Hi …Jongig has been great in responding. I will see if I can add my newbie two cents here. As I understand it the brakes are only activated when no power comes to them. So looking at my connectors on my motors …there are the power leads for the motors as well as the power leads for the brakes (all in the original wheelchair connector). It seems that Jongig felt it necessary to put rectifying diodes in the connection for the brakes. Although I don’t understand why this is necessary since the original installation in the wheelchair did not have these. I am wondering if I could not just hook them up to the Sabretooth just like they were hooked up to the wheelchair power supply and controller …with the Sabretooth taking the place of the wheelchair controller.
Of course it helps ! I thank you for all the great info. And what you described is what I thought. But just to be sure …in your diagram M1,M2 are M1,M2 on the Sabretooth …and the circle with the M in it is the actual motor. I am not sure how you are then wiring up the brakes for power …unless they too are connected to M1/M2 on the Sabretooth. I will have to look at my motors again but I only recall the positive and negative for power for them coming out of the motors. Which means to me that there must be some wiring internally for the brakes to get their power. I have not opened up the brakes to take a look yet…so they may be just like you are describing and I will have to look at your digram at that time and figure out how to wire in the diodes. With all this said …if the wheelchair already had a breaking arrangement with the brakes etc. Why did you feel the need to wire in the diodes …why couldn’t I just connect the motors as if they were connected to the wheelchair? Wouldn’t that accomplish the same thing? Again …since you have been through this and are more knowledgeable I thank you for helping a newbie here.
Why six wheels now? Are you not getting the traction that you need?
That is my thinking …but I have not tried it yet. Hopefully Jongig can respond to why he felt the diodes were necessary.
Good looking machine there …nice work!
What is the short list of electronics used in this project? I’m going to build something similar.
2 drive wheels, mixing to make it go left and right. doesn’t need to skidsteer.
I am building a rig very similar to yours. I also have the motors with the dynamic brakes. I do not, however understand your schematic. I’m quite good at the mechanical aspects (Mechanical Engineer), but the electronics still trip me up. Basically, I also need to keep the brakes active while bypassing the old wheelchair control box. Any help would be greatly appreciated.
First, I’m sorry for not replying to the recent post. I always reply but I didn’t and I’m sorry. I’m not sure why I didn’t see the post but I didn’t.
Anyway, I myself in need of a little help and I was hoping someone might simplify what I’m trying to do.
The yard-bot has been a great tool for around the house and I’ve not had to do any maintenance to it. My wife gets a kick out of me because I put
a egg crate on it, load it up with tools from inside the house and ride to wherever I need to work. It might even be part of the reason I’m gaining weight.
The yard-bot is also a great tool for moving my 10 foot trailer around the yard, even when full.
I have a new use for it, carrying and dumping dirt. I have added a removable aluminum dump box that is over 7 CU-FT. It fits inside the yardbot and doesn’t require removal of the original box or sides.
The dump is hinged to its own integral frame and I’m in the process of installing a 24 volt actuator to lift the dump.
I want to use a RC channel from my RC radio. I want to have center off, full one side would be up and full to the other side will be down.
I want to be able to stop the dump from going all the way up or down by going to center stick of the channel.
I was able to think that I could use two battle switches. The first would be on/off and the second would be up/down but this
would require two channels. It might be possible to use the battle switches to turn voltage on in one direction and the other to turn voltage on plus activate a relay to reverse the voltage.
My second thought was mechanical with the use of a single servo and some type of 3 position switch connected to it.
The actuator is 24 volt DC with limit switches.
I’ve looked for some type of electronic switch but I’ve not found one.
Any better ideas, I’d love to hear them.
I have figured out my dilemma.
Jomar products make’s a electronic double switch. I will use this with a DPDT relay and a SPST relay. At the extreme high side of the stick the dump will go up and at the extreme low side the dump will go down. At middle stick the dump will not move.
I also re-read the post asking about the diodes in my breaking schematic, the diodes are required and the breaks will not work correctly without them.
Hello, new to the forum and I am working on a similar project. I would like to compare what I am doing with your schematic. I keep looking for the attached schematic that was mentioned but I cant see it. I was trying to interface with the wheelchair controller and had some success but I decided to dump it and get the sabertooth for better control and less safety dumping of the wheelchair controller. Any help will be appreciated with the schematic. Thank you.
I’ve been using my design without any problems and I’ve since built a dump body that sits in the bed of the vehicle and has a electric ram for dumping.
I don’t see that I can add a picture so you’ll have to contact me and I’ll send you the picture.
John
Brake schematic attached.
If you follow the flow of electrons you’ll see that as soon as the Sabertooth goes forward or reverse it will provide energy to the brakes and release them. As soon as the sabertooth is back to neutral the energy is no longer present at the brakes and they lock down.
Attached is a picture of the wiring as requested. It doesn’t show the actual connections but after a couple years of use it still works perfectly and it gets used a lot in the summer. I have a chair I put in it and along with whatever tools I can drive myself to where I need to go. I weigh 200 pounds. I recently used it to bring a milling machine into my house in two pieces. The total of the two pieces was 1,100 pounds, not sure what each piece weighed but I’ll bet the one piece was 700 pounds. The tires were crushed a little but it functioned flawlessly. I also made a electric operated dump body that goes in and out. It plugs into the unit and then the one channel on the remote sends it up to where it shuts off automatically or down to where it stops automatically. I sure do love this yardbot which is now named Bubba-jr.
Just made my account for this thread. First thing’s first: YOU ARE THE MAN. This thing is awesome.
I’ve been doing a ton of research trying to figure out how to build something almost identical to this. I’m a mechanical engineering student working on a senior design project. I have a couple questions for you, if you feel like enlightening me. (=
I started off by buying 2 motors off of ebay from an old electric wheelchair with these specs:
Max Speed: 5 mph
Range: Up to 20 miles
Motor: DC 24V, 180W, 4250 rpm (2 Motors, 10" Rear Driven, 8" Front Casters)
Controller: Dynamic DL 50A
Battery: 12V 22NF x2
Weight: 197.5 lbs
Capacity: 300 lbs
Things I have thus far:
- 2 Motors above with 10" pneumatic wheels (I removed motor breaks)
- 2 Dura 12-35C Duracell Ultra SLA 12V 35Ah AGM Batteries (In series for 24V)
- Building 25x22" Square Tube Steel Frame
Things I’m scared of:
- Current rating (peak) of these motors, any idea?
- Aligning 2 rear driven wheels correctly so the robot moves straight. How hard is this to calibrate in software?
- Assuming the components below are correct, do you think the fuses should be 12A or 15A, or combination?
- Is 497.5 lbs gross weight realistic for this?
Design thoughts based on a Robotic paper I read:
- 2 Batteries in series - Fuse1 - 15A DC/DC Buck Converter - Power Switch - Fuse2 - SaberTooth 2x12A Motor Driver - Fuse3 - 2 Motors (SideA of SaberTooth) - Arduino (SideB)
Buck Converter (to maintain regulated 24V out of batteries):
[ebay.com/itm/like/271839425648?ul_noapp=true&chn=ps&lpid=82]
2x12A Sabertooth Motor Driver:
[dimensionengineering.com/products/sabertooth2x12]
What do you think? Thanks for any and all of your help. Sorry for the lengthy message.
Very interesting and thanks for the compliment.
My Bubba jr. is very useful but there is a couple things that I considered but was unable to engineer out. First is I wanted it to be very exact in how it moved since it’s being used inside and out. The 4-wheel locked wheels I used works but it does take a lot more power to turn and due to the weight it will rip up the lawn, I can’t turn quickly. I would have like to articulate the steering. I considered 4-wheel with a yoke in the middle and steering similar to a wagon. If you were to build this as a project with the consideration for the public I think the steering with handle mounted controls would work best. I’d even consider putting the brakes back on since that’s one of the best designs of the unit. I use mine with a small ladder in the basement and with the brakes locked it can’t move.
Because I wanted it to lift very heavy objects it also made it harder to have movable steering. I’ve had a lot of weight in mine without a problem.
I used 2.5 inch square tube steel, probably could have used 2.5 by 1.5 inch. The reason for the 2.5 inch width was so that based on the bolt pattern of the motors I could mill out the tube steel frame and mount the motors directly to the frame.
The stall current of the motors will probably be to much for the smaller sabertooth. If you consider the mounted controls you could get a wheel chair controller and just reconfigure the controls. If you’ve ever seen the walk around pallet lifts they use in stores, that’s my idea.
I don’t understand the electronics, dc-dc converter, where’s the need?
The wheel chairs use 50 AMP circuit breakers on two motors with less weight, consider this.
Early on I had smaller fuses and it didn’t work well. I’m now using 30 amp fuses on all 4 sets of batteries.
You can calibrate the speed of the motors with the sabertooth and a add on board, look on their site for information. I’ve never driven a wheel chair but I have an idea based on how my bot works that you need constant control to maintain a heading. With the settings on the remote controller I can get close to straight but terrain makes it impossible to go straight. Everything makes a difference and if the motors are moving at the same speed you’ll still have differences right down to tire diameter being off.
I wanted to use pneumatic wide tires but I’ve not found the right tires yet but I’d like to build another one. Time is an issue for me but I do enjoy the challenge.
One thing I don’t like about the Sabertooth, it resets everytime you turn the power on/off. So, if you have the remote control trigger pulled a little bit it will show that point as neutral when you turn the power on to the Sabertooth. I’ve never been able to figure this out and it’s dangerous. In the beginning I had found that with less power to the Sabertooth if you draw enough current while moving the Sabertooth will reset and now you have lost control. It’s not an issue with enough current to keep the voltage up enough to the Sabertooth but I wish DE could have done this differently. In other motor controllers I’ve used power on/off and current draw is not an issue.
If you do not want to fill this thread with question after question you can contact me directly.
John
Sabertooths are the norm when it comes to mobile robots. If you want something more rugged / industrial / versatile consider RoboteQ.
You could use ~60A fuses, and perhaps even a fuse between the battery and controller.
Is there any way to figure out the continuous current used by each motor, as well as the stall current? The 2x60A is quite powerful, but it’s best to check the motor’s specs just in case. If it’s not listed on the motors, then you may want to contact the manufacturer.