). I`ve tried many robot stores but since the RMF was always much much lower than 91, I tried searching ebay for 'electric motors' in general but they never say the torque, so I can`t calculate the RMF for them. They usually say the voltage, hp and rpm.
I guess robots are usually lighter than a skateboard+person so maybe I should look somewhere else for a motor this powerful, and not in robot stores?

I`m also a bit confused about how I should connect the DC motors, the battery and the switch. The batteries have an Rx connector but the motors and the switch don`t, so how do I connect everything? Will I need extra wires and connectors? If so, which?

[Admin]

The RMF result I got was 182 kg*m*rps. Is that reasonable?

yeap, entering in what I guessed you would, I got a very similar value. You could always consider reducing the velocity or acceleration . . .

I tried searching ebay for 'electric motors' in general but they never say the torque, so I can`t calculate the RMF for them. They usually say the voltage, hp and rpm.

Yea, its an unfortunate problem with DC motors - no one lists good specs!
Try here:
http://www.societyofrobots.com/robot_parts_list_motors_servos.shtml
Then ebay for the motors you like (you might get lucky)

So the reason why it is so high is your selected incline angle. Change it to 0 and you will notice that it is easy to find a motor to do what you want. If you don't mind acceleration/velocity halved when you go up a hill, 90 RMF is fine.

For example, suppose you calculate you need 180 RMF to go up a 30 degree hill. But you use a 90 RMF motor. If you go up that hill expect your velocity and acceleration to equal 90/180 = 1/2 of total.

[JonHylands]

Don't try and channel the power for the motor through a switch - that is crazy. Use a relay or a MOSFET, and switch the relay/MOSFET with your switch. That way, your switch only has maybe 30 mA going through it.

- Jon

[Admin]

 

oops! . . . yea listen to Jon . . . unless you don't mind ~40A at 12V possibly going through your hand if your wiring gets messed up . . .

(the safety freak in me failed!)

[airman00]

oops! . . . yea listen to Jon . . . unless you don't mind ~40A at 12V possibly going through your hand if your wiring gets messed up . . .

(the safety freak in me failed!)

Hmmm, what exactly is the amperage/voltage for severe injury and what is it for death?

40A@12V is injury im guessing while maybe 100@12V is death. ( total guess)

[Admin]

Most electrocution deaths occur from the electricity passing through and thereby stopping your heart from beating . . .

This however will just result in a really nasty burn to your hand . . . you could of course wear a thick glove if you're too lazy to use a mosfet/relay

[ed1380]

or a big arse switch